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.
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