Skin nonmelanocytic tumor

Adnexal tumors

Hair follicles


Editor-in-Chief: Debra L. Zynger, M.D.
Nicholas Turnbull, M.B.Ch.B.
Richard A. Carr, M.B.Ch.B.

Last author update: 1 November 2019
Last staff update: 19 June 2023

Copyright: 2002-2024,, Inc.

PubMed Search: Trichilemmoma[TI] OR tricholemmoma[TI]

Nicholas Turnbull, M.B.Ch.B.
Richard A. Carr, M.B.Ch.B.
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Cite this page: Turnbull N, Carr RA. Trichilemmoma. website. Accessed June 16th, 2024.
Essential features
  • Also called tricholemmoma
ICD coding
  • ICD-10: D23 - other benign neoplasms of skin
Clinical features
  • Clinically nondescript wart-like or smooth dome shaped appearance
  • Diagnosis is rarely made by clinical examination, more often made by pathologist via tissue examination revealing characteristic histological morphology
Case reports
  • Not required
  • Curettage or shave excision
  • Excision
  • Laser
Clinical images

Images hosted on other servers:


Central ulceration

Microscopic (histologic) description
  • Squamoproliferative lesion in continuity with the epidermis
  • Hyperkeratosis and stromal clefting are often associated
  • Pale eosinophilic or clear cells
  • Rounded lobular profile
  • Peripheral palisade of cuboidal or columnar cells
  • Clear cells (characteristic but uncommon)
  • Reverse polarity of peripheral cells (characteristic but uncommon)
  • Distinct basement membrane resembling the hair outer root sheath zone below the level of the follicular isthmus (Arch Dermatol 1962;86:430, Am J Dermatopathol 2018;40:561, Current Diagnostic Pathology 2007;13:273)
  • Basaloid cell predominance may be seen mimicking basal cell carcinoma
  • Central desmoplasia, squamous morules and mucin pools may be seen (uncommon)
Microscopic (histologic) images

Contributed by Nicholas Turnbull, M.B.Ch.B. and Richard A. Carr, M.B.Ch.B.

Bulbous basaloid tumor


Area composed of clear cells

Squamous morules and mucinous pools




Positive stains
Sample pathology report
  • Skin, right side of nose, punch biopsy:
    • Trichilemmoma (see comment)
    • Comment: This is a benign tumor. Multiple trichilemmomas may be associated with Cowden syndrome. Clinical correlation advised or specialist dermatology assessment should be considered if clinically indicated.
    • Microscopic description: A folliculocentric tumor with bulbous profile and stromal clefting is seen in the dermis with connection to the epidermis. The tumor is composed of basaloid cells and cells with clear cytoplasm. Peripheral palisading and a thickened basement membrane is noted. The overlying epidermis demonstrates hyperkeratosis. No dysplasia is seen.
Differential diagnosis
  • Inverted follicular keratosis:
    • Characterized by small basaloid cells and tight squamous eddies
  • Viral wart (verruca):
    • May be indistinguishable but typically demonstrates peripheral in turning of the rete ridges, marked hyperkeratosis, with columns of parakeratosis overlying the papillomatous projections
    • Blood is often seen with the tips of parakeratosis
  • Basal cell carcinoma:
    • May have similar silhouette, in particular to the basaloid variant trichilemmoma
    • Artifactual clefting with mucin within the space, in contrast to the stromal clefting of a benign follicular tumor, is seen
    • Mitotic activity is usually obvious
    • BerEP4 is strong and diffuse (unless superficial or eroded)
    • CD34 is negative
  • Squamous cell carcinoma:
    • In particular the follicular variant may be confused with trichilemmoma
    • Has cellular pleomorphism, brisk and abnormal mitotic activity and invasive borders
    • Lack CD34 expression
  • Trichilemmal carcinoma:
    • Considered the malignant counterpart of trichilemmoma
    • It is very rare
    • Distinction is made by cellular pleomorphism
    • Brisk and abnormal mitotic activity
    • Usually lack CD34 expression
Board review style question #1
Which of the following is true of trichilemmomas?

  1. Are a cutaneous marker of internal malignancy
  2. Are found predominantly on the trunk and acral sites
  3. Are typically present in children
  4. Multiple trichilemmomas are pathognomonic of Cowden syndrome
Board review style answer #1
D. Multiple trichilemmomas are pathognomonic of Cowden syndrome

Comment Here

Reference: Trichilemmoma
Board review style question #2
A 30 year old man had a punch biopsy of a forehead papule which was possible basal cell carcinoma based on appearance.

With respect to the pictographs above

  1. Any focal BerEP4 stain positivity confirms this as a basaloid trichilemmoma
  2. CD34 staining may be very focal and require careful sectioning to demonstrate
  3. Mucin and atypia distinguish this lesion as a follicular squamous cell carcinoma
  4. Presence of clear cells can distinguish basaloid trichilemmoma from basal cell carcinoma
Board review style answer #2
B. This is a trichilemmoma. CD34 staining may be very focal and require careful sectioning to demonstrate.

Comment Here

Reference: Trichilemmoma
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