Tubulopapillary hidradenoma: A rare case with cytohistopathological correlation.

Tubulopapillary hidradenoma is a rare adnexal neoplasm with only a few cases reported in literature. The tumor shows a female predominance with a wide age range and presents as a well-defined, non-tender nodule most often located on the scalp. Review of the literature yielded no fine-needle aspiration reports of the cytological features of the tumor. We report a rare case of tubulopapillary hidradenoma in a 30-year-old male, presenting with a scalp swelling. The cytomorphological features are described in detail with histopathological correlation.

Introduction

Tubulopapillary hidradenoma (TPH) is a dermal ductal tumor that shows both eccrine and apocrine differentiation. In the past, the term papillary eccrine adenoma (PEA) has been used to describe a TPH with eccrine differentiation whereas, the term tubular apocrine adenoma (TAA) was used to designate a TPH with apocrine differentiation.[123] It was later proposed that the term TPH should be used for such lesions as PEA and TAA can be indistinguishable both clinically, histologically and immunohistochemically.[4]

Fine needle aspiration cytology (FNAC) is an important tool in diagnosing various cutaneous and subcutaneous lesions but little has been reported about the cytological features of adnexal tumors. Review of literature did not reveal any report on the cytological features of TPH and these uncommon tumors are usually reported only after histopathological examination.

Case Report

A 30-year-old male patient was referred from surgical out patient department with complaint of a painless swelling on the scalp overlying the right frontal bone, which had slowly increased in size over the past 6 months. On local examination, a 1 × 1 cm well defined, soft to firm, non-tender, mobile swelling was palpable with no overlying skin changes [Figure 1a]. FNAC was performed, which yielded 1.5 mL of brown colored fluid. Smears prepared showed cohesive clusters, papillaroid fragments, monolayered branching sheets and few singly lying epithelial cells [Figure 1b]. On closer examination, two types of cell populations were seen. One population of cells were small cuboidal and exhibited scant to moderate amount of basophilic cytoplasm, round to oval nuclei with regular nuclear membrane, fine chromatin and inconspicuous nucleoli. At places, some of these cells showed tubular/acinar formations. The other population consisted of cells that were larger and showed abundant amount of pale bluish to grayish, fragile, granular cytoplasm, round to oval nuclei with regular nuclear membrane, fine chromatin and visible nucleoli. At places, these cells also showed attempted tubule formation [Figure 2a]. Few of these cells were singly scattered and exhibited prominent secretory activity in the form of large cytoplasmic vacuoles filled with eosinophilic material [Figure 2b]. No pleomorphism, mitoses or necrosis were noted. Background showed numerous foamy macrophages as well as few pigment laden macrophages in abundant amorphous secretions.

Figure 1

(a) 1 × 1 cm soft to firm, non-tender, mobile swelling on the scalp; (b) FNA smear showing papillaroid fragments, mono-layered branching sheets and few singly lying epithelial cells (Giemsa, ×40)

Figure 2

(a) Two types of cell populations seen-one of apocrine morphology on the left and the other of eccrine morphology on the right. Attempted tubule formation is seen (arrow) (Giemsa, ×400); (b) Few singly scattered cells showing prominent sectretory activity (Giemsa, ×1000); (c) Tumor composed of numerous irregularly shaped, closely packed tubules, few of which are cystically dilated with short papillary projections extending into the lumina (H and E, ×100)

A cytodiagnosis of “benign adnexal tumor (both eccrine and apocrine morphology seen)” was rendered. No attempt was made for specific subtyping of the adnexal tumor at this point.

Excision biopsy of the lesion was performed. The histological sample consisted of a grey white nodular tumor measuring 0.8 × 0.5 × 0.5 cm. Hematoxylin and eosin stained sections showed a well circumscribed tumor located in the dermis with no connection to the epidermis. The overlying epidermis was unremarkable. The tumor had a nodular growth pattern with the nodules separated by stroma containing loosely arranged spindle cells and areas of hyalinized collagen. These nodules consisted of numerous irregularly shaped, closely packed well-formed tubules lined by two layers of epithelial cells; the peripheral layer consisting of cuboidal to flattened cells, and the luminal layer composed of columnar cells. Many of the tubules showed luminal cells with abundant granular cytoplasm that exhibited decapitation secretions with presence of eosinophilic granular debris in some lumina. Some of the tubules were cystically dilated with short papillary projections extending into the lumina [Figure 2c]. These papillary projections were devoid of fibro-vascular cores and were also lined by double layer of epithelial cells consisting of outer cuboidal and inner columnar cells. In a focal area, few tubules showed clear cell change in the epithelial lining cells. No pleomorphism, mitoses or necrosis were seen. The light microscopic diagnosis was consistent with tubulo-papillary hidradenoma.

Periodic acid-Schiff (PAS) positive diastase resistant material was seen in some of the tubular lumina as well as in the cells that had abundant granular cytoplasm.

On immunohistochemistry, the luminal cells were diffusely positive for Pan cytokeratin (CK), while sharp luminal positivity was seen with epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA) consistent with differentiation towards the secretory epithelium of sweat glands. The abluminal cells showed diffuse intense positivity for S-100 and smooth muscle actin (SMA), whereas the periadnexal dermis was positive for vimentin and CD10 (focally).

Cytohistological correlation was then attempted considering histological diagnosis as final.

Discussion

Tubulopapillary hidradenoma is a rare adnexal neoplasm with only a few cases reported in literature.[135] It is included under the umbrella of apocrine adenomas and shows features of both TAA and papillary hidradenoma.[6]

The tumor has a female predominance (2:1), a wide age range (18-78 years) and usually presents as a well-defined nodule most often located on the scalp. Most of the lesions are less than 2 cm in size, non-tender and slightly mobile with no significant overlying skin changes. In some cases, TPH has been seen in association with syringocystadenoma papilliferum, with the latter component being situated in the superficial portion of the combined lesion.[5]

The tumor is composed of numerous irregularly shaped tubular structures that are usually lined by two layers of epithelial cells. At places, dilated duct-like structures of various sizes with intraluminal papillary projections are seen. The tubules, the dilated ducts and the papillary projections are all lined by two layers of epithelial cells. The luminal layer is composed of columnar cells whereas the peripheral layer is formed of flattened to cuboidal cells. Decapitation secretions of the luminal cells are seen in many areas where the tubules may show eosinophilic PAS positive secretions in their lumina. Other less common features include, focal clear cell change, sebaceous differentiation and connection of ducts to the epidermis.[6]

According to the clinical presentation, the first differential diagnosis was cylindroma. Cylindroma shows closely packed irregular nests of cells, whereas tubules and papillae with active decapitation secretions are absent.[4] Syringocystadenoma papilliferum also shows papillary projections into cystic invaginations, but the lesion shows connection with the overlying epidermis. The papillae are thicker, taller, with fibro-vascular cores and the papillary stroma contains abundant plasma cells.[7]

Review of the literature yielded no fine-needle aspiration reports of the cytological features of TPH. On retrospective examination of the fine needle aspiration (FNA) smears, we observed certain features that could lead to a specific cytological diagnosis. The criteria for benignancy were cohesive sheets, uniform appearing cells with bland nuclei, regular nuclear contours fine chromatin and absence of mitoses/necrosis. Presence of myoepithelial cells is also an important indicator of benignancy in ductal tumors; however, no myoepithelial cells were seen in our FNA smears. The mono-layered branching sheets and the papillaroid structures correspond to the short papillae that were seen in the cystically dilated tubules. Attempted tubule formation pointed towards the tubular architecture of the main tumor. The presence of two types of cells, one showing benign cuboidal morphology, and the other showing columnar apocrine type morphology with some cells showing evidence of active secretions indicated the eccrine and apocrine differentiation in the tumor.

Conclusion

There is paucity of reports describing the cytomorphological features of benign adnexal tumors. FNAC is a simple, safe and cost-effective procedure that can play an important role in the diagnosis of these benign but uncommon lesions.