Intraligamentous ganglion cysts of the anterior cruciate ligament: MR findings with clinical and arthroscopic correlations

Objective: Magnetic resonance findings with clinical and arthroscopic correlation of intraligamentous cysts of the anterior cruciate ligament (ACL) are presented. Materials and Methods: Three cases of intraligamentous cysts of the ACL were identified out of 681 knee MRI examinations over a 2-year period. Arthroscopy and postoperative MRI were performed in all three patients, each of whom experienced knee pain with extreme flexion and extension. Results: In all three cases the intraligamentous cyst was homogeneously hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging relative to the ACL. Two of the three ACL cysts required a 70 degrees scope for adequate visualization and establishment of posteromedial and posterolateral portals for arthroscopic treatment. One cyst could not be visualized arthroscopically and probing of the ACL from the anterior portal resulted in drainage of the cyst. No patient had presence of ACL cyst on follow-up MRI or recurrence of symptoms at a mean of 24 months. Conclusion: Intraligamentous cyst of ACL is a rare cause of knee pain. It should be suspected in patients having chronic pain with extremes of motion. Magnetic resonance findings are diagnostic and help to guide arthroscopy.