Apocrine hidrocystoma arising from nevus sebaceous on the scalp.

Nevus sebaceous is a hamartoma with an uneventful course since birth but many benign or malignant tumors are known to develop in about one third of the patients. A 37-year-old woman with asymptomatic hairless raised lesion over the scalp since birth presented with change in the morphology of the lesions associated with itching and irritation since one month. On examination, multiple well-defined hyperpigmented verrucous plaques coalescing with each other were seen over the right parietal scalp associated with alopecia. A single well-defined soft skin-colored cystic swelling of size 1 × 2 cm was seen interspersed within the plaque. After a clinical diagnosis of nevus sebaceous, a biopsy of the cyst was done, which revealed a large cyst lined by columnar and myoepithelial cells in the dermis. The columnar cells at a few places showed "decapitation secretion" giving the impression of apocrine hidrocystoma. Post-excision of the cyst, biopsy of the entire nevus was done and the histopathological diagnosis correlated with the clinical diagnosis of nevus sebaceous. Apocrine hidrocystoma developing from a sebaceous nevus over the scalp is a rarity with only three other cases of it arising on the scalp being reported and none of them developed from a sebaceous nevus.

INTRODUCTION

Nevus sebaceous also known as organoid nevus is a hamartoma that is generally found on the scalp at birth. Although the nevus as such has an uneventful course, many benign or malignant tumors are known to develop in about one third of the patients with nevus sebaceous.[1] However, apocrine hidrocystoma arising from a sebaceous nevus is rare.

CASE REPORT

A 37-year-old woman with asymptomatic raised hairless lesion over the scalp since birth presented with complaints of change in the morphology of the lesions associated with itching and irritation for the past one month. The patient had not received any treatment for the lesion. There was no history suggestive of any systemic involvement. On examination, multiple well-defined hyperpigmented verrucous plaques coalescing with each other were seen over the right parietal region of the scalp associated with alopecia. A single well-defined soft skin-colored cystic swelling of size 1 × 2 cm was seen interspersed within the plaque [Figure 1]. A clinical diagnosis of nevus sebaceous was made and a biopsy of the nevus and the nodule was done in view of suspected malignancy. Biopsy report revealed a large cyst lined by columnar and myoepithelial cells in the dermis. The columnar cells at a few places showed “decapitation secretion” giving the impression of apocrine hidrocystoma [Figures 2 and 3]. Post-excision of the cyst, histopathological examination correlated with clinical diagnosis of nevus sebaceous [Figures 4 and 5].

Figure 1

Cystic lesion arising from the nevus sebaceous over the right parietal region of the scalp

Figure 2

H and E (10×)—Multiloculated cystic lesion in the dermis lined by epithelium

Figure 3

H and E (40×)—Double layer of columnar cells with decapitation secretions

Figure 4

Post nevus excision and double opposing rotation flap

Figure 5

H and E (10×)—Nevus sebaceous showing multiple immature sebaceous glands in the upper dermis

DISCUSSION

Nevus sebaceous, also known as nevus sebaceous of Jadasohn or organoid nevus, is a hamartoma comprised predominantly of sebaceous glands. In 1904, Albrecht used the word hamartoma for a tumor that developed due to overdevelopment of some kind of tissue, which normally belonged at the site where it was formed or to any abnormal relationship of a normally situated tissue element.[2] They are cell nests or collection of abnormal number of normal cells that can be epidermal or dermal—sebaceous, apocrine, or eccrine.

The sebaceous nevus usually presents as a linear, yellow, hairless, waxy, and verrucous plaque. It can be flat at birth but as the person ages, it undergoes surface changes. During puberty, due to the hormonal changes, it becomes thickened, verrucous, or papillomatous. Tumors can arise within the nevus sebaceous; the most common being syringocystadenoma papilliferum and trichoblastoma.[1] The list of tumors that arise in nevus sebaceous are given in Table 1.[3]

Table 1

Tumors arising from nevus sebaceous

Apocrine hidrocystomas or cystadenomas are benign cystic tumors that arise from the secretory portion of apocrine sweat glands. They were first described by Mehregan in 1964.[4] They usually occur as solitary cystic lesions from the adenomatous cystic proliferation of apocrine glands. The most common sites of predilection are the head and neck with occurrence on the scalp being extremely rare.[5] Hidrocystomas may show eccrine or apocrine differentiation with the classical differentiating feature being the presence of secretory cells showing decapitation secretion in case of apocrine hidrocystomas.[6]

CONCLUSION

Apocrine hidrocystoma developing from a sebaceous nevus over the scalp is a very rare entity. Till date, only three other cases of an apocrine hidrocystoma arising on the scalp have been reported; this being the first case report from the Indian subcontinent.[789] To conclude, apocrine hidrocystoma should be considered as a differential diagnosis for any large cystic subcutaneous mass that occurs on the scalp.

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Conflicts of interest

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