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trichilemmal cyst (pilar cyst, isthmus catagen cyst)
2nd most common cutaneous cyst (after epidermoid cyst) generally occurring on the scalp in middle-aged individuals.
Epidemiology:
1) middle-aged individuals
2) more common in females
3) often familial
4) occurs in ~5-10% of the population
4) most common cutaneous skin on the scalp
Pathology:
1) cyst is not connected to epidermis
2) cyst wall
a) thick & can be removed intact
b) stratified squamous epithelium
c) palisading outer layer resembling outer root sheath of hair follicle
d) corrugated inner layer without a granular layer
3) cyst contains keratin & its catabolites which appears pink & homogeneous
4) cysts often calcify & form cholesterol clefts
5) almost always benign
6) malignant transformation extremely rare
Genetics:
- sporadic
- autosomal dominant
Clinical manifestations:
1) firm, dome-shaped 0.5-5 cm nodules or tumors
2) no central punctum as seen in epidermoid cysts
3) frequently occurs as multiple lesions
4) > 90% are on scalp
5) hair overlying cyst is generally normal, but may be thinned
6) cyst may become inflammed & painful if ruptured
Laboratory:
- bacteria may be cultured from cyst, but appear to be incidental, unrelated to inflammation
Management:
1) excision & drainage of inflamed cysts
2) intralesional injection with triamcinolone
3) in the absence of inflammation, cysts may be excised [3]
Related
epidermoid cyst (wen, infundibular cyst)
punctum
General
cyst
scalp disorder
References
- Color Atlas & Synopsis of Clinical Dermatology, Common
& Serious Diseases, 3rd ed, Fitzpatrick et al, McGraw Hill, NY,
1997, pg 163
- eMedicine: Pilar cyst
http://emedicine.medscape.com/article/1058907-overview
- Medical Knowledge Self Assessment Program (MKSAP) 15, 16.
American College of Physicians, Philadelphia 2009, 2012