The publication in the journal *Cephalalgia*, recognized as the official outlet of the International Headache Society, unveils groundbreaking findings on the neuroanatomical factors affecting treatment outcomes for individuals suffering from trigeminal neuralgia. Led by Dr Tejas Sankar from the University of Alberta, Canada, the research titled “Hippocampal and trigeminal nerve volume predict the outcome of surgical treatment for trigeminal neuralgia” casts a new light on this debilitating condition.
Trigeminal neuralgia (TG), often manifesting as intense facial pain primarily felt in the cheek or jaw, is briefly described in the 3rd Version of the International Classification of Headache Disorders (ICHD-3) as a disorder marked by recurrent, unilateral, electric shock-like pains. These pains are abrupt in onset and cessation, confined to the trigeminal nerve’s distribution, and are provoked by benign stimuli. While it may arise spontaneously, it can also stem from an underlying disorder, with a possibility of accompanying continuous, moderate-intensity pain within the affected nerve’s distribution.
The research delineates two prevalent forms of TN: the classical form, linked with neurovascular compression at the nerve’s root entry zone, and the idiopathic form, which lacks this neurovascular compression. In cases where pharmacological treatments fail, microvascular decompression emerges as a viable surgical alternative.
Dr. Sankar’s hypothesis builds on existing evidence that suggests a consistent reduction in trigeminal nerve volume and cross-sectional area on the afflicted side in TN patients. The research proposes that those failing to respond to surgical interventions may exhibit distinct neuroanatomical characteristics.
The study analyzed 37 patients diagnosed with either classical or idiopathic TN, employing neuroimaging techniques like T2-weighted magnetic resonance imaging (1.5T) performed a year before undergoing microvascular decompression surgery. The focus was on evaluating the trigeminal nerve and other subcortical brain structures, such as the thalamus, hippocampus, and amygdala, due to their roles in the trigeminal sensory relay and as potential factors in the limbic aspects of chronic pain. Comparisons were made between the ipsilateral and contralateral sides relative to the pain location, including total nerve volume and percentage differences.
The findings revealed a 68% success rate among patients post-surgery, which aligns with prior research. Key observations include a larger thalamus volume on the side opposite the pain in all patients; non-responders had a larger intracranial volume, greater trigeminal nerve volume on the side opposite the pain, and a larger contralateral hippocampus volume than responders. Moreover, the contralateral trigeminal nerve and hippocampus volumes indicated treatment outcomes, with larger volumes associated with non-response to treatment. The role of the hippocampus, both ipsilateral and contralateral, was significant in predicting treatment success.
Despite these novel findings, the researchers caution against overly simplistic interpretations of their data. Treatment resistance in chronic pain likely involves complex interactions among multiple brain structures rather than being attributable to a single entity. They advocate for future studies to explore network and connectivity patterns between responders and non-responders, emphasizing the potential of the hippocampus and other limbic structures as integral components of these networks. This approach could offer deeper insights into how chronic pain is modulated, potentially leading to more effective treatment strategies.
This research underscores the importance of the hippocampus in integrating the emotional aspects of chronic pain. It echos findings in other pain-related disorders, such as migraine, where structural brain changes and increased hippocampal connectivity have been observed. These insights enrich our understanding of trigeminal neuralgia and hint at broader implications for treating chronic pain conditions, highlighting the complex interplay between brain structure, emotional processing, and pain perception.
More information: Hayden Danyluk, Esther Kyungsu Lee, Tejas Sankar et al, Hippocampal and trigeminal nerve volume predict outcome of surgical treatment for trigeminal neuralgia, Cephalalgia. DOI: 10.1177/0333102419877659
Journal information: Cephalalgia Provided by International Headache Society
