Skin nonmelanocytic tumor
Adnexal tumors
Hair follicles
Trichoepithelioma / trichoblastoma


Minor changes: 16 November 2020

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Trichoepithelioma trichoblastoma

Eleanor Russell-Goldman, M.D., Ph.D.
Page views in 2020: 32,672
Page views in 2021 to date: 12,104
Cite this page: Russell-Goldman E. Trichoepithelioma / trichoblastoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocytictrichoepithelioma.html. Accessed April 15th, 2021.
Definition / general
  • Trichoepitheliomas and trichoblastomas are benign adnexal tumors, which may show morphologic overlap and recapitulate features of germinative hair bulb epithelium and associated mesenchymal stroma
Essential features
  • Trichoepitheliomas and trichoblastomas are benign adnexal tumors which may display some features that mimic basal cell carcinoma
  • Multiple trichoepitheliomas can be associated with Brooke-Spiegler syndrome and multiple familial trichoepithelioma (CYLD mutations)
  • Trichoblastomas are not known to be familial but are the most common tumor type found in association with nevus sebaceus
Terminology
  • Previous names not widely used: trichogenic tumors, giant solitary trichoepithelioma, trichogerminoma
ICD coding
  • ICD-10: D23.9 - Other benign neoplasm of skin, unspecified
Epidemiology
  • Adults
  • Sporadic trichoepithelioma:
    • Rare
    • Incidence unknown
  • Trichoblastoma:
    • Rare
    • F = M
  • Brooke-Spiegler syndrome / multiple familial trichoepitheliomas:
    • Multiple trichoepitheliomas may present in adolescence / early adulthood
    • F > M
    • CYLD mutations
  • Reference: Cureus 2020;12:e8272
Sites
  • Trichoepithelioma (solitary):
    • Face
    • Rarely scalp, trunk, extremities, genital area
  • Trichoepithelioma (multiple / familial):
    • Symmetrical distribution over central face
    • Rarely other sites as above
    • Rarely dermatomal
  • Trichoblastoma:
    • Scalp, head and neck
    • Occasionally trunk, extremities, genital area
Pathophysiology
  • CYLD mutations give rise to inherited forms of trichoepithelioma
    • Loss of function of CYLD, a deubiquitinating enzyme, results in constitutive NFκB signaling (Nature 2003;424:801)
  • Molecular pathogenesis of sporadic forms of trichoepithelioma unknown
  • Although there may be morphologic overlap, trichoblastomas lack PTCH mutations, distinguishing them molecularly from basal cell carcinomas (Hum Pathol 2007;38:1496)
Clinical features
Diagnosis
Prognostic factors
  • Benign tumors; good prognosis
Case reports
Treatment
  • Surgical excision
Clinical images

Images hosted on other servers:

Multiple unilateral face nodules

Multiple central facial nodules

Microscopic (histologic) description
  • Trichoepithelioma (Am J Dermatopathol 2011;33:251):
    • Usually superficial dermal tumors
    • Superficial nests of basaloid cells with keratin horn cysts
    • Can show leaf-like or frond-like architectural pattern
    • Fibrous cellular stroma closely associated with the epithelial components
    • May have papillary mesenchymal bodies and calcifications
    • May have epidermal connection
    • Ulceration rare
    • Can be basaloid cell predominant with few horn cysts making distinction from trichoblastoma or basal cell carcinoma more difficult
  • Trichoblastoma:
    • Well circumscribed, predominantly dermal tumor nodule which may extend to subcutis
    • Predominantly basaloid epithelial cells in nests with peripheral palisading
    • May have keratin cysts
    • Mitoses and apoptosis can be evident but cellular pleomorphism is minimal
    • Prominent cellular stromal component with papillary mesenchymal body formation
    • Clefting occurs between the epithelial stromal tumor mass and surrounding dermis rather than between epithelial and stromal components
    • May show cribriform, rippled or solid patterns
    • May contain dendritic melanocytes and appear pigmented
    • Typically retains CK20 positive Merkel cells (Arch Pathol Lab Med 2017;141:1490)
Microscopic (histologic) images

Contributed by Eleanor Russell-Goldman, M.D., Ph.D.

Superficial dermal tumor

Prominent keratin cysts

Dermal basaloid tumor

Bland cytology

Papillary mesenchymal body

Positive stains
  • CK20 positive Merkel cell retention is more common in benign follicular tumors versus basal cell carcinoma, although is not specific (Arch Pathol Lab Med 2017;141:1490)
    • This staining pattern should be interpreted with caution as CK20 positive Merkel cells may be only focally represented and may not be apparent without multiple sections
Sample pathology report
  • Skin, right cheek, shave biopsy:
    • Trichoepithelioma / trichoblastoma (see comment)
    • Comment: If partially sampled and a basal cell carcinoma cannot be excluded, recommend complete excision.
Differential diagnosis
  • Basal cell carcinoma
    • Nodular basal cell carcinoma:
      • Clefting between epithelial stromal components
      • Cellular pleomorphism
      • Mucin
      • Frequent epidermal connection
    • Infundibulocystic basal cell carcinoma:
      • Basaloid nests with prominent follicular differentiation
      • May have clefting between epithelial stromal components
      • Less well developed stroma
Board review style question #1

Papillary mesenchymal bodies are a feature of which of the following skin tumors, shown in the image?

  1. Basal cell carcinoma
  2. Microcystic adnexal carcinoma
  3. Spiradenoma
  4. Trichoepithelioma / trichoblastoma
Board review style answer #1
D. Trichoepithelioma / trichoblastoma. Trichoepithelioma is shown.

Comment Here

Reference: Trichoepithelioma / trichoblastoma
Back to top
Image 01 Image 02