Ultrasound-assisted Thoracic Intervertebral Foramen Block. A Cadaveric Study

Background: A thoracic paravertebral block can be a useful opioid-sparing technique for controlling postoperative pain after thoracic and visceral abdominal surgery. Objectives: Our aim was to assess dye spread into the ventral branch, connecting branch, sympathetic trunk, thoracic paravertebral space, and epidural space after performing a modified ultrasound-assisted thoracic paravertebral block via the intervertebral foramen. Study Design: This was a nonrandomized cadaveric study. Setting: The cadavers were kept at the Department of Anatomopathology of the San Salvatore Academic Hospital of L’Aquila (L’Aquila, Italy). Methods: We performed a bilateral thoracic paravertebral block via the intervertebral foramen at the second, fifth, ninth, and twelfth thoracic vertebrae. A linear array ultrasound transducer was used. Then, cadaveric dissection was performed. A Tuohy needle was gently inserted in-plane with the ultrasound beam in a lateromedial direction to contact the spinous process. Subsequently, the needle tip was advanced 2 mm along the transverse process of the vertebra, and 5 mL of methylene blue 1% dye was injected at each level. Then, 2 continuous catheter sets were inserted. Results: Forty intervertebral foramen blocks were performed in 5 cadavers. For 38 injection sites, we found dye on both sides of the thoracic paravertebral space and epidural space at each level of puncture. The retropleural organs were also stained. In 2 cases, methylene blue accumulated intramuscularly at the level of the twelfth thoracic vertebra. Results: The spread of dye into the ventral rami, communicating rami, and sympathetic trunk in the thoracic paravertebral space and the epidural space was assessed. We also evaluated the position and the distance (mm) between the catheter tip and the thoracic intervertebral foramen content. Finally, puncturing of intervertebral blood vessels, nerve rootlet and root damage, lung and pleural injuries, and the extent of intramuscular dye accumulation were evaluated and recorded as iatrogenic complications related to the anesthetic procedure. Forty thoracic paravertebral blocks in 5 cadavers were performed. For 38 injection sites, we found dye on both sides of the thoracic paravertebral space and the epidural space at each level of puncture. The ventral rami, the communicating rami, and the sympathetic trunk were also stained. In 2 cases, methylene blue accumulated intramuscularly at the level of the twelfth thoracic vertebra. Limitations: The first limitation of this study is its small sample size. In addition, the study design did not consider or measure the width of the transverse processes. Another limitation is that the ultrasound beam could not identify the thoracic intervertebral foramen content or the needle tip behind the acoustic shadow of the transverse and vertebral articular processes. Conclusion: Paravertebral block via the thoracic intervertebral foramen achieved consistent dye spread into the thoracic paravertebral space and epidural space, capturing retropleural organs.