CLINICAL INFORMATION
IMAGING OVERVIEW
IMAGING WITH RADIOGRAPHS TABLE 34-1 Types of Renal Stones | ||||||||||||||||||||
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 TABLE 34-2 Causes of Urolithiasis | |||||||||||||||||||||||||||||||||||
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Nephrolithiasis
Nephrolithiasis
Daniel J. Durand
Karen M. Horton
Nephrolithiasis is the most common cause of urinary tract obstruction. Approximately 90% of calculi are radiopaque on radiographs whereas almost all stones are radiopaque on computed tomography (CT). The only exceptions are radiolucent stones that can form in patients on protease inhibitors such as Indinavir. Renal stones are commonly classified according to their predominant chemical composition (Table 34-1). In addition to obstruction, renal calculi can also cause stricture formation, chronic renal infection, or loss of renal function.
CLINICAL INFORMATIONThe major etiologies of nephrolithiasis are listed in Table 34-2.
Symptoms and signs of passing a ureteral stone include pain and hematuria, although stone passage is occasionally asymptomatic. The pain usually begins in the flank and gradually increases over minutes to hours until it is so severe that narcotics may be required for pain control. Classically, the pain fluctuates and is known as renal colic. Downward migration of the pain toward the groin indicates passage of the stone into the distal third of the ureter. Hematuria is present in approximately 85% of cases.
Differential diagnosis of renal colic includes urinary tract infection, appendicitis, diverticulitis, gynecologic conditions, lumbar disc disease, and abdominal aortic aneurysm (with or without dissection).
IMAGING OVERVIEWRadiologic imaging has always played a central role in the evaluation of suspected nephrolithiasis. Although several imaging modalities are potentially useful in detecting stones or secondary signs of obstruction such as hydronephrosis, noncontrast CT (NCCT) has become the test of choice over the last decade due to its speed and accuracy. Nevertheless, other modalities such as ultrasonography may be of use in situations when there are concerns over radiation exposure or cost.
IMAGING WITH RADIOGRAPHSIndications.
Because most renal stones are radiopaque, the workup often begins with a plain abdominal radiograph. The stone may be difficult to visualize, however, due to overlying bowel gas, fecal material, and phleboliths. Recent studies indicate that abdominal radiographs have a sensitivity and specificity of 53-59% and 71-74%, respectively.
Protocol.
Typically, a kidney, ureter, and bladder (KUB) is obtained. Oblique views can sometimes help to determine if a suspicious calcification is in the kidney or ureter. On the oblique view, a potential stone should “move” with the kidney and the expected course of the ureter.
