Elevated yellow nodule over the scalp in a middle-aged man.

INTRODUCTION

A 36-year-old man presented to the surgical OPD with a gradually increasing painless swelling over the scalp for past two years. On local examination, a 2.5×1 cm yellow elevated nodule with a circumscribed margin [Figure 1] was seen on the frontal region of the scalp. The nodule was non-motile and non-tender. The lesion was excised and sent for histopathological examination. Microscopic examination revealed a tumor comprised of incompletely differentiated sebaceous lobules of varying shapes and sizes. Two cell types were identified within the lobules-central mature sebaceous cells and peripheral undifferentiated basaloid cells. There was no evidence of atypia or invasion [Figures 2–5].

Figure 1

External (a) and cut surface (b) of the nodule showing an elevated yellow circumscribed lesion

Figure 2

(a) Photomicrograph revealing a tumor comprised of incompletely differentiated sebaceous lobules of varying shapes and sizes (H and E, ×100) (b) Higher magnification revealing the lobules comprised of two cells-central mature sebaceous cells and peripheral undifferentiated basaloid cells (H and E, ×400)

Figure 5

High power view showing the tumor cells (H and E, ×400)

Scanner view of the lesion (H and E, ×40)

Low power views of the lesion (H and E, ×100)

WHAT IS YOUR DIAGNOSIS?

Sebaceous carcinoma (SC)

Sebaceous epithelioma (SE)

Sebaceous adenoma (SA)

Sebaceous hyperplasia (SH)

Answer: (c), Sebaceous adenoma

Sebaceous neoplasms are rare adnexal tumors that present a complex challenge to the clinician. Their nature and the wide spectrum of lesions lead to confusion regarding many facets including their nomenclature and treatment.[1]

SA is a rare epithelial neoplasm with a predilection for the forehead and scalp. Occasional cases have been reported at rare sites like oral cavity.[2] It usually presents as a raised yellow circumscribed nodule or papule.[3] In terms of differentiation, SA stands between SH, in which sebaceous lobules appear fully mature and SE which is comprised of less than 50% mature sebaceous cells. SA and SE lack nuclear atypia and invasive, asymmetric growth patterns, which are hallmarks of SC.[3] SC shows increased expression of proliferation markers like p53 and Ki-67, whereas SA shows increased bcl-2 expression.[4] SA is the most distinctive cutaneous marker of Muir-Torre Syndrome, which is characterized by the combined occurrence of at least one sebaceous skin tumor and one internal malignancy (colon/genitourinary tract/breast) in the same patient.[3] Hence, patients with SA should be evaluated for internal malignancy. Surgical excision forms the treatment of choice; however, topical photodynamic therapy is being tried currently.[5]