9-year-old, Canine, German Shepherd Dog, FS
6-week history of skin/SQ mass. Growing rapidly with purulent and serous discharge. Patient also has chronic clinical disease/infection. From the top of the neck.
Expanding the dermis and deeper tissue, there is a multilocular cystic proliferation composed of cystic structures containing abundant luminal keratin (orthokeratotic to parakeratotic) and acantholytic keratinocytes. The cystic foci occasionally connect to the overlying surface and are lined by superficial mature stratified squamous epithelium and deeper more convoluted villiform projections of squamous epithelium with a scalloped deep border and prominent acantholysis of keratinocytes. There is intervening dense collagen with entrapped additional follicular and adnexal structures and there is mild lymphoplasmacytic inflammation.
Skin (right dorsal neck): Warty dyskeratoma.
Margins: Complete, but narrow excision; less than 1 mm lateral and deep aspect).
This skin mass is a large warty dyskeratoma, which is a rare benign neoplasm in dogs. Lesions are typically solitary, though can be multicystic/multinodular, as is seen in this case. The arrangement of the lining epithelium of the cysts with prominent acantholysis is a characteristic feature. Complete excision is generally considered curative for this type of benign lesion. With incomplete or narrow excision, local recurrence is possible, though more aggressive biologic behavior would not be expected.