Superb Microvascular Imaging of Median Nerve in Carpal Tunnel Syndrome: A Novel Technique in Diagnostic Ultrasound

Thanks to ultrasound (US) has a low cost, portable, available and non-invasive, the use of diagnostic US in musculoskeletal diseases is rapidly growing in worldwide. Because it is easy to identify the limb structures such as muscle, tendon, and nerves and also, their pathologies, US is frequently used by physiatrists, orthopedics, rheumatologists, sports medicine and pain management physicians nowadays. Providing images of the median nerve (MN) and accompanying structures and give dynamic images about the anatomy of the carpal tunnel are the most superiorities of US in carpal tunnel syndrome (CTS) diagnosis. The diagnose of CTS based on history and physical examination and confirmed with electrodiagnostic studies. Although the specificity of nerve conduction tests is high, there is significant variability in sensitivity (62-85%). Therefore, US has been suggested as an additional or alternative diagnose of CTS. Especially measurement of the cross-sectional area (CSA) of the MN is significantly greater in CTS patients and shows a significant correlation with electrodiagnostic findings such as sensory nerve conduction velocity (SCV) and distal motor latency (DML). Because it enhances the diagnostic accuracy the detection of the epineural or intraneuronal blood flow, the three techniques of Doppler US, are more recently preferred. The contributions of color, power and spectral Doppler techniques in CTS diagnosis, were studied in various studies before. While for the detection of intraneural flow, the power Doppler (PD) seems to be the best way, the specify, sensitivity and diagnostic accuracy of each Doppler techniques were good in most studies.

Superb microvascular imaging (SMI) (Toshiba Medical Systems, Tokyo, Japan) is a new era in diagnostic ultrasound image processing technique. This new technology assigns accurate visualization of vascular structures with intensive clutter suppression to provide flow signals large to small vessels and represent this data at high frame rates. The both of the two modes (color SMI (cSMI) and the monochrome SMI (mSMI)) of the SMI, allows to visualizing lower velocity blood flows and smaller vessels without the use of contrast medium. To the best of our knowledge, there have been no clinical trials which studied of the healthy or injured median nerve blood flow with SMI.

The aim of the study was to compare the diagnostic value of Doppler US and SMI methods in CTS based on detection of increased intraneural flow. Moreover, investigators investigated the association of increased intraneural flow with the CSA of the MN. The null hypothesis that there is no difference between Doppler US and SMI methods in the detection of increased intraneural flow in CTS patients.