A Nod for Meckel: A Novel Surgical Position Utilizing Meckel's Cave Anatomy for Percutaneous Glycerol Rhizotomy in Trigeminal Neuralgia

Abstract

Objective  We aim to describe a novel positioning technique using a specific surgical table to achieve the optimal angle during percutaneous glycerol rhizotomy (PGR) for trigeminal neuralgia (TN).

Design  This is a descriptive and photographic analysis of successful cases for future implementation.

Setting  This study was conducted at a single-institution, academic center.

Participants  The participants were adult patients with TN who underwent PGR and provided consent for publication.

Main Outcome Measures  Primary outcomes of this study were TN symptomatic relief and surgical complications.

Results  The use of a beach chair sliding headboard surgical table for PGR is plausible and ensures precise and immobile head flexion for 1 hour postglycerol injection. There were no intraoperative or postoperative complications. All patients achieved successful reduction of TN symptoms.

Conclusions  Utilizing this new method of intraoperative navigation with a unique surgical table in the upright position, surgeons may achieve precise head adjustments post-PGR. Head flexion has been postulated as a means of ensuring glycerol containment in Meckel's cave. This method can help standardize this procedure for future systematic studies on the importance of head positioning post-PGR.

Introduction

Trigeminal neuralgia (TN) is defined by paroxysmal, short-interval, often-debilitating, lancinating pain attacks in one or more trigeminal divisions. For medically refractive TN, surgical options are explored including microvascular decompression (MVD), percutaneous trigeminal rhizotomies (glycerol, radiofrequency, or balloon compression), or stereotactic radiosurgery (SRS). ¹ MVD is the first-line option in patients with imaging showing vascular compression given it has the highest surgical success rate among TN procedures. ^{1 2} In the absence of a compressive lesion, minimally invasive ablative percutaneous procedures are used with variable outcomes. ^{1 2} Ablative percutaneous procedures work by causing temporary damage to the trigeminal nerve or ganglion, which often causes numbness that can be aggravating to specific patients. ^{3 4 5}

The choice between percutaneous glycerol rhizotomy (PGR), percutaneous balloon compression (PBC), and percutaneous radiofrequency rhizotomy (PRF) is dependent on medical comorbidities, distribution of pain, previous treatment success, and patient preference. ^{1 5 6} Each procedure has a slightly different side effect profile. There are reports of higher risks of mastication weakness or diplopia with PBC, higher risk of facial numbness with PRF, and higher risk of corneal numbness with PGR. ^{4 5 6 7 8} These three procedures each involve a common approach, designed by Härtel. ⁹ A Tuohy needle is advanced subcutaneously from 2.5 cm lateral of the oral labial commissure toward the foramen ovale, accessing the gasserian ganglion in Meckel's cave. ¹ At this point for PGR, a viscous glycerol mixture is injected into Meckel's cave and the needle is removed. In a neutral head position, glycerol may flow posteriorly with gravity into the basal cisterns, as Meckel's cave is posteriorly angled. Thus, there exist varying practices of sitting the patient upright and flexing their head for 1 to 2 hours ( Fig. 1 ).

Fig. 1.

Sagittal view of Meckel's cave. ( a ) The head in the neutral position with glycerol flowing posteriorly into the basal cisterns. ( b ) The head in flexion preventing posterior glycerol migration.

The recurrence rates for PGR vary significantly (50–99%). ^{1 10} Few studies have compared the reasons for these varying rates, but some poor predictors of success have been found including atypical TN features, no CSF return in surgery, male, cluster symptoms, duration of symptoms, and carbamazepine failure. ¹⁰ One group found some success in selecting the ophthalmic segment with prolonged head flexion. ^{11 12} The extent of this effect is not yet understood, nor is there a well-documented manner in which this sitting head flexion is achieved. Most articles report little in regard to head positioning, but some note head flexion is continued for 1 to 2 hours in the recovery area. ^{1 6 11 12 13} This positioning is difficult to obtain continuously in a postanesthesia patient, who often needs to have a lifted jaw for airway protection and may be delirious or agitated. Here, we present a novel technique using a specific orthopaedic surgical bed to achieve the exact head positioning needed to prevent migration of glycerol from Meckel's cave.

Surgical Technique

After intubation, the patient is positioned supine on a beach chair sliding headboard surgical table with the appropriate landmarks drawn. The incision site is 2.5 cm lateral to the oral labial commissure. The distal tip of the Touhy needle is aimed toward the intersection of the mid-pupillary line and 2 cm anterior of the tragus. For these cases, a Stryker Berchtold Operon Beach Chair Integrated Shoulder Table D860 with sliding headboard was used. The navigation system is attached to the bed and registered to the patient. The anatomical landmarks are drawn, the endotracheal tube is positioned to the contralateral side, C-arm fluoroscopy is positioned for a lateral X-ray, ophthalmic betadine is used to sterilely clean the face, and sterile draping is used around the site of incision ( Fig. 2 ).

Fig. 2.

( a ) Head positioning with navigation fixation to the bed frame. ( b ) Sterile draping with fluoroscopy.

A no. 11 blade is used to make incision. A 16-gauge Touhy needle is advanced percutaneously, medial to the mandible until the distal end is approximated at the foramen ovale. One hand is used to direct the needle sterilely and the other is inside the mouth palpating to ensure there is no medial breach of the oral mucosa. This glove is exchanged every time it is used in the mouth ( Fig. 3 ). A lateral X-ray obtained showing the appropriate anteroposterior and craniocaudal trajectory is shown in Fig. 4a . The inner stylet is removed and the navigation probe, designed for ventricular drain placement, is advanced through the Touhy needle until it is at the distal portion of the needle ( Fig. 4b ). With confirmation of the needle at the foramen ovale on navigation, the stylet is reintroduced and the needle is advanced through the foramen. The patient is then positioned in the sitting position with the head in at least 15 degrees of flexion ( Fig. 5a ). The preprepared glycerol is then injected into Meckel's cave. Immediately after injection, the stylet is reintroduced, the needle is removed, and a Velcro foam head holder is used to maintain stability ( Fig. 5b–d ). The patient is kept in this position for 1 hour prior to returning flat and extubating the patient.

Fig. 3.

Technique for needle advancement to the foramen ovale.

Fig. 4.

( a ) Fluoroscopy and ( b ) navigation confirmation of correct angle to the foramen ovale.

Fig. 5.

( a ) Head flexion at time of glycerol injection. ( b ) Foam head fixation. ( c,d ) Final positioning of the bed.

Illustrative Cases

This procedure has been completed in three patients who had previously had failed TN interventions. All the patients provided consent for use of pictures and publication of their case. All patients achieved adequate pain relief with these surgical techniques. Intraoperatively, there was no deviation of the head flexion or of the patient's body while seated upright, and there was no development of pressure ulcers or nerve palsies.

The first patient was a 37-year-old who presented with worsening symptoms in all three left trigeminal nerve distributions. Prior to seeing our team, he had undergone two PGRs without any postinjection head adjustments and no significant pain relief or numbness. With our team, he underwent one PGR with postprocedure head flexion at 15 degrees while intubated, maintained by the operating physician for 1 hour, prior to the development of the technique described earlier. He experienced pain relief and numbness for 6 months before symptoms recurred. He then underwent repeat PGR with the new method. No provider was required to hold the head or intervene during the hour of head flexion. The patient had complete relief without any recurrence at 6 months of follow-up.

The second patient was an 88-year-old with right V2 and V3 TN who underwent Gamma Knife radiation to his trigeminal nerve three times at another institution without significant relief. In addition to his classical lancinating trigeminal pain, he had a component of chronic, burning, aching pain in a similar area. He underwent PGR with the beach chair sliding headboard surgical table, which produced numbness and pain relief from the lancinating TN pain with significant reduction of pain medications postoperatively at 6 months of follow-up.

The third patient was a 52 year-old with right TN who had undergone a previous PGR and radiosurgery both with incomplete reduction of pain. One year after radiosurgery, she developed recurrence of symptoms predominantly in V3. She underwent PGR with the method described here and experienced satisfactory pain reduction.

Discussion

While PGR is a viable option for medically refractive TN, the outcomes vary significantly. One study reports a 73% success rate in 3,370 cases that increased to 99.6% after repeat injections. ¹⁴ On the other hand, a review article notes a success rate of only 54% at 3 years. ⁵ This variable range of success has been proposed to be partially due to the anatomy of Meckel's cave and the position of the gasserian ganglion in Meckel's cave. There are several cadaveric studies and reviews that have detailed the anatomy, embryologic origins, and physiological interactions of the gasserian ganglion in Meckel's cave. ^{15 16 17 18} This area is described as a cave with an anterior wall composed of the greater wing of the sphenoid bone, the posterior wall composed of the petrous apex of the temporal bone/clivus, and the medial wall composed of the sphenoid body/clivus. ¹⁸ Still there is little knowledge on fluid dynamics of the viscous glycerol solution in Meckel's cave with variable anatomical parameters. Nevertheless, many surgeons and articles report utilizing 1 to 2 hours of head tilt. ^{1 6 11 12 13}

With the sliding headboard surgical table, we have been able to achieve sustained precise head flexion that has not been detailed elsewhere in the literature. Anatomically, it is reasonable to believe that head flexion would ensure glycerol does not migrate out of Meckel's cave. However, clinically this has not been extensively studied in cadavers or humans. There have been some studies on head positioning after PGR, but the reports do not detail how the head positions were maintained.

Bergenheim et al described different head positions for 1 hour post glycerol injection to attempt to select the best position for each trigeminal branch, which was successful for V1 by increasing the head flexion. ^{11 12} Anatomically, this concurs with Sayaci et al's cadaveric study that found that cannulation always occurred through the posterior aspect of the foramen ovale and the trigeminal nerve was pierced retrogasserian nearest to V3 fibers. ¹⁹ These studies suggest that with head flexion, glycerol may flow anteriorly toward the V1 segment.

Bergenheim et al's article provides photographs depicting the head positioning in the recovery area with a pillow that appears beyond 15 degrees. This method is colloquially used by other surgeons but does not detail the exact degrees of head flexion nor how compliance of this position was maintained in a postanesthesia patient. ¹¹ Understanding the details of head positioning in regard to degrees, direction, and time may be important for determining more rare side effects such as cranial nerve (CN) IV palsies from injury medially or V3 motor branch palsies inferiorly. ¹³ Our study is limited by the sample size, but highlights the need for more cadaveric and prospective studies on head positioning in PGR.

Conclusion

PGR is an effective method for treating medically refractive TN, but the postinjection management remains variable. By using a beach chair sliding headboard surgical table to create specific degrees of head flexion, surgeons will no longer need to hold the patient's head intraoperatively or need close head positioning monitoring in the recovery area. The authors hope that more surgeons will adopt this new method and help create a larger series or patients with their head maintained in 15 degrees of flexion to determine how degree and duration of head flexion affect outcomes.