Infiltrative Lipoma Invading the Anal Sac in a Dog: A Rare Case Report

A 6-year-old female Chihuahua was presented to the Animal Medical Center for surgical resection of a perineal mass that had recently increased in size. Ultrasonography revealed a large, homogeneous fatty mass with irregular margins between the surrounding muscle layers due to infiltrating fatty tissues. Cytological findings from fine-needle aspirates revealed numerous sheets and clusters of adipocytes, which was consistent with the fatty mass. Based on ultrasonographic and cytological findings, an infiltrative lipoma was suspected. During the surgery, the perineal mass was found to be non-encapsulated, irregularly marginated, and extensively distributed into the surrounding muscles. The mass extended inside the pelvic cavity and left anal sac. The perineal mass was surgically removed and submitted for histopathologic examination. Histopathology confirmed that the mass was an infiltrative lipoma invading into the anal sac and surrounding muscles. The present report was an unusual presentation of infiltrative lipoma that invaded the anal sac in the perineum.