Giant congenital melanocytic naevus

**Definition:** A congenital melanocytic naevus (CMN) with a predicted or final adult maximal diameter of 400 mm or more. Giant CMNs are commonly centred on the dorsal surface of the body between the vertex and the buttocks but may occur elsewhere; they may be associated with multiple smaller satellite naevi (congenital or tardive), hypertrichosis, lipomas or benign proliferative nodules. There is a risk of pre-pubertal melanoma within giant CMN or the central nervous system (CNS). Leptomeningeal melanocytosis or focal neuromelanosis, found in 10-15% of cases, is often associated with other CNS tumours, hydrocephalus, epilepsy, arachnoid cysts, or Dandy-Walker malformation.