MRI of the Median Nerve in Carpal Tunnel Syndrome
Keywords:
carpal tunnel syndrome, median nerve, magnetic resonance imaging, MRIAbstract
Background and Aim Carpal tunnel syndrome (CTS) is the commonest compressive peripheral neuropathy, which occurs due to the compression of median nerve in a fibro-osseous tunnel at the level of the wrist. It has traditionally been diagnosed by history, clinical examination, and electrodiagnostic tests. Multiple studies have also described MRI findings in CTS, and MRI is indicated in specific conditions. The aim of this study is to describe the spectrum of MRI findings in patients diagnosed with CTS in a tertiary care hospital.
Methods A total of 35 patients with as many affected wrists, and a diagnosis of CTS based on history, clinical examination and NCV (nerve conduction velocity) results were included in the study. The median nerve at the level of the wrist was evaluated as per a predefined MRI protocol. Findings were recorded at the level of the distal radioulnar joint, pisiform and hamate and assessed.
Results The MR study revealed T2 hyperintense signal in the median nerve in 20% of patients at the level of the distal radioulnar joint and 80% of patients each at the level of the pisiform and hamate. The mean cross-section area of the nerve measured 11.8 mm2 , 16.2 mm2 and 10.7 mm2 at the level of the distal radioulnar joint, pisiform and hamate, respectively. The flattening ratio at the level of the distal radioulnar joint, pisiform and hamate was 1.7, 2.2, and 3.4, respectively. The nerve was compressed due to isolated flexor tenosynovitis in 34.3% patients, due to flexor tenosynovitis in rheumatoid arthritis in 22.85% patients and due to ganglion cyst in 2.85% patients. No obvious cause of nerve compression was detected in 40% of patients and these were classified as idiopathic.
Conclusion MRI findings in patients with CTS include T2 hyperintense signal in the median nerve, enlargement at the level of the pisiform and flattening at the level of the hamate. There was no obvious cause of median nerve compression in the majority of patients, and the commonest identified cause was isolated flexor tenosynovitis.
