When Brown Meets White and Blue: A Quiz in Three Hues

Haemosiderotic/aneurysmal dermatofibroma (HADF) is a rare variant of benign fibrous histiocytoma that often poses significant diagnostic challenges due to its variable clinical and dermoscopic presentation and its frequent resemblance to malignant melanoma and vascular tumors. We report the case of an 18-year-old woman presenting with a rapidly growing pigmented lesion on the right shoulder, characterized clinically by a progressive transition from a flat brown macule to a lesion with a palpable bluish component. Dermoscopic examination revealed an asymmetric lesion with a light-brown pigment network, an eccentrically located bluish nodular area, a structureless dark-brown blotch, and prominent shiny white lines, prompting surgical excision. Histopathological analysis demonstrated a spindle-cell fibrohistiocytic proliferation with a storiform pattern, epidermal follicular induction, basal hyperpigmentation, extracellular hemosiderin deposition, and characteristic non–endothelial-lined blood-filled spaces. Immunohistochemical staining for CD31 supported the diagnosis of haemosiderotic/aneurysmal dermatofibroma. This case highlights the broad clinicodermoscopic spectrum of HADF and underscores the limitations of dermoscopy alone in reliably distinguishing these lesions from malignant counterparts. Excisional biopsy with histopathological and immunohistochemical evaluation remains essential to establish a definitive diagnosis and to exclude melanoma or other malignancies.