Page 337 - Feline diagnostic imaging

21.4 ­olhtrholosorU hapooiqha 345
obscures visualization of structures deep to the surface of shadow revealing its presence. Close observation reveals
the gas so that the far wall is not apparent. In the absence the thin near wall superficial to the gas. Identification is
of much gas, mucosa and ingesta tend to be hyperechoic aided by the lack of contractions in the colon unless fecal
but the far wall remains visible. material is being expelled. Occasionally, both walls will be
seen and the colon will be empty or will contain fecal mate-
rial with minimal or no gas. When empty, the wall has a
21.3.4 Large Intestine
crumpled hyperechoic appearance. The ileocolic valve is
Wall layering is similar to that of the stomach and small prominent in cats and can be seen more often than in dogs.
intestine but the colonic wall is thinner because of the In one study, normal wall thickness for the ileum, colon,
thinner mucosa (Figure 21.13) [16,17,19]. Usually the and cecum was considered to be 3.2, 1.0, and 2.5 mm
colon contains gas so that there is often a dirty acoustic respectively [20].

21.4 Interventional Techniques

Ultrasonography can be used to guide aspiration or biopsy of
gastrointestinal lesions (Figure 21.14). Regional lymph
nodes should also be aspirated if sufficiently large. Fine nee-
dle aspiration can be done using either a freehand technique
or a transducer with a needle guide and 20 or 22 gauge nee-
dle. One technique involves inserting a spinal needle, remov-
ing the stylet and then pulling back on the syringe 3–6 times
[21,22]. Tru‐Cut biopsies can also be done, obtaining sam-
ples 11–20 mm in length. If the lesion is sufficiently large, a
Figure 21.13 Ultrasonography of the normal feline colon. Only “woodpecker” technique can be used, quickly moving the
the near wall is visible because reverberation artifact caused by
gas results in shadowing of the far wall. Calipers are shown needle up and down in the lesion. Regardless of the tech-
measuring the wall at 0.21 cm. nique used, it is important to avoid the lumen.

(a) (b)

Figure 21.14 Ultrasonography showing aspiration of the stomach in two cats. (a) The stomach wall is greatly thickened with a loss
of wall layering. The bevel of the needle tip shows as two short hyperechoic lines (arrow). (b) This stomach also demonstrates a loss of
wall layering and marked thickening. The tip of the needle is indicated by an arrow.