Pigmented BCC Dermoscopy — SCE Dermatology MCQ

Correct answer: C — Melanoma (which characteristically shows a pigment network; pigmented BCC does not because BCCs are non-melanocytic tumours)

The correct answer is C, melanoma, which characteristically shows a pigment network, whereas pigmented BCC does not because BCC is a non-melanocytic tumour arising from basal keratinocytes rather than melanocytes. The pigment network (a grid-like brown to black lattice) is a melanocytic feature reflecting pigmented rete ridges, so its presence signals a melanocytic lesion such as melanoma or a naevus. Pigmented BCC instead shows non-melanocytic pigmented structures, namely large blue-grey ovoid nests, spoke-wheel areas, and arborising vessels, exactly as described in the stem. The first step in any dermoscopic algorithm is to classify a lesion as melanocytic or non-melanocytic; a pigmented lesion with vascular arborisation but no network points away from melanoma and toward BCC, a distinction that is clinically critical because misdiagnosing one for the other changes management and urgency of excision. Why the other options are wrong: A. Angioma: Angiomas are vascular lesions showing red, purple or black lacunae rather than a pigment network, so network status is not the feature that separates them from BCC; the lacunar pattern is the discriminator. E. Dermatofibroma: This classically shows a central white scar-like patch surrounded by a faint peripheral pigment network, so it is distinguished from BCC by that central white fibrotic zone, not by definitive network absence. D. Seborrhoeic keratosis: Distinguished by comedo-like openings, milia-like cysts, and a cerebriform or fissured pattern, features unrelated to pigment network status. B. Cyst: Epidermal cysts show a homogeneous yellowish structureless pattern with no pigment network in either lesion, so network absence has no discriminatory value here. Key point: A pigmented lesion lacking a pigment network but showing blue-grey ovoid nests, spoke-wheel structures and arborising vessels is dermoscopically a non-melanocytic BCC, not a melanocytic melanoma.

Reference: DermNet NZ, Basal cell carcinoma dermoscopy (clinical dermoscopy reference widely used in UK dermatology practice), https://dermnetnz.org/topics/basal-cell-carcinoma-dermoscopy