Intracranial vessels in trigeminal transmitted pain: A PET study

Mechanism underlying cranial nerve rhizopathy

The cranial nerve rhizophathy, commonly presented with trigeminal neuralgia (TN) or hemifacial spasm (HFS), is a sort of hyperexcitability disorders with higher incidence in senior Asian. In this paper, a novel hypothesis on the pathogenesis is proposed and with which some clinical phenomena are explained. In those with crowded cerebellopontine angle in anatomy, the cranial nerve root and surrounding vessel are getting closer and closer to each other with aging and finally the neurovascular conflict happens. As the interfacial friction associated with pulse, the nerve incurs demyelination. Since this pathological change develops to a certain degree, some transmembrane proteins emerge from the nerve due to a series of signaling pathway mediated by inflammatory cytokines. Among them, voltage-gated (Na_v1.3) and mechanosensitive (Piezo2) ion channels may play the important role. With pulsatile compressions, the Piezo2 drives the resting potential toward depolarization forming a state of subthreshold membrane potential oscillation. Under this condition, just an appropriate pressure can make the membrane potential easy to reach threshold and activate the sodium channel, eventually generating conductible action potentials from the axon. When these ectopic action potentials propagate to the central nerve system, an illusion of sharp pain is perceived; while to the nerve-muscle junctions, an attack of irregular muscle constriction occurs. This hypothesis can well explain the symptomatic manifestation of paroxysmal attacks aroused by emotions. When we get nervous or excited, our heart rate and blood pressure alter correspondingly, which may give rise to "a just right pressure" - with specific frequency, amplitude and angle - impacting the suffered nerve to reach the threshold of impulse ignition. After a successful microvascular decompression surgery, the trigger is gone (there is no compression anymore) and the symptom is alleviated. While the postoperative recurrence could be attributable to Teflon granuloma development if had been placed improperly - for this nerve root has been susceptible no matter to arteries or to neoplasms. Besides, it may illustrate the clinical phenomenon that secondary TN or HFS cases are seldom caused by schwannoma: with a proliferative sheath, the nerve root is actually insulated. By contrast, not all neurovascular contacts can lead to the onset: it demands an exclusive extent of demyelination firstly.

An Update: Pathophysiology of Migraine

Migraine is the most common disabling primary headache globally. Attacks typically present with unilateral throbbing headache and associated symptoms including, nausea, multisensory hypersensitivity, and marked fatigue. In this article, the authors address the underlying neuroanatomical basis for migraine-related headache, associated symptomatology, and discuss key clinical and preclinical findings that indicate that migraine likely results from dysfunctional homeostatic mechanisms. Whereby, abnormal central nervous system responses to extrinsic and intrinsic cues may lead to increased attack susceptibility.

Neurovascular mechanisms of migraine and cluster headache

Vascular theories of migraine and cluster headache have dominated for many years the pathobiological concept of these disorders. This view is supported by observations that trigeminal activation induces a vascular response and that several vasodilating molecules trigger acute attacks of migraine and cluster headache in susceptible individuals. Over the past 30 years, this rationale has been questioned as it became clear that the actions of some of these molecules, in particular, calcitonin gene-related peptide and pituitary adenylate cyclase-activating peptide, extend far beyond the vasoactive effects, as they possess the ability to modulate nociceptive neuronal activity in several key regions of the trigeminovascular system. These findings have shifted our understanding of these disorders to a primarily neuronal origin with the vascular manifestations being the consequence rather than the origin of trigeminal activation. Nevertheless, the neurovascular component, or coupling, seems to be far more complex than initially thought, being involved in several accompanying features. The review will discuss in detail the anatomical basis and the functional role of the neurovascular mechanisms relevant to migraine and cluster headache.

The Use of Radiolabelled Human Serum Albumin and SPECT/MRI Co-Registration to Study Inflammation in The Cavernous Sinus of Cluster Headache Patients

A sterile inflammation in the cavernous sinus was hypothesized to underlie cluster headache (CH). Neurogenic inflammation is accompanied by the extravasation of plasma proteins in the surrounding tissue. We tested the hypothesis of an inflammatory process in the cavernous sinus in CH patients using 99mTc-human serum albumin (HSA) and single photon emission computed tomography (SPECT). Six patients with episodic CH were enrolled. After baseline imaging, CH attacks were induced by IV injection of nitroglycerin. The patients remained untreated for 20 min. A second SPECT was performed after successful treatment. Region of interest (ROI) analysis was performed on the basis of coregistered MRI/SPECT data. There was no statistical difference between the 99mTc-HSA uptake in the ipsilateral cavernous sinus before and after induction of an acute CH attack. There was no evidence for 99mTc-HSA extravasation in the cavernous sinus during the active episode as compared with the remission phase. Our results do not support the hypothesis of an inflammation in the cavernous sinus.

Temporal retinal nerve fibre layer thinning in cluster headache patients detected by optical coherence tomography

BACKGROUND

The exact pathophysiology of cluster headache (CH) is still not fully clarified. Various studies confirmed changes in ocular blood flow during CH attacks. Furthermore, vasoconstricting medication influences blood supply to the eye. We investigated the retina of CH patients for structural retinal alterations with optical coherence tomography (OCT), and how these changes correlate to headache characteristics, oxygen use and impaired visual function.

METHODS

Spectral domain OCT of 107 CH patients - 67 episodic, 35 chronic, five former chronic sufferers - were compared to OCT from 65 healthy individuals. Visual function tests with Sloan charts and a substantial ophthalmologic examination were engaged.

RESULTS

Reduction of temporal and temporal-inferior retinal nerve fibre layer (RNFL) thickness was found in both eyes for CH patients with a predominant thinning on the headache side in the temporal-inferior area. Chronic CH patients revealed thinning of the macula compared to episodic suffers and healthy individuals. Bilateral thinning of temporal RNFL was also found in users of 100% oxygen compared to non-users and healthy controls. Visual function did not differ between patients and controls.

DISCUSSION

Our OCT findings show a systemic effect causing temporal retinal thinning in both eyes of CH patients possibly due to attack-inherent or medication-induced frequent bilateral vessel diameter changes. The temporal retina with its thinly myelinated parvo-cellular axons and its more susceptible vessels for the vasoconstricting influence of oxygen inhalation seems to be predisposed for tissue damage-causing processes related to CH.

[Hypothalamic deep brain stimulation for treatment of cluster headache]

Extremely severe, unilateral, recurrent facial pain and headache, accompanied by autonomic symptoms and signs, can be identified as cluster headache attacks (CH). Despite optimal pharmacological treatment, 20% of patients will not achieve satisfactory improvement. The severity of pain is so extreme that CH has been a cause of multiple suicidal attempts among patients ineffectively treated because of CH. Hypermetabolism of ipsilateral posterior hypothalamus observed in PET studies led to multiple attempts of deep brain stimulation (DBS) utilization in CH treatment. The authors present current opinions about DBS treatment in CH. A socioeconomic analysis of neuromodulatory treatment of CH is presented.

[The window into headache research : what have we learned from functional and structural neuroimaging]

Current functional neuroimaging studies in headache patients have demonstrated that changes in vascular function are not the primary cause for the pain in migraine. Especially in headache research, functional imaging revealed for the first time important information on the pathophysiology of idiopathic syndromes beyond mere anatomical attribution. Several independent studies have reinforced the crucial role of the brainstem in migraine resulting in primary dysfunction of the endogenous antinociceptive systems, including the periaqueductal grey and the dorsal raphe nucleus (DRN) in the midbrain as well as areas involved in the neuronal regulation of cerebral blood flow (DRN and locus coeruleus). The hypothalamus on the other hand is involved in the fundamental processes leading to the acute attacks of cluster headache. These data have been repeatedly replicated by several groups and led to a new understanding of the pathophysiology of these syndromes and specifically the central role of the brain. The recent studies investigating the structural changes in migraine, chronic tension-type headache and cluster headache are not yet clear in their relevance but raise important questions and promise increasing knowledge of one of the most frequent symptoms in humans.

Cluster headache associated with a sixth nerve palsy: a case report

BACKGROUND

Cluster headache is a rare primary headache disorder characterized by recurrent, stereotyped short-lasting attacks of severe, unilateral head pain accompanied by autonomic symptoms.

METHODS/RESULTS

Ophthalmic features such as conjunctival injection, lacrimation, ptosis and miosis occur in the vast majority of patients with cluster headache, whereas co-existent ocular movement disorders are rare.

CONCLUSIONS

To the best of our knowledge, only two documented cases of cluster headache with external ocular movement disorders have been reported. We describe herein an additional case with this unusual finding and discuss the putative pathophysiology of cluster headache associated with ophthalmoparesis.

Neuroimaging in headache

The neurobiology of migraine is complex, but considerable progress has been made during recent decades with the aid of functional neuroimaging. Imaging studies have provided evidence of both abnormal brain functioning and structural changes. In migraine aura, the blood flow changes initially occur in V3A, an area also showing morphometric abnormalities. Pontine activation is also associated with increased volumetric changes. Similar findings are observed in the hypothalamic region in cluster headache. Other paroxysmal headache disorders, such as short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), hemicrania paroxistica and hemicrania continua, share this similar pattern of activation as cluster headache, pointing to a common pathogenic mechanism. Further studies are required in order to determine whether these changes are the cause or the consequence of the disease, as well as the possible role they may play in the progression into a chronic disorder.

Imaging of pain: recent developments

Brain imaging of pain has made remarkable strides in the past year and a half. The basic regional activation pattern after acute nociceptive stimulation is now fairly well clarified. The extension of imaging studies from normal subjects to include cohorts of pathological pain patients is occurring. The techniques of positron emission tomography, functional magnetic resonance imaging and single photon emission computed tomography have all been applied to the study of human pain processing and the assessment of physiological interventions or psychological manipulations. Studies using labelled ligands to trace receptor alterations have also been conducted. Although more work could be done on the pharmacology and physiology of anesthesiology, the resulting set of observations provides a deeper understanding of the basic human neurophysiology of pain and a potential neural framework for better pain management.

Magnetic resonance angiography shows dilatation of the middle cerebral artery after infusion of glyceryl trinitrate in healthy volunteers

Previous studies have reported dilatation of the middle cerebral artery (MCA) during acute glyceryl trinitrate (GTN)-induced headache, using imaging techniques such as transcranial Doppler (TCD), positron emission tomography (PET) and single photon emission computerized tomography (SPECT). In the present study we aimed to evaluate whether magnetic resonance angiography (MRA) may be used to examine the effect of GTN on the MCA, with respect to changes in diameter and cross-sectional area in healthy volunteers. In addition, we wanted to determine the intra- and inter-observer variation of the method. In a randomized, double blind, crossover study 12 healthy volunteers received intravenous infusion of GTN (0.5 microg/kg/min for 20 min) or placebo. Using 1.5 Tesla MRA, we recorded changes in the diameter and cross-sectional area of MCA before, during and after infusion of GTN. The MRA images were evaluated by two blinded, independent observers/neuroradiologists. The primary endpoints were the differences in the AUC for diameter and cross-sectional area of the MCA between the two experimental conditions and the intra- and inter-observer variation. The areas under the curve (AUC) of the MCA diameter and cross-sectional area were significantly greater after GTN than after placebo (P < 0.05). The intra-observer variation (day-to-day) at baseline was 8.3% and 10.9% for the two observers. The mean inter-observer variation of the cross-sectional MCA area was 15.5% and for the diameter measurements 8%. The present study shows that the MRA method gives a reliable semi-quantitative index of the vascular changes in the intra-cerebral arteries after infusion of GTN and may be useful for headache research.

Neuromodulatory approaches to the treatment of trigeminal autonomic cephalalgias

The trigeminal autonomic cephalalgias (TACs) are a group of primary headache syndromes characterised by intense pain and associated activation of cranial parasympathetic autonomic outflow pathways out of proportion to the pain. The TACs include cluster headache, paroxysmal hemicrania and SUNCT (short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing). The pathophysiology of these syndromes involves activation of the trigeminal-autonomic reflex, whose afferent limb projects into the trigeminocervical complex in the caudal brainstem and upper cervical spinal cord. Functional brain imaging has shown activations in the posterior hypothalamic grey matter in TACs. This paper reviews the anatomy and physiology of these conditions and the brain imaging findings. Current treatments are summarised and the role of neuromodulation procedures, such as occipital nerve stimulation and deep brain stimulation in the posterior hypothalamus are reviewed. Neuromodulatory procedures are a promising avenue for these highly disabled patients with treatment refractory TACs.

A review of diagnostic and functional imaging in headache

The neuroimaging of headache patients has revolutionised our understanding of the pathophysiology of primary headaches and provided unique insights into these syndromes. Modern imaging studies point, together with the clinical picture, towards a central triggering cause. The early functional imaging work using positron emission tomography shed light on the genesis of some syndromes, and has recently been refined, implying that the observed activation in migraine (brainstem) and in several trigeminal-autonomic headaches (hypothalamic grey) is involved in the pain process in either a permissive or triggering manner rather than simply as a response to first-division nociception per se. Using the advanced method of voxel-based morphometry, it has been suggested that there is a correlation between the brain area activated specifically in acute cluster headache--the posterior hypothalamic grey matter--and an increase in grey matter in the same region. No structural changes have been found for migraine and medication overuse headache, whereas patients with chronic tension-type headache demonstrated a significant grey matter decrease in regions known to be involved in pain processing. Modern neuroimaging thus clearly suggests that most primary headache syndromes are predominantly driven from the brain, activating the trigeminovascular reflex and needing therapeutics that act on both sides: centrally and peripherally.

Neurochemistry of Trigeminal Activation in an Animal Model of Migraine

Research techniques such as electrophysiology, cFos protein expression, and other measurements of neuronal activation provide insights into the pathophysiology of pain processing in migraine, but they do not indicate the specific neurotransmitter systems involved. This paper summarizes data from microdialysis experiments in which changes in the neurochemistry of the trigeminal nucleus caudalis (TNC) were monitored during dural stimulation. Microdialysis allows the measurement of extracellular concentrations of neurotransmitters in a small area of the brain, in vivo, by means of a probe equipped with a semipermeable membrane. Microdialysis enables direct measurement of changes in extracellular concentrations of neurotransmitters in the intact animal over time in response to dural inflammation. Following the activation of the dural nociceptors, changes in the extracellular amino acid neurotransmitters in the deep lamina of the TNC were tracked. A 5-minute application of inflammatory soup when compared with saline to the dura of rats induced a transient decrease in extracellular glutamate in the TNC at approximately 30 minutes postapplication. This short-lived decrease was followed by a continuous increase in extracellular glutamate to a level of approximately 3 times the baseline value at 3 hours after application of the inflammatory soup. The time course of this increase in extracellular glutamate correlated with changes in sensory thresholds on the face of the rat from electrophysiological recordings of secondary sensory neurons in the TNC. No significant differences between the inflammatory soup and saline conditions were observed for extracellular concentrations of aspartate (an excitatory amino acid) or the inhibitory neurotransmitters gamma-aminobutyric acid or glutamine. Results of these experiments support an integral role for glutamate in central sensitization of neurons in the TNC, and suggest an important contribution of glutamate to allodynia and hyperalgia in this animal model of migraine.

[Treatment and prophylaxis for cluster headaches and other trigeminal autonomic headaches. Revised recommendations of the German Migraine and Headache Society]

Following the new IHS classification, cluster headache, paroxysmal hemicrania, and short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT syndrome) are included in the classification as trigeminal autonomic cephalgias (TAC). The similarities of these syndromes suggest a considerable shared pathophysiology. These syndromes have in common that they involve activation of trigeminovascular nociceptive pathways with reflex cranial autonomic activation. Clinically, this physiology predicts pain with some combination of lacrimation, conjunctival injection, nasal congestion, or eyelid edema. Broadly the management of TAC comprises acute and prophylactic treatment. Some types of trigeminal autonomic headaches such as paroxysmal hemicrania and hemicrania continua have, unlike cluster headaches, a very robust response to indomethacin, leading to a consideration of indomethacin-sensitive headaches. This review covers the clinical picture and therapeutic options. Although studies following the criteria of evidence-based medicine (EBM) are rare, most patients can be treated sufficiently.

Cluster headache: pathogenesis, diagnosis, and management

Cluster headache is a stereotyped primary pain syndrome characterised by strictly unilateral severe pain, localised in or around the eye and accompanied by ipsilateral autonomic features. The syndrome is characterised by the circadian rhythmicity of the short-lived attacks, and the regular recurrence of headache bouts, which are interspersed by periods of complete remission in most individuals. Headaches often start about 1-2 h after falling asleep or in the early morning, and show seasonal variation, suggesting that the hypothalamus has a role in the illness. Consequently, the vascular theory has been superseded by recognition that neurovascular factors are more important. The increased familial risk suggests that cluster headache has a genetic component in some families. Neuroimaging has broadened our pathophysiological view and has led to successful treatment by deep brain stimulation of the hypothalamus. Although most patients can be treated effectively, some do not respond to therapy. Fortunately, time to diagnosis of cluster headache has improved. This is probably the result of a better understanding of the pathophysiology in combination with efficient treatment strategies, leading to a broader acceptance of the syndrome by doctors.

The role of imaging in the pathophysiology and diagnosis of headache

PURPOSE OF REVIEW

Functional neuroimaging in headache patients has revolutionized our understanding of these syndromes and provided unique insights into some of the most common maladies in humans, suggesting that at least migraine and cluster headache are driven primarily from the brain. This review highlights new studies and recent advances in studying headache using neuroimaging.

RECENT FINDINGS

Concerning the diagnostics of headache, an EFNS Task Force evaluated recently the usefulness of imaging procedures in non-acute headache patients on the basis of evidence from the literature and defined guidelines on when to use magnetic resonance imaging or computed tomography. Regarding the pathophysiology of primary headache syndromes, repeated and independent findings reinforce the crucial role for the brainstem in acute and probably also in chronic migraine, and the hypothalamic grey in several trigemino-autonomic headaches. If further studies confirm these findings, a better understanding will be gained of where and how acute and preventive therapy can be targeted.

SUMMARY

Given the rapid advances in functional neuroimaging, in particular newer techniques such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a significant role and opens new avenues in targeting the neural substrates in individual primary headache syndromes.

Headache: lessons learned from functional imaging

Most idiopathic headache syndromes are still recognized as vascular headaches although the clinical picture points towards a central triggering cause. The early functional imaging work using PET shed light on the genesis of some syndromes, implying that the observed activation in migraine (brainstem) and in cluster headache (hypothalamic grey) is involved in the pain process in a permissive or triggering manner rather than simply as a response to first division nociception per se. Using the advanced method of voxel-based morphometry (VBM), it has been suggested that there is a correlation between the brain area activated particularly in acute cluster headache, the posterior hypothalamic grey matter, and some change in grey matter in the same region. Moreover, also in a PET study in cluster headache and experimental headache, a vasodilation of major basal vessels has been observed which is non-specific to the cause and most likely the effect of a trigemino-parasympathetic reflex. Taken together, functional neuroimaging in headache patients has revolutionised this area of study and provided unique insights into some of the commonest maladies in man, suggesting that migraine and cluster headache are primarily driven from the brain.

Brain blood flow in the nitroglycerin (GTN) model of migraine: measurement using positron emission tomography and transcranial Doppler

Nitroglycerin has been widely used as a model of experimental migraine. Studies combining measurement of flow velocity using transcranial Doppler (TCD) concurrently with measures of cerebral blood flow (CBF) are uncommon. We report the results of a study combining TCD and positron emission tomography (PET). Healthy volunteers with no personal or family history of migraine underwent measurement of CBF using H215O PET, and velocity using TCD. Measurements were done at baseline, and following i.v. nitroglycerin at 0.125, 0.25 and 0.5 micro g/kg per min. Subcutaneous sumatriptan (6 mg) was injected, with CBF and velocity measured 15, 30, and 60 min later. Nitroglycerin was terminated and measurements obtained 30 min later. Six male and six female subjects were studied. Nitroglycerin increased global CBF while flow velocities decreased. Sumatriptan did not have a significant effect on these values. Regions of increased flow included the anterior cingulate, while regions of decreased flow included the occipital cortex. Our data suggest that nitroglycerin induces regional changes in CBF that are similar to changes reported in spontaneous migraine, but produces distinctly different effects on global CBF and velocity.

Pathophysiology of cluster headache: a trigeminal autonomic cephalgia

Cluster headache is a form of primary neurovascular headache with the following features: severe unilateral, commonly retro-orbital, pain accompanied by restlessness or agitation, and cranial (parasympathetic) autonomic symptoms, such as lacrimation or conjunctival injection. It occurs in attacks typically of less than 3 h in length and in bouts (clusters) of a few months during which the patient has one or two attacks per day. The individual attack involves activation of the trigeminal-autonomic reflex; thus, such headaches can be broadly classified with the other trigeminal-autonomic cephalgias, such as paroxysmal hemicrania and the syndrome of short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing. Observations of circadian biological changes and neuroendocrine disturbances have suggested a pivotal role for the hypothalamus in cluster headache. Functional neuroimaging with PET and anatomical imaging with voxel-based morphometry have identified the posterior hypothalamic grey matter as the key area for the basic defect in cluster headache.

Persistence of attacks of cluster headache after trigeminal nerve root section

Cluster headache is a strictly unilateral headache that occurs in association with cranial autonomic features. We report a patient with a trigeminal nerve section who continued to have attacks. A 59-year-old man described a 14-year history of left-sided episodes of excruciating pain centred on the retro-orbital and orbital regions. These episodes lasted 1-4 h, recurring 2-3 times daily. The attacks were associated with ipsilateral ptosis, conjunctival injection, lacrimation, rhinorrhoea and facial flushing. From 1986 to 1988, he had trials of medications without any benefit. In February 1988, he had complete surgical section of the left trigeminal sensory root that shortened the attacks in length for 1 month without change in their frequency or character. In April 1988, he had further surgical exploration and the root was found to be completely excised; post-operatively, there was no change in the symptoms. From 1988 to 1999, he had a number of medications, including verapamil and indomethacin, all of which were ineffective. Prednisolone 30 mg orally daily rendered the patient completely pain free. Sumatriptan 100 mg orally and 6 mg subcutaneously aborted the attack after approximately 45 and 15 min, respectively. He was completely anaesthetic over the entire left trigeminal distribution. Left corneal reflex was absent. Motor function of the left trigeminal nerve was preserved. Neurological and physical examination was otherwise normal. MRI scan showed a marked reduction in the calibre of the left trigeminal nerve from the nerve root exit zone in the pons to Meckel's cave. An ECG-gated three-dimensional multislab MRI inflow angiogram was performed. No dilatation was observed in the left internal carotid artery during the cluster attack. Blink reflexes were elicited with a standard electrode and stimulus. Stimulation of the left supraorbital nerve produced neither ipsilateral nor contralateral blink reflex response. Stimulation of the right supraorbital nerve produced an ipsilateral response with a mean R2 onset latency of 36 ms and a contralateral response with a mean R2 onset latency of 32 ms. Lack of ipsilateral vessel dilatation makes the role of vascular factors in the initiation of cluster attacks questionable. With complete section of the left trigeminal sensory root the brain would perceive neither vasodilatation nor a peripheral neural inflammatory process; however, the patient continued to have an excellent response to sumatriptan. The case illustrates that cluster headache may be generated primarily from within the brain, and that triptans may have anti-headache effects through an entirely central mechanism.

Magnetic resonance angiography in facial and other pain: neurovascular mechanisms of trigeminal sensation

For much of the twentieth century migraine and cluster headache have been considered as vascular headaches whose pathophysiology was determined by changes in cranial vascular diameter. To examine nociceptive neural influences on the cranial circulation, the authors studied healthy volunteers' responses to injection of the pain-producing compound capsaicin in terms of the caliber of the internal carotid artery. The study was conducted using magnetic resonance angiographic techniques. Injection of capsaicin into the skin innervated by the ophthalmic (first) division of the trigeminal nerve elicited 40% +/- 27% (mean +/- SD) increase in vascular cross-sectional area in the right (ipsilateral) internal carotid artery when compared with the mean baseline ( P < 0.001). Injection of capsaicin into the skin of the chin to stimulate the mandibular (third) division of the trigeminal nerve and into the leg led to a similar pain perception and failed to produce any significant change in vessel caliber. The data suggest that there is a highly functionally organized, somatotopically congruent trigeminal innervation of the cranial vessels, with a potent vasodilator effect of the ophthalmic division on the large intracranial vessels. The data are consistent with the notion that pain drives changes in vessel caliber in migraine and cluster headache, not vice versa. These conditions therefore should be regarded as primary neurovascular headaches not as vascular headaches.

Neuroimaging in headache

Neuroimaging of primary headache syndromes, such as cluster headache and migraine, has begun to provide a glimpse of the neuroanatomical and physiological basis of the conditions. Although these headache types have been widely described as vascular, there is now considerable imaging and clinical evidence to suggest that they are primarily driven from the brain. The shared anatomical and physiological substrate for both of these clinical problems is the neural innervation of the cranial circulation. Functional imaging with positron emission tomography (PET) has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine, and in the hypothalamic grey in cluster headache. These areas are involved not simply as a response to first division nociceptive pain impulses but specifically in each syndrome, probably in some permissive or dysfunctional role. In a recent PET study in cluster headache, as well as brain activation, tracer pooled in the region of the major basal arteries. This is likely to be due to vasodilatation of these vessels during the acute pain-attack and represents the first convincing activation of neural vasodilator mechanisms in humans. The author takes the view that the known physiology and pathophysiology of the systems involved dictate that these disorders should be collectively regarded as neurovascular headaches to place emphasis on the interaction between nerves and vessels, which is the underlying characteristic of these syndromes. Understanding this neurovascular relationship facilitates an understanding of the pain mechanisms, while characterising the CNS dysfunction will ultimately allow us to dissect out the basic pathogenesis of these disorders.

Hypothalamic involvement and activation in cluster headache

Cluster headache is an episodic form of primary neurovascular headache that is both severe and relatively rare. It is characterized by episodes of headache with cranial parasympathetic activation and sympathetic impairment that come in bouts, or clusters. Its pathophysiology can be divided into understanding the attack phenotype and the biotype of the periodicity. Acute attacks of cluster headache are marked by trigeminal nerve-mediated pain and with cranial autonomic activation, trigeminal-autonomic cephalalgia; an activation that characterizes the phenotype of a group of headaches. The signature feature of cluster headache is its periodicity, the daily cycle of attacks when the patient is in an active bout, or the circumannual, or other period, cycling that distinguishes the on period from the off period. Functional brain imaging with positron emission tomography and structural imaging with voxel-based morphometry have identified an area in the posterior hypothalamic gray as key in understanding cluster headache. This area is subtly enlarged in its gray matter volume, active during an acute cluster headache but inactive when patients are challenged between bouts. Cluster headache is likely to be a form of primary neurovascular pain whose phenotypic expression relies on the trigeminal-autonomic reflex, with a biotype determined by the brain area, the posterior hypothalamus, in which the lesion seems to be located. Understanding both the phenotypic expression and the biotype will, respectively, enable better acute attack treatments and better preventative management of this horrible form of headache.