Case of the Month

A 48 year old man presents with an eroded, tender nodule on his head. He said that the lesion has been there for “over 20 years” but it recently became irritated. He thinks he bumped it, but is not completely sure.

What's Your Diagnosis?

Diagnosis: A Proliferating Pilar Tumor, (also known as a Proliferating trichilemmal tumor).

A proliferating pilar tumor (PPT) is a rare neoplasm arising from the isthmus region of the outer root sheath of the hair follicle. ... Most tumors arise within a preexisting pilar cyst. Even though they usually are benign in nature, malignant transformation with local invasion and metastasis has been described. Malignant transformation may be preceded by rapid growth and ulceration.

For these reasons, the patient was sent to a dermatologic surgeon for complete removal.

Microscopic/Pathologic Description:

Histologic sections demonstrate a punch biopsy of skin with an effaced overlying epidermis. Throughout the dermis is an atypical squamoid proliferation of pilar-type epithelial islands producing keratin and infiltrating through the dermis.

Atypia is present.

The findings are of a proliferating pilar tumor. Complete removal is recommended.

Dermatopathology and photomicrographs courtesy of Erick Jacobson-Dunlop, M.D., Dermatopathologist

A proliferating pilar tumor (PPT) is a rare neoplasm arising from the isthmus region of the outer root sheath of the hair follicle. ... Most tumors arise within a preexisting pilar cyst. Even though they usually are benign in nature, malignant transformation with local invasion and metastasis has been described. For that reason, the patient was sent to a dermatologic surgeon (Neil Shah, MD) for complete removal.