Dermoscopy of Skin Adnexal Neoplasms:A Continuous Challenge.

Dear Editor, Apocrine hidradenoma is a rare benign adnexal tumor related to the more common poroma, as they both originate from sweat glands. Hidradenoma usually has an eccrine differentiation, but an apocrine differentiation is possible. Due to its rarity and non-specific clinical appearance it is difficult to differentiate it from other malignant cutaneous lesions. In this challenging task, dermatoscopy could be particularly helpful to better describe, recognize, and differentiate these lesions. Unfortunately, the literature offers only few dermatoscopic descriptions of this rare cutaneous neoplasm. A 70-year-old woman in fair general condition was referred to our Department for an asymptomatic 10×8 mm single nodule on her left scapula. This nodule was red, dome shaped, well circumscribed, firm, and mildly tender (Figure 1). The patient reported that it had been present since approximately 7 months. The lesion was neither painful nor itchy and there was no bleeding. A skin examination did not show any other lesions with the same features or other suspicious lesions. Dermatoscopy revealed milky-pinkish areas with dotted vessels, linear-irregular vessels, and hairpin vessels: some of these aspects can also be found in amelanotic melanoma (1). There were also homogeneous blue areas similar to lacunae, characteristic but not exclusive to vascular or sarcomatous neoplasms and basal cell carcinoma (1,2). Furthermore, small ulcerations covered by an amber crust were identified, which can usually be found in basal cell carcinoma. Regarding the background of the lesion, we noticed peculiar, translucent, pinkish, soft, large lobular areas (Figure 2). On the basis of this analysis, we suspected an atypical presentation of a basal cell carcinoma, an amelanotic melanoma, or a sarcomatous skin neoplasm. A metastasis of an unknown solid tumor was also taken into consideration. The histological examination revealed an adnexal neoplasm and specifically an apocrine hidradenoma. The neoplasm had variably sized nests and nodules of neoplastic epithelial cells, with a small ductular lumens confined within the upper dermis. The lesion was composed mainly of two cell types: polygonal and smaller, elongated, and darker cells. The cuboidal/polygonal cells were seen lining the duct-like spaces and slots and resembled those of poroma (Figure 3). The adnexal skin tumors group includes a complex variety of uncommon tumors that can be distinguished only histologically, and most of them are benign (3). Searching the literature for "hidradenoma dermoscopy" and "adnexal dermoscopy" yields multiple descriptions of poromas but few dermatoscopic descriptions of hidradenoma (4). There was only one report of the presence of "arborizing vessels"(5), and another described "reddish purple areas and some linear or hairpin-like vessels on the surface of the tumor" (6). In another paper we found: "irregular scar like whitish areas and a polymorphous vascular pattern including irregular reddish-purple areas mimicking lacunar appearance of hemangiomas with thick hairpin vessels at the periphery" (7). It is very difficult make use of such scant data especially in order to detect a leading pattern for a specific diagnosis. Moreover, the described structures lack in specificity, being also present in many other lesions. Analyzing our dermatoscopic image and comparing it to the other ones available in the literature, we identified a peculiar background. It consisted in the presence of multilobular translucent and pinkish soft areas, which fit the previously described dermatoscopic criteria. We hypothesize there is a correlation between this feature and the histopathological presentation with variably sized nests and nodules. Of course, further case reports of hidradenoma are needed to identify the soft lobular background as a distinctive dermatoscopic feature. Due to the lack of specific features both clinically than dermatoscopically, histopathological analysis remains the only gold standard for diagnosis of these benign mimicking lesions.