Fibroadnexal Hamartoma
(CANINE ADNEXAL NEVUS)
A focal proliferation of the pilosebaceous units. It is likely that some lesions are congenital and others occur following trauma to the area.
Gross Appearance:
•Elevated, hyperpigmented skin mass
•May be polyploid
•On cut section often reveals multiple, small, keratin-filled cysts
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Histology:
•Circumscribed nodular lesion
•Composed of folliculosebaceous units lying in an abundant dermal collagenous matrix
•Folliculosebaceous units have no association with the overlying epidermis which may be hyperplastic or ulcerated
•Folliculosebaceous units are arranged in a haphazard and disorganized fashion
•Surrounding dermal stroma is well demarcated from the adjacent normal dermal collagenous stroma
•Lesions are often secondarily inflamed with focal aggregates of neutrophils and pyogranulomatous foci within the lesion
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