Infundibular Cyst
(EPIDERMOID CYST, EPIDERMAL CYST, EPIDERMAL INCLUSION CYST)
A simple cyst lined by a stratified squamous epidermal or infundibular
epithelium. All four layers of the normal epidermis or infundibulum, including
the granular cell layer are present.
Gross Appearance:
•Intradermal mass
•Vary in size from 0.3-2.0 cm in diameter
•On cut section reveals central soft grey/brown material (keratin) with a thin
wall at periphery
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Histology:
•Cyst present within the dermis
•Large cysts may extend into the panniculus adiposus
•Lesions may be solitary or multiple
•A small pore may be found between the cyst and the overlying epidermis
•Basal, spinous and granular cell layers may all be well developed
•Cornified cells that occupy the cyst may be loosely packed (basketweave
orthokeratosis) or tightly compressed (compact orthokeratosis)
•Rupture of the cyst wall will evoke a granulomatous inflammatory response to
the keratin
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Cytology:
•Canine epidermal inclusion cysts; top 3 images show cholesterol crystals
typical of these cysts
•Bottom two show mainly keratinaceous debris and a few bare nuclei.
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Prognosis:
Excellent; however rupture of cyst wall releases keratin into dermis where it
evokes pyogranulomatous response
