Is a Retrolaminar Approach to the Thoracic Paravertebral Space Possible?: A Human Cadaveric Study

Background and Objectives The retrolaminar block (RB) is used for truncal analgesia, but its mechanism of neural blockade remains obscure. We sought to learn the pattern of local anesthetic spread after thoracic RB using cadaveric models. Methods In 8 fresh cadavers, an ultrasound-guided T4 RB was performed with 20 mL of methylene blue 1% and bupivacaine 0.5%. For comparison, an RB at T9 in 1 cadaver and a T4 thoracic paravertebral block in another cadaver were performed. Subsequently, posterior and anterior thoracic dissections were performed to examination where the dye spread. Results After T4 RB, dye was noted to spread in the ipsilateral retrolaminar plane (all 8 cadavers, median cephalad spread 3.5 cm, caudad spread 10.7 cm, lateral spread 2.5 cm), the contralateral retrolaminar plane (6 cadavers), the paravertebral space (5 cadavers, median of 3 segments, T3–T5), the intercostal space (5 cadavers, median of 3.5 cm laterally), the T4 epidural space (6 cadavers), and the intervertebral foramina (4 cadavers, median of 2 segments, T4–T5). After T9 retrolaminar injection, dye was noted in the ipsilateral retrolaminar plane (5.5 cm cephalad, 13.5 cm caudad, and 2.5 cm lateral), the contralateral retrolaminar plane, and the epidural space. Dye after T4 traditional paravertebral block spread to T1–T6 paravertebral space with 15-cm lateral spread. Conclusions Injectate spread to the paravertebral space, epidural space, intercostal space, and intervertebral foramina is possible in the RB but is quite variable. In comparison to the thoracic paravertebral block, injectate spread within the paravertebral space is more limited. Accepted for publication April 23, 2018. Address correspondence to: A. Sassan Sabouri, MD, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, 55 Fruit St, GRJ 446, Boston, MA 02114 (e-mail: asabouri@mgh.harvard.edu). This work is attributed to the Department of Anesthesiology, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA. This study was supported by DACCPM Clinical Pilot Grant (no. 1200-218309). Primary results of this study were presented at the 41st American Society of Regional Anesthesia Annual Regional Anesthesia and Acute Pain Medicine Meeting, New Orleans, LA, as a poster presentation on April 2, 2016, and final results were presented as a poster at the Department of Anesthesia, Critical Care and Pain Medicine Research Day, Massachusetts General Hospital, Boston, MA, on October 18, 2017. The authors declare no conflict of interest. Copyright © 2018 by American Society of Regional Anesthesia and Pain Medicine.

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