The pathway of injectate spread during thoracic intertransverse process (ITP) block: Micro-computed tomography findings and anatomical evaluations.

Study Objective: To investigate the mechanism of action of the thoracic intertransverse process (ITP) block.

Design: Three-dimensional micro-computed tomography (3D micro-CT) study and cadaveric evaluation.

Setting: A translational research unit for anatomy and analgesia in a university hospital.

Patients: Twelve embalmed and three non-embalmed human cadavers were used in this study.

Measurements: Micro-CT images of the mid-thoracic paravertebral space and its adjacent ligamentous tissues were acquired and 3D images were reconstructed. Manual dissection and histologic examination of these structures complemented the images. To confirm our findings, the dye-spreading pattern after ultrasound-guided ITP injection of 20 mL dye solution at T4-T5 was evaluated.

Main Results: Micro-CT and histologic findings showed that the costotransverse foramen (the medial slit of the superior costotransverse ligament) and the costotransverse space (between the rib and the transverse process) were potential pathways to the thoracic paravertebral space during ITP block. Single-level ITP injection with a dye solution resulted in a multilevel segmental paravertebral spread in cadaveric evaluation.

Conclusions: The space posterior to the superior costotransverse ligament, the target area for ITP blocks, has potential anatomical pathways to the thoracic paravertebral space. The costotransverse foramen and the costotransverse space provided the anatomical conduit for the anterior and intersegmental paravertebral spread of the ITP block.