Pathology of Tumour of the Follicular Infundibulum

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Pathology of Tumour of the

Follicular Infundibulum

Dr Sampurna Roy MD 2022

Tumour of the follicular infundibulum (TFI) is an uncommon benign neoplasm manifested histopathologically by a superficial epithelial plate-like growth pattern with multiple thin epidermal connections comprised of monomorphic cells with abundant cytoplasm.

Clinically, presents as a small asymptomatic, smooth or slightly keratotic papule or plaque.

The two main clinical variants are :

1) Solitary: Presents as a solitary keratotic papule.

2) Multiple

Classified as:

(1) solitary tumours,

(2) eruptive tumours,

(3) TFI - associated with other lesions of Cowden's disease,

(4) TFI- associated with a single tumour such as nevus sebaceus, and

(5) TFI-like epidermal changes.

Sites: Head and neck or upper chest.

Microscopic features:

Symmetrical tumour with plate-like growth pattern of the squamous cell (similar to isthmic or outer root sheath epithelium) parallel to the surface epithelium ;

Multiple attachments to the epidermis ;

Basal cell palisade ;

Acanthotic epithelium eosinophilic and pale staining than the overlying epidermis ;

Small ducts and microcavities with keratin in the lesion; PAS- positive basement membrane.

Differential diagnosis:

Inverted follicular keratoses ;

Trichilemmomas ;

Plaque-like seborrheic keratosis ;

Superficial basal cell carcinoma;

Multiple infundibular tumors of the head and neck.