Page 72 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Cysts, Tumour-like Lesions and Response to Tissue Injury
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7.2 (Sweat Gland) Apocrine Cyst
VetBooks.ir Non-neoplastic lesion lined by a single layer of apocrine secretory epithelial cells.

Clinical features
• Relatively common in dogs; rare in cats.
• Age: 6 years or older.
• In dogs, it predominantly occurs on the head, legs, neck and trunk. In cats, it is often
observed on the head.
• Cysts are usually solitary, occasionally multiple (apocrine cystomatosis). They are vari-
ably sized, well defined and fluctuant. They may have a blue tint when viewed through
the overlying skin. Cyst content is usually clear and watery, but is occasionally brown
and gelatinous due to inspissation.
• It is a benign lesion and carries a good prognosis.
• Over-represented breeds:
• Dogs: Old English Sheepdog and Weimaraner.
• Cats: Persian cat.

Cytological features
• Background: generally clear. It may contain cholesterol crystals.
• Aspirates may be acellular or contain low numbers of macrophages.
• Cuboidal apocrine epithelial cells rarely exfoliate (for morphology, refer to ‘Sweat gland
adenoma and carcinoma’ in section 8.5, Apocrine Gland Tumours).
• Following trauma, a variable degree of haemorrhage can occur within the cyst. In this case,
macrophages may display erythrophagia or contain haemosiderin granules and/or haematoidin
crystals.

Differential diagnosis
Cystic apocrine adenoma

Pearls and Pitfalls
Variants of apocrine cyst are the ceruminous gland cysts in the inner pinnae and ear canal.
These are more common in adult cats, especially in Abyssinian and Persian cats. These lesions
appear as multiple, often numerous, nodules or vesicles. They are often dark in colour and
may be mistaken clinically for melanocytic or vascular neoplasms.