Pilar cyst

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Pilar cyst
Diagnosis in short

Pilar cyst. H&E stain.

LM cyst lining by a stratified squamous epithelium without a granular layer - contains keratin; no significant nuclear atypia; +/-granulomatous inflammation (due to rupture)
LM DDx epidermal inclusion cyst
Gross nodule +/-yellow colour
Site skin - usu. scalp

Prevalence very common
Prognosis benign
Clin. DDx other skin cysts

Pilar cyst, also known as a trichilemmal cyst, is a common benign skin cyst.

General

  • Very common.
  • Benign.‡
  • The clinical history for these typically says sebaceous cyst.

Note:

  • ‡A super rare malignant counter part is described; approximately 40 cases are reported in the english literature.[1]

Gross

  • Classic location: head ~90%.[2]

Microscopic

Features:[3]

  • Keratin.
  • Cyst lining:
    • Has no granular layer - key feature.
      • Keratohyaline granules (as seen in the granular layer) may be seen focally.
    • Inner most cyst lining cells are large cells with abundant eosinophilic cytoplasm.

DDx:

Images

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Scalp (Cyst), Excision:
- Benign trichilemmal cyst (pilar cyst).

Block letters

SCALP (CYST), EXCISION:
- TRICHILEMMAL CYST (PILAR CYST).
SKIN CYST, LEFT FLANK, EXCISION:
- TRICHILEMMAL CYST (PILAR CYST).
SCALP (CYST), ANTERIOR, EXCISION:
- TRICHILEMMAL CYST (PILAR CYST), RUPTURED.

Micro

The sections show a cyst that is lined by squamous epithelium without a granular layer. Focally, keratohyaline granules are seen in the cyst lining cells. The innermost cyst lining cells are large and have abundant eosinophilic cytoplasm. The cyst contains keratin.

See also

References

  1. Goyal, S.; Jain, BB.; Jana, S.; Bhattacharya, SK. (Jan 2012). "Malignant proliferating trichilemmal tumor.". Indian J Dermatol 57 (1): 50-2. doi:10.4103/0019-5154.92679. PMID 22470211.
  2. URL: http://emedicine.medscape.com/article/1058907-overview. Accessed on: 15 April 2012.
  3. Busam, Klaus J. (2009). Dermatopathology: A Volume in the Foundations in Diagnostic Pathology Series (1st ed.). Saunders. pp. 309. ISBN 978-0443066542.