Abstract Archives of the RSNA, 2008
Mark E. Schweitzer MD, Presenter: Nothing to Disclose
Carpal tunnel syndrome (CTS) is the most common and best understood of the compression neuropathies. CTS also has the best understood pathogenesis related to repetitive overuse. The usual imaging signs of carpal tunnel syndrome are not overly specific, as there is a reasonable range of normal. These include focal thickening, and edema within the median nerve, masses in the tunnel, non-united fractures, especially of the hook of the hamate, bowing of the flexor retinaculum, and flexor synovitis. Although we often use excessive fluid as a surrogate for synovitis, this is imperfect, especially so in the wrist. Usually the MR signal of flexor synovitis is gray rather then fluid like. In addition bowing of the retinaculum should only be described if it is excessive or overt.
CTS MR was really the birthplace of neurography which is becoming a standard part of most skeletal imaging practices. To do this we use several combinations of sequences; T1 to see fat around nerves, proton density to see edema in nerves, and quite heavily T2 weighted images to see the true extent of the edema and to visualize the nerve fascicles as well as perineural edema. Part of neurography is also to assess for motor changes in muscle; edema when acute, and fatty replacement when long term. For CTS we do this in the thenar eminence.
True neurography of smaller nerves like CTS should be done at 3T or above and the sequences above should be complemented by more innovative ones. DTI is the best known of these with its application in practice being useful although somewhat less then ideal for CTS. 3D slab techniques, inversion recovery, gradient techniques with ultrashort TE’s among other choices, and contrast all show promise. IV contrast at this time is probably not recommended for preoperative cases.
The diagnosis of CTS should be made with a combination of morphologic signs, focality of nerve abnormal signal and diffusion abnormalities. Perhaps a better use of MR is in the evaluation of the failed CTS surgery with morphologic signs being somewhat more useful and there can be MR findings of long term, irreversible ischemia. Somewhat counterintutively an excessively palmer nerve is a poor result following surgery.
Musculoskeletal Keynote Speaker: Current Status of Imaging in Carpal Tunnel Syndrome. Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/7002489.html