The ganglion impar, also known as the ganglion of Walther or sacrococcygeal ganglion is a singular retroperitoneal structure located at the level of the sacrococcygeal junction (SCJ). It is of particular importance when considering patients who suffer from pain in the pelvic and perineal structures as it provides nociceptive and sympathetic supply to those regions. It receives afferent innervation from the perineum, distal rectum, anus, distal urethra, and distal vagina. Plancarte et al first reported the successful relief of perineal pain through the blockade of the ganglion impar in 1990.1 The initial approach as offered by Plancarte involved a bent spinal needle. Through the years, techniques have evolved with the use of fluoroscopy, computed tomography (CT), and ultrasound, and the utility for its potential relief of patient remains relatively unquestioned.
The indications for blockade based on anatomical location of pain include:
Perineal pain, with or without malignancy
Rectal/Anal pain (proctitis)
Distal urethral pain
Female pelvic/vaginal pain (distal 1/3)
Sympathetically-maintained pain to the region (ie, Complex Regional Pain Syndrome)
Burning and localized perineal pain associated with urgency
Each sympathetic trunk in the pelvic area is positioned anterior to the sacrum, situated medially to the anterior sacral foramina. There are 4 or 5 small sacral ganglia with the ganglion impar being the most caudal segment of the confluence of the sacral sympathetic chain as it passes anteromedially over the sacrum. More specifically, the ganglion Impar is the terminal fusion of the 2 sacral sympathetic chains and is located with some anatomical variability between the SCJ and the lower segment of the first coccyx. The fusion of the 2 chains typically positions the ganglion midline, which makes it relatively easy to find (Figure 49-1). However, there is a wide range of variability in the anatomical location with respect to the SCJ (Figure 49-2).5
Illustration of the ganglion Impar with relation to nearby anatomical structures on the left. The illustration on the right represents the path and trajectory of the needle through the sacrococcygeal disc at the SCJ to the ganglion impar.
Illustration of variable locations of the ganglion Impar with respect to the SCJ and the coccyx as reported by Chang-seok et al. Distances of the ganglion impar were measured using a digital caliper and a relative index was calculated. The percentages at each respective index are reported above.5
The key to successfully locating the ganglion Impar lies in identifying the following structures:
The 4 bilateral sacral foramina—for correct assessment of ...
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