Para-articular and intra-articular soft tissue lesions: Radiologic-pathologic correlation.

Articular masses comprise various disease entities including benign or malignant proliferative processes and other non-neoplastic processes such as infection, deposition diseases, vascular malformations, and other lesions. Many diseases that lead to intra-articular or para-articular masses have distinct imaging features, particularly on MRI. Radiologists can localize masses to the joint space by knowing the articular anatomy and can reach a suggested diagnosis by looking at precise imaging findings. In this review article, we first define the concept of articular space (intraarticular, para-articular) and the normal joint anatomy and histology. We provide a general and comprehensive approach for evaluation of articular lesions on MRI. We then describe specific imaging and histologic features of typical benign and malignant soft tissue articular neoplasms and some non-neoplastic mimickers; and provide a radio-pathologic correlation of the different described entities.