Cyclops lesions are typically the result of complications in the reconstruction of an anterior cruciate ligament (ACL). Also referred to as localized anterior arthrofibrosis, this fibrous anterior knee mass2 is a common cause of extension loss. Predisposing factors include “non-isomeric” or abnormal graft tunnel placement, small or dysplastic femoral notch, and unrecognized injuries of other ligaments.
Cyclops Lesion: Clinical Presentation
Extension of the repaired knee results in pain to the patient. Within 8 to 32 weeks of ACL repair, the patient may experience an audible and palpable “clunk”. Post ACL reconstruction, cyclops lesions are estimated to occur in approximately 5% of patients. 1
Cyclops Lesion: Pathology
Though the pathophysiology in not completely certain, the possible reasons could be:
- Fraying of remnant ACL fibres
- Excessive fibrosis
- Uplifting of fibrocartilaginous tissue during ACL reconstruction 2
Cyclops Lesion: MRI
In all pulse sequences, the signal intensity of a cyclops lesion is intermediate to low. This is due to the fibrous structure of the lesion. Close to the tibial insertion of the reconstructed ACL, a mass such as this one is located anteriorly / anterolaterally in the intercondylar notch. 2
Cyclops Lesion: Treatment
Typically, arthroscopic excision is recommended. 2
Cyclops Lesion: References
- Runyan BR, Bancroft LW, Peterson JJ et-al. Cyclops lesions that occur in the absence of prior anterior ligament reconstruction. Radiographics. 27 (6): e26.
- Weerakkody Y., Gaillard F., et-al. Cyclops Lesion (Knee): Radiopaedia (sourced 10Jan2018): https://radiopaedia.org/articles/cyclops-lesion-knee
Cyclops Lesion: Example
Knee pain. No injury.
Image 1 - Axial T2 FSE Image 2 - Sagittal T2 FSE
- No microtrabecular or macrotrabecular fracture.
- Slightly laterally displaced patella. Massive induration of Hoffa fat pad.
- No high-grade chondromalacia of the patellofemoral compartment.
- Flexors and extensors are intact.
- Partial-thickness chondral thinning of the weight bearing medial femoral condyle. Minimal marginal spurring medial femoral condyle. Stable healing complex vertical tear in the outer red-red zone posterior horn to posterior body of the medial meniscus likely from original pivot-shift injury.
- PCL is intact. ACL graft is intact. Giant cyclops lesion (images 1 and 2, green arrows) anterior to the ACL graft favored over localized PVNS (also known as giant cell tumor of tendon sheath, intra-articular).
- MCL and LCL are intact.
- No high-grade chondromalacia of the lateral compartment. Minimal marginal spurring lateral femoral condyle. No lateral meniscus tear.
- Posterolateral corner is intact.
- 2+ proteinaceous effusion.
- Swelling of the subcutaneous tissues anteriorly.
- ACL graft is intact with giant cyclops lesion anterior to the ACL graft favored over localized PVNS.
- Stable healing complex vertical tear outer healing red-red zone posterior horn to posterior body of the medial meniscus likely from original pivot-shift injury.