June 2010

Case A

open slide in the AHA AAPSP Digital Slide Server

History

Lesion from the head of a dog

Example histopathological description

The section is haired skin 26 mm wide x 7 mm deep containing a localised but non-encapsulated lesion approximately 5 x12 mm.  The lesion consists of a dense dermal infiltrate of round cells, each with a moderate amount of pale eosinophilic cytoplasm and an oval to indented nucleus. There are 1-2 mitotic figures per high power field. The round cells are in close apposition to the epidermis which is hyperplastic in some areas and ulcerated in others with surface exudation including fibrin and cell debris. Moderate numbers of lymphocytes are infiltrating the lesion. The lesion extends through the deep dermis, with neoplastic cells present less than 1 mm from the deep margin of excision.

Diagnosis

Benign cutaneous histiocytoma

Differential diagnosis

Other round cell tumours considered were transmissible venereal tumour (lesions usually on genital mucosa, cells would appear more lymphoid with abundant clear cytoplasm), mast cell tumour (cells would typically have blue-grey cytoplasmic granulation demonstrable with toluidine blue stain, nuclei would not be indented and the mass would commonly be infiltrated with eosinophils), cutaneous lymphoma (lesions are usually multiple in older animal and cells are more pleomorphic) and one of the malignant and/or systemic forms of histiocytic disease (young age of dog favours benign form, cells are not anaplastic or arranged perivascularly).

The histiocytic nature of the infiltrate could conceivably represent a granulomatous inflammatory response, although in that case the cells would typically be arranged in irregular nodules rather than dense sheets.  The infiltrate would often be accompanied by at least some neutrophils and/or multinucleated giant cells, with associated necrosis typical of an inflammatory response and possibly even a visible aetiologic agent.


Case B

open slide in the AHA AAPSP Digital Slide Server

History

Lesion from the head of a young Tasmanian Devil (Sarcophilus harrisii)

Example histopathological description

The slide is a wedge section of skin with a multi-lobulated mass of neoplastic tissue expanding the dermis. There is ulceration of the skin towards the edge of the section with a thick covering of necrotic cellular debris, fibrin, degenerative leucocytes and many prominent bacterial colonies. Adjacent to this ulcerated area there are three cross sections of parasitic organisms measuring approximately 1 mm wide and 2-3 mm long, with a thin cuticle and small curved barbs projecting from the surface. These organisms appear to have penetrated through the hair follicle and are embedded within the dermis. There are small numbers of eosinophils, macrophages and some oedema fluid around these organisms.

The neoplastic mass consists of cords of large, round to polygonal cells, a fine connective tissue stroma and moderate numbers of mononuclear leucocytes and eosinophils. The neoplastic cells contain small to moderate amounts of pale eosinophilic cytoplasm, and have a round to ovoid, pale-staining, vesiculated and centrally located nucleus often containing 1-3 prominent nucleoli. Mitotic figures are present in moderate numbers, averaging 0.5-1 per high power field. The mass extends fully to the lateral and deep margins of the section.

Diagnosis

Devil facial tumour disease.

Comments

The parasite present in the superficial dermis is most likely the larval form of Uropsylla tasmanica (a flea). It is unusual that there is no neutrophilic inflammation surrounding this organism. The other possibility to consider is the Satanicoptes armatus mite, although these do not usually invade the dermis. It is possible that the ulceration resulting from the tumour allowed invasion of what is normally an epidermal mite into the dermis.