# Ganglion Impar Block

## Introduction

The ganglion impar (ganglion of Walther) is the terminal, unpaired ganglion of the sympathetic chain, located at the level of the sacrococcygeal junction. Blockade of this structure targets visceral and sympathetic afferent pain from the perineum, rectum, distal urethra, vulva/scrotum, and coccyx. First described by Plancarte et al. in 1990, ganglion impar block has become an important tool for managing both malignant and benign pain conditions in the pelvic floor and perineal region.

## Anatomy

The ganglion impar is a single, midline ganglion formed by the fusion of the terminal ganglia of the bilateral sympathetic chains. It is located in the retroperitoneal presacral space, anterior to the sacrococcygeal junction or the coccyx, though its exact position varies from the sacrococcygeal ligament to the tip of the coccyx. The ganglion measures approximately 0.5 cm in diameter and is often described as a small, irregularly shaped structure.

It provides sympathetic and visceral afferent innervation to the perineum, distal rectum, distal urethra, vulva or scrotum, and the coccygeal region. The ganglion lies in close proximity to the rectum anteriorly and the sacrococcygeal ligament posteriorly. Visceral afferent fibers from perineal structures converge at the ganglion impar before ascending through the sympathetic chain.

<image>Sagittal anatomical illustration of the sacrococcygeal region showing the ganglion impar as a small oval structure positioned anterior to the sacrococcygeal junction in the presacral space. The bilateral sympathetic chains are shown converging to form the single midline ganglion. The rectum is shown anterior to the ganglion with a thin layer of presacral fascia separating them. The sacrococcygeal ligament, coccyx (with individual segments Co1-Co4 labeled), and the sacrococcygeal disc are clearly identified. The needle trajectory for the trans-sacrococcygeal approach is illustrated passing through the sacrococcygeal ligament to reach the ganglion.</image>

## Indications

### Malignant Pain

Cancer-related indications include rectal and anal cancer pain (particularly visceral and burning components), cervical, vaginal, and vulvar cancer with perineal extension, perianal metastatic disease from any primary malignancy, and visceral pain from pelvic floor malignancies that is not adequately addressed by superior hypogastric plexus block alone.

### Benign Pain Conditions

Non-malignant indications include coccydynia (coccygeal pain) refractory to conservative management, chronic perineal pain syndromes with burning or sympathetically mediated features, vulvodynia with visceral/sympathetic pain features, chronic proctalgia and levator ani syndrome (when a visceral component is suspected), postherpetic neuralgia of the sacral and perineal dermatomes, and radiation proctitis with chronic pelvic pain.

## Techniques

| Approach | Needle Trajectory | Guidance | Advantages | Disadvantages |
|----------|------------------|----------|-----------|---------------|
| Trans-sacrococcygeal (preferred) | Through sacrococcygeal ligament/disc | Lateral fluoroscopy | Straightforward; low complication rate | Fails if junction fused/calcified |
| Transcoccygeal | Through coccygeal bone | Lateral fluoroscopy | Useful when junction is fused | Requires stiffer needle |
| Anococcygeal (Plancarte, original) | Curved around coccyx tip | Lateral fluoroscopy | Historical; original description | Higher rectal puncture risk; largely obsolete |
| CT-guided | Variable | CT | Excellent visualization of rectum | Radiation; time-consuming |

### Trans-Sacrococcygeal Approach (Preferred)

The patient is positioned prone with a pillow under the pelvis to flex the sacrococcygeal junction. The sacrococcygeal junction (or intercoccygeal junction) is identified on lateral fluoroscopy. A 22-gauge, 8-10 cm spinal needle is inserted in the midline and directed through the sacrococcygeal ligament (or intercoccygeal disc) under lateral fluoroscopic guidance. The needle is advanced until the tip is positioned anterior to the ventral surface of the sacrococcygeal junction, confirmed on lateral fluoroscopy.

After negative aspiration (to exclude rectal puncture), 1-2 mL of contrast is injected to confirm spread in the presacral retrorectal space, which appears as a smooth, comma-shaped or teardrop-shaped pattern anterior to the coccyx. For a diagnostic block, 4-6 mL of 0.25% bupivacaine (with or without corticosteroid) is injected. For a neurolytic block, 2-4 mL of 6-10% phenol or absolute alcohol is used after a confirmed diagnostic response.

### Transcoccygeal Approach

In this variation, the needle is directed through the body of the coccyx rather than through the ligament or disc space. This is useful when the sacrococcygeal junction is fused or calcified, preventing passage through the ligament. It requires a stiffer needle or a slight bending technique to navigate through the thin coccygeal bone.

### Original Plancarte (Anococcygeal Ligament) Approach

The original technique described the needle being inserted through the anococcygeal ligament, curving anteriorly around the tip of the coccyx. A bent needle (manually curved) is directed through the midline, anterior to the coccyx tip, and advanced superiorly to the sacrococcygeal junction. This approach has largely been superseded by the trans-sacrococcygeal technique due to the latter's simplicity and more predictable needle trajectory. The original approach carries a higher risk of rectal puncture as the needle curves around the coccyx tip in close proximity to the rectum.

<image>Lateral fluoroscopic illustration comparing the trans-sacrococcygeal and transcoccygeal approaches for ganglion impar block. The trans-sacrococcygeal approach shows a straight needle passing through the sacrococcygeal ligament with the tip anterior to the coccyx in the presacral space, with a comma-shaped contrast pattern visible anterior to the sacrococcygeal junction. The transcoccygeal approach shows the needle traversing the coccygeal bone at the first intercoccygeal level. The rectum is shown as a reference structure anterior to the presacral space. Anatomic landmarks include the sacrum, coccygeal segments, sacrococcygeal ligament, and presacral fascia.</image>

## CT-Guided and Ultrasound-Guided Approaches

CT guidance provides excellent visualization of the presacral space and the relationship of the needle to the rectum, and is particularly useful for neurolytic procedures. Ultrasound guidance has been described using a curvilinear transducer placed longitudinally over the sacrococcygeal junction, with the sacrococcygeal ligament and ventral coccygeal surface serving as sonographic landmarks. Ultrasound avoids radiation exposure but has limited visualization of the deep presacral space in some patients.

## Neurolytic Block Considerations

Phenol (6-10%) is the most commonly used neurolytic agent for ganglion impar neurolysis because of its viscous nature and limited spread. Alcohol may also be used but requires pre-injection of local anesthetic due to severe burning on injection. Neurolysis is typically reserved for cancer pain that has demonstrated consistent response to diagnostic local anesthetic blocks. Duration of neurolysis is generally 2-6 months, potentially longer. Radiofrequency ablation of the ganglion impar has been described as an alternative to chemical neurolysis, with reports of prolonged relief.

## Complications

The most feared complication is rectal puncture, confirmed by aspiration of fecal material or air. If the needle enters the rectum, it must be withdrawn and the procedure rescheduled with antibiotic prophylaxis. Infection or abscess can develop, particularly if rectal puncture occurs unrecognized during neurolysis. Neuritis — temporary worsening of perineal pain — is usually self-limited. Bowel or bladder dysfunction is rare with appropriate volumes but more common with neurolysis. Vascular injection into presacral vessels is another risk. Overall complication rates are low when proper image guidance and technique are employed.

## Clinical Pearls

The trans-sacrococcygeal approach is the current preferred technique due to its straightforward trajectory and low complication rate; the original anococcygeal approach is largely historical. On lateral fluoroscopy, the needle tip must be anterior to the ventral cortex of the coccyx but posterior to the rectum, and contrast should flow freely in the presacral space without rectal filling. For coccydynia, a combination of ganglion impar block and local anesthetic/steroid injection at the sacrococcygeal junction may address both visceral and somatic pain components. The ganglion impar block complements the superior hypogastric plexus block for comprehensive pelvic visceral denervation in cancer patients with pain spanning the pelvis and perineum. A digital rectal examination should always be performed before the procedure to assess the distance between the coccyx and rectum and to identify any presacral masses.

## References

1. Plancarte R, Amescua C, Patt RB. Presacral blockade of the ganglion of Walther (ganglion impar). *Anesthesiology*. 1990;73(5):A751.
2. Forero M, Sala-Blanch X, Reina MA, et al. The ganglion impar and its clinical applications: a cadaveric and radiological study. *Reg Anesth Pain Med*. 2016;41(4):508-513.
3. Toshniwal GR, Dureja GP, Prashanth SM. Transsacrococcygeal approach to ganglion impar block for management of chronic perineal pain: a prospective observational study. *Pain Physician*. 2007;10(5):661-666.
4. Oh CS, Chung IH, Ji HJ, Yoon DM. Clinical implications of topographic anatomy on the ganglion impar. *Anesthesiology*. 2004;101(1):249-250.