Case A (Malignant melanoma)
Adult goat with an ulcerated cutaneous interdigital mass.
Example histopathological description
The section comprises mainly dermis, expanded and replaced by a 20 x 8mm, densely-cellular, poorly-demarcated, multinodular mass, subjacent to an extensive area of epidermal ulceration and a small residual segment of hyperplastic epidermis. The neoplastic cells form densely packed sheets in a fine fibrovascular stroma; they are pleomorphic (predominantly polygonal), 10-20 μm in diameter, with variably distinct borders, abundant amphophilic, granular cytoplasm which occasionally contains dark brown pigment consistent with melanin (within an area of tumour cells underlying the segment of intact epidermis). Tumour cells have a 5-15 μm centrally located oval nucleus with vesicular chromatin and 1-3 nucleoli. There is marked anisocytosis and anisokaryosis. Mitoses average 5-8 per high power field with rare bizarre mitotic figures. Throughout the neoplasm are multifocal to coalescing areas of necrosis and haemorrhage. Small numbers of melanophages are scattered through the mass.
The ulcerated area overlying the dermal mass has a thick surface zone of fibrinocellular debris and degenerate leukocytes colonized superficially by bacteria, and is separated from the tumour by a zone of granulation tissue which surrounds and dissects the mass in bands. The small residual segment of epidermis has surface neutrophilic and fibrinocellular crusting, erosion and spongiosis of the superficial layers, marked acanthosis and irregular and prominent rete peg formation. The subjacent superficial dermis is oedematous and contains areas of fibrovascular proliferation, neoplastic cell infiltration and vessel neutrophilia. Throughout the section, and particularly in the superficial dermis, there is a small, scattered population of melanophages. Neoplastic cells extend to the deep and lateral surgical margins.
Malignant melanoma, dermal, with incomplete excision
Case B (Acidophil adenoma)
Aged sheep with a lesion at the base of the brain in an enlarged sella tursica
Example histopathological description
Markedly expanding the pars distalis of the pituitary gland, to 22 x 14 mm, and displacing and compressing the pars intermedia and pars nervosa, is a well-circumscribed, ovoid, non-encapsulated neoplastic mass. The tumour is composed of polyhedral to columnar elongated cells (14 – 20 µm in diameter) arranged in cords and packets, supported by a fine fibrovascular stroma and multifocally separated by congested sinusoidal blood vessels. Individual cells have distinct cell borders and moderately abundant, faintly to brightly eosinophilic, finely granular cytoplasm. Nuclei are round (6 -12 µm in diameter), with basal polarity in columnar cells, with darkly stippled chromatin and 1-3 pinpoint nucleoli. Mitoses are rare (< 1 per 10 high power fields), and there is moderate anisocytosis and mild anisokaryosis. Multifocally, a layer of cuboidal to flattened cells line small follicle-like structures (30 – 60 µm in diameter) containing pink hyalinised proteinaceous material. Sparsely scattered individual cells have vacuolated cytoplasm and pyknotic nuclei.
Acidophil adenoma of the pituitary gland (pars distalis)
Comment on the significance of the lesion
Acidophil adenomas in sheep may be endocrinologically inactive but can grow to a considerable size, with potential for neurological dysfunction from local compression. In sheep, these tumours tend to remain confined to the sella turcica due to a well developed diaphragma sellae separating the pituitary fossa from the brain. Any residual adenohypophyseal and neurohypophyseal tissues are severely compressed, with dilatation and deepening of the sella turcica associated with pressure-induced osteolysis.
Acidophil cells may secrete prolactin and growth hormone. In sheep, increased development of mammary tissue and galactorrhoea (inappropriate lactation syndrome) has been observed with acidophil adenomas, suggesting excessive prolactin secretion by tumour cells. Positive immunohistochemical staining for prolactin +/- growth hormone has been described in a few case reports of pituitary adenomas in ewes.