Ultrasonographic Features in Feline Splenic Mast Cell Tumors

Mast cell tumors (MTCs) are a common splenic neoplasia in cats, although their ultrasonographic characteristics have been reported to be nonspecific and overlap with those of other proliferative diseases. The objective of this study was to describe ultrasonographic findings of the spleen and metastatic sites in a large cohort of cats with cytologically or histopathologically confirmed primary or disseminated splenic involvement by MCTs with high-frequency transducers, and to determine whether specific ultrasonographic characteristics could be identified. Cats with available ultrasonographic images and cytological or histological confirmation of splenic involvement by MCTs were retrospectively included in a multicenter study. Forty-one cats met the inclusion criteria. A linear transducer was used for the majority of cats (80%). Splenic abnormalities were identified in 85% of cats. The most common finding was diffuse splenomegaly (63%) with irregular margins (46%) and homogeneously hypoechoic parenchyma (24%). Specific patterns were uncommon, with a reticulonodular pattern present in 27% and a marbled appearance in 12% of cats. Discrete nodular lesions or masses were present in 44%. The liver was sampled in 66% of cats, and hepatic disseminated disease was confirmed in 59%; however, the liver was ultrasonographically normal in the majority of those cases. For the cats with hepatic MCTs and ultrasonographic abnormalities, diffuse hepatomegaly with abnormal echogenicity or echotexture was observed. Lymph node metastasis was confirmed in 20% of cats. Only one cat had confirmed gastrointestinal involvement by MCTs, and gastrointestinal ulceration was ultrasonographically noted in 7% of cats. In conclusion, to the authors’ knowledge, this is the largest study describing findings in splenic MCTs in which images were acquired predominantly using a high-frequency linear transducer. Nonspecific ultrasonographic splenic changes were associated with this disease. A normal ultrasonographic spleen or liver did not exclude mast cell tumor (MCT) involvement. Cytology or histopathology remains warranted when an MCT is suspected, particularly in the presence of splenomegaly in combination with suspicion of disseminated disease and a cutaneous MCT. Lymph node metastasis, gastrointestinal involvement by MCTs, and gastrointestinal ulceration were uncommon findings.