Squamous Eddies in Irritated Seborrheic Keratosis

Seborrheic keratosis is related to the intraepidermal hair follicle in its morphogenesis. Squamous eddies in irritated seborrheic keratosis (ISK) are known to develop by focal maturation of basaloid cells, but the significance of squamous eddies is not understood. The purpose of this study was to elucidate the nature of squamous eddies in ISK. Serial sections of paraffin blocks of 20 cases of ISK were examined. We tracked each squamous eddy through the serial sections to observe the different shapes and positions of the same squamous eddy. In 4 cases, squamous eddies revealed hair shafts at their centers in different sections. In 14 cases, squamous eddies contained acrotrichial canals. In 13 cases, squamous eddies were connected to keratotic invaginations we thought to be follicular infundibula. Eighteen of the 20 cases of ISK showed at least 1 of the morphological features of intraepidermal hair follicle structures. We have found that the squamous eddies of ISK are anatomically related to acrotrichia.

Apocrine poroma: a distinctive case in a patient with nevoid basal cell carcinoma syndrome

Traditionally, poromas have been classified as eccrine neoplasms, but several recent reports of poroid tumors with sebaceous, follicular, and apocrine differentiation have challenged this idea. In support of alternative differentiation, a case of an "apocrine" poroma is reported in a 19-year-old man with the nevoid basal cell carcinoma syndrome. A papule on the right cheek, thought clinically to be a basal cell carcinoma, was excised. Anastomosing lobules of small uniform basaloid (poroid) cells formed small ductular structures lined by eosinophilic cuticles and extended into the superficial reticular dermis. The neoplasm originated from follicular infundibula and was surrounded by a myxoid stroma. Focally, primitive hair bulb and papillae differentiation was present, and some of the ducts were lined by cells suggesting decapitation secretion. The histologic pattern and the common embryologic origin of the folliculosebaceous-apocrine unit support apocrine differentiation of this tumor. The association with the nevoid basal carcinoma syndrome appears to be unique. This case, in addition, demonstrates overlapping features with the infundibulocystic type of basal cell carcinoma commonly seen in the basal cell nevus syndrome.

Multiple infundibular tumours of the head and neck

A condition of multiple benign and sometimes self-healing infundibular tumours of the skin is described. It effects the sun-exposed areas of the head and neck in Caucasians. The individual lesions consist of a cluster of thick pockets, representing in many details the supra-sebaceous portions of the follicular unit. Follicular poroma, tumours of the deeper part of the follicular infundibulum, virus warts, inverted follicular keratosis and prurigo nodules do not correspond adequately with the appearance described in the present series of six cases.

Inverted follicular keratosis

Inverted follicular keratosis, a benign tumor of the skin believed to arise from the infundibular portion of the hair follicle that can involve perioral skin, has a unique histologic picture. It can be confused with forms of skin cancer; with knowledge of this entity, oral and maxillofacial surgeons may be able to avoid unnecessary surgery. The clinical and microscopic findings of 12 cases of inverted follicular keratosis are reported.

Inverted follicular keratosis of the lip

Nine cases of inverted follicular keratosis (IFK) of the lips are reported. Eight of these occurred on the lower lip, a previously unreported location. The clinical and histologic features of IFK are discussed. The possibility of confusing this lesion with squamous cell carcinoma is emphasized, and the histologic criteria for differentiation are enumerated.

Trichilemmal tumor undergoing specific keratinization: "keratinizing trichilemmoma"

Numerous tumors with follicle-like direction of differentiation have been described. At least three of them connected to the overlying epidermis are related to the outer root sheath or trichilemma: the tumor of follicular infundibulum (Mehregan & Butler 1961) and the inverted follicular keratosis (Helwig 1955) or follicular poroma (Duperrat & Mascaro 1963) have been related to the infundibulum, the tricholemmoma (Headington & French 1961) to the lower outer root sheath. On the occasion of a case first diagnosed as proliferating trichilemmal cyst of the scalp, we think we have individualized a tumor exhibiting ability to undergo trichilemmal keratinization. We describe its histogenesis and stress its peculiarties compared with other lesions showing trichilemmal keratinization.

Seborrheic keratoses and trichostasis spinulosa

In 54 of 325 seborrheic keratoses, trichostasis spinulosa was found within the keratinous cysts and between papillomatous surface keratin, in addition to being present in contiguous hair follicles. Trichostasis in seborrheic keratoses and trichostasis spinulosa are both more frequent in older age groups. Trichostasis spinulosa represents a marker of vellus hair follicles and indicates that some seborrheic keratoses incorporate and may be partially derived from the cells of the infundibular portion of the follicle.

Inverted follicular keratosis

We reviewed 17 cases of inverted follicular keratosis. The median age of the patients at the time of surgery was 69 years. Follow-up in 14 cases showed no recurrences of inverted follicular keratosis, which is a benign skin lesion, often mistaken clinically and pathologically for a malignancy. Inverted follicular keratosis is characterized histologically by the presence of squamous eddies, acantholysis, acanthosis, and hyperkeratosis.