Microvascular proliferation in congenital vascular malformations of skin and soft tissue.

Congenital vascular malformations (VMs) are mass-forming lesions that usually progress slowly, but may become symptomatic because of episodes of sudden growth and pain, particularly those with a substantial component of arteriovenous shunting. To systematically investigate the features of microvascular proliferation in a large series of surgically treated VMs. 107 resection specimens of clinically and histologically well-documented VMs were screened for the presence and extent of microvascular proliferation, based on morphological parameters, microvessel density (MVD), mast cell density (MCD) and proliferative activity (Ki-67 labelling index) of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). The extent of microvascular proliferation was correlated with the histological type of VM and clinical characteristics of patients. Microvascular proliferation was observed in 32 (30%) of all VMs, of which 30 cases seemed to be arteriovenous malformations. MVD in areas of microvascular proliferation was 282 (186)/mm(2) vs 13 (9)/mm(2) in areas with mature vessels. Both ECs and VSMCs in these areas showed high Ki-67 labelling indexes (mean (SD) 15 (18) and 17 (24)/mm(2), respectively). In all lesions, a positive correlation was found between MCD and MVD. Age, sex and location of VM had no predictive value for the occurrence of microvascular proliferation. However, if present, the involved tissue areas were larger and the proliferative activity of EC was higher in male patients than in female patients. Recognition of microvascular proliferation as a not uncommon feature, congenital arteriovenous malformations provide new insight into the growth behaviour and vascular composition of these lesions.