Pilomatrixoma in a child
Xanthogranuloma, Spitz naevus and giant molluscum wart might be considered but it was a pilomatrixoma. These are benign tumours derived from hair follicles which are usually seen on the face in young children. There is a very rare malignant version in adults.
The tumour is firm to hard because of calcification, which can make the surface colour blue. Sample this with a punch, shave or preferably, excision biopsy.