At first glance, this mass is concerning for a large pseduoaneurysm as it has similar enhancement as the arterial blood pool. It was surgically excised with final pathology of hyaline vascular Castleman disease. 

Castleman disease is a non-neoplastic, non-clonal lymph node hyperplasia which can be idiopathic or associated with HIV, lymphoma, POEMS and other disorders. It commonly presents as avidly-enhancing adenopathy. Most cases (90%) are hyaline vascular, which occurs in younger patients, is unicentric, asymptomatic, and follows a benign course.