Genitourinary Radiology, 6e by unknow

Author:unknow
Language: eng
Format: epub

The plain abdominal radiograph is a useful examination in evaluating patients suspected of having urolithiasis. While up to 90% of urinary tract calculi are radiopaque, as many as 50% of urinary tract stones may not be detected on conventional abdominal radiographs, due to overlying bowel gas and stool, as well as overlying bones (ribs, lumbar spine, iliac bones, and sacrum). The lateral tips of the transverse processes can be especially confusing because their cortical margin may mimic a ureteral stone.

Calcium oxalate and phosphate, magnesium ammonium phosphate, and cystine stones are generally well seen on plain abdominal radiographs (Figs. 11.1 and 11.2). Calcium oxalate monohydrate stones are the most radiopaque (Fig. 11.3), while most cystine stones are often only faintly opaque. Uric acid stones are insufficiently radiopaque to be seen on an abdominal radiograph and account for the majority of radiolucent stones. Xanthene, matrix, and metabolic stones are also radiolucent.

Many common calcifications in the abdomen must be distinguished from urinary tract stones. Hepatic or splenic calcifications are seldom a problem because they rarely overlie the kidneys. However, stones in a low-lying gallbladder may overlie the right renal collecting system. In most cases, gallstones are larger than kidney stones and have a characteristic rounded or ovoid shape. This allows them to be distinguished from renal calculi. However, renal calculi in an obstructed portion of the collecting system or within a calyceal diverticulum (Fig. 11.4) may mimic gallstones. On an oblique radiograph, gallstones should rotate anteriorly, whereas renal stones remain in a more posterior location.

FIGURE 11.1. Calcium oxalate stone. An abdominal radiograph shows a small radiopaque stone in the upper pole of the left kidney (arrow).

FIGURE 11.2. Magnesium ammonium phosphate stone. An abdominal radiograph in a patient with chronic urinary tract infection shows a large calculus composed of magnesium ammonium phosphate in the lower pole of the right kidney (arrow).

FIGURE 11.3. Calcium oxalate monohydrate stone. An abdominal radiograph shows multiple stones in both kidneys (arrows). The stones are very radiopaque, a finding characteristic of calcium oxalate monohydrate stones. On chemical analysis, the stone consisted of 70% calcium oxalate monohydrate and 30% calcium phosphate.

FIGURE 11.4. Plain radiograph of stones in a calyceal diverticulum. A conventional abdominal radiograph shows a cluster of multiple small rounded stones in the right upper quadrant. These were subsequently confirmed to reside within a renal calyceal diverticulum. Most renal stones are ovoid or triangular in shape rather than round. In fact, these calcifications could be confused with gallstones.

Pancreatic calcification is most frequently seen in patients with chronic pancreatitis. These usually affect the entire pancreas and cross from one side of the abdomen to the other. The involvement of the entire gland helps distinguish these calcifications from renal stones. Calcification of the costal cartilage of the lower thoracic ribs and arterial calcifications are usually linear, which helps differentiate them from renal stones. Furthermore, arterial and rib calcifications lie in predictable locations.

The calcifications most often confused with urinary tract calculi are phleboliths and calcified mesenteric lymph nodes. Typically, phleboliths, which are calcifications

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