Page 73 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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7.3 Fibroadnexal Hamartoma
VetBooks.ir Developmental anomaly of the pilosebaceous unit. It may contain apocrine glands.

Clinical features
• Reported in dogs and accounting for 1.7–2.7% of all cutaneous lesions.
• It is observed in middle-aged or older dogs.
• It may be secondary to chronic trauma and/or scar tissue formation, both resulting in
entrapment and subsequent distortion of the adnexal structures. A primary defect of
the pilosebaceous units cannot be excluded.
• Hamartomatous lesions can originate from follicles, collagen or from sebaceous glands.
However, the coexistence of more adnexal structures is usually observed, hence the
term fibroadnexal hamartoma.
• Solitary, firm, circumscribed and nodular to polypoid, dermal mass of variable sizes.
It may extend to the subcutaneous tissue. The lesion may also be pigmented, alopecic
and ulcerated.
• Fibroadnexal hamartoma is observed more frequently on the distal legs, especially on
pressure points. Head and trunk may also be affected.
• It is a benign lesion and carries a good prognosis.
• Over-represented canine breeds: large breed dogs, in particularly Labrador Retriever but
also Basset Hound, Maremma Sheepdog and Bracco Italiano.

Cytological features
• Cellularity: generally very low.
• Background: clear to lightly basophilic, with variable degree of haemodilution. Keratin bars
are frequently seen.
• Several of the following components may simultaneously be observed:
• Small clusters of mature sebocytes (for morphology, refer to ‘Sebaceous adenoma’ in
section 8.4, Sebaceous Tumours).
• Small clusters of sweat gland apocrine epithelial cells (for morphology, refer to ‘Sweat
gland adenoma and carcinoma’ in section 8.5, Apocrine Gland Tumours).
• Variable numbers of spindle-shaped stromal cells.
• Mixed inflammation may be present.

Differential diagnoses
• Sebaceous adenoma/hyperplasia (when the sebaceous component prevails)
• Follicular hamartoma
• Trichofolliculoma