A case of solitary collagenoma localized on the upper lip mimicking mucocele

Abstract

Conflict of interest: none declared. Collagenomas are rare hamartomatous malformations of the dermis, characterized by a proliferation of normal collagen tissue. We present a case of isolated (solitary) collagenoma arising in the upper lip, an uncommon location for this disease, and clinically mimicking mucocele. A 56‐year‐old Japanese woman was referred to us with a 3‐month history of an asymptomatic soft mass on the left upper lip. She was otherwise in good health. Her medical history was not relevant, and there was no family history of a similar disorder. Physical examination found a slightly raised, soft, elastic, bluish‐white nodule on the inner surface of the left upper labial mucosa (Fig. 1). The lesion was well demarcated, and measured 5 mm in diameter with a round shape and smooth surface. No lesions were observed on the trunk, limbs or any other body sites. Because of the suspicion of mucocele, an excisional skin biopsy was taken for both diagnostic and therapeutic purposes. Histopathological examination found an increased number of collagen bundles in the dermis, which were arranged randomly (Fig. 2a). The collagen bundles stained strongly with Azan–Mallory stain, showing an intense blue colour (Fig. 2b). The lesion had no capsule and was relatively well‐defined. Elastic van Gieson stain showed a mild decrease in elastic bundles. Based on the histopathological findings, a diagnosis of solitary collagenoma was made.