Delayed diagnosis of pseudoaneurysm formation in a patient with diaphyseal aclasis.

A 15 year old boy, with known diaphyseal aclasis, presented with a swollen left leg. The diagnosis of popliteal pseudoaneurysm, a known and well understood vascular complication, was delayed due to presentation suggestive of a chondrosarcoma. In this age group, sarcomatous change is more common and a potentially sinister complication of diaphyseal aclasis. Following a sarcoma MDT referral, the correct diagnosis was confirmed by ultrasound and CT angiogram. This case identifies one of the largest, non-ruptured popliteal pseudoaneurysms reported and illustrates an unusual complication of a rare orthopaedic genetic condition, which is potentially limb threatening.