Cyclops lesion (anterior arthrofibrosis) is a fibrous nodule which is located just anterior of the distal part of ACL and extends anteriorly in the intercondylar region of the femur. The origin of this lesion is not known, but a reaction to exposed ACL graft material or operative debris has been postulated. Cyclops nodule generally seems with ACL reconstruction, but recent reports have documented its occurance after ACL injury in the absence of ACL reconstruction.

At MR imaging, the cyclops lesion typically has intermediate to low signal intensity on all pulse sequences because of its fibrous content. An associated effusion may be present. The mass can result in anterior knee pain and loss of full extension.

Case Report

A professional soccer player who had anterior cruciate ligament reconstruction three years ago, admitted to the hospital with pain and restricted motion.

MR imaging revealed cyclops lesion in the intercondylar region just anterior of ACL with heterogeneous or intermediate signal intensity on T1 and PD weighted sequences. Lesion contains hypointens signal intensity in the anterior part reflecting its fibrous content.

Cyclops syndrome should be suspected in any patient in whom an ACL nodule is identified at MR imaging, and similarly a cyclops nodule should be considered as a possible cause of pain and loss of extension in any patient who has sustained ACL injury.


1) Recht MP, Piraino DW, Cohen MAH, Parker RD, Bergfeld JA. Localized anterior arthro-fibrosis (cyclops lesion) after reconstruction of the anterior cruciate ligament: MR imaging findings. AJR (1995); 165:383-385.
2) Runyan BR, Bancroft LW, Peterson JJ, Kransdorf MJ, Berquist TH, Ortiguera CJ. Cyclops lesions that occur in the absence of prior anterior ligament reconstruction. Radiographics (2007); Nov-Dec;27(6):e26. Epub 2007 Aug 21.

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