Objectives and MethodsA variety of benign cystic or “cyst-like” lesions may be encountered during a routine magnetic resonance imaging (MRI) of the knee. These lesions comprise a diverse group of entities from benign cysts to complications of underlying diseases. In addition, normal anatomic bursae and recesses may be misdiagnosed as an intra-articular cystic lesion when they are distended. However, the majority of the aforementioned lesions have characteristic MR appearances that allow a confident diagnosis, thus obviating the need for additional imaging or interventional procedures.ResultsThis article includes a comprehensive pictorial essay of the characteristic MRI features of common and uncommon benign cysts and “cyst-like” lesions in and around the knee joint.DiscussionFor accurate assessment of the “cystic structure”, a radiologist should be able to identify typical MRI patterns that contribute in establishing the correct diagnosis and thus guiding specific therapy and avoiding unwarranted interventional procedures such as biopsy or arthroscopy.Teaching points• Cystic lesions are common in knee MRI and the commonest, the Baker’s cyst, has an incidence of 38 %.• Synovial cysts, meniscal cysts, normal knee bursae and recesses have characteristic MR appearances.• Miscellaneous “cyst-like” lesions may require a more dedicated MR protocol for a correct diagnosis.

Interobserver reproducibility with MRa is very good for labral tearing assessment. MRa is better for assessing labral tears. CTa shows better, but not statistically significant, demonstration of the articular cartilage.

The presence of multiple accessory navicular bone ossicles, not previously described with cross-sectional imaging, is reported herein. The pathogenesis and clinical relevance of this uncommon variant needs to be elucidated with further studies.

No differences were found for the technical success rate of the aforementioned techniques. A CT-guided posterior approach seems to be a more comfortable method for the patient.