Chronic ACL tear(PM EQUAL TO PCL IN MEDIAL SIDE OF THE NOTCH)The MR reader will not uncommonly encounter non-acute ACL tears. These injuries are often associated with medial meniscal tears, and secondary osteoarthritis.
Chronic tear of the anterior cruciate ligament (ACL) with empty notch sign. T1-weighted coronal MRI shows only fat in the lateral intercondylar notch; the ACL is absent. A normal posterior cruciate ligament (PCL) is present in the medial aspect of the notch (arrow). This is a frequent MRI appearance of a chronic ACL
tear after the resolution of acute edema and hemorrhage.
MRI signs of chronic ACL tear are largely the same as those of acute ACL injury except that bone bruises and edema about the knee are absent.
The most common MR finding with chronic tear is a fragmented ACL.Complete nonvisualization of the ACL may also occur with only fat signal intensity evident in the lateral intercondylar notch, the "empty notch" sign.
The chronically torn ACL tear may attach to the PCL.The authors, however, have noted that this is most often an endoscopic observation and is less frequently appreciated on MRI, even in retrospect. Patients with this finding may have a clinical endpoint of anterior translation of the tibia with Lachman testing, resulting in a false-negative finding on clinical examination.
While the diagnosis of chronic ACL tear by MRI is usually straightforward. However, in some instances, the only sign of a chronic ACL tear is a subtle angulated appearance or flattened axis of the ACL,and, in fact, a chronic nondisplaced ACL tear may appear entirely normal. This presumably occurs because hypointense mature scarring may be difficult to distinguish from the normal low-signal ligament. Therefore, the MR reader must be especially diligent in the nonacute setting to avoid underdiagnosing chronic tears. In the setting of a positive Lachman test and a suspected chronic tear, a negative MRI should be viewed as a possible false negative.
The most common MR finding with chronic tear is a fragmented ACL.Complete nonvisualization of the ACL may also occur with only fat signal intensity evident in the lateral intercondylar notch, the "empty notch" sign.
The chronically torn ACL tear may attach to the PCL.The authors, however, have noted that this is most often an endoscopic observation and is less frequently appreciated on MRI, even in retrospect. Patients with this finding may have a clinical endpoint of anterior translation of the tibia with Lachman testing, resulting in a false-negative finding on clinical examination.
While the diagnosis of chronic ACL tear by MRI is usually straightforward. However, in some instances, the only sign of a chronic ACL tear is a subtle angulated appearance or flattened axis of the ACL,and, in fact, a chronic nondisplaced ACL tear may appear entirely normal. This presumably occurs because hypointense mature scarring may be difficult to distinguish from the normal low-signal ligament. Therefore, the MR reader must be especially diligent in the nonacute setting to avoid underdiagnosing chronic tears. In the setting of a positive Lachman test and a suspected chronic tear, a negative MRI should be viewed as a possible false negative.
No comments:
Post a Comment