New Insights in Trigeminal Anatomy: A Double Orofacial Tract for Nociceptive Input

Abstract

Orofacial pain in patients relies on the anatomical pathways that conduct nociceptive information, originating from the periphery towards the trigeminal sensory nucleus complex (TSNC) and finally, to the thalami and the somatosensorical cortical regions. The anatomy and function of the so-called trigeminothalamic tracts have been investigated before. In these animal-based studies from the previous century, the intracerebral pathways were mapped using different retro- and anterograde tracing methods. We review the literature on the trigeminothalamic tracts focusing on these animal tracer studies. Subsequently, we related the observations of these studies to clinical findings using fMRI trials. The intracerebral trigeminal pathways can be subdivided into three pathways: a ventral (contralateral) and dorsal (mainly ipsilateral) trigeminothalamic tract and the intranuclear pathway. Based on the reviewed evidence we hypothesize the co-existence of an ipsilateral nociceptive conduction tract to the cerebral cortex and we translate evidence from animal-based research to the human anatomy. Our hypothesis differs from the classical idea that orofacial pain arises only from nociceptive information via the contralateral, ventral trigeminothalamic pathway. Better understanding of the histology, anatomy and connectivity of the trigeminal fibers could contribute to the discovery of a more effective pain treatment in patients suffering from various orofacial pain syndromes.

Responsivity of Periaqueductal Gray Connectivity Is Related to Headache Frequency in Episodic Migraine

“…Notably, the effect was on the ipsilateral side of stimulation. Henssen et al recently proposed the co-existence of an ipsilateral nociceptive conduction tract to the cerebral cortex ( 43 ), with ipsilateral sensory projections via the dorsal primary sensory nucleus, and ipsilateral PAG modulation via the caudal part of the spinal nucleus. Given our results, this potential ipsilateral pathway may have precedence in migraine.…”

Long-term effect of motor cortex stimulation in patients suffering from chronic neuropathic pain: An observational study

“…If both thalami get involved into nociceptic processing due to a peripheral lesion, MCS might not be capable to provide a complete analgesic effect in this group. The significant difference in response to MCS in orofacial pain could be the result of a recent review, hypothesizing a double tract that conducts orofacial pain[ 47 ]. However, in general, classic trigeminal neuralgia is not considered an etiology which is treatable by MCS.…”

Ex vivo visualization of the trigeminal pathways in the human brainstem using 11.7T diffusion MRI combined with microscopy polarized light imaging

“…However, they also conclude that the exact anatomy of the trigeminal pathways in the human brainstem remain elusive (Solstrand Dahlberg et al 2018 ). In 2016, a review of tracing studies in animals and functional MRI studies in humans provided an overview of the trigeminal tracts in the brainstem (Henssen et al 2016 ). Figure 1 depicts two trigeminothalamic tracts sprouting from the principal sensory nucleus (PSN), the ventral- and dorsal trigeminothalamic tract ( vtt and dtt , respectively).…”