Tibial Bone Transcortical Erosion Caused by a Posterior Tibial Artery Pseudoaneurysm: A Rare Case Report.

Pseudoaneurysm is an abnormal outpouching from the arterial wall containing only the outermost adventitial layer. As compared with this, true aneurysms contain all three layers: intima, media, and adventitia. Pseudoaneurysms are formed when blood traverses through the intima and media but is held by an adventitial layer. There are several etiologies for the formation of pseudoaneurysms, the most common one being posttraumatic laceration or dissection of the vessel wall. Postprocedural iatrogenic injury during surgery or biopsy is also another common cause for the development of pseudoaneurysms. Vasculitis, regional inflammatory conditions (like pancreatitis causing splenic pseudoaneurysm), and penetrating atheromatous ulcer are among the less common causes. Here, we present a case of a chronic posterior tibial artery pseudoaneurysm following a remote gunshot injury that resulted in extensive transcortical erosion with intraosseous extension and tibial bone transcortical erosion on a 33-year-old male patient with no known prior medical illness. Multimodal imaging including Doppler ultrasound, MRI (with contrast), and CT angiography established the diagnosis after an initial fine-needle aspiration (FNA) attempt led to significant hemorrhage. Only a few cases have been reported on pseudoaneurysms of this size and tibia bone erosion. To our knowledge, full tibial transcortical erosion caused by a chronic posterior tibial artery pseudoaneurysm has not been clearly documented in the literature. This case highlights the importance of early vascular imaging prior to biopsy of pulsatile or indeterminate soft tissue masses.