A Diffusion Tensor Protocol for the Stria Medullaris in Chronic Pain Patients

Chronic pain may be modulated by descending pathways, resulting in monoaminergic changes in the mid-brain. One such pathway, the dorsal diencephalic conduction system, integrates frontolimbic inputs through the stria medullaris (SM) and habenula to directly influence midbrain dopamine serotonin and noradrenaline. A role for the habenula has already been suggested in chronic pain; however, it has been impossible to investigate the SM in vivo until now. We present an anatomically validated and reliable protocol diffusion-weighted magnetic resonance protocol for tractographic identification and quantification of the SM. Fifty subjects were scanned using advanced diffusion imaging (61 directions, b-value 1500 [mm.sup.3], 3T) combined with a higher-order tractography algorithm as part of the ongoing REDEEM study. Two independent raters and a neuroanatomist isolated the SM using a novel tractography protocol. The SM was reconstructed with excellent inter-rater reliability (P = 0.88 between raters) and consistent tract diffusion metrics (P = 0.92). Diffusion-rendered tracts were compared with cadaveric anatomical measurements, suggesting satisfactory face validity. As such, we present the first investigation showing reliable diffusion tractography reconstruction of the SM in vivo. Analyzing diffusion metrics may allow investigation of this structure's role in the descending neuromodulation of pain pathways in chronic pain states. Additionally, accurate stereotactic localization of the SM through this technique may allow deep brain stimulation of this structure as a treatment for chronic pain. References: 1) Shelton L, Becerra L, Borsook D. Unmasking the mysteries of the habenula in pain and analgesia. Prog Neurobiol 2012;96(2):208-19. 2) Erpelding N, Sava S, Simons LE, et al. Habenula functional resting-state connectivity in pediatric CRPS. J Neurophysiol 2014;111(2):239-47. 3) Gardon O, Faget L, Chu Sin Chung P, Matifas A, Massotte D, Kieffer BL. Expression of mu opioid receptor in dorsal diencephalic conduction system: New insights for the medial habenula. Neuroscience 2014;277:595-609.