Intracranial nociception

Understanding intracranial nociceptive innervation is essential to understand the pathophysiology of headaches. Our knowledge about human intracranial nociception comes from sparse observations during neurosurgical procedures performed in awake patients, from human anatomical studies and from experimental studies in animals. In this article we review the anatomical and functional organization underlying nociceptive innervation. Intracranial nociception is mainly mediated by the trigeminal system, except in the posterior cranial fossa that is innervated by the first cervical roots. For decades, the dura mater, its vessels and major cerebral blood vessels were considered as the only intracranial pain-sensitive structures. Recent animal and human studies have suggested that smaller brain arteries and potentially pia mater might also be pain sensitive. Nociceptive neurons innervating intracranial blood vessels project via the ophthalmic division (V1) to the trigeminal ganglion and store several neurotransmitters including glutamate, substance P and calcitonin gene-related peptide (CGRP). The trigeminal ganglion, root and brainstem nuclei have a specific topographic and functional somatotopy. Progressive transition between the trigeminal spinal nucleus and the dorsal horn of the cervical spinal cord, and convergence of nociceptive inputs from the face, intracranial structures and the occipital area on the so-called "trigemino-cervical complex" may explain some headache features, relations between facial and occipital pain, and efficacy of occipital nerve stimulation in headache. The specific anatomic organization of the trigeminal system, from the primary-order neuron in the trigeminal ganglion, to the second-order neuron is the trigeminal nuclei, may explain a part of the various characteristics of headaches.

The Clinical Characteristics and Surgical Treatment of Glossopharyngeal Neuralgia With Pain Radiating to the Innervated Area of the Trigeminal Nerve

OBJECTIVE

The aim of this study was to investigate the clinical characteristics and surgical outcome of microvascular decompression (MVD) with or without glossopharyngeal nerve and partial vagus nerve rhizotomy for treating glossopharyngeal neuralgia (GPN) patients with pain radiating to the area innervated by the trigeminal nerve.

METHODS

A retrospective review was performed to collect the clinical data from GPN patients who had pain in the area innervated by the glossopharyngeal and vagus nerves and radiating to the innervated area of the trigeminal nerve. All patients underwent surgical treatment. The immediate and long-term outcomes were investigated to show the efficacy and safety of the treatment. Information on pain recurrence and complications was collected.

RESULTS

Fourteen patients were recruited. The pain area radiated to the trigeminal nerve distribution, including the anterior auricle (57.1%), temple (50%), cheek (28.6%), mandibular gingiva (42.9%), and anterior part of the tongue (14.3%). Swallowing was the most common trigger (85.7%) in these patients. Seven patients underwent MVD of the offending vessel at the root entry zone (REZ) of the glossopharyngeal and vagus nerves. Seven patients underwent MVD plus glossopharyngeal nerve rhizotomy with or without partial vagus nerve rhizotomy. Thirteen patients experienced complete pain relief during the follow-up (mean 49.3 months).

CONCLUSIONS

GPN patients with pain radiating to the area innervated by the trigeminal nerve could be successfully treated solely by management of the glossopharyngeal and vagus nerves. In these GPN patients, differential diagnosis is extremely important to identify the true diagnosis, which would reduce the occurrence of iatrogenic injury of the trigeminal nerve during treatment.