Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 405
der wall; and the presence or absence of material within the contrast puddle on the double-contrast
cystogram.
Shape. Changes in the shape of the bladder may indicate the presence of a bladder diverticulum,
persistent urachal remnant, localized mural or extramural inflammation, or neoplasm.
Diverticula are protrusions of the lumen and cystic mucosa through a rent in the
serosa. 692 They will appear as extensions of either the gas or contrast medium beyond the
serosal border of the bladder but are contained within the bladder wall. These may be congenital
or acquired as a result of trauma. The urachus normally involutes immediately after
birth to become the middle ligament of the bladder. When this occurs, the cranial wall of
the bladder remains regular and smooth. In some instances, involution is incomplete or the
urachal remnant becomes recanalized and provides an outpouching of the bladder lumen
on its cranioventral aspect (Fig. 3-198). Diverticula and persistent urachal remnants provide
an area for urine retention and stagnation. This situation may predispose to chronic
cystitis but also can be the result of the dysuria from cystitis.
Infiltrative tumors and granulomas (e.g., from a uterine stump) may interfere with
normal bladder distention and may alter the shape of the bladder. These also produce a
mass within the bladder lumen that is much more easily detected on a cystogram than is
the lack of bladder wall distensibility.
Bladder Wall Changes. Bladder wall changes are the most common cystographic abnormality.
The normal bladder wall appears very smooth and consistent in thickness, approximately
1 to 2 mm. The appearance of even a few millimeters of increased thickness
compared with the rest of the bladder wall is significant. Bladder wall thickening and irregularity,
which is associated with the inflammation of cystitis, usually is seen in the cranial
ventral aspect of the bladder (Fig. 3-199). One theory is that this site is predisposed to
change because it is normally the most dependent portion of the bladder; therefore bacteria
and other particulate matter tend to accumulate there. Another consideration is that it
may be the site most predisposed to retention of small amounts of urine and, therefore, to
the greatest exposure to toxic or inflammatory substances. The entire bladder circumference
may become thickened and irregular secondary to chronic inflammation. This is common
in the sterile cystitis associated with cyclophosphamide therapy. 693-695 Bladder wall
ulceration is most commonly associated with cystitis. The ulcers appear as small areas of
contrast medium adhering to the bladder wall (Fig. 3-200). However, when severe ulceration
is noted, more aggressive processes should be considered. 696-698 The other major cause
of bladder wall thickening is neoplasia. The most common tumor of the bladder is transitional
cell carcinoma. This is usually focal in nature but may, on occasion, be generalized
and diffuse. The mucosal surface may be smooth, but more commonly it is thrown up into
folds, with masses protruding into the lumen of the bladder. Occasionally, a focal tumor
may cause bladder wall thickening on the cranial ventral aspect of the bladder, making
Fig. 3-198 A 1-year-old neutered
female domestic short-haired cat
with urinary tract infections for the
past 5 months. A, There is a projection
of a tubular-shaped, soft-tissue
density extending from the apex of
the urinary bladder toward the
umbilicus (white arrows). B, The
double-contrast cystogram revealed
contrast medium within the tubular
structure (white arrow). Differential
diagnoses include persistent urachal
remnant or cystic diverticulum due
to other causes (trauma). Diagnosis:
Persistent urachal remnant.
A
B