Trichilemmal cyst L72.1

Author: Prof. Dr. med. Peter Altmeyer

Last updated on: 07.05.2022

Synonym(s)

Atheroma; Cyst pilars; Cyst trichilemmal; Isthmus catagen-cyst; isthmus-cathagen cyst; pilar cyst; Trichilemmal cyst; trichilemmal cyst (e); Tricholemmal cyst; Tricholemm cyst; who

Definition
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Rare, benign follicular epithelial cyst with tricholemmal keratinization mechanism (see tricholemma, see also hair follicle tumor, epidermal cysts), i.e., keratinization that occurs abruptly without flattening of the uppermost epithelial layers and without formation of a stratum granulosum.

Etiopathogenesis
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Autosomal dominant heredity has been described in some cases.

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Dermatology

Contact dermatitis allergic

Acute, sub-acute or chronic dermatitis caused by contact with topical allergens (usually in type IV allergy...

Manifestation
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Women are more frequently affected than men.

Localization
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Located on the capillitium in more than 90% of patients. Other localizations are: extremities, genitals.

Clinical features
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Solitary, but usually multiple 0.5-5 cm, dome-shaped raised, usually hairless, bulging, firm, round, well-displaced over the base, asymptomatic nodules without demonstrable central porus (see also epidermal cysts).

In rare cases, trichilemmal cysts, usually in combination with acne efflorescences, manifest as organoid epidermal nevus in a strip-like arrangement (see nevus trichlemmocysticus).

Histology
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Cystic wall of stratified squamous epithelium, which keratinizes without formation of a stratum granulosum. The multi-layered wall epithelium is characterized by glassy, cylindrical epithelial cells whose nuclei slowly diminish in size towards the lumen. In contrast to the keratinizing squamous epithelium of the skin surface which keratinizes via a stratum granulosum and the formation of keratohyalin granules, the epithelial cells do not flatten. The boundary line to the cyst lumen is undulating. The horn material in the lumen of the cyst appears compact and distinctly eosinophil. It contains cholesterol, more rarely calcium.

Differential diagnosis
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Cylindrome; proliferating tricholemic cyst; epidermal cyst.

Therapy
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Therapy only in case of disturbing cosmetics or complaints (very large knots, mechanically disturbing). Extirpation of the entire cyst sac and layered closure.

Cave! Remaining cyst wall remains cause recurrences!

Progression/forecast
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Excision is curative, no recurrence.

Note(s)
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The wall epithelium of the tricholemic cysts can proliferate, widen and at the expense of the horn material, turn into a solid tumour. See also proliferating tricholemmal cyst.

Literature
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Haas N et al (2002) Carcinoma arising in a proliferating trichilemmal cyst expresses fetal and trichilemmal hair phenotype. At J Dermatopathol 24: 340-344
Lopez-Rios F et al (2000) Proliferating trichilemmal cyst with focal invasion: report of a case and a review of the literature. At J Dermatopathol 22: 183-187
Riemann H et al (1999) Proliferating trichilemmal cyst with focal segments of metastatic squamous epithelial carcinoma. dermatologist 50: 42-46
Seidenari S et al (2012) Hereditary trichilemmal cysts: a proposal for the assessment of diagnostic clinical criteria. Clin Genet 84:65-69
Sethi S et al (2002) Proliferating trichilemmal cyst: report of two cases, one benign and the other malignant. J Dermatol 29: 214-220
Tola EN et al (2013) Simple vulval trichilemmal cyst. J Obstet Gynaecol 33:320-321