MRI of Cyclops Lesions
Abstract & Commentary
Synopsis: MagneAtic resonance imaging is sensitive, specific, and accurate in demonstrating cyclops lesions in patients with extension loss following reconstruction of the anterior cruciate ligament.
Source: Bradley DM, et al. MR imaging of cyclops lesions. AJR Am J Roentgenol 2000;174:719-726.
The cyclops lesion is a well-recognized cause of loss of extension following anterior cruciate ligament (ACL) repair. This is a mass composed of fibrous granulation tissue that is situated anterior to some ACL grafts before they enter the tibial tunnel. The mass has the appearance of an eye during arthroscopy—thus the name "cyclops." The cyclops lesion can be identified on magnetic resonance imaging (MRI). This study describes the experience of an orthopedic surgery group that used MRI for patients with ACL grafts who experienced loss of extension. The images were retrospectively reviewed by a musculoskeletal radiologist and an orthopedist who were blinded to clinical and arthroscopic results.
This paper evaluated 33 MRI studies of 31 patients with loss of knee extension following ACL repair. This patient population was a subgroup of a total of 689 patients who had ACL reconstruction of which 52 had persistent extension loss. All ACL reconstruction was performed using patellar tendon autograft. The interval between the ACL repair and the second therapeutic arthroscopy ranged between three and 30 months.
The following features were evaluated on MRI: 1) ACL graft signal intensity and course; 2) tibial and femoral tunnel placement; 3) notch size and shape; and 4) the presence or absence of cyclops lesions. When a cyclops lesion was seen by MRI, the signal intensity characteristics, location, and size were recorded. These findings were then correlated with findings at arthroscopy.
Twenty of the patients were found to have a cyclops lesion at surgery (including one patient who had cyclops lesions twice in the same knee at different times). The sensitivity, specificity, and accuracy of revealing a cyclops lesion on MRI was 85.0%, 84.6%, and 84.8%, respectively. Bradley and colleagues found no statistically significant differences in the size of the intercondylar notches for patients with and patients without cyclops lesions.
Cyclops lesions are predominantly intermediate signal intensity on proton density and T2-weighted MRIs. A few more of the grafts with cyclops lesions were intermediate signal intensity rather than low signal intensity on proton density-weighted images. This difference was not statistically significant. Results were best for nodules measuring more than 10 mm in any dimension and for knees without previous cyclops resection.
Bradley et al conclude that MRI is sensitive, specific, and accurate in revealing cyclops lesions in a subgroup of patients with extension loss after ACL reconstruction.
Comment by Lynne S. Steinbach, MD
A cyclops lesion is a treatable cause of failure to gain full knee extension following ACL reconstruction.1-3 It is seen in up to 2% of those patients. Once this lesion is detected, the fibrous nodule can be resected with good postoperative results. It is important for radiologists to be aware of this lesion and to identify its presence. MRI is one of the only ways to identify this lesion preoperatively.
This is the largest study to date to evaluate the ability of MRI to detect the cyclops lesion.
The study is limited by the fact that it is retrospective, and even though the radiologist was blinded to the clinical history, all patients presented with lack of extension following ACL reconstruction. This could skew the results to be more favorable toward MRI. It seems that the study also used one of the orthopedic surgeon authors to evaluate the MRIs. One could argue that the study would be more realistic if it had relied only upon readings by radiologists, since most orthopedic surgeons are not trained to read MRIs.
References
1. Jackson DW, Schaefer RK. Cyclops syndrome: Loss of extension following intra-articular anterior cruciate ligament reconstruction. Arthroscopy 1990;6:171-178.
2. Marzo JM, et al. Intraarticular fibrous nodule as a cause of loss of extension following anterior cruciate ligament reconstruction. Arthroscopy 1992;8:10-18.
3. Fullerton LR Jr., Andrews JR. Mechanical block to extension following augmentation of the anterior cruciate ligament. Am J Sports Med 1984;12:166-168.
Above what size is the cyclops lesion best seen on MRI?
a. 5 mm
b. 8 mm
c. 10 mm
d. 15 mm
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