Pseudomalignant perineurial invasion in cellular ('infantile') capillary haemangiomas

One hundred and sixty-eight cellular ('infantile') capillary haemangiomas were assessed for the presence of perineurial invasion, a feature that can lead to the erroneous diagnosis of malignancy. Fourteen tumours (8%) showed unequivocal, usually prominent, involvement of small and medium sized nerves. Eleven of these lesions presented in infants at birth or shortly thereafter, two in young adults and one in a middle-aged adult. Ten patients were females. Ten of the lesions arose in the head and neck region, one in the arm, one in the chest wall, and in two the site was not stated. Follow-up revealed a local recurrence in only one of six cases. Histologically, all cases were typical pure capillary haemangiomas composed of lobules of small blood vessels, lined by bland endothelial cells, involving the dermis, subcutis or both. One case was an intramuscular capillary haemangioma. Long-standing cases, especially those in adults, were less cellular, with focal fibrosis and a myxoid stroma. Neural invasion was detected either in the centre or at the periphery of tumour lobules and was characterized by the presence of variable numbers of capillaries within the perineurium and in close contact with Schwann cells. This feature was highlighted by immunostaining for S-100 protein and EMA. In one case, extensive invasion of medium-sized deep dermal veins was also present, focally simulating an intravascular pyogenic granuloma. This study demonstrates that perineurial invasion in infantile capillary haemangiomas is a relatively common finding and should not be regarded as evidence of malignancy.