To Map Human Lower Thoracic Dermatomes by Epidural Block

Significant differences exist among various dermatome maps. In addition, there were no anatomical landmarks to evaluate the dermatome at the back. The investigators aim to map the sensory innervations of lower thoracic nerves and find the dorsal landmarks to evaluate sensory innervations by epidural block. Patients undergoing urological surgery will receive epidural block. Fifty patients with superior border of complete sensory loss to ice from T9 to T12 (anterior median line) will be included in this study. The sensory loss to ice will be evaluated at midclavicular line, anterior axillary line, posterior axillary line, scapular line and posterior median line. The level of vertebrae will be identified and marked by ultrasound. The superior border of complete sensory loss to ice from anterior median line to posterior median line will be recorded for every patient. The dermatome map of T9 to T12 will be drawn. The landmarks of sensory innervations at posterior median line will be established using vertebrae.