Intra-articular Neoplasms and Masslike Lesions of the Knee: Emphasis on MR Imaging.

Intra-articular masses affecting the knee joint are uncommon lesions that encompass a range of neoplastic and nonneoplastic disorders. A joint mass limited to a single articulation is most commonly related to neoplastic or focal proliferative disease, whereas masses affecting multiple articulations are typically caused by underlying inflammatory arthritides, metabolic abnormalities, or systemic deposition disorders. This article focuses on those masses that present in a monoarticular fashion, emphasizing the lesions that most commonly affect the knee joint. MR imaging is the modality of choice for evaluation of knee masses, allowing specific diagnosis in most cases.