Inverted Follicular Keratosis

Periocular inverted follicular keratosis: a retrospective series over 17 years

PURPOSE

To evaluate the demographic, clinical, and histopathologic characteristics of periocular inverted follicular keratosis (IFK), a very rare lesion with poorly defined characteristics.

STUDY DESIGN

Retrospective case series.

METHODS

We evaluated 11 patients with clinically diagnosed IFK confirmed by histologic analysis. Data were collected on the patients' demographics, clinical presentation and course of the disease, signs and symptoms, location of the lesion, and outcomes of treatment.

RESULTS

The patients' mean age was 71 years (range, 32-91 years). Seven (64%) of the patients were female. Eight of the patients (72.7%) had no symptoms, two (18.2%) reported itching, and one (9.1%) had edema and bleeding of the lesion. The lesion affected the upper eyelid in 4 of the patients (36%), the lower lid in 3 of the patients (27%), and the inner canthus in 4 of the patients (36%).

CONCLUSIONS

IFK has no specific clinical characteristic and thus requires histologic confirmation for its diagnosis and appropriate management.

Epithelial keratin and filaggrin expression in seborrheic keratosis: evaluation based on histopathological classification

OBJECTIVES

Seborrheic keratosis (SK) is classified into six types: hyperkeratotic; acanthotic; irritated; clonal; reticulated; and adenoid. However, the origins of the respective types of SK remain unclear.

METHODS

To clarify the histogenetic origins of SK, we performed immunohistochemical studies of keratin (K) and filaggrin expression, taking into account the histopathological classifications of SK.

RESULTS

Hyperkeratotic SK mainly expressed K1, K10, and filaggrin. Acanthotic SK mainly expressed K14 with some K15. Irritated SK mainly expressed K14 and K17 in squamous eddies. Clonal SK, reticulated SK, and adenoid SK mainly expressed K14. The results show that hyperkeratotic SK differentiated towards squamoid terminal keratinization, whereas acanthotic, irritated, clonal, reticulated, and adenoid SK mainly differentiated towards basaloid undifferentiated cells. In addition, acanthotic SK differentiated towards the hair bulge, and irritated SK differentiated towards the follicular infrainfundibulum.

CONCLUSIONS

Based on the patterns of keratin and filaggrin expression demonstrated by the histopathological types, SK demonstrated diverse differentiation towards epidermal keratinization, basaloid cells, the infrainfundibulum and hair follicle bulges, which suggests that SK is in an undifferentiated and hyperproliferative state with heterogeneous differentiation. The immunohistochemical method of investigating patterns of keratin expression is useful in the differential diagnosis of cutaneous epithelial tumors.

Inverted follicular keratosis simulating malignant melanoma

A 93-year-old woman was noted to have a single pigmented lesion on the posterior aspect of her neck. Clinical examination revealed a 12 x 8-mm flat lesion, with an irregular border and variegated pigmentation. Dermatoscopic examination revealed a lesion with multiple colours, featureless areas and black dots, suggestive of malignant melanoma. With a presumed clinical diagnosis of malignant melanoma, an elliptical excision was performed, with a 1-cm margin. However, histological examination revealed the unexpected diagnosis of pigmented inverted follicular keratosis.

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.

Inverted follicular keratosis of the vulvar skin: a lesion that can be confused with squamous cell carcinoma

Although seborrheic keratoses of the vulva are described in textbooks, to our knowledge, inverted follicular keratosis has not been reported. A 27-year-old woman underwent an excisional biopsy for a small lesion of the left labium majus. Squamous cell carcinoma was considered in the clinical differential diagnosis. The initial pathologic diagnosis suggested squamous cell carcinoma in situ, and the consultation diagnosis was superficially invasive squamous cell carcinoma. On pathologic examination, a symmetrical, endophytic, epithelial tumor was observed consisting of a proliferation of basaloid cells with many areas of reactive squamous cells showing numerous squamous eddies, focal reactive nuclear atypia, and occasional mitotic figures. After the pathologic diagnosis of inverted follicular keratosis was made, a history of close perineal shaving and total body tanning was obtained. Because inverted follicular keratosis is postulated to be related to follicular injury, it is likely that the trauma of close shaving is a significant etiologic factor. There is less evidence that ultraviolet ray exposure is of etiologic importance.

Proliferating epithelial cysts. Clinicopathological analysis of 96 cases

Ninety-six proliferating cutaneous epithelial cysts were classified into two subtypes, proliferating trichilemmal cysts (PTC) and proliferating epidermoid cysts (PEC), depending on the mode of keratinization or the origin of the tumors. The clinicopathological features and the biological behavior of these two subtypes were compared. Among 63 patients with PTC, 45 (71%) were women and 18 (29%) were men. The most common site was the scalp (78%), followed by the trunk (13%). These tumors were well circumscribed subepidermal lesions and demonstrated uniform histologic pattern with varying degrees of cytologic atypia. A few tumors extended into the epidermis and occasionally became ulcerated. Follow-up of 59 (94%) PTC for an average of 4 years revealed recurrence in one. Ten tumors demonstrated carcinomatous changes including one with anaplastic carcinoma and regional lymph node metastasis. None of these tumors recurred or developed further metastasis following wide excision. Of 33 PECs, 12 (36%) occurred in women and 21 (64%) in men. These tumors were widely distributed in the pelvic and anogenital areas (36%), followed by the scalp (21%), upper extremities (18%), and trunk (15%). Seventy-nine percent of the PECs were located in areas outside the scalp. The PECs were subepidermal tumors but often communicated to the surface. The histologic pattern of PEC was more variable than that of PTC. Seven tumors exhibited carcinomatous changes. Follow-up of 30 (91%) PEC revealed local recurrences in 6, with multiple recurrences in 3, and extensive local invasion in 2, resulting in death in one. Greater anaplasia, high mitotic rate and deeper invasion were associated with increased incidence of recurrence and aggressive behavior. Although both PTC and PEC were locally aggressive tumors and potentially malignant, distant metastasis was unusual. These tumors should be treated with wide local excision, especially those showing cytologic atypia and carcinomatous changes.

Infundibular keratosis--report of two cases

Two cases of infundibular keratosis are presented, characterized histopathologically by funnel-shaped, invaginating, epithelial lobules showing infundibular keratinization and connection with pilosebaceous structures. Lightly-staining, glycogen-laden epithelial cells predominated within the two tumors. Differential diagnoses with other infundibular tumors and relationships to trichilemmoma are discussed.

Infundibular keratosis--a prototype of benign infundibular tumours

Three cases of a benign follicular tumour of infundibular origin are reported. The neoplasms were solitary, verrucous, slowly-growing papules or nodules on the face, which were diagnosed clinically as verruca vulgaris or seborrhoeic keratoses. Histologically, several epithelial lobules were seen, mainly above the level of the surface of the surrounding skin, with characteristic funnel-shaped invaginations. The tumours occasionally contained vellus hairs or were connected with sebaceous glands and/or hair follicles at their bases, indicating their follicular origin. The tumour masses consisted of peripherally arranged basaloid and inner squamoid cells. The latter cells contained more glycogen and appeared paler with haematoxylin and eosin (H&E) stains than the normal inter-follicular squamous cells. Neither clear cells nor squamous eddies were observed. Palisading of the basaloid cells was not a prominent feature. The name 'infundibular keratosis' is proposed for such tumours, which probably represent the prototype of infundibular tumours of the hair follicle.

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.

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.

Inverted follicular keratosis

Attention is drawn to a benign skin tumour which has escaped recognition in the British lieterautre. Inverted folliculr keratosis can be mistaken clinically for basal cell carcinoma and a variety of benign skin lesions. Pathologically it is easliy confused with squamous carcinoma, a serious error because this lesion occurs dominantly on the face. The lesion is thought to arise from the infundibulum of hair follicte.