[The Nikolowski trichoadenoma: a rare tumor of the ENT area]

[Anatomoclinical and dermatoscopic study of trichoadenoma]

INTRODUCTION

Trichoadenoma is a very rare follicular tumour with a remarkable histopathological appearance. In this article we present a series of 12 cases of trichoadenoma, as well as the anatomoclinical and dermatoscopic findings in a typical case. We discuss these findings in the light of an extensive literature research.

PATIENTS AND METHODS

We collated 12 cases of trichoadenoma of indisputable diagnosis made at the dermatopathology laboratory of the Dermatological Clinic of the University Hospitals of Strasbourg over a 30-year period (1989-2018).

RESULTS

The 12 cases comprised 7 women and 5 men, of average age 58.9 years, the majority having lesions on the cephalic extremity followed by the buttocks and thighs. Histopathological examination, which was similar in all 12 cases, showed multiple epidermal cysts containing an eosinophil lamellar keratin with a stratified wall without any visible hair, located in the superficial and mid dermis and appearing to be stacked on top of one another. In immunohistochemistry, broad spectrum keratin markers were still positive, the follicular marker Ber-EP4 weakly expressed and PHLDA1 was negative. For the case examined using polarized-light dermatoscopy, small rounded white-yellow areas were observed corresponding to cystic structures surrounded by irregular linear vessels.

DISCUSSION

Trichoadenoma is a rare tumour seen in middle-aged adults of mean age 45 years, and has no sexual predominance. It is asymptomatic, slow-growing, variable in colour, measures less than one centimeter and is most often located on the face or buttocks. In terms of histology, the juxtaposition of multiple small cystic structures suggests a follicular origin. Differential diagnosis is made with trichoblastomas, which always intensely express PHLDA1 and/or Ber-EP4, desmoplastic trichoepithelioma, which consists of multiple much thinner spans in a highly fibrous stroma with clearly visible arborescent vessels over a white-yellow ivory background at dermatoscopy, microcystic carcinoma, which has a deeper extension, and plaque milium, in which the cysts are larger.

Tricoadenoma of Nikolowski

The patient, aged 50 years, with no relevant clinical history, complained of a symptomless, soft tumor of the right buttock that had been present for many years. On examination, it was found to be pediculate, oval, somewhat erythematous, firm on palpation, and with a central keratin plug. The greatest diameter of the lesion was 1.2 cm (Fig. 1). On surgical removal of the lesion, it was seen to be composed of a symmetric intradermal proliferation of cystic formations, uniformly distributed throughout and made up of flat, pluristratified epithelium with laminated keratin. There was little difference in the thickness of the walls of the cysts (Fig. 2). Some cysts were attached to a short tadpole-shaped, epithelial cord and surrounded by a scanty fibroblastic stroma. No hairmatrix-like differentiation nor basaloid structures were seen, nor were atypical cells present. There was hardly any inflammatory infiltration.