MRI findings of prepatellar Morel-Lavallée effusions

To describe MR imaging characteristics and treatment options for prepatellar closed degloving injuries or Morel-Lavallée effusions. Imaging features are discussed that may aid in the distinguishing of this entity from "housemaid's knee" or prepatellar bursitis.

MR images of four young wrestlers were reviewed by two attending radiologists and one fellow, and correlative clinical data were collected using the electronic medical database.

MR images in all cases showed a unilocular, T2 hyperintense prepatellar collection extending beyond the normal boundaries of the prepatellar bursa. No necrotic fat or blood products were identified in the collections. Surgical pathology proving the absence of synovial tissue was available for one case, and differentiation of the collection from the adjacent bursa was confirmed visually by the surgeon in a second case.

Although prepatellar hemorrhagic bursitis and Morel-Lavallée effusions share many imaging features, making a specific diagnosis in most cases is not necessary, as treatment is often similar for both entities.