A slowly enlarging purple nodule on the arm

A 50-year-old Caucasian gentleman presented with a one-year history of a gradually enlarging pigmented lump on the right forearm. On examination there was a 1 cm blue-purple nodule, which was hard in consistency (Figure 1). A mobile dermal cystic component was palpated after lateral pressure. Further dermoscopic examination revealed a homogeneous blue-purple pigmentation surrounded by a subtle brown hyperpigmentation and a central white area with fine linear whitish structures. No pigment network was noticed (Figure 2). Histopathological examination was performed to exclude melanoma. It revealed an ill-defined nodular dermal proliferation of spindle-shaped fibroblasts and myofibroblasts arranged as short intersecting bundles. There were multiple dilated vascular channels and numerous hemosiderin-laden macrophages (Figure 3).