Vascular malformation rupture in a patient affected by Costello syndrome.

Costello syndrome (CS) is a rare genetic syndrome affecting multiple organs, generally caused by mutations of the HRAS gene, belonging to the RAS/MAPK genes family.A male patient with CS developed a painful pulsatile mass on the lateral side of the wrist. An initial ultrasonographic investigation confirmed the presence of a radial artery lesion, possibly an arterial aneurysm. On surgical resection, histological evaluation showed a tangle of vascular structures with variable calibre and abnormal wall histology. Immunohistochemical stainings revealed a very poor endothelial contribution to the central vascular wall structure. These histological observations led us to conclude we had managed an acute vascular malformation (VM) rupture, rather than a common arterial aneurysmal condition. Considering the molecular mechanisms regulated by RAS/MAPK genes, CS patients might have a higher risk of developing VMs and, in the presence of a pulsatile mass with acute onset, VM rupture should be considered.