Nerves in Wrist MRI

The median nerve travels through the carpal tunnel and normally should not present variations in signal or thickness. Main findings in cases of compressive neuropathy (carpal tunnel syndrome) are thickening of the nerve proximal to the entrance of the tunnel with associated increased signal on the fluid-sensitive sequences (Figure 13). However, the findings may not be specific. More recently, diffusion tensor MRI (DTI) has been studied as a new tool for diagnosing neuropathy.25The role of MRI in carpal tunnel syndrome is to exclude a potential cause for the symptoms, such as flexor tenosynovitis, or masses/cysts within the carpal tunnel.26An incidental bifid median nerve and/or a persistent median artery should also be depicted and reported (Figure 14).27
MRI after carpal tunnel release is sometimes indicated to evaluate recurrence of symptoms. Normal postoperative findings include a complete surgical defect of the flexor retinaculum and volar extrusion of the carpal tunnel components through it, with improvement of neural signal changes. Persistent altered neural thickness may be seen (Figure 15).28 Rarely, median nerve lipomatosis (fibrolipomatous hamartoma) is detected in the investigation of macrodystrophia lipomatosa or carpal tunnel syndrome.29,30 In these situations the nerve presents a “spaghetti-” or “multi-cable-like” appearance, with thickened fascicles and prominent fatty interstitial tissue.
The ulnar nerve travels through the canal of Guyon (ulnar nerve tunnel) along the ulnar aspect of the wrist and is the most ulnar structure in the canal, in close proximity to the pisiform and hook of the hamate. Neuropathy may be associated with ganglia and masses within the tunnel,compression due to accessory muscle slips around the nerve, or even fractures or stress injuries of the hook of the hamate