Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 351
Position Changes. The cecum and ascending colon have a relatively constant position
within the abdomen. In a small percentage of dogs (and occasionally in cats), the colon
will be reversed from its normal position without generalized situs inversus being present.
In both species, the transverse colon usually is found immediately caudal to the
stomach on the ventrodorsal view. If the transverse colon is displaced caudally, a pancreatic
or splenic mass may be present. Colonic displacement to the left can occur secondary
to pancreatic or right renal masses or with intussusception of the distal small
intestine or cecum, or both, into the ascending and transverse colon. Torsion may cause
gross alteration in the normal location of the colon with marked distention of the colon
with gas. Fortunately this is uncommon. As the colon passes through the pelvic canal,
displacement from the midline on the ventrodorsal view may indicate a pelvic canal
mass, a perineal hernia, or pararectal tumor. On the lateral view the colon may be ventrally
displaced as it passes through the cranial portion of the pelvic canal. This usually
indicates enlargement of the sublumbar (external iliac, internal iliac, and coccygeal)
lymph nodes or some other caudal retroperitoneal mass (extension of a pelvic canal neoplasm).
Dorsal colonic displacement in this area indicates a ventral mass that usually is
due to prostatic or uterine enlargement or urethral tumor. Both dorsal and ventral narrowing
may occur in cases of prostatic carcinoma with metastasis to the sublumbar
lymph nodes, or may be due to a tumor or stricture within the wall of the colon. Because
the position of the colon varies normally depending on its content, displacement of the
colon from its normal position indicates that the area from which the colon is displaced
should be examined carefully. If a mass displacing the colon is not seen, then the displacement
is a normal variation.
The dog’s cecum often contains gas. It is not always identifiable, however. In a dog with
a history of chronic tenesmus, failure to identify the cecum or identification of a small
tubular mass in the proximal colon may indicate cecocolic intussusception (Fig 3-125). 406
Special Procedure Findings. Many colonic diseases are apparent only by direct examination
such as endoscopy or by use of contrast radiography, including pneumocolon or barium
enema. The fiberoptic endoscope is usually more accurate than most radiographic
special procedures for evaluation of the colon. The major exception occurs when luminal
narrowing or stricture does not permit passage of an endoscope or the process in the colon
has no mucosal extension.
Fig. 3-125 An adult mixed breed
dog with tenesmus and abdominal
tenderness. Radiographic findings
include ascending colonic lumina
outlining a blunted-ended ovoid
object extending from the ileocecocolic
junction without visible gas in
the cecum (arrow, expected to be
adjacent to the proximal portion of
the ascending colon). Diagnosis:
Cecocolic intussusception confirmed
by barium enema.