Principles of Surgery, Companion Handbook

Chapter 40 Neurosurgery

Principles of Surgery Companion Handbook

GENERAL CONSIDERATIONS

A detailed history and physical examination are the foundation of neurosurgical diagnosis. For patients with nervous system disorders, an accurate history needs to be taken once, but the neurologic examination must be repeated and recorded often to gauge the course of the illness and to judge the urgency of subsequent diagnostic and surgical interventions.

Diagnostic Studies Plain films of the spine are useful in the evaluation of traumatic and degenerative spine disorders. Myelography and postmyelogram computed tomographic (CT) scanning remain valuable imaging tools in the assessment of spinal nerve root and spinal cord integrity in trauma and neoplastic and degenerative spine disease. CT is the initial study of choice in the evaluation of head injury, subarachnoid hemorrhage, and hydrocephalus. Magnetic resonance imaging (MRI) is an unparalleled modality for imaging the cranial spinal junction and provides exquisite anatomic detail throughout the neuraxis, exclusive of the assessment of bony involvement, which might require CT. MR angiography is used increasingly in assessments of the extracranial (i.e., carotid) and intracranial (i.e., circle of Willis) circulatory system. For the present, however, cerebral angiography is the “gold standard” in the diagnosis of aneurysms and arteriovenous malformations (AVMs) and provides a vehicle for the application of sophisticated interventional techniques. These therapeutic angiographic techniques include transfemoral microballoon dilation of vasospastic intracranial arteries, occlusion of carotid-cavernous fistulas, and embolization of tumors, aneurysms, and AVMs. Ultrasound is useful in the assessment of neonatal hydrocephalus and in real-time intraoperative localization procedures. Neurophysiologic tests including visual, auditory, and somatosensory evoked potentials provide evidence of nervous system integrity during cranial and spinal operative procedures. The electroencephalogram (EEG) provides an important tool in perioperative diagnosis and as an indicator of physiologic integrity during cerebrovascular surgery. Electromyography and nerve conduction velocity testing (EMG/NCV) are often used in the diagnosis of peripheral nerve and nerve root lesions both to localize lesions and to assess recovery from injury.

SPECIAL SITUATIONS

Seizures Seizures are presenting signs of cerebral neoplasms in 40–90 percent of patients harboring these lesions and also occur in the setting of cerebral trauma and infection. Repetitive seizures or status epilepticus must be treated vigorously. A benzodiazepine such as lorazepam (0.02–0.12 mg/kg I.V. slowly over 2 min) or diazepam (10 mg) should be administered as initial doses and may be repeated if ineffective. Simultaneously, the patient should be loaded with phenytoin (18 mg/kg, <50 mg/min), watching for hypotension during infusion. If this fails, phenobarbital infusion (< 100 mg/min until seizures stop or 20 mg/kg total dose) is recommended, with attention at all times to airway maintenance.

Raised Intracranial Pressure Space-occupying lesions, trauma, and hypoxia/ischemia are all associated with increased intracranial pressure (ICP). Symptoms of elevated ICP include headache, stupor, diplopia, nausea and vomiting, and neck stiffness. Hypertension, bradycardia, and respiratory irregularity (Cushing's triad) are late signs. The upper limits of normal ICP are 10–15 mmHg, with ICPs greater than 20 mmHg considered clearly pathologic.

The treatment of elevated ICP may include head of bed elevation, hyperventilation (PCO₂ 25–30 mmHg), and osmotic diuresis (mannitol 1.5 g/kg/24 h) to a maximum serum osmolality of 300–310 mOsm/L. Steroids (dexamethasone, 4–6 mg, q4h) are effective in the setting of brain tumors associated with ICP elevations but are generally not employed following head injury. High fever may exacerbate brain swelling and should be controlled with alcohol sponging, antipyretics, and hypothermia blankets.

Infections Among the common central nervous system (CNS) infections, meningitis may be treated with antibiotics alone, whereas subdural empyema, brain abscess, and epidural abscess are generally treated with a combination of surgical debridement and prolonged antibiotic therapy. Variable antibiotic penetration of the normal blood-brain barrier and specific targeting of antibiotics to specific infections are important considerations. Pending definitive culture results, broad-spectrum antibiotics are recommended for life-threatening infections. These include nafcillin (2.0 g I.V. q4h) or vancomycin (1.0 g I.V. bid) and gentamicin (75 mg I.V. q8h). Prophylactic antibiotic therapy in the setting of persistent cerebrospinal fluid (CSF) leak is not recommended.

Fluid Balance Mild fluid restriction (2000 mL/24 h, D₅, 0.5% NS) and avoidance of free water in intravenous solutions are recommended in neurosurgical patients. Fluid balance should be monitored carefully (I/O, daily weight) and enteral feedings initiated, if possible, 3 days after injury or after surgery.

Disturbances of fluid balance include the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and diabetes insipidus. In SIADH, inappropriately high antidiuretic hormone (ADH) levels are associated with retention of free water, hyponatremia, high urinary sodium, low serum osmolarity, and high urinary specific gravity and is best treated with fluid restriction. In diabetes insipidus, inappropriately low levels of ADH cause serum hypernatremia and hyperosmolarity along with high urine volumes and low urinary specific gravity. Careful rehydration and administration of antidiuretic hormone are essential.

State of Altered Consciousness Coma is an alteration in the level of consciousness from which the patient cannot be aroused by any stimulus. In stupor, the patient can be partially aroused by loud command or painful stimulus but promptly lapses into unconsciousness with withdrawal of stimulation. Common causes of coma and stupor include acute alcoholic intoxication with blood alcohol levels greater than 400 g/10 dL, narcotic poisoning, diabetic coma, and hypoglycemia precipitated by insulin overdose, starvation, or vigorous exercise.

Emergency management measures include intubation if the respiratory rate is less than 10 breaths per minute, the PO₂ is less than 70 mmHg, or the PCO₂ is greater than 50 mmHg with the patient breathing oxygen through a mask. Arterial blood-gas (ABG) monitoring, blood glucose determination, and toxicologic analysis are recommended. For possible hypoglycemia, narcotic overdose, and Wernicke's encephalopathy, 50 mL of 50% dextrose in water, 0.4 mg naloxone, and 100 mg thiamine are administered intravenously, respectively.

TRAUMA

Severe head injury (Glasgow coma scale score > 7) is associated with injury to other organ systems in 60 percent of patients. In neurosurgical evaluation, it is important to remember that loss of consciousness may have preceded the traumatic event and may have a separate etiology (aneurysmal subarachnoid hemorrhage, seizure, hypoglycemia, etc.). Primary consideration must be given to respiratory exchange, control of hemorrhage, and maintenance of peripheral vascular circulation. As vital functions are stabilized, a preliminary evaluation of the nervous system is essential, followed by careful repetitive neurologic examinations to detect improvement or deterioration.

Scalp Injury Scalp lacerations may cause hemorrhage and shock and should be treated promptly with pressure dressings or by clamps applied to the galea, which pull it back over the dermis. If lacerations are found to overlay a depressed skull fracture or penetrating wound, neurosurgical consultation and debridement/closure in the operating room are essential. In the absence of such injury, simple scalp lacerations should be debrided and irrigated to prevent infection and should be closed primarily, with particular attention paid to galeal closure to provide hemostasis. Scalp avulsions may require split-thickness skin grafts or free myocutaneous flaps attached by microsurgical vascular anastomosis.

Skull Fractures Skull fractures are classified on the basis of intactness of overlying skin or mucous membrane (closed or open/compound), degree of inward displacement (depressed or nondepressed), involvement of the skull base (basilar), and geometric pattern (linear, stellate, comminuted). Simple fractures (linear, stellate, or comminuted nondepressed) do not usually require treatment but may lead to hemorrhage if they cross vascular channels in the skull or to infection if assessory nasal sinuses are involved. Linear or stellate nondepressed open fractures may be treated with simple debridement and closure of the scalp wound. Severely comminuted open fractures and depressed open fractures require debridement and closure in the operating room with inspection of the dura to identify lacerations not visualized on the CT scan. Basilar skull fractures involve the floor of the calvarium and may be associated with ecchymosis in the periorbital region (raccoon sign) or behind the ear (Battle's sign), suggesting the location of the basilar skull fracture. Basilar skull fractures may be associated with facial nerve paralysis, usually with spontaneous resolution of most facial nerve deficits and rarely requiring operative decompression. CSF rhinorrhea or otorrhea are important concomitants of basilar skull fractures and usually resolve spontaneously within 7–10 days. Persistence of CSF leak is treated with lumbar CSF drainage, followed by surgical exploration if this is ineffective. Prophylactic antibiotics are not usually recommended in the setting of CSF leak following trauma.

Brain Injury Mechanisms of brain injury include direct disruption of the brain by a penetrating object, focal injury to the brain from rapid deceleration/rotation of the brain within the confines of the rigid skull, or diffuse axonal injury caused by rotational/shear stresses. The initial impact producing neuronal and axonal disruption constitutes the primary injury. Subsequent events including the development of intracranial hematoma, cerebral edema, hypoxia, hypotension, hydrocephalus, and endocrine disturbance may lead to secondary injury that compounds the initial insult to the nervous system.

Mild head injury or concussion is not usually associated with significant primary brain injury or neurologic deficits. Moderate–severe head injury is more likely to be associated with neurologic deficits of variable reversibility. Accompanying secondary injury is often present.

Elevated ICP may contribute to secondary brain injury by reducing cerebral perfusion pressure (CPP), which is defined by the difference between mean arterial blood pressure (MABP) and cerebral venous pressure or ICP (CPP = MABP – ICP). Elevation of ICP in the setting of a stable MABP results in the decline in CPP. When CPP falls below 50 mmHg, cerebral ischemia and secondary injury may occur. Intracranial hypertension associated with cerebral ischemia constitutes a potentially reversible mechanism of secondary insult; thus aggressive management is indicated.

Evaluation Rapid clinical assessment is essential following head injury, and the Glasgow Coma Scale (GCS) is used to follow the neurologic status and to predict the ultimate outcome in individual patients. A GCS score of more than 7 constitutes “severe closed head injury” (Table 40-1).

TABLE 40-1 GLASGOW COMA SCALE

The initial evaluation includes a detailed history of the etiology and mechanism of injury, the level of neurologic and autonomic function at the scene of the accident and during transport, as well as a careful neurologic assessment on arrival in the emergency room. CT scan is generally not indicated in patients without headache, lethargy, or a focal neurologic deficit, in whom observation and discharge in the care of responsible family members often will suffice. Patients who are symptomatic, with or without a focal deficit, require CT scanning of the head. If the CT is unremarkable and a high index of clinical suspicion exists, additional observation, angiography, and/or spinal imaging may be necessary.

In the unconscious patient, the examiner must rely on serial evaluations of brainstem reflexes to determine the level of brain compromise. These serial evaluations may reveal subtle changes in status that may herald impending problems, warranting further investigation and/or surgical intervention.

Treatment The global objectives of treatment include maintenance of adequate oxygenation and brain circulation, removal or amelioration of mass effect, control of ICP, prevention of infection, and ultimately, rehabilitation. Frequent monitoring of vital signs, arterial blood gases, and fluid intake and output is a reactive necessity. Any focal mass from hemorrhage, devitalized brain, or swelling that alters level of consciousness usually should be removed. The subsequent goals of management are normalization of CPP and prevention of secondary injury to the damaged brain. ICP monitoring is usually indicated in patients with a GCS score of more than 7 or in comatose patients requiring emergency extracranial (abdominal, thoracic, orthopaedic, etc.) surgery.

Ventriculostomy allows continuous assessment of ICP and therapeutic intervention via drainage of CSF to lower ICP. Other methods of ICP management include head elevation in the neutral position, pharmacologic sedation if posturing and combative activity are present, hyperventilation (PCO₂ 25–28 mmHg), anticonvulsant prophylaxis, mild fluid restriction, prompt treatment of SIADH, prevention of hypotension, aggressive treatment of hypertensive episodes, and management of hyperthermia. If the ICP remains elevated, mannitol (0.5–1.0 g/kg) and furosemide (0.1 mg/kg) are useful. Deep sedation with narcotics and the use of paralytic agents may provide additional benefit. Barbiturate coma in refractory ICP elevation is seldom used. Corticosteroids have no proven benefit in patients with brain injury. Attention must be paid from the outset to pulmonary hygiene, venous stasis, and skin care to prevent pneumonia, pulmonary embolism, and skin breakdown that may complicate recuperation from head injury.

SPECIFIC INJURIES

Diffuse Axonal Injury

Diffuse white matter injury from rotational/shear forces is associated with high mortality and substantial neurologic morbidity. Despite massive anatomic disruption, both the CT scan and the ICP may be relatively normal.

Epidural Hematoma

The most common cause of epidural hematoma is a fracture of the temporal bone leading to disruption of the middle meningeal artery and the accumulation of arterial blood between the cranium and the dura mater. Little or no brain injury occurs at the time of the skull fracture; thus, if properly recognized and treated, these lesions can be evacuated and neurologic morbidity completely prevented. Classically, a blow to the head fractures the skull and causes a brief period of unconsciousness. The patient may then regain consciousness, entering a “lucid interval,” where there are minimal neurologic symptoms or signs. With enlargement of the hematoma over several hours, hemispheric distortion ensues, leading to compression of the temporal lobe and “herniation” of the medial temporal lobe over the tentorial edge. Uncal herniation causes compression of the ipsilateral cerebral peduncle and adjacent oculomotor nerve (transtentorial herniation). The neurologic concomitants are ipsilateral pupillary dilatation and contralateral decerebrate posturing. Coma, fixed and dilated pupil(s), and decerebration are the classic triad indicating transtentorial herniation.

Although epidural hematomas resulting from arterial or venous bleeding in the epidural space are curable lesions, the mortality rate remains unacceptably high due to a lack of recognition of this entity. A patient may be seen during the “lucid interval” and discharged; thus, if a high index of suspicion for epidural hematoma exists, a CT scan or careful period of observation (6–8 h) is recommended.

Subdural Hematoma

Acute subdural hematomas are associated with severe head injury and arise from a combination of torn bridging veins, disrupted cortical vessels, and cortical lacerations. Surgical evacuation of clot may lead to improvement of symptoms attributable to mass effect. Persistent deficits, however, often remain attendant to the widespread parenchymal injuries often seen in these patients. Subacute subdural hematomas are associated with progressive lethargy, confusion, and focal neurologic deficits that appear over several days and which may reverse following hematoma removal. Chronic subdural hematomas usually arise from tears in bridging veins resulting from a minor and often unrecognized head injury. These hematomas are seen most common in elderly individuals with brain atrophy or in infants. Slowly progressive mental status changes with or without focal signs are noted. Hematoma drainage often results in complete recovery.

Spinal Cord Injury

Mechanism of Injury Traumatic injury of the spinal cord may result from vertebral fracture, fracture/subluxation, hyperextension of the cervical spine in a patient with a narrow spinal canal, acute herniation of intervertebral disc material into the canal, and penetrating injuries including gun-shots and stabbings. In recognition of the common association of head injury with spinal cord trauma, head-injured patients should be immobilized on a backboard with a hard cervical collar and cervical immobilization maintained until a thorough examination and radiographic assessment are completed.

Clinical Findings Spinal tenderness to palpation, extremity weakness, numbness or paresthesias, respiratory embarrassment, and hypotension suggest spine or spinal cord injury. When spinal nerve roots are involved, radiculopathy, characterized by motor and sensory impairments in corresponding myotomes and dermatomes, may be seen (Fig. 40-1). When the spinal cord itself is involved, myelopathy ensues with variable manifestations.

FIGURE 40-1 Diagram of sensory nerve root distribution.

Complete lesions of the spinal cord result in the loss of all motor and sensory function below the level of injury. Areflexia, lucidity, anesthesia, and autonomic paralysis below the level of the lesion are seen. Arterial hypotension may occur with lesions above T5 (Fig. 40-2).

FIGURE 40-2 Diagram of spinal cord anatomy and common clinical syndromes that accompany spinal cord lesions.

Incomplete spinal cord lesions have variable presentations. The Brown-Séquard syndrome is produced by a cord hemisection resulting in ipsilateral motor paralysis and loss of position/vibratory sensation (dorsal columns and corticospinal tract injury) and contralateral loss of pain and temperature sensation (spinothalamic tract injury) below the level of injury. The central cord syndrome often follows a flexion/extension injury of the cervical spine in the setting of a narrow spinal canal and is characterized by bilateral weakness and loss of pain/temperature sensation in the upper extremities, with relative preservation of these modalities in the lower extremities. The anterior spinal artery syndrome constitutes an ischemic deficit in the irrigation territory of this artery, with a lesion of the anterior two-thirds of the spinal cord and preservation principally of the dorsal columns. Bilateral loss of motor function and pain/temperature sensation with sparing of position, vibratory, and light touch sensations constitute the classic picture. The cauda equina syndrome may result from lumbar spine trauma below the conus (L1–L2) and has a variable presentation. Lower extremity motor, sensory, and reflex functions may be affected, along with compromise of bowel and bladder performance.

Myriad autonomic concomitants of spinal cord injury bear recognition. With cord injury above C3, respiratory effort is lost completely. In C4–C6 injuries, insufficient tidal volumes may lead to progressive hypoxia and CO₂ retention. Spinal cord injury may lead to ileus and gastric distention, necessitating nasogastric drainage, and bladder distention, requiring catheterization. Injuries above T5 compromise sympathetic tone, with a resulting hypotension requiring the administration of intravenous fluids. Postural changes (i.e., upper body elevation) may lead to precipitous declines in blood pressure because reflex tachycardia and peripheral vasoconstriction that often compensate hypotensive episodes are compromised.

Evaluation Once hemodynamic stability is ensured, spinal radiographs with the patient still immobilized on a backboard with a hard cervical collar are obtained. Comatose or severely injured patients require plain-film imaging of the complete spine. Flexion/extension views should not be performed in the setting of neurologic deficit or in patients with compromised mental status. Adjunctive imaging studies include CT scans, myelograms and post-myelogram CT scans, and MRI.

Treatment The objectives of treatment include correction of spinal alignment, protection of undamaged neural tissue, restoration of function to reversibly damaged neural tissue, and achievement of permanent spinal stability. Closed reduction of cervical dislocation involves progressive axial traction using a halo or skull tongs under x-ray control to a maximum of approximately 50 lb. Open reduction combined with fusion is reserved for patients in whom attempts at closed reduction are unsuccessful (i.e., locked facets). Thoracic and lumbar injuries are treated by immobilization on a firm surface without traction. Early operation is indicated when closed reduction of malalignment is unsuccessful, when neurologic deterioration is identified in a patient with an incomplete cord lesion initially, when severe spinal cord compression via an intraspinal mass is revealed by imaging studies in a patient with some preservation of cord function, or when a penetrating injury with or without a CSF leak is identified. Emergent decompression does not improve neurologic recovery in patients with complete transverse deficits, and reports of worsening of existing deficits in patients with incomplete lesions undergoing emergent operations have lead to a more conservative approach to these individuals.

External immobilization for a period of approximately 3 months is usually recommended following either closed or open (surgical) reduction. A Philadelphia collar may suffice when anterior and posterior metal plating procedures are used.

Peripheral Nerve Injury

Acute peripheral nerve injuries encompass three pathophysiologic processes: (1) neurapraxia is a temporary loss of function in the absence of axonal disruption, usually following a compression injury; (2) axonotmesis is disruption of the axon with preservation of the myelin sheath due to prolonged compression or stretch injuries, leading to a complete sensory/motor deficit and a variable proximal to distal recovery (1–2 mm/day) depending on axonal regrowth; and (3) neurotmesis is a disruption of both the axon and axon sheath resulting from nerve transection, which requires surgical repair to facilitate nerve regeneration (1 in/month).

Evaluation of peripheral nerve injury requires a detailed history and precise neurologic examination through which the site of injury can be localized with great accuracy. Radiographs of the injury site may identify any occult fracture or foreign body. EMG constitutes an effective aid to the evaluation of the degeneration/regeneration process but is not useful within the first 3 weeks following injury.

Treatment Surgical repair of nerve lacerations may incorporate end-to-end anastomosis or interpositional grafts. Immediate repair is indicated when the wound is clean and uncomplicated (e.g., stab wounds, glass lacerations, and surgical incisions). Secondary or delayed repair (i.e., 6 weeks) is performed when wounds are dirty or complicated (e.g., gunshots, avulsions with tissue disruption, and wounds older than 5–6 h). Significant motor return cannot be expected in any muscle more than 15 in from a nerve suture.

Nerve injuries in continuity (contusion/compression) are often explored if they do not improve within 6 weeks of injury and may respond to neurolysis or removal of scar tissue that inhibits axonal regrowth. Stretch injuries are common in the brachial plexus and are usually treated conservatively with careful recording of motor/sensory loss via serial examinations and MRI to identify root avulsions.

Prompt institution of physical therapy to improve muscle function and maintain joint motion minimizes the complications of denervation. Orthopedic reconstruction and long-term rehabilitation are often appropriate.

NEOPLASMS

Nervous system tumors represent almost 10 percent of all neoplasia. Of these, 15–20 percent occur in children. Most adult tumors are found above the tentorium (supratentorial), whereas most childhood tumors are found below (infratentorial). CNS tumors are the most common solid tumors in children and of all pediatric cancers are second only to leukemia in frequency.

Intracranial Tumors

Clinical Manifestations Intracranial tumors may exert local effects due to focal irritation or destruction of neural tissue. Focal seizures are a common presenting sign of intracranial tumors, whereas focal neurologic deficits may occur as a result of invasion, compression, or destruction of essential cerebral centers. Tumors also may exert more generalized effects resulting from raised ICP due to the presence of the tumor mass, which may be compounded by obstructive hydrocephalus and cerebral edema. These generalized effects may lead to headache, nausea and vomiting, depressed consciousness, and/or impaired cognition. If tumor enlargement is gradual, substantial volumes may be attained with only subtle alterations in personality, behavior, recent memory, or attention and concentration. A patient's family may notice gradual changes over months or years. However, as intracranial compensatory mechanisms are exhausted, a precipitous clinical demise may occur at the time of presentation. Evaluation requires a careful history of progressive and often subtle neurologic deficits and behavioral/cognitive symptoms followed by imaging with CT or MRI.

Treatment Histologically benign tumors (i.e., meningiomas or schwannomas) are curable if totally removed; however, proximity to vital brain structures may preclude resection. Solitary, symptomatic metastases from extracranial sites are removed if accessible and if the patient's systemic cancer is under control or treatable. Primary malignant brain tumors are not usually curable, but significant palliation may be obtained with a combination of surgery, radiation, and chemotherapy. The recent introduction of external stereotactic radiosurgical methods (gamma-knife and Linnac) offer great promise for the treatment of both benign and malignant neoplasms. In addition, stereotactic biopsy methods have been useful in the safe identification of deep-seated neoplasms. Finally, stereotactic surgical methods are rapidly evolving and promise to facilitate resection of intraaxial tumors.

Classification of Intracranial Tumors Intrinsic brain neoplasms (Table 40-2) are classified on the basis of their cells of origin. Glial neoplasms (e.g., astrocytoma, oligodendroglioma, ependymoma, microglioma, and choroid plexus papilloma) are classified as low- rade (astrocytoma), intermediate-grade (anaplastic astrocytoma), and high-grade (glioblastoma) tumors. Low-grade astrocytomas in children have an 80 percent 10-year survival rate. In adults, low-grade astrocytomas are accompanied by a 5-year survival rate of 35–50 percent, whereas high-grade tumors are extremely malignant and carry a life expectancy of 1–2 years. Neuronal tumors (ganglioglioma) are associated with a possibility of surgical cure. Leptomeningeal cells give rise to meningiomas, which arise from the dura mater, in an extraaxial location, and which are completely curable if surgically removed.

TABLE 40-2 BRAIN TUMORS

The most common adult primary tumor is malignant astrocytoma, followed by meningioma, pituitary tumor, and neurilemoma (see Table 40-2). In childhood, the most common primary tumor is the astrocytoma of the posterior fossa, followed by medulloblastoma, appendemoma, and cranial pharyngioma. Pituitary tumors are generally benign adenomas of anterior pituitary lobe origin and may cause symptoms by hormonal overproduction including amenorrhea/galactorrhea from hyperprolactinemia, acromegaly/gigantism from hypersecretion of growth hormone, and Cushing's disease from hypersecretion of adrenocorticotropic hormone (ACTH). Alternatively, mass effect may result in compromised anterior pituitary function or neurologic symptoms through compression of adjacent structures (e.g., optic nerve, carotid arteries, cavernous sinus). Finally, hemorrhagic infarction of the pituitary or pituitary apoplexy may present with subarachnoid hemorrhage, acute headache, oculomotor paresis, visual loss, and a decline in the level of consciousness.

Spinal Cord Tumors

Classification Spinal tumors constitute 20 percent of all CNS tumors and are classified according to the compartment in which they appear. Intramedullary tumors constitute 16 percent of spinal cord tumors and include ependymomas, astrocytomas, hemangioblastomas, and epidermoid/dermoid tumors. Intradural, extramedullary tumors are almost always primary CNS tumors, including neurofibroma, schwannoma, meningioma, metastasis of a primary brain tumor, ependymoma, and lipoma. Most intradural spinal neoplasms are benign and amenable to surgical excision. Intramedullary lesions may produce weakness, spasticity, and sensory loss. Extramedullary lesions may present with radicular pain from nerve root involvement as well as long tract signs from compression of corticospinal tract pathways. With conus involvement, early loss of bowel and bladder function may predominate.

Extradural Tumors Extradural tumors include metastatic lesions, myeloma, lymphoma, chordoma, sarcoma, and neuroblastoma, and 90 percent of these tumors are malignant. About 75 percent of extradural tumors are metastatic (e.g., lung, breast, lymphoid, prostatic, kidney, and thyroid), whereas 98 percent of intradural tumors are primary CNS neoplasms. Extradural tumors produce neurologic manifestations either by direct cord compression or by bony involvement with vertebral collapse, leading to progressive paraparesis and sensory loss. Malignant extradural tumors are treated with an emphasis on decompression of the spinal cord, stabilization of the vertebral column, and reduction of tumor volume.

The identification of spinal cord tumors requires the careful assessment of any evidence of bilateral progressive neurologic loss below any transverse level of the body. MRI and CT scans following the injection of intrathecal contrast material constitute the definitive imaging studies.

Peripheral Nerve Tumors

Tumors can arise from peripheral and cranial nerves, spinal roots, and the autonomic nervous system. The more common tumors are schwannoma, neurofibroma, and malignant nerve sheath tumor. Malignant transformation of schwannoma is rare and more common for neurofibromas.

CEREBROVASCULAR DISEASE

Cerebrovascular disease represents a leading cause of death and disability. Approximately 140 per 100,000 persons suffer an ischemic cerebral event each year, and over 30 percent of these individuals die or have significant retained neurologic deficit. Another 20 per 100,000 persons sustain a hemorrhagic cerebral event (hypertensive hemorrhage, subarachnoid hemorrhage) each year, and in excess of 50 percent of such patients suffer a fatal outcome. The human suffering is incalculable; the economic cost is estimated at over $2 billion per year.

Cerebral Ischemia

The brain normally receives approximately 60–80 mL of blood per 100 g of brain tissue per minute. If cerebral blood flow (CBF) falls below 20 mL/min, symptoms of ischemia and frank infarction occur. A normal cerebrovasculature has significant “reserve” owed to autoregulation, which allows cerebral vessels to dilate in the face of falling flow. Systolic blood pressures as low as 50 mmHg will maintain adequate flow in a healthy individual. Patients with atherosclerotic changes, altered autoregulation due to trauma, or subarachnoid hemorrhage are less able to adapt to decreasing flows.

Cerebral ischemia is divided into those events caused by (1) emboli and (2) primary occlusive disease of the vasculature. The former causes ischemia as the emboli pass through the cerebral circulation and lodge at various locations (usually in the middle cerebral artery territory), whereas the latter is owed to a direct loss of flow due to stenosis of extracranial or intracranial vessels.

Embolic Ischemia

Recent data strongly support the concept that approximately 70 percent of all ischemic strokes are due to emboli. The emboli can originate at any location from the heart to the cerebral vessels themselves. The ischemia caused by embolic occlusion may present as a wide variety of neurologic deficits. The flow pattern in the cerebral vessels favors passage of the embolus into the middle cerebral artery; most commonly presenting as a weakness in the contralateral face and arm. Ischemia in the dominant hemisphere middle cerebral region also causes loss of expressive and/or receptive speech. Ischemia in the anterior cerebral territory may cause weakness in the contralateral leg. Vertebrobasilar ischemia, clinically much less common than carotid circulation ischemia, may cause diplopia, difficulty swallowing, multiple cranial nerve palsies with or without weakness, and frank syncope.

The duration and severity of the neurologic deficit vary according to the degree of ischemia. Deficits that resolve within 24 h are termed a transient ischemic attack (TIA). Deficits that resolve between 1 and 7 days are termed a reversible ischemic neurologic deficit (RIND). Those deficits which persist are cerebral infarctions. The definitions are somewhat arbitrary but serve a useful purpose for clinical classification.

The evaluation of a patient with an ischemic neurologic deficit requires a search for the source of potential emboli. This endeavor should begin at the heart. Electrocardiogram (ECG) and enzyme studies will screen for myocardial infarction, a potential cause of mural thrombi and therefore emboli, which may find their way to the brain. Atrial fibrillation also may cause embolization into the cerebral vasculature. An echocardiogram is also indicated in the setting of cerebral ischemia. The clinical evaluation simply proceeds through the vascular tree from the heart to the brain. If no clear source is identified in the heart, the thoracic arch and carotid arteries should be evaluated with noninvasive (e.g., ultrasound, MR angiography) or invasive (e.g., angiogram) techniques. The patient who sustains a TIA or RIND has been found to have a significant risk for recurrent ischemia and potential infarction. Identification of the source of the emboli allows treatment options to be selected. Cardiac origin may require formal anticoagulation with Coumadin; carotid plaques without significant stenosis may be treated with antiplatelet therapies; those with significant stenosis may warrant carotid endarterectomy.

Occlusive Ischemia

Narrowing of extracranial or intracranial vessels may cause “low flow” states in the absence of any embolic phenomena. Once felt to be the leading cause of cerebral ischemia, it is now felt to be less common than embolic ischemia. The vasculature may be stenosed by a variety of mechanisms: atherosclerosis at the thoracic arch or carotid or vertebral arteries, fibromuscular dysplasia or other vasculopathies such as Moya Moya disease.

The clinical presentation of occlusive (low-flow) ischemia is very similar to that with ischemic phenomena. The neurologic deficit depends on the zone of ischemia and its severity. As is the case in evaluation of embolic events, a search for occlusive ischemia must include a thorough investigation of the major vessels supplying the brain. MR angiography is improving rapidly and in the future may replace formal angiography, but at the time of this writing, four-vessel cerebral angiography remains the study of choice.

Both embolic and occlusive ischemia cause a zone of nonfunctional or suboptimally functional neural tissue. The size of this area and the time it remains in a suboptimal state depend on the degree and duration of ischemia. If the tissue is hypoperfused for a sufficient period (the exact time frame depends on location, metabolic rate, and many as yet undetermined factors), an infarction occurs. Urgent revascularization procedures and endovascular “salvage” procedures to acutely open vessels are being investigated, but thus far definitive data are not available. A fixed area of infarct can become a hematoma if excessive reflow is established, and complications have been recorded with successful revascularization in such a setting. Prevention of future episodes remains a cornerstone of treatment, using medical therapies such as antiplatelet agents, anticoagulation coupled with carotid end-arterectomy, and other vascular procedures. Extracranial-to-intracranial bypass procedures, such as the superficial temporal artery to middle cerebral artery bypass, have occasional indications but were not found to be widely applicable in a large multi-center study.

Intracranial Aneurysm

An intracranial aneurysm is a saccular distention of the cerebral blood vessels generally found at the bifurcation points in the circle of Willis. Cerebral vasculature has a high elastin content and decreased muscularis, making the vessels less stress resistant. The blood vessels of the brain also lack a firm parenchyma immediately surrounding the vessel wall, therefore making them susceptible to internal stress due to lack of wall support (cerebral vessels at the circle of Willis are essentially “free floating” within the subarachnoid space). These factors, associated with the constant stress on the bifurcation of the vessel due to the flow of blood, can lead to aneurysm formation. There may be congenital weakening and other as yet undetermined factors that potentiate the risk of aneurysm development. They are seen only rarely in children but are noted in 1–2 percent of cerebral angiograms done for various reasons in adults. Approximately 28,000 people per year sustain a subarachnoid hemorrhage in North America, the incidence being fairly constant throughout the world at approximately 12 per 100,000 population.

Subarachnoid hemorrhage from an aneurysmal bleed is heralded by a sudden, “thunderclap” headache. This symptom alone, severe sudden headache, is the most reliable diagnostic tool. Because the blood is in the subarachnoid space, as opposed to the brain itself, the patient may have a normal or near-normal neurologic examination. In fact, the patients with the best chance of a good outcome have only the headache and other subjective symptoms. The mortality and morbidity of aneurysmal subarachnoid hemorrhage are devastating. Fully 25 percent of the patients die within 24 h, and another 25 percent die over the first week. Nearly 50 percent of the survivors will have a retained neurologic deficit. Prompt diagnosis, particularly in a good-risk patient based on the history of sudden severe headache, can allow a cure for this morbid disease.

Once the history suggests subarachnoid hemorrhage, a CT scan of the head with and without contrast should be performed. Over 85 percent of subarachnoid bleeds can now be seen on CT scan. The CT scan also will exclude other important processes such as tumor or cerebellar hemorrhage. If the CT scan is negative, a lumbar puncture should be performed. Lumbar puncture has a nearly uniform diagnostic capability for detecting fresh blood (RBCs in the thousands) as well as xanthochromic staining on a spun specimen, which can detect blood in the CSF for 10–14 days after a bleed. If either the CT scan or the lumbar puncture suggest a hemorrhage, cerebral angiography is mandatory to search for an aneurysmal lesion.

Patients with a ruptured aneurysm are at risk for two major morbidities after the initial bleed. Approximately 20 percent of patients will have a rebleed in the 14-day period after the first bleed. This carries a nearly 75 percent death rate if unchecked. Another 10–15 percent will sustain vasospasm (a tight, spasmodic stenosing of the vessels) that can lead to cerebral infarction. Rebleeding can be prevented by prompt craniotomy and clip placement on the aneurysm neck, thereby occluding the aneurysm from the circulation. Vasospasm is treated by maintenance of adequate vascular volume and occasionally by induced hypertension, both factors aimed at optimizing flow through the stenosed vessels. Calcium channel blockers are now used extensively in the treatment of subarachnoid hemorrhage to reduce the risk of ischemic injury from vasospasm. Although they appear to reduce the risk of infarction, the mechanism by which this is accomplished is not established.

The outcome in patients with aneurysmal subarachnoid hemorrhage is directly related to the neurologic status on arrival. Those patients who are arousable, verbal, and following commands (Grades I and II) have a death rate of approximately 10–20 percent. Patients who are comatose or near comatose (Grades III and IV) have a death rate in excess of 65 percent. Once the diagnosis is suspected, a rapid CT scan and lumbar puncture, if needed, may lead to prompt clipping of the aneurysm and effectively eliminate the risk of a rebleed. Intravenous fluids at 100 mL/h of D₅ NS plus 20 mEq KCl and Nimodipine (60 mg PO/NG q4h) should be started on admission. Patients stuporous and who might have difficulty protecting their airway are best intubated “prophylactically” rather than waiting for a hypoxic arterial blood gas, by which time the neurologic damage has already begun. Steroids (Decadron, etc.) have not been conclusively shown to benefit the subarachnoid patient although Decadron, 4 mg, q6h, is currently the drug of choice. Because of the risk of seizures with cortical irritation, Dilantin, 100 mg, tid, is started on admission.

Arteriovenous Malformation of the Brain

Arteriovenous malformations (AVMs) are congenitally abnormal connections between arteries and veins without the proper intervening capillaries and small-caliber vessels. Such an abnormal connection allows high-flow, high-pressure arterial blood to pass into relatively weak-walled veins without a steady cascade of small vessels to dampen the flow. The physiologic stress involved in such a system can lead to rupture of the AVM. The AVMs are located in the brain itself (unlike aneurysms, which are in the subarachnoid space) and therefore generally cause intracerebral hematomas as opposed to subarachnoid hemorrhage. Any hemorrhage into the brain parenchyma should raise the suspicion of an AVM. AVM bleeds can occur at any age but tend to occur in the first two to three decades of life. Each bleed carries an approximately 10 percent mortality and 20 percent morbidity. The neurologic presentation depends on the location of the AVM. Intracerebral hematomas in the dominant hemisphere may cause aphasia associated with hemiplegia of the contralateral arm and/or leg. Those in the occipital region may cause visual field cuts.

Hematomas large enough to cause elevated ICP and possible herniation need to be surgically evacuated. Those of smaller dimensions, found on angiography to be the result of an AVM, may be carefully observed in hospital in the acute phase. The early rebleed rate with AVMs is low, and definitive surgical removal of the AVM by craniotomy is often intentionally delayed 3–4 weeks to allow the brain edema to recede. Although complete surgical removal remains the goal of therapy, radiosurgical techniques are showing promise in the treatment of AVMs, particularly those smaller than 3 cm in difficult surgical locations.

Hypertensive Brain Hemorrhage

Chronically elevated blood pressure (generally well in excess of 150/90 mmHg) may lead to changes in the cerebral vasculature. Most of the significant changes are at the branching points of small blood vessels such as the lenticulostriate arteries that originate from the middle cerebral arterial trunk. Small aneurysms and weak spots occur, eventually leading to intracerebral hemorrhage. Most intracerebral bleeds are at the basal ganglia, pons, or cerebellum. Those in the basal ganglia lead to a contralateral hemiplegia. Pontine bleeds are often acutely catastrophic, the patient being rendered comatose with pinpoint pupils, quadriplegia, and labored breathing. Cerebellar bleeds have a subtle clinical presentation if small in size, often with only minor cerebellar signs. Large cerebellar bleeds present with a decreased level of consciousness and cranial nerve loss.

The patient often has a relatively “silent” onset of sudden neurologic deficit. The key point, as with all the vascular syndromes, is the sudden onset. Although headache often is present, it is usually moderate, the deficit being the predominant complaint. The death rate with large hematomas is high, in excess of 40 percent. Surgery is generally deferred in basal ganglia bleeds unless life-threatening hematoma exists. Surgical removal has not been found to improve functional outcome in small to moderate-sized hematomas. Cerebellar bleeds are a surgical emergency because the posterior fossa tolerates raised pressure very poorly, and sudden death may occur. The cerebellum also is a “forgiving” neurologic structure, and even fairly poor-grade cerebellar bleeds may have a good functional outcome with surgery. Pontine bleeds are not surgical candidates and have a death rate in excess of 75 percent. The best treatment of hypertensive hemorrhage is prophylactic treatment—aggressive treatment of hypertension before a bleed occurs. Hemorrhage of this type has decreased over the last 30 years, probably owing in large part to improved treatment of hypertension.

DEGENERATIVE SPINE DISEASE

Degenerative changes in the spine are a normal part of the aging process, as they are in other bodily subsystems. Only a subset of individuals eventually has clinical problems from this degenerative change. The cervical and lumbar regions are at greatest risk because of the constant motion (and therefore stress) seen in those regions of the spine. The rib cage “struts” the thoracic spine, and degenerative problems of a clinical magnitude are much less common in this region.

Intervertebral Disc Disease

Lumbar Lumbar discs are subjected to tremendous physiologic stress in humans because of our biped nature. The discs are greater than 60 percent water in infancy but rapidly desiccate after age 30. This process of desiccation and degenerative changes in the joints and ligaments of the spine predispose the disc to shearing forces. The disc may “fail,” forcing a fragmented piece of nucleus pulposus through the annulus, which surrounds the disc. The posterior longitudinal ligament (lining the back of the vertebral body) generally keeps the disc fragment from going directly posterior into the spinal canal. Instead, the fragment forces its way into the neural foramen. The cartilaginous disc material may cause a compressive force on the nerve at the level of the foramen, the clinical picture of this process being termed lumbar radiculopathy. Lumbar radiculopathy may occur at any level (L1–S1 nerve roots), and the clinical picture varies accordingly. The most common compressive lumbar radiculopathy occurs at the L4–5 and L5–S1 interspaces. Nearly all radiculopathies present as a painful extremity. Most of the pain will be in the buttock, posterior thigh, and calf. Generally, paresthesias are present in the foot. A disc fragment at the L4–5 level causes an L5 nerve root compression (because the L4 root exits the spinal canal above the disc space). Radiculopathy at the L5 root causes intense pain in the extremity, as noted above, and may be associated with a weak dorsiflexion of the foot (the extreme case being a foot drop). Numbness will be present on the dorsum of the great toe. A disc fragment at the L5–S1 level will entrap the S1 nerve root (the L5 nerve exits above the L5–S1 disc; the S1 nerve crosses it) and may cause a decreased ankle reflex and a weak plantar flexion of the foot.

The hallmark of true lumbar nerve entrapment is significant lower extremity pain in the aforementioned location, with a lesser degree of low back pain per se. Patients with intense low back pain without lower extremity symptoms generally have musculoskeletal insults and/or lumbar joint disease, spondylolisthesis, etc. rather than nerve compression. The first, and most important, clinical decision to make in evaluation of the “back pain” patient is whether it represents a mechanical lumbar spine process (with predominant low back pain) or a neural compressive (lumbar radicular) process. The symptoms often are aggravated by activity, as well as by coughing and sneezing. Coughing and sneezing cause an increase in spinal fluid pressure, which is transmitted to the irritated nerve root.

Other subsystem diseases can mimic lumbar radiculopathy (sciatica) very closely. The patient with lumbar pain and lumbar pain with true radiculopathy should always have a thorough review of subsystems. Nephritis, invasive colonic or gynecologic neoplasia, metastatic spine tumors, diabetic neuropathy, ectopic pregnancy, abdominal aortic aneurysm, and hip arthritis can all present with low back pain and/or symptoms consistent with radiculopathy. Careful attention to the history and other subsystem symptoms will avoid this serious pitfall.

Physical examination often will find an increase in the pain when the leg is raised, thereby flexing the patient at the hip and stretching the involved root (straight leg raising test). Although not essential for the diagnosis, it is often present. The reflexes should be normal to decreased. An L3 or L4 nerve root may cause a decreased knee reflex, L5 often causes no change, and S1 radiculopathy may decrease the ankle reflex. Motor loss in the quadriceps would be noted in the L3 nerve root presentations; the L5 and S1 nerve losses are as noted above.

The natural history of lumbar radiculopathy is often one of natural resolution. Greater than 80 percent of patients with true lumbar root entrapment improve dramatically over 2–4 weeks with no specific intervention. Although many “conservative” measures have been used (e.g., bed rest, chiropractic, traction, physical therapy, etc.), most studies suggest that the simple passage of time allows many such radiculopathies to clear. Patients seen acutely should have a thorough subsystem clearance as noted above (a complete blood count and urinalysis will aid in this regard), possible plain films of the lumbar spine to rule out occult compression, fracture from metastatic disease, spondylolisthesis, etc., and then patient observation for 2–3 weeks. Analgesics such as the modest use of codeine (30 mg PO q3–4h) and an anti-inflammatory agent usually will suffice to tide the patient over the acute phase. Only if there is no improvement after 3 weeks should intervention be contemplated. Final diagnosis can be made with MRI of the lumbar spine or lumbar myelography and a postmyelogram CT scan. If a disc fragment is found as the cause of the problem, surgical decompression and disc fragment removal are effective. The results in properly selected patients (i.e., those with primarily neural compressive presentations as opposed to pure low back pain) are good.

Cervical As noted in the lumbar spine, degenerative changes may cause compression of neural structures in the cervical spine. This may present as nerve root entrapment (cervical radiculopathy) or as spinal cord compression (cervical myelopathy).

Cervical radiculopathy most commonly affects the C5, C6, or C7 roots. Neck pain is present in most patients, but the predominant pain courses into the muscle masses of the arm and terminates as numbness in the appropriate dermatome in the hand. Weakness in the deltoid (C5), biceps (C6), or triceps (C7) may be present. A review of subsystems must be made to exclude high lung tumors (Pancoast) as a cause of nerve involvement. Many patients improve with conservative care (from collar and analgesics, occasionally traction) over 3–4 weeks. Those who fail become candidates for MRI or myelogram to define the diagnosis. Both posterior surgical approaches (posterolateral foraminotomy) and anterior cervical discectomy are effective means of alleviating the problem. In properly selected patients, over 90 percent are improved after surgery.

Cervical myelopathy is a more serious disorder that presents as progressive spinal cord dysfunction owing to a decrease in the dimension of the spinal canal with advancing degenerative changes. Some or all of five clinical examination hallmarks will be present with myelopathy: (1) clonus, (2) hyperreflexia, (3) decreased position sense, (4) abnormal heel to toe walk, and (5) an extensor Babinski sign. A combination of these findings should lead to MRI or myelogram. Decompressive laminectomy, multiple-level anterior decompression, and decompression with instrumentation with fusion have all been effective in relieving the compression in the spinal cord. Results vary with the severity of the spinal cord dysfunction at the time of admission.

INFECTIONS

Infections may enter the central nervous system by (1) hematogenous spread (e.g., a cardiac anomaly such as atrial septal defect or ventricular septal defect), (2) contiguous spread (e.g., middle ear, sinus infections), or (3) contamination by penetrating trauma. The infection may accumulate in the brain itself (cerebral abscess) or in the subdural or epidural spaces (empyemas). The mortality rate is very high (>35–40 percent) if left untreated. The patient generally complains of severe headache and may have focal deficits such as hemiparesis, speech loss, etc. Emesis may accompany the headache due to an elevation in ICP. The empyema patient often is “toxic” on presentation with febrile episodes, chills, and leukocytosis. The cerebral abscess patient may have a normal white blood count and only a modest temperature. The erythrocyte sedimentation rate (ESR) is usually elevated in both cases. Diagnosis is established with CT scanning. Emergent craniectomy or craniotomy is needed for drainage and culture. Multiweek intravenous antibiotics (i.e., ceftriaxone, metronidazole, and nafcillin combined) are used postoperatively.

CONGENITAL AND DEVELOPMENTAL ABNORMALITIES

Approximately 2 percent of newborns possess some type of congenital abnormality. Sixty percent of these involve the central nervous system, and over half of these are related to defective development or closure dorsal midline structure (Table 40-3).

TABLE 40-3 CONGENITAL NEUROLOGIC MALFORMATIONS

Spinal Dysraphism

This is a failure of the neural groove to close posteriorly in the midline to form a neural tube. Dysraphism implies an abnormal fusion of normally united parts. Spina bifida occulta is the failure of bony structures to close. Patients with this anomaly have a normal spinal cord and normal cord function. This is usually a radiographic finding. If the meninges fail to close, a meningocele develops, producing a cutaneous abnormality without compromise of neurologic function.

Failure of the neural tissue to fuse is called spina bifida aperta. Myelomeningocele is the more common form and usually occurs in the lumbar region. It may be partially or totally covered with epithelium, and the accompanying neurologic deficit usually consists of complete absence of motor and sensory function below the level of cord involvement. The most severe form of spinal dysraphism is myeloschisis, which occurs in the thoracolumbar region and usually is associated with paraplegia.

Both myelomeningocele and myeloschisis are associated with hydrocephalus, which is caused by a developmental abnormality of the hindbrain. The treatment of spinal dysraphism is surgical. Meningoceles are excised; myelomeningoceles and myeloschisis are closed as early as possible to reduce the risk of meningitis.

Cranial Dysraphism

This is about one-tenth as common as spinal dysraphism and consists of a midline skull defect through which small portions of the brain protrude, creating an encephalocele. It should be treated by surgical repair, and only 35 percent of the patients attain normal intelligence.

Hydrocephalus

Hydrocephalus implies an increase in the amount of CSF within the ventricular system. It is almost always due to a decrease in the absorption of fluid and is classified as communicating and noncommunicating, related to the presence or absence of communication with the subarachnoid spaces outside the brain through the fourth ventricular foramina.

Infantile Hydrocephalus This usually occurs before the second year of age and frequently is due to a congenital abnormality but occasionally is the result of meningitis or ICP. The patients often have a bulging anterior fontanelle and distended scalp veins.

Childhood Hydrocephalus Causes include tumors, meningitis, and intracranial hemorrhage. The patients present with headache, nausea, vomiting, lethargy, and coma.

Adult Hydrocephalus This results from obstructive tumors, meningitis, and hemorrhage. It may be idiopathic.

The treatment of all types of hydrocephalus is by ventricular fluid shunting. The most commonly used procedure is a lateral ventricle to peritoneal cavity shunt with a one-way pressure-regulating valve in the system.

Craniosynostosis

This is the premature closure of one or more of the cranial sutures. It usually manifests within the first 6 months of life. This may compromise brain growth, and treatment is surgical, with opening of the affected suture(s) along its entire length. The operation should be carried as soon as the diagnosis is made to accommodate brain growth.

NEUROSURGICAL MANAGEMENT OF PAIN

Cranial Nerves Trigeminal neuralgia is one of the more commonly occurring neuropathic painful conditions. It presents as pain in one of the divisions of the trigeminal nerve and may be extremely severe. The evaluation should include a CT scan or MRI. The surgical treatment is the production of preganglionic lesions in the involved branch(es). Retrogasserian rhinotomy may be performed. A nonablative approach involves microvascular decompression of the trigeminal nerve in the posterior fascia.

Spinal Cord Surgical procedures on the spinal cord for ablation of pain include cordotomy to obliterate the spinothalamic tract. This rarely is effective for chronic pain conditions. Ablative lesions can be made in the dorsal route entry zones of the spinal cord, and about 50 percent of patients obtain relief. Intrathecal morphine can be given temporarily or permanently by infusion of small doses. In chronic painful states of nonmalignant spinal origin, transcutaneous excitatory nerve stimulation (TENS), which blocks nerve conduction of pain impulses, may be effective.

Peripheral Nerve Pain from a partial or complete nerve injury follows the sensory distribution of that nerve. Chronic pain may be altered by interruption of the sympathic nerve supply to the affected extremity. Major causalgia is most commonly related to partial injury of the sciatic or median nerve and may be treated by sympathetic denervation.

EPILEPSY AND MOVEMENT DISORDERS

Epilepsy

The removal of specific areas of the brain can cure epilepsy. Epilepsy has many causes. Congenital anomalies of the brain are common in the pediatric age group. Birth injury also has been implicated. EEG and MRI are monitoring tools to select the patients who will benefit from an operation and to define the region to be ablated. Seizure surgery is performed with the patient under local anesthesia, and electrocorticography is carried out to identify the focus of the seizures.

Movement Disorders

The most commonly recognized of these is Parkinson's disease. The symptoms of tremor and cogwheel rigidity have been controlled with dopamine supplements. Surgical approaches have been used, and currently, stereotactic methods to accomplish pallidotomy have become popular.

RADIOSURGERY

Radiosurgery is a highly focused ionizing radiation used to treat lesions in the depths of the brain. The technique using the so-called gamma-knife allows delivery of radiation to a specific target without adverse affects on the surrounding tissue. Other systems use different techniques to achieve focused-radiation ablation of tumors. Radiation surgery is particularly adaptable to deep intracerebral lesions. It causes sclerosis of vascular structures and necrosis of tumors. It is used to treat neoplasms such as intracranial schwannomas and meningiomas.

PEDIATRIC NEUROSURGERY

Myelomeningocele is expressed as a failure of closure of the neural tube, generally in the lumbar region. The patient often has a significant neurologic deficit below the lesion. Chiari II malformation (caudal descent of cerebellar tonsils with brainstem compression and microgyria) and hydrocephalus are present in over 80 percent of patients. The myelomeningocele is closed within 24–48 h to reduce the risk of meningitis. The hydrocephalus and Chiari malformation are treated if clinically appropriate as the child progresses. The incidence of this anomaly has decreased markedly with the advent of perinatal ultrasound, alpha-fetoprotein protein testing, etc.

Hydrocephalus in children may result from a multitude of causes: aqueductal stenosis, after meningitis, after intraventricular hemorrhage, and less commonly owing to tumors blocking CSF drainage pathways. The patient often presents with progressive enlargement of the skull, a full fontanelle (if patent), headache, emesis, and blunting of developmental milestones. Therapy is primarily surgical; placement of a ventriculoperitoneal shunt system is preferred. Intellectual capabilities in later years depend on the cause and severity of the hydrocephalus.

For a more detailed discussion, see Hoff JT, Boland MF: Neurosurgery, chap. 40 in Principles of Surgery, 7th ed.

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Copyright © 1998 McGraw-Hill

Seymour I. Schwartz

Principles of Surgery Companion Handbook