A Neurotrophic Mechanism Directs Sensory Nerve Transit in Cranial Bone.

The flat bones of the skull are densely innervated during development, but little is known regarding their role during repair. We describe a neurotrophic mechanism that directs sensory nerve transit in the mouse calvaria. Patent cranial suture mesenchyme represents an NGF (nerve growth factor)-rich domain, in which sensory nerves transit. Experimental calvarial injury upregulates Ngf in an IL-1ß/TNF-α-rich defect niche, with consequent axonal ingrowth. In calvarial osteoblasts, IL-1ß and TNF-α stimulate Ngf and downstream NF-κB signaling. Locoregional deletion of Ngf delays defect site re-innervation and blunted repair. Genetic disruption of Ngf among LysM-expressing macrophages phenocopies these observations, whereas conditional knockout of Ngf among Pdgfra-expressing cells does not. Finally, inhibition of TrkA catalytic activity similarly delays re-innervation and repair. These results demonstrate an essential role of NGF-TrkA signaling in bone healing and implicate macrophage-derived NGF-induced ingrowth of skeletal sensory nerves as an important mediator of this repair.

Roles of Collagen XXV and Its Putative Receptors PTPσ/δ in Intramuscular Motor Innervation and Congenital Cranial Dysinnervation Disorder.

Intramuscular motor innervation is an essential process in neuromuscular development. Recently, mutations in COL25A1, encoding CLAC-P/collagen XXV, have been linked to the development of a congenital cranial dysinnervation disorder (CCDD). Yet the molecular mechanisms of intramuscular innervation and the etiology of CCDD related to COL25A1 have remained elusive. Here, we report that muscle-derived collagen XXV is indispensable for intramuscular innervation. In developing skeletal muscles, Col25a1 expression is tightly regulated by muscle excitation. In vitro and cell-based assays reveal a direct interaction between collagen XXV and receptor protein tyrosine phosphatases (PTPs) σ and δ. Motor explant assays show that expression of collagen XXV in target cells attracts motor axons, but this is inhibited by exogenous PTPσ/δ. CCDD mutations attenuate motor axon attraction by reducing collagen XXV-PTPσ/δ interaction. Overall, our study identifies PTPσ/δ as putative receptors for collagen XXV, implicating collagen XXV and PTPσ/δ in intramuscular innervation and a developmental ocular motor disorder.

Neurolocalization of taste disorders.

Neurolocalization of taste disorders requires a knowledge of the functional anatomy involved in mediating taste information from the peripheral mucosal surfaces through numerous peripheral cranial nerves to complex subcortical and cortical brain regions. Our understanding of this functional anatomy has advanced in recent years. Taste is an experience that is both innate and learned, and the "taste" experience involves the integration of information from other sensory modalities, such as olfaction and somatosensation. Normal taste perception is influenced by different neurophysiologic states, which involve endocrine function, emotions, and even attitudes and expectations toward eating. At its core, the normal effective ability to taste is a reflection of the proper function of many organ systems within the body and may be considered a marker for good health. Clinical taste disorders, on the other hand, involve the dysfunction of the normal neural taste pathways and/or aberrant influences on multisensory integration and cortical taste processing. The number of disease processes, which can adversely affect taste, are numerous and quite varied in their presentation. There may be contributory involvement of other organ systems within the body, and the appropriate management of taste disorders often requires a multidisciplinary approach to fully understand the disorder. Depending on the underlying cause, taste disorders can be effectively managed when identified. Treatments may include correcting underlying metabolic disturbances, eliminating infections, changing offending medications, replenishing nutritional deficiencies, operating on structural impairments, calming autoimmune processes, and even stabilizing electrochemical interactions.

Description of a regional anaesthesia technique for the dorsal cranium in the dog: a cadaveric study.

OBJECTIVE: To identify landmarks and to describe a technique for nerve blockade of the dorsal cranium in dogs. STUDY DESIGN: Anatomic cadaveric study. ANIMALS: A total of 39 dog cadavers, weighing 18.0 ± 9.7 kg (mean ± standard deviation). METHODS: The study was performed in three parts. In the initial part, cadavers were dissected to determine the location of the frontal, zygomaticotemporal, and major occipital nerves, and to identify prominent landmarks for their blockade. In the second part, one technique was developed to block each of the frontal and zygomaticotemporal nerves, and two techniques, rostral and caudal, were developed to block the major occipital nerve. Injection solution was 0.05% methylene blue in 0.5% bupivacaine. In the third part, cadavers were used to test the techniques developed in the second part with 0.04 mL kg-1 of the same injectate administered at each site (maximal volume 0.5 mL per site). The length of nerve stained was measured, with a length ≥6 mm considered successful. Confidence intervals were calculated using Fisher's exact test. RESULTS: Success rates (95% confidence interval) for the frontal, zygomaticotemporal, and rostral and caudal locations for the major occipital nerve were 94% (80-99%), 91% (76-98%), 74% (58-86%) and 77% (59-89%), respectively. With a combination of both locations, the success rate for the major occipital nerve was 100% (90-100%). CONCLUSION AND CLINICAL RELEVANCE: This study describes a simple regional anaesthesia technique using palpable anatomical landmarks that may provide analgesia for dogs undergoing craniotomy.

The greater occipital nerve and its spinal and brainstem afferent projections: A stereological and tract-tracing study in the rat.

The neuromodulation of the greater occipital nerve (GON) has proved effective to treat chronic refractory neurovascular headaches, in particular migraine and cluster headache. Moreover, animal studies have shown convergence of cervical and trigeminal afferents on the same territories of the upper cervical and lower medullary dorsal horn (DH), the so-called trigeminocervical complex (TCC), and recent studies in rat models of migraine and craniofacial neuropathy have shown that GON block or stimulation alter nociceptive processing in TCC. The present study examines in detail the anatomy of GON and its central projections in the rat applying different tracers to the nerve and quantifying its ultrastructure, the ganglion neurons subserving GON, and their innervation territories in the spinal cord and brainstem. With considerable intersubject variability in size, GON contains on average 900 myelinated and 3,300 unmyelinated axons, more than 90% of which emerge from C2 ganglion neurons. Unmyelinated afferents from GON innervates exclusively laminae I-II of the lateral DH, mostly extending along segments C2-3 . Myelinated fibers distribute mainly in laminae I and III-V of the lateral DH between C1 and C6 and, with different terminal patterns, in medial parts of the DH at upper cervical segments, and ventrolateral rostral cuneate, paratrigeminal, and marginal part of the spinal caudal and interpolar nuclei. Sparse projections also appear in other locations nearby. These findings will help to better understand the bases of sensory convergence on spinomedullary systems, a critical pathophysiological factor for pain referral and spread in severe painful craniofacial disorders.

Annexin A6 controls neuronal membrane dynamics throughout chick cranial sensory gangliogenesis.

Cranial sensory ganglia are components of the peripheral nervous system that possess a significant somatosensory role and include neurons within the trigeminal and epibranchial nerve bundles. Although it is well established that these ganglia arise from interactions between neural crest and neurogenic placode cells, the molecular basis of ganglia assembly is still poorly understood. Members of the Annexin protein superfamily play key roles in sensory nervous system development throughout metazoans. Annexin A6 is expressed in chick trigeminal and epibranchial placode cell-derived neuroblasts and neurons, but its function in cranial ganglia formation has not been elucidated. To this end, we interrogated the role of Annexin A6 using gene perturbation studies in the chick embryo. Our data reveal that placode cell-derived neuroblasts with reduced Annexin A6 levels ingress and migrate normally to the ganglionic anlage, where neural crest cell corridors correctly form around them. Strikingly, while Annexin A6-depleted placode cell-derived neurons still express mature neuronal markers, they fail to form two long processes, which are considered morphological features of mature neurons, and no longer innervate their designated targets due to the absence of this bipolar morphology. Moreover, overexpression of Annexin A6 causes some placode cell-derived neurons to form extra protrusions alongside these bipolar processes. These data demonstrate that the molecular program associated with neuronal maturation is distinct from that orchestrating changes in neuronal morphology, and, importantly, reveal Annexin A6 to be a key membrane scaffolding protein during sensory neuron membrane biogenesis. Collectively, our results provide novel insight into mechanisms underscoring morphological changes within placode cell-derived neurons that are essential for cranial gangliogenesis.

SCN2B in the Rat Trigeminal Ganglion and Trigeminal Sensory Nuclei.

The beta-2 subunit of the mammalian brain voltage-gated sodium channel (SCN2B) was examined in the rat trigeminal ganglion (TG) and trigeminal sensory nuclei. In the TG, 42.6 % of sensory neurons were immunoreactive (IR) for SCN2B. These neurons had various cell body sizes. In facial skins and oral mucosae, corpuscular nerve endings contained SCN2B-immunoreactivity. SCN2B-IR nerve fibers formed nerve plexuses beneath taste buds in the tongue and incisive papilla. However, SCN2B-IR free nerve endings were rare in cutaneous and mucosal epithelia. Tooth pulps, muscle spindles and major salivary glands were also innervated by SCN2B-IR nerve fibers. A double immunofluorescence method revealed that about 40 % of SCN2B-IR neurons exhibited calcitonin gene-related peptide (CGRP)-immunoreactivity. However, distributions of SCN2B- and CGRP-IR nerve fibers were mostly different in facial, oral and cranial structures. By retrograde tracing method, 60.4 and 85.3 % of TG neurons innervating the facial skin and tooth pulp, respectively, showed SCN2B-immunoreactivity. CGRP-immunoreactivity was co-localized by about 40 % of SCN2B-IR cutaneous and tooth pulp TG neurons. In trigeminal sensory nuclei of the brainstem, SCN2B-IR neuronal cell bodies were common in deep laminae of the subnucleus caudalis, and the subnuclei interpolaris and oralis. In the mesencephalic trigeminal tract nucleus, primary sensory neurons also exhibited SCN2B-immunoreactivity. In other regions of trigeminal sensory nuclei, SCN2B-IR cells were very infrequent. SCN2B-IR neuropil was detected in deep laminae of the subnucleus caudalis as well as in the subnuclei interpolaris, oralis and principalis. These findings suggest that SCN2B is expressed by various types of sensory neurons in the TG. There appears to be SCN2B-containing pathway in the TG and trigeminal sensory nuclei.

Expression of serotonin receptor genes in cranial ganglia.

Taste cells release neurotransmitters to gustatory neurons to transmit chemical information they received. Sweet, umami, and bitter taste cells use ATP as a neurotransmitter. However, ATP release from sour taste cells has not been observed so far. Instead, they release serotonin when they are activated by sour/acid stimuli. Thus it is still controversial whether sour taste cells use ATP, serotonin, or both. By reverse transcription-polymerase chain reaction and subsequent in situ hybridization (ISH) analyses, we revealed that of 14 serotonin receptor genes only 5-HT3A and 5-HT3B showed significant/clear signals in a subset of neurons of cranial sensory ganglia in which gustatory neurons reside. Double-fluorescent labeling analyses of ISH for serotonin receptor genes with wheat germ agglutinin (WGA) in cranial sensory ganglia of pkd1l3-WGA mice whose sour neural pathway is visualized by the distribution of WGA originating from sour taste cells in the posterior region of the tongue revealed that WGA-positive cranial sensory neurons rarely express either of serotonin receptor gene. These results suggest that serotonin receptors expressed in cranial sensory neurons do not play any role as neurotransmitter receptor from sour taste cells.

Meis2 is essential for cranial and cardiac neural crest development.

BACKGROUND: TALE-class homeodomain transcription factors Meis and Pbx play important roles in formation of the embryonic brain, eye, heart, cartilage or hematopoiesis. Loss-of-function studies of Pbx1, 2 and 3 and Meis1 documented specific functions in embryogenesis, however, functional studies of Meis2 in mouse are still missing. We have generated a conditional allele of Meis2 in mice and shown that systemic inactivation of the Meis2 gene results in lethality by the embryonic day 14 that is accompanied with hemorrhaging. RESULTS: We show that neural crest cells express Meis2 and Meis2-defficient embryos display defects in tissues that are derived from the neural crest, such as an abnormal heart outflow tract with the persistent truncus arteriosus and abnormal cranial nerves. The importance of Meis2 for neural crest cells is further confirmed by means of conditional inactivation of Meis2 using crest-specific AP2α-IRES-Cre mouse. Conditional mutants display perturbed development of the craniofacial skeleton with severe anomalies in cranial bones and cartilages, heart and cranial nerve abnormalities. CONCLUSIONS: Meis2-null mice are embryonic lethal. Our results reveal a critical role of Meis2 during cranial and cardiac neural crest cells development in mouse.

Temperature differentially facilitates spontaneous but not evoked glutamate release from cranial visceral primary afferents.

Temperature is fundamentally important to all biological functions including synaptic glutamate release. Vagal afferents from the solitary tract (ST) synapse on second order neurons in the nucleus of the solitary tract, and glutamate release at this first central synapse controls autonomic reflex function. Expression of the temperature-sensitive Transient Receptor Potential Vanilloid Type 1 receptor separates ST afferents into C-fibers (TRPV1+) and A-fibers (TRPV1-). Action potential-evoked glutamate release is similar between C- and A-fiber afferents, but TRPV1 expression facilitates a second form of synaptic glutamate release in C-fibers by promoting substantially more spontaneous glutamate release. The influence of temperature on different forms of glutamate release is not well understood. Here we tested how temperature impacts the generation of evoked and spontaneous release of glutamate and its relation to TRPV1 expression. In horizontal brainstem slices of rats, activation of ST primary afferents generated synchronous evoked glutamate release (ST-eEPSCs) at constant latency whose amplitude reflects the probability of evoked glutamate release. The frequency of spontaneous EPSCs in these same neurons measured the probability of spontaneous glutamate release. We measured both forms of glutamate from each neuron during ramp changes in bath temperature of 4-5 °C. Spontaneous glutamate release from TRPV1+ closely tracked with these thermal changes indicating changes in the probability of spontaneous glutamate release. In the same neurons, temperature changed axon conduction registered as latency shifts but ST-eEPSC amplitudes were constant and independent of TRPV1 expression. These data indicate that TRPV1-operated glutamate release is independent of action potential-evoked glutamate release in the same neurons. Together, these support the hypothesis that evoked and spontaneous glutamate release originate from two pools of vesicles that are independently modulated and are distinct processes.

The lesser occipital nerve visualized by high-resolution sonography--normal and initial suspect findings.

BACKGROUND: The lesser occipital nerve (LON) supplies the lateral part of the occiput and is-together with the greater occipital nerve (GON)-involved in headache pathogenesis. While the GON was described in high-resolution ultrasound (HRUS), the same does not apply to the LON. We aimed at characterizing the LON in HRUS, and present cases of suspect findings in the course of the LON identified by HRUS. METHODS: The LON was examined bilaterally in eight anatomical specimens with HRUS (n = 16). HRUS-guided ink marking and consecutive dissection was performed. Further, measurements of the LON diameter were performed in 10 healthy volunteers (n = 20), and patient charts were reviewed to identify patients who were considered to have possible pathology of the LON. RESULTS: The LON was identified correctly in all cadavers on both sides and all volunteers except for one side (n = 19). The average diameter was 1.08 ± 0.30 mm. Four patients with pain within the LON territory and presumed peripheral origin of headache (defined as resolution of headache after diagnostic HRUS-guided selective blockade) were identified, and three of these showed interference of the LON with lymph nodes or an accessory muscle belly. DISCUSSION: We confirm the possibility of visualization of the LON using HRUS. HRUS may be a helpful adjunct tool in the assessment of patients with atypical headache.

Identification of the posterior deep temporal nerve groove and canal, and its relationship to basicranial angle.

The posterior deep temporal nerve (PDTN) groove accommodates the posterior deep temporal nerve and is infrequently described. This area is important for some clinical procedures including mandibular nerve blockade. This study assesses the prevalence and morphological variations of the PDTN groove in a single population, investigating its relationship with basicranial angle to assess predictive value for the existence of this feature. The infratemporal regions of 101 contemporary Sinhalese Sri Lankan skulls were examined bilaterally and ordinally scored for PDTN groove morphology (six point scale); 11 random skulls were radiographed and basicranial angles measured. Descriptive statistics and significance testing (P < 0.05) were used for analysis, including symmetry (Wilcoxon matched-pairs signed rank test), sex differences (Mann and Whitney U test), and between basicranial angle and PDTN morphology (Pearson's product-moment correlation coefficient). Ninety skulls (44 males) were included for analysis (180 sides). PDTN groove morphology on individual sides ranged from non-existent (20.6%) to partial (5.6%) and complete canals (1.1%); 93.3% of skulls had a PDTN groove or canal. Skulls exhibited bilateral symmetry (P = 0.12) and males had significantly deeper PDTN grooves or canals (P = 0.018). Basicranial flexion correlated strongly with PDTN groove or canal prevalence (P = 0.0028). Sri Lankan skulls have a high prevalence of PDTN grooves and also canals, a feature not previously described. Prevalence was related significantly to sex but not symmetry, and PDTN grooves and canals correlated significantly with basicranial angle. Knowledge of this morphology is important for some clinical procedures, anthropological assessment, and as a location for PDTN entrapment.

Occipital nerve block prior to occipital nerve stimulation for refractory chronic migraine and chronic cluster headache: myth or prediction?

BACKGROUND: Occipital nerve stimulation (ONS) results in beneficial outcomes, with marked pain relief, in otherwise intractable chronic migraine (CM) and chronic cluster headache (CCH). Some studies have reported that a positive response to occipital nerve block (ONB) administered prior to ONS predicts a positive response to ONS. However, other studies concerned with proper patient selection claimed no predictive value for ONB. The aim of this study was to re-evaluate the usefulness and predictive value of ONB prior to ONS. METHODS: Literature searches on the predictive value of ONB were performed in MEDLINE and PubMed. Patient data were extracted and a pooled analysis was performed. RESULTS: The literature review revealed 133 patients with CM and seven patients with CCH who received preoperative ONB. To date, a randomized controlled study examining the relationship between ONB and ONS has not been conducted in patients with CM. CONCLUSIONS: Current literature suggests that ONB does not sufficiently predict ONS responsiveness in patients with refractory CM and CCH; this important issue requires further investigation.

Safety and efficacy of peripheral nerve stimulation of the occipital nerves for the management of chronic migraine: long-term results from a randomized, multicenter, double-blinded, controlled study.

BACKGROUND: Recent studies evaluated short-term efficacy and safety of peripheral nerve stimulation (PNS) of the occipital nerves for managing chronic migraine. We present 52-week safety and efficacy results from an open-label extension of a randomized, sham-controlled trial. METHODS: In this institutional review board-approved, randomized, multicenter, double-blinded study, patients were implanted with a neurostimulation system, randomized to an active or control group for 12 weeks, and received open-label treatment for an additional 40 weeks. Outcomes collected included number of headache days, pain intensity, migraine disability assessment (MIDAS), Zung Pain and Distress (PAD), direct patient reports of headache pain relief, quality of life, satisfaction and adverse events. Statistical tests assessed change from baseline to 52 weeks using paired t-tests. Intent-to-treat (ITT) analyses of all patients (N = 157) and analyses of only patients who met criteria for intractable chronic migraine (ICM; N = 125) were performed. RESULTS: Headache days were significantly reduced by 6.7 (±8.4) days in the ITT population (p < 0.001) and by 7.7 (±8.7) days in the ICM population (p < 0.001). The percentages of patients who achieved a 30% and 50% reduction in headache days and/or pain intensity were 59.5% and 47.8%, respectively. MIDAS and Zung PAD scores were significantly reduced for both populations. Excellent or good headache relief was reported by 65.4% of the ITT population and 67.9% of the ICM population. More than half the patients in both cohorts were satisfied with the headache relief provided by the device. A total of 183 device/procedure-related adverse events occurred during the study, of which 18 (8.6%) required hospitalization and 85 (40.7%) required surgical intervention; 70% of patients experienced an adverse event. CONCLUSION: Our results support the 12-month efficacy of PNS of the occipital nerves for headache pain and disability associated with chronic migraine. More emphasis on adverse event mitigation is needed in future research. TRIAL REGISTRATION: Clinical trials.gov (NCT00615342).

The sensory innervation of the calvarial periosteum is nociceptive and contributes to headache-like behavior.

Headaches are thought to result from the activation and sensitization of nociceptors that innervate deep cephalic tissues. A large body of evidence supports the view that some types of headaches originate intracranially, from activation of sensory neurons that innervate the cranial meninges. However, the notion of an extracranial origin of headaches continues to be entertained, although the identity of deep extracranial cephalic tissues that might contribute to headaches remains elusive. Here we employed anatomical, electrophysiological, and behavioral approaches in rats to test the hypothesis that the sensory innervation of the calvarial periosteum is nociceptive. Neural tracing indicated that the calvarial periosteum overlying the frontal and parietal bones is innervated primarily by small and medium-sized neurons in the trigeminal ganglion's ophthalmic division. In vivo single-unit recording in the trigeminal ganglion revealed that calvarial periosteal afferents have slowly conducting axons, are mechanosensitive, and respond to inflammatory mediators, consistent with a nociceptive function. Two distinct neuronal populations were distinguished based on their peripheral axonal trajectory: one that reached the periosteum through extracranial branches of the trigeminal nerve, and another that took an intracranial trajectory, innervating the cranial dura and apparently reaching the periosteum via the calvarial sutures. In behavioral studies, inflammatory stimulation of these afferents promoted periorbital tactile hypersensitivity, a sensory change linked to primary headaches. Activation and sensitization of calvarial periosteal afferents could play a role in mediating primary headaches of extracranial and perhaps also intracranial origin, as well as secondary headaches such as postcraniotomy and posttraumatic headaches. Targeting calvarial periosteal afferents may be effective in ameliorating these headaches.

Occipital nerve stimulation in medically intractable, chronic cluster headache. The ICON study: rationale and protocol of a randomised trial.

BACKGROUND: About 10% of cluster headache patients have the chronic form. At least 10% of this chronic group is intractable to or cannot tolerate medical treatment. Open pilot studies suggest that occipital nerve stimulation (ONS) might offer effective prevention in these patients. Controlled neuromodulation studies in treatments inducing paraesthesias have a general problem in blinding. We have introduced a new design in pain neuromodulation by which we think we can overcome this problem. METHODS/DESIGN: We propose a prospective, randomised, double-blind, parallel-group international clinical study in medically intractable, chronic cluster headache patients of high- versus low-amplitude ONS. Primary outcome measure is the mean number of attacks over the last four weeks. After a study period of six months there is an open extension phase of six months. Alongside the randomised trial an economic evaluation study is performed. DISCUSSION: The ICON study will show if ONS is an effective preventive therapy for patients suffering medically intractable chronic cluster headache and if there is a difference between high- and low-amplitude stimulation. The innovative design of the study will, for the first time, assess efficacy of ONS in a blinded way.

Ric-8A, a guanine nucleotide exchange factor for heterotrimeric G proteins, is critical for cranial neural crest cell migration.

The neural crest (NC) is a transient embryonic structure induced at the border of the neural plate. NC cells extensively migrate towards diverse regions of the embryo, where they differentiate into various derivatives, including most of the craniofacial skeleton and the peripheral nervous system. The Ric-8A protein acts as a guanine nucleotide exchange factor for several Gα subunits, and thus behaves as an activator of signaling pathways mediated by heterotrimeric G proteins. Using in vivo transplantation assays, we demonstrate that Ric-8A levels are critical for the migration of cranial NC cells and their subsequent differentiation into craniofacial cartilage during Xenopus development. NC cells explanted from Ric-8A morphant embryos are unable to migrate directionally towards a source of the Sdf1 peptide, a potent chemoattractant for NC cells. Consistently, Ric-8A knock-down showed anomalous radial migratory behavior, displaying a strong reduction in cell spreading and focal adhesion formation. We further show that during in vivo and in vitro neural crest migration, Ric-8A localizes to the cell membrane, in agreement with its role as a G protein activator. We propose that Ric-8A plays essential roles during the migration of cranial NC cells, possibly by regulating cell adhesion and spreading.

Emissary foramens of the human skull: anatomical characteristics and its relations with clinical neurosurgery / Forámenes emisarios del cráneo humano: características anatómicas y sus relaciones con la neurocirugía clínica

The recognition of emissary foramens is important not only for understanding the regional neurovascular anatomy, but also to distinguish normal from potentially abnormal structures. Thus, the aim of this study was to review the literature on anatomical and clinical aspects of the mastoid, parietal and sphenoid emissary foramens. It was found that the emissary foramen presents importance in clinical practice because it acts as a route of spread of extracranial infection to the intracranial structures and also possible complications in neurosurgery, due to its influence in the performance of techniques such as radiofrequency rhizotomy for treatment of trigeminal neuralgia. The anatomical knowledge of the emissary foramens is important due to variability in their incidence in the human skull and its relation to the dura mater sinuses.

El reconocimiento de forámenes emisarios es importante no sólo para la comprensión de la anatomía neurovascular regional, sino también para distinguir lo normal a partir de estructuras potencialmente anormales. El objetivo de este estudio fue revisar la literatura sobre los aspectos anatómicos y clínicos del proceso mastoide, huesos parietal y esfenoides y forámenes emisarios. El foramen emisario adquiere importancia en la práctica clínica debido a que actúa como una vía de propagación de la infección extracraneal a las estructuras intracraneales, y también con las posibles complicaciones en neurocirugía, debido a su influencia en el desarrollo de técnicas como rizotomía por radiofrecuencia en el tratamiento de neuralgia del trigémino. El conocimiento anatómico de los forámenes emisarios es importante debido a la variabilidad en su incidencia en el cráneo humano y su relación con los senos de la duramadre.