Tumor of follicular infundibulum
TFI usually occurs in elderly individuals. Its incidence is estimated to range between 3-20 cases per 100 000 skin biopsies. Epidemiological reports comparing rates between males and females have been inconsistent.
While the etiology of TFI is not completely understood, some describe its origin from follicular infundibulum, whereas other studies state that the name is a misnomer, as the tumor cells resemble isthmic differentiation. TFI has been described to coexist with other cutaneous lesions (both seen within the same biopsy specimen), including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), actinic keratosis, epidermal cysts, nevus sebaceus, malignant melanoma, and nevi. It is therefore also postulated that TFI lesions could represent an epidermal reactive process to the presence of the adjacent tumor.
D23.9 – Other benign neoplasm of skin, unspecified
254694002 – Tumor of follicular infundibulum
Differential Diagnosis & Pitfalls
- Seborrheic keratosis – Look for a "stuck-on" appearing verrucous papule that can range from skin-colored to brown.
- BCC – TFI may mimic BCC clinically and is often found incidentally in the margin of excised BCC tissue. These are distinguished through histopathology. In contrast to BCC, TFI shows a dense elastic fiber network and lacks cellular atypia and expression of Ber-EP4.
- Fibroepithelioma of Pinkus – Presents as a sharply demarcated, smooth, exophytic lesion, usually located on the lower back.
- Trichilemmoma – Presents as a skin-colored papule that can sometimes be hyperpigmented or verrucous in appearance.
- Actinic keratosis – Presents as a hypertrophic, rough papule with irregular borders on sun-damaged skin.
- Acne scars (see acne vulgaris)
- Atrophic lichen planus
- Lichen sclerosus
- Discoid lupus erythematosus
- Morpheaform BCC
- Tinea versicolor – Involves a mild scale. A negative potassium hydroxide (KOH) preparation will rule out tinea versicolor.
- Pityriasis alba – Typically affects the cheeks of atopic individuals.
- Vitiligo – The patches are completely depigmented and very well demarcated.
- Tuberculoid leprosy – Seen in patients living in endemic areas.
- Idiopathic guttate hypomelanosis – Rarely involves the face. More commonly occurs on the extensor forearms and shins.