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Sebaceous hyperplasia consists of multiple asymptomatic small yellow papules with a central depression, occurring most commonly on the forehead and cheeks, but occasionally affecting the areola,1 chest2 or genital skin.3 The lesions are sometimes mistaken clinically for basal-cell carcinoma. Sebaceous hyperplasia belongs to the group of epidermal tumours with sebaceous differentiation. Farina et al4 suggested that hyperplasia in the sebaceous gland is analogous with trichofolliculoma. Although termed hyperplasia, they concluded that sebaceous hyperplasia is a benign neoplasm rather than hyperplasia as these lesions do not involute clinically. By contrast, the absence of significant enlargement of sebaceous lobules, and the sharp demarcation of the lesion distinguish it from hypertrophy. Thus, sebaceous hyperplasia is now considered as a hamartoma rather than a true neoplasm.5,6
A universally accepted definition of sebaceous hyperplasia is not yet available. However, Barnhill and Crowson7 defined sebaceous hyperplasia by the presence of ⩾4 sebaceous lobules attached to the infundibulum of each pilosebaceous unit.
A 31-year-old woman presented to the dermatology outpatients clinic with the appearance of two newly pigmented areas on the vulva, within the past 6 months. On examination, the lesions were darkly pigmented polypoidal papule (12 mm in diameter) and macule (5 mm in diameter) on the left labium minus and at the vestibule, respectively. They were non-tender without obvious textural change, and the surrounding skin was normal. Her gynaecological history was uncomplicated and she had had one normal pregnancy at the age of 20 years. Two biopsy specimens were taken. One was from the left vulva and the other one was from the mid-line region. Both lesions showed pigmented areas. The clinical diagnoses offered included melanocytic macule and benign tumour.
Sections were examined under routine light microscope using formalin-fixed, paraffin-wax-embedded tissue stained routinely with H&E. Immunohistochemical examination with …