Ji Hyun Lee, Yoon Young Kim, Sun Young Yoon, Jeong Deuk Lee and Sang Hyun Cho*

Department of Dermatology, Our Lady of Mercy Hospital, College of Medicine, The Catholic University of Korea, 665 Bupyung-Dong, Bupyung-Gu, 403-720 Inchon, Korea. *E-mail: drchosh@hotmail.com

Accepted October 24, 2007.

Sir,

Trichoadenoma is a rare solitary tumour that is usually found on the face or buttock of adults (1). Trichoadenoma was first described in 1958 by Nikolowski (2). Clinically, this lesion is a few mm to 1.5 cm in diameter, and appears as solitary, slowly growing, greyish nodules. Trichoadenoma is less mature than trichofolliculoma and more differentiated than trichoepithelioma (3). We report here a case of trichoadenoma that presented typical histological findings, but clinically resembled milia.

Case report

A 20-month-old male infant presented with asymptomatic, multiple, whitish, grouped, tiny papules. These first presented as sharply demarcated papules on the erythematous macule, which measured 0.4 cm in diameter, seen on the patient’s nose for several months (Fig. 1). Physical examination was otherwise normal.

Fig. 1. A 0.4-cm, erythematous macule composed of multiple, grouped, whitish, tiny papules that resembled milia on magnification (inset).

Histopathological examination demonstrated dome-shaped, sharply defined, papules composed of numerous, round-to-oval, infundibulocystic structures in the dermis (Fig. 2). The infundibulocystic structures were lined by squamous epithelium. The histological features indicated trichoadenoma. The sebaceous glands were intact and there was no evidence of hair follicle formation.

Fig. 2. Numerous, round-to-oval, infundibulocystic structures in the dermis (haematoxylin-eosin stain ×100).

Discussion

Nikolowski (2) first reported on a case of trichoadenoma that occurred on the thigh of a 63-year-old man, and 16 more cases have since been reported in the literature (2–5). The histogenesis of trichoadenoma remains unclear. It is assumed to have an association with trichofolliculoma and trichoepithelioma. Moreover, the histological similarity of trichoadenoma with trichoepithelioma suggests the development of immature hair structures. However, because the cyst wall consists of epidermoid cells and keratinization may take place with formation of keratohyalin, it has been suggested that the tumour differentiates largely toward the infundibular portion of the pilosebaceous unit (1). Trichoadenoma is found mostly in adults, and the mean age of the reported cases is about 43 years with no sexual predilection (2–7). A 7-year-old boy was the youngest previously reported patient (5). The typical clinical feature of trichoadenoma is a mainly solitary, nodular lesion on the face or buttock. However in our case, the lesion presented on the nose as multiple, whitish, grouped, tiny papules on an erythematous macule, which clinically resembled milia. The clinical differential diagnosis for whitish, grouped, tiny papules includes clustered milia and nevus comedonicus. Nevus comedonicus is characterized by unilateral distribution and consist of closely set comedone-like papules that have a dilated follicular orifice at the centres. Milia consist of miniature epidermoid cysts in the superficial dermis just beneath the epithelium. The main histological features of our patient were the existence of numerous infundibulocystic structures in the dermis, lined with stratified squamous epithelium that resembles the external root lamina of the hair follicle. These cysts are of fairly uniform size and contain laminated keratin, that is similar to the follicular infundibulum, and this indicated trichoadenoma (8). The fact that trichoadenoma with unusual clinical features and typical histological findings presented in the infant suggests the possibility that age can have an effect on the clinical aspects of trichoadenoma.

References

1. Klein W, Chan E, Seykora JT. Tumors of the epidermal appendage. In: Elder DE, Elenitsas R, Johnson BL Jr, Murphy GF, editors. Lever’s histopathology of the skin, 9th edn. Philadelphia: Lippincott-Raven; 2004: p. 877.

2. Nikolowski, W. Trichoadenoma (organoid follicular hamartoma). Arch Klin Exp Dermatol 1958; 207: 34.

3. Rahbari H, Mehregan A, Pinkus H. Trichoadenoma of Nikolowski. J Cutan Pathol 1977; 4: 90.

4. Kurokawa I, Mizutani H, Nishijima S, Kato N, Yasui K, Tsubura A. Trichoadenoma: cytokeratin expression suggesting differentiation towards the follicular infundibulum and follicular bulge regions. Br J Dermatol 2005; 153: 1084.

5. Reibold R, Undeutsch W, Fleiner J. Trichoadenoma of Nikolowski – review of four decades and seven new cases. Hautarzt 1998; 49: 925.

6. Jaqueti G, Requena L, Sanchez Yus E. Verrucous trichoadenoma. J Cutan Pathol 1989; 16: 145.

7. Yamaguchi J, Takino C. A case of trichoadenoma arising in the buttock. J Dermatol 1992; 19: 503.

8. Banuls J, Silvestre JF, Sevila A, Morell A, Betlloch I, Botella R. Trichoadenoma of Nikolowski. Int J Dermatol 1995; 34: 711.