Tumor of the Follicular Infundibulum

David Cassarino, MD, PhD

Key Facts

Terminology

Tumor of the follicular infundibulum (TFI)
Basal cell hamartoma with follicular differentiation
Bland, superficial, plate-like adnexal proliferation with multiple epidermal attachments

Etiology/Pathogenesis

May be sporadic (most cases) or part of Cowden syndrome (multiple, often with tricholemmomas)

Microscopic Pathology

Multiple connections between lesion and epidermis
Cells show abundant pale to clear-staining cytoplasm
Peripheral cells often show palisading

Top Differential Diagnoses

Basal cell carcinoma
Inverted follicular keratosis
Tricholemmoma

Tumor of the follicular infundibulum (TFI) is characterized by a superficial, plate-like distribution parallel to the epidermis. Note the multiple connections to an adjacent follicular structure

High magnification of TFI shows a central area of infundibular-type keratinization surrounded by bland squamous cells showing focal cytoplasmic granules