Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 451
extramedullary hematopoiesis, or immune-mediated anemia. Infiltrative diseases of
the spleen, such as lymphosarcoma, can also cause splenic enlargement without altering the
echo intensity or architecture of the spleen. Diffuse alterations in echo intensity of the
spleen may be seen in association with disseminated mast cell tumors and lymphosarcoma,
which may cause a diffuse increase in echo intensity and in splenic torsion which, in turn,
may cause a diffuse decrease in echo intensity (Fig. 3-270). 901-907 Lymphosarcoma most
often produces multifocal hypoechoic lesions that do not alter the splenic contour. 266,907
Focal splenic lesions are more common. Splenic tumor, nodular hyperplasia, hematoma, or
abscess may produce solitary or multifocal lesions (Fig. 3-271). 267,908 These may be hyperechoic
or hypoechoic relative to the normal spleen. Splenic hemangiosarcoma may produce
a mixed or heteroechoic mass with areas ranging from hyperechoic to hypoechoic
when compared with the normal spleen. The hypoechoic regions most likely represent
blood-filled cavernous regions, chronic hematomas, or cysts, while the hyperechoic areas
may represent fibrosis or more recent hemorrhage. 907-911 Myelolipoma may produce large
hyperechoic areas within the spleen. Hyperechoic areas that cause shadowing may be
observed if mineralization of the lesion has occurred. Hematomas may have a similar
appearance, with heteroechoic lesions representing the hematoma in varying states of
organization. Biopsy or aspiration usually is required for a specific diagnosis. 912 Even with
a biopsy diagnosis, the final diagnosis may be unknown, because some reportedly benign
lesions subsequently develop metastatic neoplasia and prove the original tissue diagnosis
incorrect. The presence of other lesions, such as peritoneal or pericardial fluid, or additional
lesions in the liver, are indicators of neoplasia. 913 Lymphosarcoma may be diffuse,
causing a general increase in splenic echo intensity or may produce multiple, poorly marginated
hypoechoic nodules. These nodules do not often alter the splenic contour (i.e.,
bulge from the margin of the spleen). 907 Splenic masses may be very large, and at times
localization of the mass to a portion of the spleen can be difficult. Invasion of the gastrosplenic
ligament and peritoneal seeding with tumor may occur (Fig. 3-272).
In humans, an acute splenic infarct may be hypoechoic or anechoic, wedge-shaped or
round, irregularly delineated or smooth. In dogs, the appearance of splenic infarct (diffuse
hypoechoic) is similar to that of splenic torsion. 902 Splenic necrosis and infarct may produce
focal hypoechoic or isoechoic, circular, well-defined nodular masses with alteration of
Fig. 3-270 Longitudinal sonogram
of the spleen of a 5-year-old female
Great Dane with a history of vomiting,
anorexia, and fever of 8 days
duration. The spleen is enlarged and
uniformly hypoechoic. This is
indicative of splenic torsion or
infarct. Diagnosis: Splenic torsion.