Smiths General Urology, Seventeenth Edition (LANGE Clinical Medicine)

Authors: Macfarlane, Michael T.

Title: Urology, 4th Edition

Copyright 2006 Lippincott Williams & Wilkins

> Table of Contents > Part One - Chief Presentations > Chapter 15 - Abdominal Masses

Chapter 15

Abdominal Masses

Pediatrics

An abdominal mass in children most commonly arises from the urinary tract or adrenals and should therefore be worked up by a urologist until imaging studies prove otherwise. A hydronephrotic kidney secondary to ureteropelvic junction (UPJ) obstruction is the most common cause of a unilateral abdominal mass in childhood, followed by a multicystic kidney. Neuroblastomas or Wilms' tumors are the most common causes of a solid abdominal mass in children.

Differential Diagnosis of Abdominal Mass in Children

Imaging Techniques

• Ultrasound should be the first imaging study performed. It will provide differentiation of solid from fluid- or blood-filled masses in most cases and give localization to a specific area of the abdomen.

• Intravenous (IV) urography is often unsatisfactory during the first weeks of life because of the poor concentrating ability of the neonatal kidney. However, it provides valuable anatomic and functional detail for diagnosis of retroperitoneal masses. The addition of a furosemide (Lasix) washout test can help identify partial obstruction.

• Mertiatide (MAG3) renal scan with Lasix is an alternative first choice for the clearly cystic mass. It will give information on renal function and identify partial UPJ obstruction.

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• Computed tomography (CT) will give more accurate anatomic localization of solid masses and help further differentiate equivocal masses as solid versus cystic.

• Voiding cystourethrography (VCUG) should be performed on all hydronephrotic masses to differentiate obstruction from reflux.

• Anterograde pyelography via a percutaneous nephrostomy is often helpful to determine the level of obstruction while providing urinary drainage and information on the potential for functional recovery of the kidney.

• Cystoscopy with retrograde pyelography will provide information on the status of the lower ureter and bladder when needed.

Adults

Renal masses are increasingly being discovered incidentally during abdominal CT scans, ultrasound, or IV urography performed for unrelated reasons. These masses will require further workup for definitive diagnosis and treatment if indicated. The classic triad of flank mass, flank pain, and hematuria that heralds a renal cell carcinoma occurs in only less than 10% of patients.

Differential Diagnosis of a Flank Mass in Adults

Imaging Techniques (see Chapter 36)

• Ultrasound is the simplest method of differentiating a solid from cystic structure, and a cyst can be diagnosed with 98% accuracy if all criteria are met.

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• IV urography is still the best imaging technique for the renal collecting system and gives good definition of a renal mass when tomography is used. Improved diagnostic and staging accuracy can be obtained from CT or magnetic resonance imaging (MRI).

• CT scan first without and then with IV contrast enhancement is the single best method to evaluate a retroperitoneal flank mass. It discriminates well between solid and cystic lesions and can often demonstrate renal vein and/or inferior vena caval extension.

• MRI is an important modality for evaluating abdominal mass. Renal vein and inferior vena cava extension can be accurately determined. MRI can be used in patients who cannot receive IV contrast agents because of contrast allergy, renal insufficiency, or renal failure. MRI with gadolinium-diethylenetriamine pentaacetic acid (DTPA) has no nephrotoxic effects.

• Cyst puncture by ultrasound or CT guidance for cysts that do not meet the full criteria of a simple cyst may be helpful.

• Renal arteriography can demonstrate the classic hypervascularity of renal cell carcinoma; however, it has largely been displaced by CT scans and MRI for diagnostic purposes. Arteriography is still indicated when vascular anatomy is needed to help plan a partial nephrectomy.

• Venacavography should be performed if renal vein and inferior vena cava involvement is in doubt.

Renal Cysts

Approximately 20% to 25% of routine ultrasonography and abdominal CT scans reveal unexpected renal cysts. Differentiating simple cysts (benign) from complex renal cysts (15% potentially malignant) can be a challenge. Using the Bosniak classification can help categorize various renal cysts to help make clinical management decisions. Renal ultrasound and a renal protocol CT scan (thin section without and with IV contrast) are the most useful diagnostic techniques. Differentiation of Bosniak II and III cysts can be difficult.

Bosniak I Simple Cyst

A simple renal cyst has thin walls, no internal echoes or septations, no calcifications, and CT Hounsfield units (HU) of 0 to 20 with no contrast enhancement. These are extremely common and require no further workup.

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Bosniak II Benign Minimally Complex Cyst

Bosniak II cysts can include a few thin septa, minimal calcification, infected cysts, and high-density hemorrhagic cysts. These have low malignant potential and can be treated nonsurgically. If any criteria are in question, then these cysts should be followed with repeat CT scan in 3 to 6 months and annually as indicated.

Bosniak III Moderately Complex Cyst

These are truly indeterminate cysts, with 50% of these lesions being malignant. Bosniak III cysts have numerous or thick septa, thickened walls, irregular calcification, or multiloculated features. These cysts should generally be managed with surgical exploration and partial nephrectomy if technically feasible.

Bosniak IV Cystic Malignant Tumors

These are characterized by enhancing nodular walls or obvious solid components. Greater than 90% of these will prove to be malignant and should be managed with partial or radical nephrectomy.

Hydronephrosis

Hydronephrosis can be detected by ultrasound and is best evaluated by IV urography and retrograde studies.

Solid Tumor

A solid tumor by ultrasound can best be localized to the kidney or adrenal by CT or MRI. A solitary solid renal tumor must be presumed to be renal cell carcinoma and should undergo surgical removal (see Chapter 24). An exception is a solid renal tumor with clear evidence of fat within the tumor on CT scan (-50 to -150 HU). This is strong evidence for an angiomyolipoma and may be followed up. An adrenal tumor will require the appropriate workup (see Chapter 25).

Tumor Calcifications

Calcifications, although occurring in less than 5% of renal masses, increase the suspicion of malignancy. Mottled central calcifications indicate a solid mass and are usually a sign of renal cell carcinoma (>90% specificity). A peripheral calcification, although often a cyst, is associated with renal cell carcinoma in at least 20% of cases.

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