Proliferating trichilemmal cyst with apocrine-acrosyringeal and sebaceous differentiation An adnexal tumor on the scalp of a 74-year-old woman is described. Histologically, the tumor was composed of cystic structures showing typical trichilemmal keratinization. The tumor cells in the cyst walls often formed duct-like or squamous eddylike structures and occasionally showed vacuolation or poromalike change. Ultrastructurally, some tumor cells showed differentiation either toward the acrosyringium or sebaceous cells. From these findings, the present tumor is considered to differentiate toward various parts of the hair follicle including infundibulo-isthmus epithelium, apocrine acrosyringium, and sebaceous cells. Sakamoto F, Ito M, Nakamura A, Sato Y. Proliferating trichilemmal cyst with apocrine-acrosyringeal and sebaceous differentiation. J Cutan Pathol 1991: 18: 137-141.

Proliferating trichilemmal cyst is known as a neoplasm that arises exclusively on the scalp in elderly women and shows trichilemmal keratinization (1-4). On the other hand, recently, a type of adnexal tumor that exhibits dual differentiation into sebaceous and apocrine-acrosyringeal cells has been reported under the terms infundibular adenoma (5), complex poroma-like adnexal adenoma (6), or sebocrine adenoma (7). Reported herein is a benign cystic neoplasm arising on the scalp of an elderly woman that showed features compatible with those of both proliferating trichilemmal cyst and sebocrine adenoma.

F. Sakamoto, M. Ito, A. Nakamura, Y. Sato Department of Dermatology, Niigata University School of Medicine, Niigata 951, Japan

Fumiko Sakamoto, Department of Dermatology, Niigata University, School of Medicine, 1Asahimachidori, Niigafa 951 Japan Accepted June 18, 1990

Material and methods

The tumor tissue was divided into small pieces and prepared for light and electron microscopic study using standard methods. Deparaffinized sections

Case report

A 74-year-old woman had noticed a wen on her scalp for 10 years. The lesion had markedly increased in size for 2 years prior to her seeking consultation at our clinic. By physical examination, the tumor was 4.6 X 6.0 cm, dome-shaped, and covered by skin with a smooth surface, depilation, and telangiectasia. The tumor was surgically removed under a local anesthesia. The cut surface revealed, in the dermis and subcutaneous tissue, multiple cystic cavities of variable size covered by whitish tumor tissue (Fig. 1). Two years after the operation, there had been no recurrence.

Fis^. /. A cross section of the jMcsent tumor. Many cavities of varied sizes are seen inside.

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were Stained with lieniatoxylin-eosin (HE), periodic acid-Schiff (PAS), and dia,stase-digested PAS. Ultratliin, pla,stic-embedded .sections were doublestained with 1% uranyl acetate and Reynolds' lead citrate (8) and observed under an electron microscope (JEM lOOS). Results Light microscopy

The tumor consisted o( multilobulated cysts that contained compact keratinous masses. The stroma surrounding the cysts was (lbrous and/or hyaline. 138

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with occasional foci of calcification (Fig. 2A). The cyst walls were composed primarily of" squamous epithelium showing trichilemmal keratinization. Within the walls, small duct-like and squamous eddy-like structures were often observed (Figs. 2A—D). The latter structures were composed of concentrically-arranged, keratinizing tumor cells and contained plugs of keratin (Figs. 2A—G). In some areas, basaloid cells proliferated on the basalar aspect of the walls, resulting in papiliomatous indentations of the basal layer (Fig. 2B). Vacuolated cells and squamous eddy-like structures occupied the cyst walls in some foci (Fig. 2C). In other areas. Hat

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cells with eosinophilic cytoplasm protruded into the cystic cavity, producing numerous keratohyaline granules prior to keratinization (Fig. 2D). Both the vacuolated cells and the keratin substance were occasionally stained with PAS which was not abolished alter diastase digestion.

Electron microscopy Intramural duet-like structures consisted of intraeytoplasmic cavities lined by irregularly distributed, short microvilli and surrounded by sparse to dense, cireularly arranged tonolilaments (Fig. 3). Large pools o( glycogen granules and rounded keratohyaline granules were lound in the same cytoplasm. On the innermost layer of the cyst walls, tumor cells exhibited incomplete keratinization; the keratinized tumor cells contained varied sized vacuoles and/or lipid droplets and did not show a well organized keratin pattern (Fig. 3). Another type of intracytoplasmic cavity was also noted. It was ovoid or irregular in shape, had few microvilli, and was surrounded by a pericavernous zone of dense tonofila-

ments. Such cavities contained line librillar or amorphous, electron-dense, granular material (Fig. 4). Intercellular spaces adjacent to some tumor cells were dilated and contained amorphotis substances (Fig. 4). Whorled, squamous eddy-like strticttnes contained, in their centers, a condensed cell wilh line tonofilaments and glycogen granules, and, at their jKMi])heries, concentrically arranged, lamellar tumor cells. Of tlie latter, the inner ones contained abundant concentrically arranged lonolilaments, whereas the outer ones acctmuilated tonolilaments, primarily in the more central portions of their cytoplasms. Adjacent to these concentric slructtu-es, many tumor cells often had a chister of lipid droj)lets, irregtilary distribtited or locally arranged tonolilamenfs, and vactioles in their cytoplasm (Fig. 5). In the areas where Hat cells protruded into the cystic cavity (Fig, 2C), the tumor cells exhibited a cluster of lipid droj)Iels as well as a number of tonofilaments. 'Fhey underwent incomplete keratinization, lacking the formation of a typical keratin pattern.

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Discussion

I he cyst walls in the present tumor light microscopically and ultrastructurally exhibited triehilemmal keratinization, that is, keratinization similar to that seen in the epithelium of the isthmus (9). Therefore, the major feature of the present tumor was compatible with that of proliferating trichilemmal cyst (1—4). On the other hand, the basaloid and vacuolated cells that proliferated in s(jme areas of the cyst walls were analogous to the type of proliferation seen in sebocrine ademoma (5—7), where the basaloid cells are considered to be aprocrine poroma cells (7). Intraeytoplasmic cavities with a circular shape and microvilli were also formed in the present tumor. This type of cavity has been described to occur in the embryonal acrosyringial portions of either apocrine or eccrin(" glands (10, 11) and in eccrine poroma (12). Another type of intracytoplasmic cavity, with fewer microvilli, was also noted in our case and resembled that seen in apocrine ducts rather than in eeerine ducts (13). The presence of dilated intercellular spaces, intermingled with tumor cells containing cytojjlasmic lipid droplets, may indicate 140

differentiation toward apocrine duct structures, as lipid droplets are known to be formed in peripheral cells of the apocrine duct, near its orifice into the hair follicle (13). The flat tumor cells that protruded into the cyst cavities resembled sebaceous duct cells rather than sebaceous gland cells (14), because they contained abundant tonofilaments but no lipid droplets. Squamous eddy-like structures, consisting of lamellar tumor cells containing concentrically arranged tonofilaments and glycogen granules, may represent dual diflerentiation towards both apocrine and sebaceous ducts. From these findings, the present tumor is interpreted as differentiating toward various portions of the hair follicle, including infundibulo-isthmus epithelium, apocrine acrosyringium, and sebaceous cells.

References 1, WiLson Jones E, Proliferating e|)idermoid cysts. Arch Dermatol 196(3: 94: 11, 2, Reed RJ, Lamar LM, Inva,sive hair matrix tumors of the scalp. Arch Dermatol 1966: 94: ;^1(),

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