Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

424 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-226 A 10-year-old male
Poodle with urinary obstruction,
pyrexia, and swelling of the inguinal
and perineal areas. There were three
radiopaque calculi located approximately
2 cm proximal to the base of
the os penis as well as several cystic
calculi seen on the survey radiograph.
The urethrogram revealed
extravasation of contrast medium
into the corpus cavernosum urethra
(white arrow) at the site of the urethral
calculi. The urethra proximal to
this is narrowed, which may be the
result of urethral spasm or periurethral
edema or fibrosis.
Diagnosis: Ruptured urethra secondary
to urethral calculi, urethral
spasm, and cystic calculi.
Congenital anomalies, such as urethrorectal fistulas, urethral diverticula, and duplicate
urethra, have been demonstrated by urethrography (Fig. 3-230). 740-743 The contrast will be
observed entering the abnormal location if a fistula is present. 741 Urethral diverticula are
easily identified as outpouchings of the urethra that contain contrast material. These outpouchings
should be consistent on two views or on the same view after two separate contrast
injections.
Urethral Ultrasonography. The urethra does not lend itself to ultrasonographic examination
because it is contained within the pelvic canal. The prostatic urethra may be
observed as an anechoic linear or oval area within the prostate if the prostate gland can be
visualized. 54,57 In most cases, the prostatic urethra is not identified in its entirety. Calculi
may be identified within the urethra as hyperechoic focal lesions that cause shadows. This
is rarely observed, however, and is not necessary for the diagnosis or evaluation of urinary
calculi. Urethral carcinoma may extend onto the bladder neck, and this lesion may be identified
using ultrasonography. 716 An increase in the urethral diameter producing a heteroechoic
round or oval structure without an increase in the size of the urethral lumen usually
is observed in these cases.
OVERVIEW LOWER URINARY TRACT
The techniques and diseases relevant to the lower urinary tract have been described in the
preceding sections. However, some perspective is necessary. First, there is no one lower urinary
tract contrast procedure that can identify all abnormalities. Therefore one of the
authors recommends using a lower urinary tract contrast series that includes a pneumocystogram,
lateral view only; a double-contrast cystogram, one lateral and ventrodorsal
view at a minimum, with the opposite recumbency lateral view and a dorsoventral view
considered as options if there are questions; a positive-contrast cystogram, lateral and ventrodorsal
views; and either a voiding or retrograde urethrogram, lateral and ventrodorsal
(oblique in male dogs) views. This sequence eliminates questions on the survey radiographs,
such as suspicious bladder radiopacities, that disappear on the pneumocystogram.
These opacities would reappear as filling defects on the double-contrast study.
Some equivocation is expected with lower urinary tract imaging techniques, but this series
eliminates unnecessary confusion.