I read with great interest the case report published recently in the Korean Journal of Anesthesiology concerning a block performed at the retro superior costotransverse ligament (SCTL) space [1] and wish to present my reflections.

Lee et al. [1] state that “The retro superior costotransverse ligament space (RSS) block is a novel thoracic paraspinal block (TPSB)” [1]. However, this is just another intertransverse process (ITP) block with the retro SCTL space as a different target, as mentioned in the referenced article [2]. Furthermore, caution must be exercised over the term “thoracic paraspinal block” (TPSB), as it includes diverse blocks such as the erector spinae plane block (ESPB), retrolaminar block, and ITP blocks [3]. I would like to emphasize that the term “RSS block” should be avoided, as it is misleading and might confuse readers, as various terms for similar blocks already exist.

Another aspect requiring further clarification is the spread of injectate with TPSBs. Lee et al. [1] state that “the local anesthetic within the RSS spreads to the thoracic parabertebral space through many fenestrations, similar to the mechanism seen in TPSBs like the ESPB.” However, the injectate spread with ESPBs is different from that with ITP blocks. Specifically, the spread to the anterior rami is more reliable with ITP blocks because the injection is administered closer to the paravertebral space. Notably, a cadaveric study found that the medial slit of the SCTL (costotransverse foramen) and costotransverse space may be potential pathways for the spread of injectate to the thoracic paravertebral space [4]. In contrast, the spread of injectate with ESPBs occurs in various directions, with less paravertebral spread as the injection is administered slightly distant from this space.