Sir,

Nodular hidradenoma is a rare, benign adnexal tumor usually located in the head, neck, and extremities [1]. The difficulty of the diagnosis is due to the non-specificity of the clinical and histological presentation, often requiring a clinicopathological correlation [2]. Herein, we report a case of atypical abdominal hidradenoma mimicking lipoma.

Our patient was a 51-year-old Moroccan female operated for bowel obstruction and fibroma presenting with a slowly growing, painless, subcutaneous abdominal nodule persistent for the last two years. The nodule had gradually increased in size in a context of apyrexia and general state preservation.

A clinical examination was remarkable for a subcutaneous nodule (2.5 cm long axis) at the left iliac fossa, painless, indurated, and not fixed to the deep tissues, with slightly purplish skin (Fig. 1). The rest of the examination was featureless. In addition, dermoscopy was non-specific.

Figure 1: Subcutaneous nodule with bluish skin in the abdominal area.

The initial diagnosis was lipoma or neurofibroma. However, the histology of an excisional biopsy revealed a lobulated, nodular tumor proliferation involving the reticular dermis, consisting of spindle-shaped round cells with clear acidophilic cytoplasm and rare mitotic activity. The proliferation associated with a fibrohyaline stroma (Fig. 2) was in favor of hidradenoma.

Figure 2: The tubes lined with a regular double cell base, the stroma with fibrohyaline, and the presence of eosinophilic substances inside the tubes (400×).

At two years of follow-up after surgery, no recurrence was observed.

Hidradenoma is a rare, sweat gland, adnexal tumor that arises from either eccrine or apocrine sweat glands [1]. It represents 1% of primary cutaneous tumors. Females between the age of twenty and fifty are at the biggest risk of developing these tumors [3]. Although no etiological factor has been determined, the presence of estrogen receptors in benign nodular hidradenomas and the predominance in females suggest a possible role of these hormones in the development of the tumors [1].

Clinically, it is a solitary nodule localized in the dermis or hypodermis, violaceous red or brown in color. They are of variable size and grow slowly (less than 5 mm up to 10 cm). Although most often asymptomatic, they may ulcerate, sometimes expressing a watery light or hematic discharge [1,3,4].

Studies have shown that hidradenomas are mainly located in the thorax [5,6], followed by the cervicofacial and, in some cases, plantar regions [2]. Sites of other localizations include the ankles [4], palms [6], and breasts [7]. However, to our knowledge and up to this day, no case of abdominal hidradenoma has been described.

The histopathological diagnosis is difficult because of the different clinical signs and the variable prevalence of various components, yet the clear-cell form is the most common. The histological features of hidradenoma include a cystic cavity lined with an epithelium with a hyalinized stroma and polygonal cells with clear cytoplasm [1,3,5].

Because of the potential for recurrences and the risk of transformation into hidradenocarcinoma, surgery remains the preferred treatment with regular clinical surveillance [1,3].

In conclusion, hidradenoma is a rare adnexal tumor. It is characterized by non-specific clinical or histological morphology, with a varying localization, making a clinical and pathologic correlation essential for an accurate diagnosis. The recommended treatment is surgical excision because of the risk of malignant transformation with long-term follow-up.

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