Ganglion impar block a matter of safety and efficacy

We want to congratulate Dr Celenlioglu and Sir for their recent original research on predictive factors affecting treatment success in ganglion impar block (GIB). When our group first described the approach, it was thought to help patients with visceral cancer pain; nevertheless, since its first description, the indications and approaches have been evolving to different guided techniques, including fluoroscopy, CT, ultrasound and MRI. As the authors mentioned, the effects of various demographic, clinical and radiological parameters on the success of GIB are yet to be fully elucidated. This solitary retroperitoneal ganglion is located anywhere from the sacrococcygeal joint’s anterior aspect to the coccyx’s tip. It varies considerably in size and shape: oval 26% and irregular 20%, 14% triangular, elongated 10% and 8% rectangular or Ushaped. The diameters ranged from 0.7 to 4.2 mm, with the average elongated ganglia measuring 4.4 mm in length. In addition to its complex anatomy, the paper mentioned that many coccyx curvature types were included. Unfortunately, with fluoroscopy guidance is impossible to visualize the ganglion impar; sometimes is difficult even with MRI; therefore, the use of contrast medium is an indirect way to guarantee the precise location and the only way to validate the procedure. Accordingly, anatomical variation may affect the success rate. Our main concern is related to the validity of this study. When analyzing predictive factors affecting treatment success in fluoroscopyguided GIB (including patients with curvature variations), not describing contrast medium patterns is a big mistake. This misstep is more serious if one of the independent predictive factors is related to anatomical variations. First, we must remember that with the transcoccygeal approach, the needle enters perpendicular to the rectum. Hence, the risk of perforation, although less than the original anococcygeal approach, is still a concern. Second, the contrast medium not only detects that complication but also confirms the tip needle’s proper location. There are four structures to keep in mind when performing a GIB (figure 1): the superficial posterior sacrococcygeal ligament, the deep posterior sacrococcygeal ligament, the disc and the anterior sacrococcygeal ligament. When learning this technique, some physicians use blunt tip needles to reduce the rate of bowel perforation. Nevertheless, in our experience, blunt tips sometimes cannot perforate the anterior sacrococcygeal ligament, and the medication remains in a plane between the ligament and the ventral surface of the sacrum or coccyx. This is particularly important in patients with subluxation or anatomical variations like those mentioned in the study, but it is detectable with contrast medium. Another critical issue is the risk of discitis, especially when firstpass success is not possible because the disc at this level is tiny compared with the lumbar level (figure 1). Recent evidence suggests that innervation of the tailbone may be more complex. New approaches regarding coccydynia are trying to block not only the ganglion impar, but other structures of the coccygeal plexus and coccygeal nerves arising from the dorsal rami innervating the posterior coccyx. 5 Therefore, we suggest analyzing pain pathways (anterior, posterior, somatic, visceral or both components). Finally, when performing a study with fluoroscopyguided GIB, we strongly recommend describing contrast medium patterns, especially in patients with curvature variations. This takes on greater importance if subluxation is identified in conclusion as an independent predictive factor of success.