Abdominal Radiography - Radiology of the Urinary Tract: Techniques and Normal Anatomy

TECHNIQUES AND NORMAL ANATOMY

This section introduces the common radiologic techniques used in evaluation of the urinary tract, with emphasis on an overview of each technique as it applies to the urinary tract. A discussion of normal anatomy and some important funda-mental concepts of interpretation are included. A basic knowledge of the gross anatomy is assumed, with emphasis placed on the radiographic anatomic correlations.

Abdominal Radiography

Conventional radiographs, or “plain films,” are an inexpen-sive, quick overview of the abdomen and can occasionally provide useful diagnostic information for selected urinary tract indications. A radiograph of the abdomen when used to evaluate the urinary tract is often referred to as a KUB (kidney, ureter, and bladder). “Gas, mass, bones, stones” can be used as a reminder of main areas to examine on the abdominalradiograph. On the normal abdominal radiograph, the renal outline may be visible adjacent to the upper lumbar spine and should be bilaterally symmetric and measure between 3 and 4 lumbar vertebrae in length. The ureters are not discernable, although knowledge of their normal course, between the tips of lumbar transverse process tips and pedicles, along the mid sacral ala, and finally gently coursing laterally below the sacrum to enter the bladder, allows for potential stone identi-fication. The distended bladder may also be visible, if out-lined by fat, on the KUB. The most common genitourinary findings seen on abdominal radiography will be in the form of urinary tract calcifications (Figure 9-1). Unfortunately, the KUB suffers from poor sensitivity and specificity regarding urinary tract calcifications. In the past, it was reported that 80% of calculi were radiopaque and could be identified on conventional radiographs. However, recent studies suggest that no more than 40% to 60% of urinary tract stones are de-tected and accurately diagnosed on plain radiographs. The sensitivity for detection of stones is limited when the calculi are small, of lower density composition, or when there is overlapping stool, bony structures, or air obscuring the stones. Additionally, the specificity of conventional radiography is somewhat limited because a multitude of other calcifications occur in the abdomen, including arterial vascular calcifica-tions, pancreatic calcifications, gallstones, leiomyomas, and many more (more than 200 causes of calcification in the ab-domen have been described). Phleboliths, which are calcified venous thromboses, are especially problematic because they frequently overlap the urinary tract and are difficult to differ-entiate from distal ureteral stones. Lucent centers are a hall-mark of phleboliths, whereas renal calculi are often most dense centrally. Rarely, the conventional radiograph may sug-gest a soft-tissue mass or abnormal air (gas) within the urinary tract. Emphysematous pyelonephritis, a urologic emergency with high mortality, is the result of a renal infection by gas-producing organisms and may be diagnosed on plain films by mottled or linear collections of air within the renal parenchyma. Bony lesions, such as sclerotic bony changes, can suggest metastatic prostate cancer, and lytic bony lesions can be seen with disseminated renal cell carcinoma. Addi-tionally, the bony changes of renal osteodystrophy (diffuse bony sclerosis) may be identified on plain radiographs. Verte-bral anomalies are associated with congenital malformations of the urinary tract. Thus, although the KUB is limited by low sensitivity and specificity, close examination of the “gas, mass, bones, stones” may yield important, sometimes critical, diagnostic information.