Understanding the Anatomy of Retroperitoneal Interfascial Space: Implications for Regional Anesthesia

Background: Fascial plane block techniques have evolved considerably in recent years. Unlike the conventional peripheral nerve block methods, the fascial plane block's effect can be predicted based on fascial anatomy and does not require a clear vision of the target nerves. The anatomy of the retroperitoneal interfascial space is complex, since it comprises multiple compartments, including the transversalis fascia (TF), the retroperitoneal fasciae (RF), and the peritoneum. For this reason, an in-depth, accurate understanding of the retroperitoneal interfascial space's anatomical characteristics is necessary for perceiving the related regional blocks and mechanisms that lie underlie the dissemination of local anesthetics (LAs) outside or within the various retroperitoneal compartments. Objectives: This review aims to summarize the retroperitoneum's anatomical characteristics and elucidate the various communications among different interfascial spaces as well as their clinical significance in regional blocks, including but not limited to the anterior quadratus lumborum block (QLB), the fascia iliaca compartment block (FICB), the transversalis fascia plane block (TFPB), and the preperitoneal compartment block (PCB). Study Design: This is a narrative review of pertinent studies on the use of retroperitoneal spaces in regional anesthesia (RA). Methods: We conducted searches in multiple databases, including PubMed, MEDLINE, and Embase, using "retroperitoneal space," "transversalis fascia," "renal fascia," "quadratus lumborum block," "nerve block," and "liquid diffusion" as some of the keywords. Results: The anatomy of the retroperitoneal interfascial space has a significant influence on the injectate spread in numerous RA blocking techniques, particularly the QLB, FICB, and TFPB approaches. Furthermore, the TF is closely associated with the QLB, and the extension between the TF and iliac fascia offers a potential pathway for LAs. Limitations: The generalizability of our findings is limited by the insufficient number of randomized controlled trials (RCTs). Conclusions: Familiarity with the anatomy of the retroperitoneal fascial space could enhance our understanding of peripheral nerve blocks. By examining the circulation in the fascial space, we may gain a more comprehensive understanding of the direction and degree of injectate diffusion during RA as well as the block's plane and scope, possibly resulting in effective analgesia and fewer harmful clinical consequences