Adipose tissue around the knee; A pictorial review of normal anatomy and common pathologies.

The periarticular adipose tissues play a crucial role in knee biomechanics, yet they are often overlooked in daily radiology practice. As the primary mechanical shock absorbers of the knee, intra-articular fat pads reduce the friction between intra-articular structures during joint movement. They also contribute to inflammatory regulation, endocrine secretion, and pain detection. Periarticular fat pads are susceptible to a spectrum of traumatic, degenerative, inflammatory, and neoplastic changes. MRI enables radiologists to assess the anatomy of periarticular fat pads and their related pathologies to make accurate diagnoses and to guide appropriate management. The MRI presentation of these pathologies can be categorized into three groups: (a) signal change and thickening of synovial lining, (b) edema-like change in fat pads, and (c) mass-like lesions. While degeneration and impingement appear as high signal edema-like intensity on fluid-sensitive sequences, inflammatory or infectious synovitis, hemosiderin deposition, and lipoma arborescens can change the signal intensity of the synovial lining. A mass-like lesion arising from these structures could be a true neoplastic lesion, or a variety of non-neoplastic pathologies. A comprehensive understanding of adipose tissues and their pathologies is fundamental for accurate diagnosis and interpretation. In this review, we aim to provide an in-depth assessment of the anatomy and common pathologies of these adipose tissues.