Pilar (Tricholemmal) Cyst

 Architecturally more complex

image Multiloculated

image Squamous eddies

image Mitotic activity

• Malignant proliferating pilar cyst/tumor
image Infiltrative growth

image Cytologic atypia and mitotic activity

• Epidermoid cyst
image Well-developed granular layer

image Epidermal keratinization

• Hybrid cyst
image Has distinct features of both epidermoid and pilar cyst

Diagnostic Checklist

• Abrupt tricholemmal keratinization is key diagnostic feature
• Simple unilocular cyst

image If architectural complexity is present, consider proliferating pilar cyst or malignant pilar cyst

Pilar Cyst Involving Scalp
The scalp is the most common location for pilar cysts, though they can rarely occur almost anywhere.

Well-Circumscribed Simple Cyst
Pilar cysts are well-circumscribed simple cysts involving the dermis &/or subcutis. No granular layer is seen, even at low magnification.

High-Power Image of Pilar Cyst
The epithelium at the interface with the keratin is composed of large polygonal keratinocytes with abundant eosinophilic cytoplasm. There is abrupt keratinization image without a granular layer, but scattered keratohyaline granules may be seen.

Ruptured Pilar Cyst
Pilar cysts often rupture, resulting in granulomatous inflammation. Recognition of cyst remnants image help make the diagnosis.



• Pilar cyst

• Trichilemmal cyst

• Isthmus-catagen cyst


• Benign unilocular cyst lined by squamous epithelium lacking granular layer and containing abundant dense keratin material

Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Pilar (Tricholemmal) Cyst

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