Discussion: Musculoskeletal ultrasound in comparison to the MRI is a reliable,
noninvasive,
bed side and inexpensive method that can investigate the peripheral nerves in the osteofibrous tunnels in the upper extremity as a possible site of nerve entrapment and can give a clue to the etiology of the entrapment.
Ultrasound criteria for diagnosing nerve entrapment in the osteofibrous tunnels at the upper extremity which were coinciding with those used by Bianchi and Martinoli,
(2007):
· Common features:
- Echo textural changes where the compressed nerve becomes uniformly hypoechoic with loss of the fascicular pattern
- Increased cross sectional area (>7.5 mm2 at the cubital tunnel,
>10 mm2 at the carpal tunnel)
- The presence or absence of masses
· Specific features:
• At the suprascapular and spinoglenoid notches:
- Depict the cause of compression which is most commonly ganglion cyst.
• At the carpal tunnel:
- Flattening of the median nerve with flattening ratio more than 2.
- Bowing of the flexor retinaculum with the distance equal or more than 4 mm.
MRI criteria for diagnosing nerve entrapment in the osteofibrous tunnels at the upper extremitywhich were coinciding with those used by Rodrigues and Rosenberg,
(2004):
· Common features:
- Nerve signal alteration in T2 WI’s
- Nerve swelling
- Muscles signal alteration due to edema or fatty atrophy
· Specific features:
• At the suprascapular and spinoglenoid notches:
- Detect the cause of compression which is commonly ganglion cyst.
• At the carpal tunnel:
- The size of the median nerve at the pisiform level is 1.6 to 3.5 greater than its size at the radio-ulnar joint in patients with carpal tunnel syndrome.
- Flattening of the median nerve with flattening ratio more than 3 at the level of hamate.
- The bowing ratio exceeding 15%
Conclusion: High-resolution ultrasonography can be used as an ancillary method to the electrophysiologic tests in diagnosing the patients in whom the median,
ulnar or suprascapular nerves are compressed at the osteofibrous tunnels.
Also,
those patients who cannot be diagnosed electrophysiologically because of the false negativity of the NCS will be able to be diagnosed after establishing those criteria by ultrasonography where it can be used as an available and low cost diagnostic modality.