The C-arm was adjusted to project the bilateral petrous pyramids onto the middle part of the maxillary sinus, and foramen rotundum was identified within the maxillary sinus superior to the petrous pyramid (Fig. 3A). Using posteroanterior fluoroscopy, the needle and stylet were introduced into the posterolateral wall of the maxillary sinus and advanced toward foramen rotundum. The needle tip was positioned anteriorly to the pterygopalatine fossa and foramen rotundum (Fig. 3B). The needle was rotated so that the tip faced posteriorly toward foramen rotundum and advanced until the tip was within the foramen (Fig. 3C). The C-arm was placed in a lateral position and the needle was slowly advanced until the tip was observed entering the middle fossa (Fig. 3D). In some cases, patients experienced paresthesia along the course of the maxillary branch of the trigeminal nerve during advancement of the needle through the foramen rotundum to the middle cranial fossa. In 15 of these cases (60%), patients could not tolerate this paresthesia and the needle was withdrawn to the external opening of the foramen rotundum so that 1 mL of 2% lidocaine could be injected before re-advancing the needle.
The stylet was removed from the needle and a radiofrequency electrode (ET-20S, Smith & Nephew, USA) was inserted through the needle. The probe was stimulated with an initial pulse of 50 Hz. Patients experienced paresthesia in the distribution area of the maxillary branch at 0.2 V which intensified with increased voltage. No paresthesia was noticed in the distribution areas of the ophthalmic and mandibular branches at 0.7 V, indicating that the needle was correctly placed within the maxillary branch and not within the ophthalmic and mandibular branches. The position of the needle within the foramen was confirmed using 3D-reconstruction in the coronal, sagittal, and needle trajectory planes (Fig. 4).
After positioning of the needle was confirmed, the radiofrequency probe was removed, 0.3 mL of 2% lidocaine was slowly injected through the needle, and patients were monitored for 3 to 10 minutes until the pain along the maxillary branch was replaced by a feeling of numbness. The radiofrequency electrode was reinserted into the needle and thermocoagulation was performed at 75°C for 4 minutes. During thermocoagulation, functions of the ophthalmic and mandibular branches were repeatedly assessed by physical examination and patient feedback.
Assessment of Pain Reduction
The visual analogue scale (VAS), a widely used metric for measuring pain, was completed by patients both pre- and postoperatively.11 Patients were shown a horizontal line marked from 0 (no pain) to 10 (most severe pain) and asked to rank the severity of their pain.
The mean preoperative VAS score was 8.6 ± 0.8. Of the 25 patients, 22 (88%) indicated a postoperative VAS scores of 0, indicating complete resolution of pain after the procedure (Table 1). Of the remaining 3 patients, 2 had postoperative VAS scores of 5 and 3, respectively, and each subsequently underwent a second interventional procedure that resulted in complete resolution of pain. The remaining patient had a postoperative VAS score of 2 which resolved several weeks postoperatively without subsequent treatment. Mild persistent facial numbness was noted in 23 patients and no other complications were observed. Patients were followed up between 1 and 29 months, with a mean follow-up period of 14.74 ± 11.34 months. Recurrence was observed in 9 patients (36%) at follow-up. All patients with recurrent symptoms were successfully managed with repeat thermocoagulation, as of the time of publication. Thus, the total reoperation rate was 44%.
Operative time was very short at an average of 15 minutes. Average puncture time (from insertion to placement) was about 5 minutes with an average radiofrequency time of approximately 4 minutes. Surgical complexity was similar to that of traditional percutaneous image-guided trigeminal thermocoagulation.
Trigeminal neuralgia is a neuropathy involving intense pain limited to the distribution of 1 or more of the branches of the trigeminal nerve.1 Percutaneous treatment modalities for TN consist of balloon compression, glycerol rhizotomy, and radiofrequency thermocoagulation. All 3 treatments have been shown to induce pain relief by directed injury to the trigeminal nerve and are generally considered to be safe, efficient, and effective.12 Recent improvements in percutaneous radiofrequency thermocoagulation have involved improving the targeting accuracy of the procedure through the use of intraoperative computed tomography neuronavigation and frameless stereotactic cannulation of the foramen ovale, with good success.13–15
Xu and colleagues16 described their experience with 54 patients and reported increased rates of long-term pain relief (85% vs 54% at 12 months and 62% vs 35% at 36 months) in the patients undergoing percutaneous radiofrequency thermocoagulation with navigation compared with the previously standard procedure. A later study by Yang and colleagues17 in 2010 involved 79 patients with TN who underwent radiofrequency rhizotomy. Yang et al reported no difference in surgical outcome or pain relief between CT-guidance with 3D reconstruction and fluoroscopy-guided groups. However, CT-guidance significantly decreased the median time for needle placement (14 vs 40 min) and intraoperative patient discomfort.
The classic approach to radiofrequency thermocoagulation involves placement of the needle through foramen ovale. However, tracing the maxillary branch of the trigeminal nerve from its origin at the Gasserian ganglion involves passing through foramen rotundum to exit the cranium, subsequently crossing the pterygopalatine fossa, and entering the orbit through the inferior orbital fissure. Thus, an approach through the foramen rotundum, rather than the foramen ovale, has the potential to simplify targeted treatment of the maxillary branch of the trigeminal nerve in TN patients.
Huang et al proposed a computed tomography-guided technique through foramen rotundum to block the maxillary branch of the trigeminal nerve4 and found that, compared to an approach through foramen ovale, thermocoagulation through foramen rotundum showed similar results for pain relief both immediately postoperative and at 1-year follow-up. In addition, approaching the trigeminal nerve through the foramen rotundum was associated with a shorter procedural time and fewer serious adverse effects including masticatory weakness and corneal perforation. All patients treated by Huang et al through foramen rotundum experienced some degree of facial numbness. However, while this group had a greater incidence of facial numbness than the foramen ovale group, their degree of numbness was typically less extensive.
In the present study, we performed a similar technique using 3D image-guided radiofrequency thermocoagulation of the maxillary branch through the foramen rotundum. No patient underwent more than 2 intervention procedures and all but 1 patient experienced immediate and sustained pain relief after initial or secondary treatment. Recurrence occurred in a minority of patients (36%), similar to that of comparable techniques. The complications observed following this technique were mild and usually did not require additional treatment. No incidence of masticatory weakness or corneal perforation—both known complications of radiofrequency coagulation through foramen ovale4—were observed. The vast majority of our patients (92%) experienced facial numbness; however, this numbness was considered tolerable and corroborates the findings by Huang et al that numbness caused by a foramen rotundum approach is typically not extensive or deteriorative to quality of life.
This series of 25 cases of TN of the maxillary nerve treated with 3D image-guided radiofrequency thermocoagulation through foramen rotundum demonstrates that this technique may help mitigate the risk of iatrogenic damage to the ophthalmic and mandibular nerves through repeated movements of the needle intracranially—which could result in weakened mastication and/or corneal damage. Furthermore, this technique may reduce the need for repeated intraoperative electrical stimulation and thus reduce patient discomfort. However, larger prospective clinical studies are necessary to determine the true efficacy of at this technique.
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