The nature and significance of cysts found at MR imaging behind the posterior cruciate ligament of the knee

Objective: Intra-articular cysts behind the posterior cruciate ligament are rare and generally described as ganglion cysts. We describe five cases where such cysts were thought to be synovial cysts. Materials and methods: Five patients where MRI showed a cyst behind the posterior cruciate ligament were prospectively identified. All were subsequently rescanned. Results: The cyst was absent in all cases on rescanning. In only one case was the cyst thought to be symptomatic. Conclusion: Cysts behind the posterior cruciate ligament may often be transient synovial cysts, are rarely symptomatic and are best treated expectantly.