A 6-year-old boy was referred for a firm 3 cm x 2 cm size smooth-surfaced, dome-shaped blue nodule on the scalp for three years. A possibility of pigmented histiocytoma/dermatofibroma, pilomatricoma, ossifying fibroma or blue nevus was kept. Histology revealed a nodular collection of poorly melanized spindled melanocytes and deeply pigmented dendritic melanocytes within thickened collagen bundles which was consistent with a diagnosis of common blue nevus.

Fig. 1 Firm, blue nodule, with a smooth surface and prominence of follicular openings.

The differentials of a blue nodule include cavernous haemangioma (soft and large), dermatofibroma (firm, small and painful), angiokeratoma (soft and bleeds), blue rubber bleb navus (multiple and painful), glomus tumour (single, painful) and pilomatricoma (hard). Blue nevi are rarely seen on the scalp. They are consequent to a dermal arrest in embryonal migration of neural crest melanocytes. Larger (>3 cm) lesions warrant a biopsy to rule out malignant changes. A yearly follow up is advisable for any recurrence.