Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

456 Small Animal Radiolo g y and Ultrasono graphy
the root of the mesentery, along the mesentery adjacent to the intestines, caudal to the
stomach, along the course of the portal vein, adjacent to the ileocecocolic junction, and in
the sublumbar region. The ultrasonographic appearance of the lymph nodes is not particularly
helpful in distinguishing neoplastic from infectious or reactive lymphadenopathy.
Lymph node masses may become large and can be misinterpreted as splenic, hepatic, or
intestinal masses.
END O CRINE SYSTEM
ABNORMAL FINDINGS
A D R E N A L G L A N D S
The major abdominal endocrine organs are the adrenal glands and the pancreas (discussed
previously in this chapter under the GI system). In the normal animal, the adrenal
glands are not seen radiographically. In some cases of neoplasia, the adrenal
enlargement may be mineralized and apparent on the survey radiograph (Figs. 3-278 and
3-279). In cats, dense mineralization has been noted without evidence of adrenal
enlargement, neoplasia, or other disease (Fig. 3-280). The significance of this
mineralization is unknown. One radiographic special procedure that may be helpful in
evaluating the adrenal gland is the pneumoperitoneum, using a dorsoventral or standing
lateral view with a horizontal x-ray beam (Fig. 3-281). An indirect indication of hyperfunctioning
adrenal cortical status, although not specific, is symmetric hepatomegaly
and nominal vertebral osteopenia, actually osteoporosis. 914-917 Some adrenal, as well as
some renal, tumors extend into the caudal vena cava or surround the aorta or both. A
nonselective contrast venogram may show the obstruction or abnormal venous blood
flow patterns. The reproducibility of lesions on serial studies is a key factor in differentiating
the normal turbulent renal venous flow into the caudal vena cava and true infiltrative
and invasive lesions.
Ultrasonography of Adrenal Abnormalities. The adrenal glands can be measured
directly from the ultrasonographic image. 39,41,918 Changes in size can be detected provided
care is exercised in obtaining a true sagittal and transverse image so that the
dimension of the adrenal gland is not altered due to obliquity. There are several reports
of what is thought to represent normal adrenal measurements by ultrasonography.
39,41,918 How adrenal measurements are interpreted seems to depend on a combination
of technical skills and the desired interpretive sensitivity. Readers are referred to the
cited reports and from them the individual’s comfort level of interpreting normal versus
abnormal size can be determined. If the range is set too narrow, the problem of false-positive
assessment occurs. If the range is set too wide, the problem of false-negative diagnoses
occurs. Currently we use anything less than 20 mm long and less than 5 to 6 mm
wide with reasonable glandular symmetry as normal in dogs, but that may change with
further refined measurements. In our experience, it is possible for there to be hyperadrenocorticism,
usually pituitary dependent, in the presence of what would be considered
sonographically normal adrenal glands. Most abnormalities result in an adrenal
gland that is asymmetric (e.g., a focal bulge), diffusely enlarged, and hypoechoic,
although large masses may be heteroechoic (Figs. 3-282 and 3-283). 43-45,919-926 The echo
intensity of adrenal masses often is similar to that of the renal cortex, although adrenocortical
tumors range from hypoechoic to hyperechoic. The hypoechoic regions may represent
hemorrhage, necrosis, or very tightly packed cells (e.g., lymphoma). 43,924
Distortion of the shape of the gland may be evident, with rounded nodules causing the
gland to be asymmetrically shaped. Nonmalignant hyperfunctioning nodules and early
tumors are indistinguishable. Cavitation of the adrenal mass may produce hypoechoic
areas within a heteroechoic mass. Pheochromocytomas appear heteroechoic with ultra-