Atypical clear cell hidradenoma

Introduction

Clear cell hidradenoma (CCH) is an uncommon, benign, slowly growing cutaneous tumor of the sweat glands. It has been known by various other names such as nodular hidradenoma, eccrine acrospiroma, and solid-cystic hidradenoma.[1] It is mostly seen in adults and is characterized clinically by solitary and firm intradermal nodule. Histopathologically both solid and cystic portions are present with characteristic clear cells, which contain a large amount of glycogen and thus appear clear under light microscopy.[1],[2] Presence of malignant change is suggested clinically by a rapid growth and cutaneous ulceration and histologically by an increased number of mitotic figures, nuclear atypia and angiolymphatic or perineural invasion.[3] Lesions having frequent mitoses or nuclear atypia but lacking clear evidence of asymmetric invasive growth are termed as atypical CH and require an aggressive management in view of a risk of recurrence and malignant transormation.[1],[2] We report a patient with large, pigmented and ulcerated CCH that clinically resembled a pigmented basal cell carcinoma.

Case Report

A 72-year-old man presented with a 2-year history of an asymptomatic dark, raised lesion over the trunk. The lesion was noticed to have ulcerated along with an increase in size for the last two months. His general health was preserved and he had no significant past or medical history. Examination revealed a single, non-tender, round, firm, blackish brown, 3x3 cm sized nodulo-plaque lesion over the left lateral chest wall with superficial ulceration and exudation [Figure - 1]. It had a well-defined, pigmented, regular and raised margins and was free from underlying structures. There was no regional lymphadenopathy; general physical and systemic examination was normal. A clinical possibility of pigmented basal cell carcinoma was considered. An incisional skin biopsy revealed a well circumscribed tumor in the dermis composed of variably sized tubular lumina and cystic spaces. In addition the tumor had numerous polyhedral and clear cells and a moderate number of mitotic figures, but without nuclear atypia or vascular invasion [Figure - 2], [Figure - 3] consistent with the diagnosis of atypical CCH. Surgical excision was carried out with adequate tumor free margins, confirmed on histopathology. No recurrence has been observed over 6 months of follow up.

Discussion

Clear cell hidradenomas CCH are usually seen in 4th to 8th decade of life and are twice more common in females.[2] Clinically the tumor appears as asymptomatic, usually solitary, 0.5 to 1 cm sized, skin colored intradermal nodule, slightly elevated above the surrounding skin.[1],[2] Occasionally brown, blue or red discoloration and surface erosions or ulceration may be observed. It is a slow growing tumour and rapid growth may represent trauma, hemorrhage or a malignant change.[2],[5]

Clinical differential diagnosis includes basal cell and squamous cell carcinoma, melanoma, metastatic tumor, dermatofibroma, pyogenic granulomas, hemangioma, leiomyoma and other cutaneous adenexal tumors.[1],[2] Differentiation depends upon biopsy and immunohistochemical staining.[2] Histopathology shows both solid and cystic components in varying proportions. The tumor has tubular lumina lined by cuboidal or columnar cells and variably sized cystic spaces. The solid portions contain two types of cells: polyhedral cells with basophilic cytoplasm and glycogen containing pale or clear cells with a clear cytoplasm and a round nucleus.[1]

Criteria for assessing malignancy include overt nuclear atypia, readily observed mitotic figures, infiltrative patterns, lymphatic or perineural invasion and areas of necrosis. CCH is labeled as atypical when there is no evidence of invasive features but it has a high mitotic rate or nuclear atypia. The exact frequency of atypical CCH and their risk of transformation into malignant tumors is not known. However, mitotic activity and cellular pleomorphism may not be accurate predictors of clinical behavior. Malignant CCH usually arise de novo and malignant transformation of benign CCH has rarely been reported.[3] Biddlestone et al have described a young girl with progression of a histologically benign hidradenoma to a malignant sweat gland carcinoma with metastasis over a period of 11 years.[3] However, mitotic activity and cellular pleomorphism may not be accurate predictors of clinical behavior.[2] Clinically benign CCH with focal nuclear pleomorphism and increased mitotic activity have been reported, while tumors with aggressive clinical behavior and metastasis may have deceptively benign histological appearance.[3],[5] In the reported case, potential for aggressive behavior was suggested by the clinical findings of a rapid growth, pigmentation and ulceration. However there were no features of nuclear atypia or angiolymphatic invasion and thus the lesion was histologically benign. It was labelled as an atypical CCH because of presence of mitotic figures. The present case thus illustrates that an aggressive clinical behavior may not always parallel the histologic features.

Treatment of benign, atypical and malignant CCH is surgical excision with adequate margins to minimize the risk of recurrence followed by histologic confirmation of adequacy of excision.2,3 In view of reported malignant transformation, howsoever rare, even the histologically benign lesions should be promptly diagnosed followed by surgical excision and histologic confirmation of clearance.