The usage of high resolution ultrasound imaging in median nerve studying Essay

The use of high resolution ultrasound imaging to study the median nerve is relatively new compared to nerve conduction studies, as only recently have ultrasound scanners been able to produce images of the requisite quality. Recent advances like better post-processing capability, transducer technology, image resolution, signal strength, spectral analysis and speckle reduction techniques have improved its ability to visualize and grade abnormalities of the peripheral nerve.
Although the role of grey-scale US in CTS has been investigated by several authors , only a few studies have been performed to investigate the role of colour Doppler US in the evaluation of CTS(3) .
Doppler studies identify the vascular changes to the median nerve and quantification of hypervascularization within the nerve can be applied in detecting and grading CTS.
There are few studies reporting the usefulness of Median nerve stiffness (34)measurement by shear wave elastography in diagnosing CTS. However literature is limited and further studies are required before it can be used in clinical settings.
MRI
The MRI with its higher spatial resolution can detect the morphological changes of the median in carpal tunnel syndrome. Increased signal on T2w signal, flattening of the median nerve and changes of the CSA are the most common abnormalities in CTS patients.
The MRI has added benefit that, it recognises pathological muscle signal changes that may point to the affected nerve. However the drawback of MRI is in the cost and its availability cost, allergic reactions to contrast, claustrophobia, long scan times, and contraindications in patients with cardiac pacemakers or certain metallic implants(35) .
Current MRI research is focusing on the use of diffusion tensor imaging (DTI) and tractography (36) of the median nerve in the diagnosis of carpal tunnel syndrome.
Imaging criteria for detection of CTS for MRI and sonography for carpal tunnel syndrome are the same and includes
Swelling of the median nerve - The most extensively studied change in patients with CTS is swelling of the median nerve. The causes for swelling are not clearly established but possible causes include Endoneural oedema, Demyelination and Inflammation. This can be assessed at varying levels within the carpal tunnel.
Flattening ratio - usually the median nerve is swollen in the proximal tunnel and flattens in the distal tunnel. This is measured by the flattening ratio.
Palmer bowing of the flexor retinaculum This is seen secondary to increased pressure in the carpal tunnel.
The benefits of US over magnetic resonance (MR) imaging include higher soft-tissue resolution, cost effectiveness, portability, real-time and dynamic imaging, and the ability to scan extremity quickly and efficiently. US can be performed on patients who are not eligible for MR imaging. Metallic implant artifacts are usually not problematic. Any abnormal findings can be easily compared with the contralateral side
Ultrasonography (US) can become a first-line modality for the evaluation of the peripheral nerves of the upper extremity, in particular median nerve. US has been shown to have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves(10).