Intertransverse process block (ITPB) at the retro-superior costotransverse ligament (retro-SCTL) space: Evaluation of local anesthetic spread using MRI and sensory blockade in healthy volunteers

Abstract

Background: This study evaluated the spread of a local anesthetic, using MRI and sensory blockade, after an intertransverse process block (ITPB) at the medial aspect of the retro-superior costotransverse ligament (retro-SCTL) space – the medial retro-SCTL space block. Methods: Ten healthy volunteers received a single-injection ultrasound-guided medial retro-SCTL space block at the T4-T5 level using a mixture of 10 ml 0.5 % bupivacaine with 0.5 ml gadolinium. At 15 min, they underwent a high resolution, fat suppressed, T1 weighted MRI scan of the cervicothoracic spine. Loss of sensation to cold was assessed at 15 and 60 min, and then hourly for 5-h, after the block. Results: MRI showed consistent (100 %) spread of local anesthetic to the intercostal and paravertebral spaces, anterolateral aspect of the vertebral body (sympathetic chain), costotransverse space, neural foramina, and epidural space in all participants. However, sensory blockade was variable across the ipsilateral hemithorax. Hypoesthesia was more common than anesthesia in both the anterior (median [IQR], 3.5 [2–5] vs 0 [0–1.25], p < 0.001) and posterior (median [IQR], 6[3–7] vs 2[1–3], p < 0.001) hemithorax. Additionally, more dermatomes exhibited anesthesia in the posterior compared to the anterior hemithorax (median [IQR], 2[1–3] vs 0[0–1.25], p = 0.01). A variable number of contralateral dermatomes were also affected in 3 (30 %) volunteers. There was no statistically significant correlation between the local anesthetic spread and the number of hypoesthetic (r = 0.53, p = 0.11) or anesthetic (r = 0.09, p = 0.78) dermatomes on the ipsilateral hemithorax. Conclusions: A single-injection medial retro-SCTL space block, at the T4-T5 level with 10.5 ml of local anesthetic, consistently spreads to the ipsilateral intercostal and paravertebral spaces, sympathetic chain, costotransverse space, neural foramina and epidural space, but produces ipsilateral sensory blockade that is variable and wider over the posterior than anterior hemithorax.