FOLLICULAR ACANTHOMA HAVING COMBINED FEATURES OF TRICHILEMMOMA AND INVERTED FOLLICULAR KERATOSIS
Multiple interconnected tumor lobules communicate extensively with the epidermis. Squamous eddies, which can be found in irritated seborrheic keratoses, inverted follicular keratoses, and in squamous cell carcinomas are present. This particular lesion is more vertically oriented than an irritated seborrheic keratosis, and it is cytologically benign. The same architecture can be seen in trichilemmomas, and there is focal clear cell differenctiation. This type of 'hybrid' tumor is not rare, and one could assign a generic term such as 'follicular acanthoma' to it.
 
Scan power view. This type of architecture can be seen in inverted follicular keratoses and in trichilemmomas. The tumor extends much deeper into the dermis than an irritated seborrheic keratosis.
Low power view. The tumor is cytologically benign, and there are squamous eddies at the tips of the arrows. 
High power view of above. Clear cell differentiation is also noted. The basement membrane is slightly thickened.

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