German Shepherd with warty skin

SIGNALMENT
9-year-old, Canine, German Shepherd Dog, FS

SOURCE/HISTORY:
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. 

Figure 1. (5X magnification, H&E stain); Multiple keratin-filled cystic spaces with occasional connection to the surface.
Figure 2. (20X magnification, H&E stain); Keratin-filled cystic space with opening to the skin surface and with deep scalloped border.
Figure 3. (50X magnification, H&E stain); Scalloped deep border of a cystic focus with acantholytic change evident at the luminal aspect.
Figure 4. (50X magnification, H&E stain); prominent accumulation of keratin material including parakeratin with acantholytic change and a scalloped border to the epithelial lining.
Figure 5. (200X magnification, H&E stain); prominent acantholytic change evident at the luminal aspect of the cystic structures.
Figure 6. (400X magnification, H&E stain); prominent acantholytic change luminally.

MICROSCOPIC DESCRIPTION:
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.

MICROSCOPIC INTERPRETATION:

Skin (right dorsal neck): Warty dyskeratoma.

Margins: Complete, but narrow excision; less than 1 mm lateral and deep aspect).

COMMENTS:

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.

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