Extensor Carpi Ulnaris Tendon: Normal Signal Intensity

The normal extensor carpi ulnaris (ECU) tendon can have central increased signal intensity at the level of the distal radioulnar joint (the extensor carpi ulnaris tendon pseudolesion). It has been suggested that the increased signal is due to the tendinous slips from the proximal and distal muscle bellies interdigitating at the level of the wrist with spiraling or decussating fibers that approach the magic angle. This explanation is needed because the main fibers of the tendon are parallel to the forearm and at a 90° angle relative to B₀ in the standard wrist position during MR imaging. That is, the main tendon fibers are no where near the magic angle.

Extensor carpi ulnaris tendinosis can be diagnosed when you see diffuse, full-thickness high signal intensity within the tendon or when there is thickening or attenuation of the tendon.

The image above shows a normal extensor carpi ulnaris tendon with central high signal or T1- and T2-weighted images.

References

Timins ME, O'Connell SE, Erickson SJ, Oneson SR. MR imaging of the wrist: normal findings that may simulate disease. Radiographics. 1996 Sep;16(5):987-95.