Viewing the ganglion impar in vivo utilizing ultrasound: A feasibility study and literature review

“Ganglion impar” is the final unpaired ganglion demarcating the caudal convergence of the sympathetic chain ganglia in the pelvic region of the human body. The general position of the ganglion impar is anterior to the coccyx, but both researchers and practitioners note significant variability in its location, size and shape. Direct visualization of the ganglion by ultrasound has not been carried out to date. Cadaveric studies have been informative, but limited in their ability to sufficiently assist physicians in non-invasively locating and targeting the surprisingly inconsistent ganglion impar for clinical procedures in patients. RESOURCES. Literature on the ganglion impar is scarce. Cadaveric studies focusing on ganglion impar anatomy describe variations in the ganglion's size and location. Clinical studies show that ganglion impar nerve block, with varying degrees of success, can result in significant pain relief in patients with coccydynia and other forms of pelvic pain. A recently published case report involved an innovative ultrasound guided approach was attempted in this study. DESCRIPTION. This study utilized ultrasound to investigate the ganglion impar in one subject in both prone and transverse positions to assess its sonographic visibility and anatomical morphology. However, by the use of this technique the ganglion structure was not visualized. SIGNIFICANCE. Failure to view the ganglion in both positions suggests that the ganglion impar cannot be visualized using ultrasound in this case study. Previous studies used ultrasound to monitor needle insertion targeting ganglion impar, but not specifically to visualize the ganglion itself. This may help explain the variations seen in therapeutic outcomes and pain relief after administration of nerve blocks. The use of other landmarks, such as the coccyx and sacro-coccygeal junction, might be more useful in locating the ganglion impar.