Tricholemmoma

 Benign clear cell adnexal proliferation with external root sheath differentiation

• Subtype: Desmoplastic tricholemmoma

Etiology/Pathogenesis

• Some cases are associated with Cowden syndrome (PTEN hamartoma syndrome)
image Multiple tricholemmomas, hamartomas, and visceral tumors including breast and thyroid carcinomas
image Mutations in PTEN gene on 10q23.31
• Some have considered TL to be related to HPV infection (“tricholemmal verrucae”), but not well-accepted

Clinical Issues

• Relatively common tumors
• Usually occur in adults, although Cowden syndrome patients present at earlier age
• Most occur on face, especially nose and upper lip

Microscopic

• Lobular proliferation of mature squamoid cells with pale- to clear-staining cytoplasm
• Peripheral palisading of basaloid cells
• Cells are surrounded by thickened, glassy-appearing basement membrane
• Multiple broad connections to epidermis and follicles
• Desmoplastic tricholemmoma
image Variant with prominent desmoplastic stroma
image Typically in center of tumor, surrounded by conventional-appearing TL

Top Differential Diagnoses

• Tumor of follicular infundibulum
• Clear cell acanthoma
• Tricholemmal carcinoma
• Clear cell squamous cell carcinoma in situ (clear cell Bowen disease)
• Clear cell basal cell carcinoma
image
Clinical Photograph of Multiple TricholemmomasMultiple tricholemmomas (TLs) are shown on and around the nose of a patient with Cowden syndrome. (Courtesy B. Hall, MD.)

image
Superficial TricholemmomaThis is a small, superficial tricholemmoma on the eyelid showing multifocal epidermal attachments image. The tumor is composed of pale- to clear-staining epithelioid cells.
image
Superficial TricholemmomaHigher magnification of a superficial TL shows a lobular proliferation of small, pale- to clear-staining image adnexal cells. Note the thickened basement membrane surrounding the tumor image.
image
High Magnification of Tricholemmoma Basement MembraneHigh magnification of the periphery of a TL shows bland-appearing small cells with pale to clear-staining cytoplasm and small nucleoli. The peripheral cells show palisading, and there is a thickened peripheral basement membrane image.

TERMINOLOGY

Abbreviations

• Tricholemmoma (TL)
• Desmoplastic tricholemmoma (DTL)

Synonyms

• Trichilemmoma

Definitions

• Benign clear cell adnexal proliferation with external root sheath differentiation

ETIOLOGY/PATHOGENESIS

Unknown in Most Cases

• Some have considered TL to be related to HPV infection (“tricholemmal verrucae”)
image Not generally accepted, and most PCR studies for HPV have been negative

Genetic

• Some cases are associated with Cowden syndrome (PTEN hamartoma syndrome)
image Characterized by multiple tricholemmomas, hamartomas, and visceral tumors including breast and thyroid carcinomas
image Mutations in PTEN, a tumor suppressor gene, on 10q23.31

CLINICAL ISSUES

Epidemiology

• Incidence
image Relatively common tumors
• Age
image Usually adults, although Cowden syndrome patients present at earlier age

Site

• Most occur on face, especially nose and upper lip

Presentation

• Small papular lesion
image Usually flesh-colored
image Often clinically mimics basal cell carcinoma or verruca

Treatment

• Surgical approaches
image Usually not necessary, as these are benign tumors

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Tricholemmoma

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