Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 52 8 2014 08 15 613 618 EN Payam Sarraf Department of Neurology, Iranian Center of Neurological Research, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mahrooz Malek Department of Radiology, Medical Imaging Center, Advanced Diagnostic and Interventional Radiology Research Center (ADIR), Imam Khomeini Hospital, Tehran Iran. Mahsa Ghajarzadeh Department of Neurology, Brain and Spinal Injury Research Center (BASIR), Tehran University of Medical Sciences, Tehran, Iran. Shahin Miri Department of Medical, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Ehsan Parhizgar Department of Medical, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Seyedeh Zahra Emami-Razavi Department of Physical Medicine & Rehabilitation, Brain and Spinal Injury Research Center (BASIR), Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 11 Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. It accounts 90% of all entrapment neuropathies all over the world. Ultrasound is a non-invasive, cost effective and available para-clinical method which could be applied for CTS diagnosis. Cross-sectional area of the median nerve at the level of the inlet is considered as a diagnostic criterion in CTS cases. In this study, thirty-eight patients with electrophysiologically confirmed idiopathic CTS and 22 healthy controls were enrolled. Seventy-one affected nerves and 42 unaffected nerves were evaluated within 14 days after electrophysiological examination. The largest cross-sectional area (CSA) was measured at the level of the carpal tunnel inlet and the maximum nerve perimeter was also recorded by means of the software. Mean CSA and perimeter were 14.02 ± 4.5 mm2 and 1.7±0.28m in all patients and 8.2±2.1 mm2, 1.3±0.19 m in controls (P<0.001, P<0.001). Mean CSA and Perimeter were significantly different between patient's groups and control. The best cut off point for CSA of the tunnel inlet was 10.5 mm2 with sensitivity and specificity of 80% and 76% (AUC (Area under the Curve) = 0.9, P<0.001). The best cut off point for inlet perimeter was 1.44 m with sensitivity and specificity of 85% and 77 % (AUC=0.87, P<0.001). Our findings showed that median nerve CSA at carpal tunnel inlet could be used as the diagnostic criteria for CTS. https://acta.tums.ac.ir/index.php/acta/article/view/4565 https://acta.tums.ac.ir/index.php/acta/article/download/4565/4332