Identifying a Novel Critical Access Difficulty Factor in Percutaneous Radiofrequency Rhizotomy for Trigeminal Neuralgia: Pterygoid Process Ridge

BACKGROUND: Percutaneous stereotactic radiofrequency rhizotomy (PSR) is an ablative procedure for trigeminal neuralgia (TN). The anatomic structures that pass through, or around, the foramen ovale (FO) play vital roles in the success rate of PSR. The presence of a variant pterygoid process ridge (PPR) obscuring the FO renders the cannulation procedure difficult but had not been described in the literature before. OBJECTIVE: To identify the variations of the PPR to assess cannulation difficulty. METHODS: Fifty seven FOs of 57 patients with TN (TN group) and 438 FOs of 232 patients without TN (non-TN group) were analyzed using 3-dimensional computed tomography reconstruction images of cranial bases. Three-dimensional printer models were also used for TN patients with PPR-obscured FOs. Measurements were obtained for shape, size, and morphometric variability effect on cannulation. RESULTS: We identified 5 PPR-obscured FOs (8.8%) in the TN group and 32 FOs (7.3%) in the non-TN group. In the TN group, the transverse diameter obstruction ranged from 19.2% to 39.7% in 4 patients, and 1 case was 100%. Of particular note, approximately one-quarter to one-third of FO preset targets were affected by PPR. CONCLUSION: A PPR-obscured FO represents a new confounding factor in the conduct of PSR. Confirming the PPR-obscured FO is a critical step in improving the effectiveness of puncture target presetting, ie, evaluating the target with actual FO data is an improvement over the use of surgical view FO data. Discernment of the PPR can improve the success rate of difficult-to-access FO punctures, thereby rendering PSR more effective.