Imaging Findings

Bladder calculi often are nonopaque or only faintly opaque, allowing them to be frequently overlooked. Fecal material and gas in the rectosigmoid colon and the sacrum itself also overlie the area and may further obscure them. Bladder calculi usually are located centrally in the pelvis (Fig. 29-1). Those that are found more laterally may lie in a bladder diverticulum.²⁰

Clinical Comments

The presentation of vesical calculi varies from completely asymptomatic to symptoms of suprapubic pain, dysuria, intermittency, frequency, hesitancy, nocturia, and urinary retention. Bladder calculi may abrade and irritate the mucosa and predispose to infection. Bladder infections are more difficult to treat when calculi are present. Ureteral or bladder outlet obstruction may also be present.²⁰ Approximately 15% of patients with gout, as well as hyperuricemic patients, produce uric acid stones.²⁰

Standard treatment of bladder stones consists of endoscopic visualization and fragmentation by electrohydraulic probe.⁴⁶ Massive calculi may require open surgery.⁴⁶

Imaging Findings

Wilms tumor appears radiographically as a complex renal mass (Fig. 29-2). Approximately 5% to 10% of these lesions show areas of calcification, but calcium, when seen in a mass in this area, is much more likely to be in a neuroblastoma of the adrenal or other similar tissue.²⁷ Intravenous pyelography shows either a displaced or a nonfunctioning kidney. Ultrasonography typically reveals a well-defined tumor, often surrounded by a hyperechoic halo of compressed normal renal tissue.^17,21 Noncontrast computed tomography (CT) usually reveals a large intrarenal mass of lower attenuation than the adjacent normal kidney. Cystic spaces or areas of tumor necrosis appearing as inhomogeneous, low-density areas are seen in most tumors.¹⁷

Clinical Comments

Patients with Wilms tumor present with an abdominal mass in more than 90% of cases.¹⁷ Approximately 50% of patients experience hypertension or fever. Hematuria is relatively uncommon.17,27 No male or female predominance is noted.¹⁷ Up to 30% with the rare condition of aniridia (congenital absence of the iris) develop nephroblastoma.²⁷ A total of 4% to 5% of cases show bilateral tumors.²⁷

Imaging Findings

Radiographically, cortical nephrocalcinosis can be differentiated from the medullary variety by the peripheral location of the calcification. Medullary calcification is typically that of bilateral, diffuse, fan-shaped clusters of stippled calcifications, primarily in the renal pyramids (Fig. 29-3). Although precipitating conditions are most often systemic, the presentation of calcification is not universally bilateral and symmetrical. Unilateral and focal presentations are common (Fig 29-4), suggesting that intrinsic factors, such as vascularity, may be involved.

Clinical Comments

The two most common etiologies of cortical nephrocalcinosis are acute cortical necrosis and chronic glomerulonephritis, although radiographically evident calcification is rare in both conditions. Persons on chronic dialysis may have similar calcifications.

Roughly 40% of cases of medullary nephrocalcinosis are attributable to primary hyperparathyroidism, another 20% to renal tubular acidosis, and the remaining 40% divided among many other causes.

Imaging Findings

Ultrasonographically, most stones larger than a few millimeters show shadowing. However, ultrasonography is not the procedure of choice in diagnosis because too many false-negative studies exist. In intravenous pyelography, the radiolucent stones can be difficult to differentiate from blood clots or sloughed tissue. (All of these can obstruct drainage from the kidney.) With CT, all stones are denser than unenhanced renal parenchyma and urine.

Segments of the urinary tract proximal to the stone may show varying degrees of dilatation depending on the degree and chronicity of occlusion created by the stone (Fig. 29-7). Not all dilated drainage systems are from stones and other intrinsic filling defects; crossing bands of vessels or congenital narrowing can give the same appearance on intravenous pyelograms. Up to 90% of renal calculi are opaque enough to be seen on plain film radiographs.

Clinical Comments

Low urine volume and stasis contribute to formation of both calcareous and noncalcareous stones by increasing the urinary concentration of stone-forming constituents.

Renal calculi in the ureters cause renal colic, which has a dramatic clinical presentation, often with severe flank pain. Stones remaining in the renal pelvis may lead to obstruction. If they pass into the bladder, on unusual occasions, they may act as the nidus of a bladder calculus.