Epidermal inclusion or epidermoid cysts are fairly common cutaneous lesions, microscopically characterized by keratinizing stratified squamous epithelial lining with no adnexal structures. Seborrheic keratosis-like changes in epidermal inclusion cyst are of rare occurrence, with only a handful of cases recorded in the English literature.
A 58-year-old male patient presented with a nodular swelling on the calf of the left leg. It was of 6 months duration with recent increase in size. There was no pain or discharge associated with the swelling. No history of previous trauma to the site was obtained. On local examination, solitary, nodular, subcutaneous lesion was found which was slightly mobile, soft to cystic in consistency, and non-tender. Fine-needle aspiration yielded pultaceous material and showed admixture of nucleate and anucleate squames on a keratinous background. A diagnosis of epidermal inclusion cyst was made and total excision was performed. On gross examination, a cystic swelling of 2 cm diameter filled with yellowish material was seen below the epidermal surface. Histopathologic examination showed an epidermoid cyst with seborrheic keratosis-like features. The cyst wall displayed marked acanthosis, papillomatosis, pseudohorn cysts, tiny squamous eddies, basaloid cell proliferation, and clumps of keratohyalin granules [Figure 1]. No cytologic atypia was noted. The cyst was filled with laminated tiers of keratin. The overlying epidermis showed mild acanthosis with anastomosing rete ridges. The surrounding dermis was largely unremarkable, except for mild perivascular lymphocytic infiltrates. No recurrence was noted at a 6-month follow-up visit.
Epidermoid cyst with seborrheic keratosis-like change in the cyst wall is a rare variant. This entity has been also referred to as “seborrheic inclusion cyst (SIC),” “seborrheic cyst,” and “epidermoid cyst with seborrheic verruca-like cyst wall.” It is usually seen in the elderly population, similar to the present case. However, there is no gender or site predilection. As a quick initial investigation modality, fine-needle aspiration cytology helps in excluding other clinical possibilities. A definitive diagnosis of this variant is made upon histopathologic examination. A single case of SIC reported by Terada showed cytoplasmic eosinophilic inclusions which were immunoreactive for human papillomavirus (HPV). In contrast, Fernandez-Flores failed to detect HPV by polymerase chain reaction (PCR) in SIC. Treatment includes complete surgical excision and recurrence is seldom noticed.
The term “verrucous cysts” was coined by Meyer et al. to describe epidermal inclusion cysts with histomorphologic findings consistent with HPV infection in the cyst wall. Meyer et al. and Soyer et al. demonstrated HPV-specific DNA sequences by PCR in all five cases of verrucous cysts in their respective study cohorts. All these cases showed focal prominent hypergranulosis and irregular keratohyalin granules, microscopically. HPV antigens in the wall of a verrucous cyst can also be detected with immunohistochemistry. In our case, the cyst wall showed both seborrheic keratosis-like features (irregular acanthosis, papillomatosis, pseudohorn cysts, and squamous eddies) and verruca-like features (vertical hyperkeratotic tiers and irregular clumps of keratohyalin granules) on light microscopic analysis. However, no koilocytic changes were noted. In our opinion, the term “verrucous cyst” should only be applied to cases with definitive viral cytopathic changes or where HPV is detected by ancillary techniques.
In conclusion should be aware of this rare entity and all the histopathological changes noted in the cyst wall should be clearly transcribed in the report. It would alert the clinician of a possible HPV etiology and ensure appropriate management. Careful attention should also be paid to rule out any cytologic atypia or dermal infiltration.
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