Superficial folliculocystic structures and calcifications
Deeper infiltrative-appearing cords and small islands in densely fibrotic stroma
Top Differential Diagnoses
• Basal cell carcinoma
• Microcystic adnexal carcinoma
• Trichoblastoma
• Trichoadenoma
• Sebaceoma
Clinical Photograph of Multiple Lesions Multiple trichoepitheliomas are scattered over the central face and nasolabial area presenting as flesh-colored, 1- to 4-mm papules. (Courtesy B. Hall, MD.)
Trichoepithelioma at Low Magnification Scanning magnification of trichoepithelioma (TE) shows irregular islands of bland basaloid cells with prominent horn cysts and clefts between collagen bundles , rather than the tumor-stromal retraction artifact seen in basal cell carcinoma (BCC).
Higher Magnification of Papillary Mesenchymal Bodies High-power view of a TE demonstrates characteristic papillary mesenchymal bodies invaginating into the basaloid cells. (Courtesy A. Bowen, MD.)
Desmoplastic Trichoepithelioma Desmoplastic TE can mimic a morpheaform BCC in some cases. However, the prominent horn cysts and calcifications are more consistent with a TE. (Courtesy G. Fraga, MD.)
TERMINOLOGY
Abbreviations
• Trichoepithelioma (TE)
Synonyms
• Superficial trichoblastoma
Definitions
• Basaloid proliferation with mixture of primitive follicular structures and mature infundibulocystic keratinizing areas
ETIOLOGY/PATHOGENESIS
Genetic
• Some cases are inherited as part of a genetic syndrome, including Brooke-Spiegler, familial TEs, or Rombo syndrome
• Autosomal dominant inheritance
• Present as multiple lesions, often with cylindromas and spiradenomas (Brooke-Spiegler syndrome)
CLINICAL ISSUES
Epidemiology
• Incidence
Relatively common tumors
• Age
Usually present in adults
– Genetic forms present in adolescence
• Sex
Slight male predominance
Site
• Most commonly occur on face, but may involve other head and neck sites
Presentation
• Solitary or multiple papules
Sporadic cases are typically solitary
Inherited cases are usually multiple
Usually small (< 5 mm), especially the sporadic cases
Large or giant trichoepitheliomas are better referred to as trichoblastoma
Treatment
• Options, risks, complications
Surgical excision is curative
Should be recommended in partial biopsies in order to exclude basal cell carcinoma (BCC)
Prognosis
• Excellent; very low recurrence or malignant potential
• However, rare cases have been associated with (or progressed to) BCC
MACROSCOPIC
General Features
• Small, superficial dermal-based lesion
MICROSCOPIC
Histologic Features
• Multiple lobules and nests of basaloid cells, typically confined to superficial dermis
• Areas of infundibulocystic differentiation (keratinizing cysts) are present
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are scattered over the central face and nasolabial area presenting as flesh-colored, 1- to 4-mm papules. (Courtesy B. Hall, MD.)
with prominent horn cysts 
and clefts between collagen bundles 
, rather than the tumor-stromal retraction artifact seen in basal cell carcinoma (BCC).
invaginating into the basaloid cells. (Courtesy A. Bowen, MD.)
and calcifications 
are more consistent with a TE. (Courtesy G. Fraga, MD.)
