Larger contralateral trigeminal nerve and hippocampus volumes—as seen on standard clinical magnetic resonance imaging (MRI)—are predictive of early nonresponse to surgical treatment of trigeminal neuralgia, according to study findings published in Cephalalgia.

Although many patients with medically refractory trigeminal neuralgia are also nonresponders to surgical treatment, few studies have explored how trigeminal nerve characteristics relate to surgical outcome. In addition, none have investigated the relationship between subcortical brain structure and treatment outcomes. To this end, researchers retrospectively studied patients (n=34) with trigeminal neuralgia undergoing microvascular decompression at the University of Alberta Hospital between 2005 and 2018.

Researchers conducted preoperative MRIs for manual tracing of trigeminal nerves and automated segmentation of hippocampus, amygdala, and thalamus. For the purposes of this study, the investigators compared responders and nonresponders to surgical management in relation to nerve and subcortical structure volumes. Additionally, nerve and subcortical structure volumes were evaluated to determine their potential in predicting postoperative pain outcome.

Compared with responders, patients who did not respond to surgical treatment of trigeminal neuralgia had a significantly larger contralateral trigeminal nerve volume (31.3 ± 11.5 mm3 vs 53.3 ± 19.5 mm3, respectively; P =.009). Nonresponders also had a larger ipsilateral hippocampus volume (3821 ± 274 mm3 and 3545 ± 378 mm3; P =.012), contralateral hippocampus volume (3830 ± 206 mm3 vs 3479 ± 385 mm3 respectively; P =.032), and total hippocampus volume (7651 ± 388 mm3and 7024 ± 668 mm3; P =.008).

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Treatment outcome was correctly classified with contralateral hippocampus volume in 82% of cases (91% sensitive, 78% specific, P =.008) and with contralateral nerve volume in 81% of cases (91% sensitive, 75% specific, P <.001). Likewise, a binomial logistic regression analysis found that both contralateral hippocampus and contralateral nerve volumes combined classified treatment outcome with an 84% accuracy (Nagelkerke R2 = 65.1).

Limitations of the study include its observational and retrospective nature, as well as the use of only chart review to classify responders and nonresponders.

The researchers concluded that these findings suggest “pain-state maintenance and treatment resistance in medically refractory trigeminal neuralgia may depend on the structural features of both [cranial nerve V] and structures involved in limbic contributions to chronic pain.”

Reference

Danyluk H, Lee EK, Wong S, et al. Hippocampal and trigeminal nerve volume predict outcome of surgical treatment for trigeminal neuralgia [published online November 21, 2019]. Cephalalgia. doi:10.1177/0333102419877659