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

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

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.

 

Prognosis: 
Excellent; however rupture of cyst wall releases keratin into dermis where it evokes pyogranulomatous response


Copyright © 2000 - University of Pennsylvania School of Veterinary Medicine
Faculty: Michael H. Goldschmidt, BVMS & Patricia Mcmanus,VMD, PhD
Student: Kyle Goldschmidt
Comments: goldsch@vet.upenn.edu