Anterior Ethmoidal Nerve Research Articles

The forgotten foramina: a study of the anterior cribriform plate.

The olfactory cleft has garnered interest since the advent of endoscopic skull base surgery. Its precise anatomy, however, is still partially unknown. According to Rouvière, an "ethmoidal foramen" is located in its antero-medial part and contains a process of the dura mater. In a more lateral and anterior location, a second foramen, the "cribroethmoidal foramen", contains the anterior ethmoidal nerve. The aim of this study was to verify the existence of these elements and to establish landmarks for surgery. We performed an anatomical and histological study of eight olfactory clefts in four cadavers using both endonasal endoscopic and endocranial dissection. An ethmoidal and a cribroethmoidal foramen were found in, respectively, 100 and 75% of cases. Their mean length was, respectively, 4.1 and 1.8 mm. They were located, respectively, in mean at 5.3 and 5.8 mm from the anterior ethmoidal artery. Our anatomical study demonstrates the existence of both foramina. The ethmoidal foramen clearly represents an area of least resistance in the anterior part of the olfactory cleft, which could predispose to anterior skull base cerebrospinal fluid leaks and meningoceles.

Anatomy of anterior ethmoidal foramen, medial canthal tendon, and lacrimal fossa for transcutaneous anterior ethmoidal nerve block in Japanese individuals.

To examine the anatomical relationships of the anterior ethmoidal foramen (AEF), medial canthal tendon (MCT), and lacrimal fossa (LF) in Japanese individuals. Thirty-eight orbits from 19 Japanese cadavers (7 men and 12 women; average age at death, 89.3 years) were used in this experimental anatomical study. The AEF, MCT, and superior border of the LF were exposed. The following distances were then measured: 1) from the point at the medial orbital rim directly anterior to the AEF to the superior border of the MCT (AEF-MCT), and 2) from the superior border of the LF to the superior border of the MCT (LF-MCT). (AEF-MCT) and (LF-MCT) distances were 9.40±1.92 (mean±standard deviation) and 4.21±1.18 mm, respectively. No values of (LF-MCT) exceeded the mean (AEF-MCT) (9.40 mm). The transcutaneous anterior ethmoidal nerve block can be reliably performed without injury to the lacrimal sac by inserting a needle approximately 9 mm superior to the superior border of the MCT.

Direct reticular projections of trigeminal sensory fibers immunoreactive to CGRP: potential monosynaptic somatoautonomic projections.

Few trigeminal sensory fibers project centrally beyond the trigeminal sensory complex, with only projections of fibers carried in its sensory anterior ethmoidal (AEN) and intraoral nerves described. Fibers of the AEN project into the brainstem reticular formation where immunoreactivity against substance P and CGRP are found. We investigated whether the source of these peptides could be from trigeminal ganglion neurons by performing unilateral rhizotomies of the trigeminal root and looking for absence of label. After an 8–14 days survival, substance P immunoreactivity in the trigeminal sensory complex was diminished, but we could not conclude that the sole source of this peptide in the lateral parabrachial area and lateral reticular formation arises from primary afferent fibers. Immunoreactivity to CGRP after rhizotomy however was greatly diminished in the trigeminal sensory complex, confirming the observations of others. Moreover, CGRP immunoreactivity was nearly eliminated in fibers in the lateral parabrachial area, the caudal ventrolateral medulla, both the peri-ambiguus and ventral parts of the rostral ventrolateral medulla, in the external formation of the nucleus ambiguus, and diminished in the caudal pressor area. The nearly complete elimination of CGRP in the lateral reticular formation after rhizotomy suggests this peptide is carried in primary afferent fibers. Moreover, the arborization of CGRP immunoreactive fibers in these areas mimics that of direct projections from the AEN. Since electrical stimulation of the AEN induces cardiorespiratory adjustments including an apnea, peripheral vasoconstriction, and bradycardia similar to those seen in the mammalian diving response, we suggest these perturbations of autonomic behavior are enhanced by direct somatic primary afferent projections to these reticular neurons. We believe this to be first description of potential direct somatoautonomic projections to brainstem neurons regulating autonomic activity.

Neuronal plasticity within the medullary dorsal horn: the nasopharyngeal response returns 3 days after bilateral sectioning of the anterior ethmoidal nerve (1130.19)

Stimulation of the nasal passages with ammonia vapors can reflexly produce bradycardia, apnea, and increased peripheral resistance. However, after acute bilateral sectioning of the anterior ethmoidal nerve (AEN), the nerve that innervates the nasal passages, this nasopharyngeal response consists of only a slight apnea and an increase in arterial pressure. In the present experiments, in urethane‐anesthetized Sprague‐Dawley rats, we recorded the cardiorespiratory responses to ammonia vapor stimulation of the nasal passages 3, 5, 7 and 9 days after bilateral sectioning of the AEN, and compared these responses to those from rats with sham and acute (0 day) AEN sectioning. After nasal stimulation, heart rate (HR) decreased 62% in Sham rats but only 12% in Acute rats. After waiting 3 days following AEN sectioning, HR decreased 26%, and when waiting 9 days by 32%. The re‐establishment of the cardiorespiratory responses to nasal stimulation after bilateral AEN sectioning suggests that other nerves that innervate the nasal passages are able to provide an afferent signal sufficient to initiate the nasopharyngeal reflex. Additionally, because the bradycardia is strongly attenuated after acute AEN sectioning, our research suggests that neuronal plasticity within the medullary dorsal horn, the brainstem termination site of the AEN, may be necessary before the re‐establishment of the nasopharyngeal response can occur.Grant Funding Source: Supported by MWU Office of Research and Sponsored Programs.

Trigeminal Medullary Dorsal Horn Neurons Activated by Nasal Stimulation Coexpress AMPA, NMDA, and NK1 Receptors

Afferent information initiating the cardiorespiratory responses during nasal stimulation projects from the nasal passages to neurons within the trigeminal medullary dorsal horn (MDH) via the anterior ethmoidal nerve (AEN). Central AEN terminals are thought to release glutamate to activate the MDH neurons. This study was designed to determine which neurotransmitter receptors (AMPA, kainate, or NMDA glutamate receptor subtypes or the Substance P receptor NK1) are expressed by these activated MDH neurons. Fos was used as a neuronal marker of activated neurons, and immunohistochemistry combined with epifluorescent microscopy was used to determine which neurotransmitter receptor subunits were coexpressed by activated MDH neurons. Results indicate that, during nasal stimulation with ammonia vapors in urethane-anesthetized Sprague-Dawley rats, activated neurons within the superficial MDH coexpress the AMPA glutamate receptor subunits GluA1 (95.8%) and GluA2/3 (88.2%), the NMDA glutamate receptor subunits GluN1 (89.1%) and GluN2A (41.4%), and NK1 receptors (64.0%). It is therefore likely that during nasal stimulation the central terminals of the AEN release glutamate and substance P that then produces activation of these MDH neurons. The involvement of AMPA and NMDA receptors may mediate fast and slow neurotransmission, respectively, while NK1 receptor involvement may indicate activation of a nociceptive pathway.

Bilateral sectioning of the anterior ethmoidal nerves does not eliminate the diving response in voluntarily diving rats

The diving response is characterized by bradycardia, apnea, and increased peripheral resistance. This reflex response is initiated by immersing the nose in water. Because the anterior ethmoidal nerve (AEN) innervates the nose, our hypothesis was that intact AENs are essential for initiating the diving response in voluntarily diving rats. Heart rate (HR) and arterial blood pressure (BPa) were monitored using implanted biotransmitters. Sprague-Dawley rats were trained to voluntarily swim 5 m underwater. During diving, HR decreased from 480 ± 15 to 99 ± 5 bpm and BPa increased from 136 ± 2 to 187 ± 3 mmHg. Experimental rats (N = 9) then received bilateral AEN sectioning, while Sham rats (N = 8) did not. During diving in Experimental rats 7 days after AEN surgery, HR decreased from 478 ± 13 to 76 ± 4 bpm and BPa increased from 134 ± 3 to 186 ± 4 mmHg. Responses were similar in Sham rats. Then, during nasal stimulation with ammonia vapors in urethane-anesthetized Experimental rats, HR decreased from 368 ± 7 to 83 ± 4 bpm, and BPa increased from 126 ± 7 to 175 ± 4 mmHg. Responses were similar in Sham rats. Thus, 1 week after being sectioned the AENs are not essential for initiating a full cardiorespiratory response during both voluntary diving and nasal stimulation. We conclude that other nerve(s) innervating the nose are able to provide an afferent signal sufficient to initiate the diving response, although neuronal plasticity within the medullary dorsal horn may be necessary for this to occur.

Anterior fossa schwannoma mimicking an olfactory groove meningioma: Case report and literature review

Intracranial schwannomas not associated with cranial nerves account for less than 1% of surgically treated schwannomas of the central and peripheral nervous system. With only 45 cases reported to date, subfrontal schwannomas are very rare tumors, leaving the issue of their origin controversial. A 66-year-old woman presented with a 1-year history of progressive headaches. Clinical examination revealed hypoesthesia of the nasal tip. CT-scan and MRI studies revealed a large subfrontal tumor thought preoperatively to be a meningioma. Intraoperatively, a large extra-axial tumor arising from the floor of the right frontal fossa was encountered. Histopathology identified the tumor as a schwannoma. This current case gives strong clinical presumption of an origin from the anterior ethmoidal nerve. We reviewed the literature in order to establish the epidemiology of these tumors, from which there appear to be divergent profiles depending on tumor origin and histology. Despite close similarities with olfactory groove meningiomas, patient history and radiological findings provide substantial evidence for differential diagnosis.

Decreased postoperative pain after reduction of fractured nasal bones using a nerve block of the anterior ethmoidal nerve

There is consensus that all patients should experience minimal pain following reduction of a fractured nasal bone. The issue requiring further study is what technique will provide patients with the greatest pain relief following the reduction of nasal fractures. This study investigated the use of an anterior ethmoidal nerve block as preemptive analgesia for the management of postoperative pain associated with reduction of nasal bone fractures. The medical documents of 85 patients were reviewed for a retrospective case-controlled comparative study. Patients in the nerve block group (n=45) were injected with 2% lidocaine containing epinephrine into the anterior ethmoidal nerve and dorsal periosteum, and those in the control group (n=40) were not. The rate of patients requiring postoperative injectable analgesics was compared between the two groups. The rate of patients who received a postoperative analgesic injection was significantly lower in the nerve block group than in the control group (P=0.034). The use of an anterior ethmoidal nerve block and dorsal periosteal injection of anaesthetic solution during reduction of fractured nasal bones under general anaesthesia resulted in the effective reduction of postoperative pain. Thus, this is regarded as a good method for enhancing patient quality of care and compliance in the reduction of fractured nasal bones.

Pulsed radiofrequency treatment of the anterior ethmoidal nerve under nasal endoscopic guidance for the treatment of postherpetic neuralgia

Pulsed radiofrequency treatment of the anterior ethmoidal nerve under nasal endoscopic guidance for the treatment of postherpetic neuralgia

Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit.

The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate the submergence of rats brought past their aerobic dive limit, defined as the diving duration beyond which blood lactate concentration increases above resting levels. Hemodynamic measurements were made during underwater submergence with biotelemetric transmitters, and blood was drawn from cannulas previously implanted in the rats' carotid arteries. Such prolonged submersion induces radical changes in blood chemistry; mean arterial PCO(2) rose to 62.4 Torr, while mean arterial PO(2) and pH reached nadirs of 21.8 Torr and 7.18, respectively. Despite these radical changes in blood chemistry, the rats neither attempted to gasp nor breathe while underwater. Immunohistochemistry for Fos protein done on their brains revealed numerous Fos-positive profiles. Especially noteworthy were the large number of immunopositive profiles in loci where presumptive chemoreceptors are found. Despite the activation of these presumptive chemoreceptors, the rats did not attempt to breathe. Injections of biotinylated dextran amine were made into ventral parts of the medullary dorsal horn, where central fibers of the anterior ethmoidal nerve terminate. Labeled fibers coursed caudal, ventral, and medial from the injection to neurons on the ventral surface of the medulla, where numerous Fos-labeled profiles were seen in the rats brought past their aerobic dive limit. We propose that this projection inhibits the homeostatic chemoreceptor reflex, despite the gross activation of chemoreceptors.

The Puzzling Olfactory Groove Schwannoma: A Systematic Review

We systematically reviewed the literature concerning the anterior cranial fossa schwannomas to understand their pathogenesis, determine their origin, and standardize the terminology. We performed a MEDLINE, EMBASE, and Science Citation Index Expanded search of the literature; age, gender, clinical presentation, presence or absence of hyposmia, radiological features, and apparent origin were analyzed and tabulated. Cases in a context of neurofibromatosis and nasal schwannomas with intracranial extension were not included. Age varied between 14 and 63 years (mean = 30.9). There were 22 male and 11 female patients. The clinical presentation included seizures (n = 15), headache (n = 16), visual deficits (n = 7), cognitive disturbances (n = 3), and rhinorrhea (n = 1). Hyposmia was present in 14 cases, absent in 13 cases (39.3%), and unreported in five. Homogeneous and heterogeneous contrast enhancement was observed in 14 and 15 cases, respectively. The region of the olfactory groove was the probable site in 96.5%. Olfactory tract could be identified in 39.3%. The most probable origin is the meningeal branches of trigeminal nerve or anterior ethmoidal nerves. Thus, olfactory groove schwannoma would better describe its origin and pathogenesis and should be the term preferentially used to name it.

Anaesthesia for dacryocystorhinostomy

Excessive tearing due to obstruction of the nasolacrimal duct is a common ophthalmic problem. Dacryocystorhinostomy (DCR) is the procedure designed to treat primary or secondary adult anatomical obstruction. External DCR is the traditional surgical approach, however endoscopic DCR can be done. In the past, general anaesthesia (GA) has been considered as the gold standard for DCR surgery; endotracheal intubation and throat pack offer an important function as protective mechanisms of the patient’s airway against blood aspiration. Head up position, hypotensive anaesthesia, incision infiltration with lidocaine/epinephrine together with insertion of nasal pack soaked in decongestant solution are a routine measures to guard against intraoperative bleeding that may hinder surgical site visualization. Increase awareness of regional anaesthesia efficacy contemplated the surgeons towards the use of such techniques. The basic concept of local anaesthesia for DCR involves blockade of infratrochlear, infraorbital and anterior ethmoidal nerves either by separate injections or by local infiltration along with intranasal preparation. It has been found that DCR under regional anaesthesia minimizes intraoperative bleeding, inpatient stay and reduce health care expenditure. Further, many patients prefer regional anaesthesia due to less postoperative pain. These benefits are desirable particularly in elderly population in whom GA constitute a threat for their life.

Regional nerve blockade prior to direct injection to achieve anaesthesia of the nasal ala

Dermatological surgical procedures involving the nasal alae are commonplace in clinical practice. Direct infiltration of local anaesthetic into the nasal ala is extremely uncomfortable. In this prospective clinical study, we investigate the effectiveness of alar anaesthesia provided by an infraorbital nerve block (IOB). We recruited 100 consecutive patients requiring dermatological surgical procedures involving the nasal ala (or other sites necessitating an IOB). Following topical mucosal anaesthesia, an IOB was administered via the intraoral route. Effectiveness of anaesthesia was assessed after 10 min by testing the perception of a sharp stimulus at five standardized reference points on the nasal ala. If the ala was not completely anaesthetized, blockade of the external nasal branch of the anterior ethmoidal nerve (external nerve block, ENB) was performed. Sensation of the nasal ala was re-assessed after 10 min using the above method. Complete anaesthesia of the nasal ala was achieved with an IOB in 66 of 100 (66%) patients. Of the remaining 34 patients, the addition of an ENB achieved complete anaesthesia in 15 (44%). An IOB provides effective alar anaesthesia in the majority of patients. In those where it is ineffective for complete anaesthesia, an ENB is a useful adjunct. We recommend using an IOB (and ENB if required) prior to direct infiltration of local anaesthetic into the nasal ala to reduce patient discomfort.

Unmyelinated fibers of the anterior ethmoidal nerve in the rat co-localize with neurons in the medullary dorsal horn and ventrolateral medulla activated by nasal stimulation

The anterior ethmoidal nerve (AEN) innervates the nasal passages and external nares, and serves as the afferent limb of the nasopharyngeal and diving responses. However, although 65% of the AEN is composed of unmyelinated fibers, it has not been determined whether this afferent signal is carried by unmyelinated or myelinated fibers. We used the transganglionic tracers WGA-HRP, IB4-HRP, and CTB-HRP to trace the central projections of the AEN of the rat. Interpretation of the labeling patterns suggests that AEN unmyelinated fibers project primarily to the ventral tip of the ipsilateral medullary dorsal horn (MDH) at the level of the area postrema. Other unmyelinated projections were to the ventral paratrigeminal nucleus and ventrolateral medulla, specifically the Bötzinger and RVLM/C1 regions. Myelinated AEN fibers projected to the ventral paratrigeminal and mesencephalic trigeminal nuclei. Stimulating the nasal passages of urethane-anesthetized rats with ammonia vapors produced the nasopharyngeal response that included apnea, bradycardia and an increase in arterial blood pressure. Central projections of the AEN co-localized with neurons within both MDH and RVLM/C1 that were activated by nasal stimulation. Within the ventral MDH the density of AEN terminal projections positively correlated with the rostral–caudal location of activated neurons, especially at and just caudal to the obex. We conclude that unmyelinated AEN terminal projections are involved in the activation of neurons in the MDH and ventrolateral medulla that participate in the nasopharyngeal response in the rat. We also found that IB4-HRP was a much less robust tracer than WGA-HRP.

Post‐Traumatic External Nasal Pain Syndrome (a Trigeminal Based Pain Disorder)

Little has been written about persistent external nasal pain after injury to the nose in the neurologic or headache literature. In clinical practice, this can be a disabling and treatment refractory condition. The external portion of the nose is highly innervated by branches of the ophthalmic and maxillary divisions of the trigeminal nerve including the nasociliary nerve, external nasal nerve, infratrochlear nerve, anterior ethmoidal nerve, and infraorbital nerve. As these nerves are located on the external portion of the nose just deep enough to the skin they can be easily traumatized with any impact to the nose. Four patients with what is termed the post-traumatic external nasal pain syndrome are reported in this paper, describing the clinical presentation of the disorder and providing treatment options. Post-traumatic external nasal pain syndrome appears to be a novel form of trigeminal-based pain not previously reported in the neurologic literature.

A Lacrimal Sac Abscess Incision and Drainage Technique

A comfortable, anatomically based lacrimal sac abscess incision and drainage technique is described. The records of 52 patients were reviewed. The procedure was relieving and well tolerated because of adequate infraorbital and anterior ethmoidal nerve blocks. To promote rapid resolution, both components of the abscess were drained: the distended lacrimal sac and its associated submuscular pocket. The contiguous cavities were packed and allowed to heal by secondary intention. Of 49 cases, 39 (79.6%) were done as outpatient procedures and 41 (83.7%) were performed under locoregional anesthesia. Edema completely resolved by a median of 7 days. A repeat drainage procedure within 1 month was required in only 4 of 48 cases (8.3%). Fistulas and ectropion were not found. Four of 16 patients (25.0%) who did not eventually receive a definitive procedure (dacryocystorhinostomy or dacryocystectomy) developed a recurrent lacrimal sac abscess after complete resolution of the primary episode.

Unmyelinated anterior ethmoidal nerve fibers provide the afferent signal that induces activation of MDH neurons during nasal stimulation

The anterior ethmoidal nerve (AEN) innervates the nasal passages and constitutes the afferent limb of the cardiorespiratory reflex resulting from nasal stimulation. However it is currently unknown whether the AEN afferent signal is transmitted to the brainstem via unmyelinated or myelinated fibers. Our objective was to determine which of these fiber types connect with brainstem neurons activated during nasal stimulation. Initially AEN central projections were traced in the rat using WGA‐HRP (a non‐specific tracer), IB4‐HRP (specific for unmyelinated fibers) and CTB‐HRP (specific for myelinated fibers). Using TMB histochemistry, AEN terminal label was located ipsilaterally, ventrally and superficially within the medullary dorsal horn (MDH); in juxtaposition with the paratrigeminal nucleus (Pa5); and along the dorsal edge of the mesencephalic trigeminal nucleus (Me5). Unmyelinated fibers primarily project to MDH, while myelinated fibers primarily project to Pa5 and Me5. In other animals, after AEN tracer injections, nasal stimulation with ammonia vapors induced Fos production within activated neurons. Using fluorescent double‐labeling, unmyelinated fiber terminations clustered around Fos positive neurons within the MDH. We conclude that during nasal stimulation unmyelinated AEN fibers provide the afferent signal that induces activation of secondary trigeminal neurons within the MDH. Supported by NIH R15 HL080007.

Recognizing trigeminal trophic syndrome

Recognizing trigeminal trophic syndrome

The anterior ethmoidal nerve is necessary for the initiation of the nasopharyngeal response in the rat

Stimulation of the nasal passages with ammonia vapors can initiate a nasopharyngeal response that resembles the diving response. This response consists of a sympathetically mediated increase in peripheral vascular resistance, parasympathetically mediated bradycardia and an apnea. The current study investigated the role of the anterior ethmoidal nerve (AEN) in the nasopharyngeal response in the rat, as it is thought that the AEN provides the main sensory innervation of the nasal passages. When both AENs were intact, nasal stimulation caused significant bradycardia, hypertension, and apnea and produced Fos label ventrally within the ipsilateral medullary dorsal horn (MDH) and paratrigeminal nucleus just caudal to the obex. This labeling presumably represents activation of second-order trigeminal neurons. When only one AEN was intact, the nasopharyngeal response was slightly attenuated, and a similar pattern of Fos labeling was only seen in the trigeminal nucleus ipsilateral to the intact AEN. The trigeminal labeling contralateral to the intact AEN was significantly reduced. When both AENs were cut, the nasopharyngeal response to nasal stimulation consisted of only a slight apnea and an increase in arterial pressure; the resultant Fos labeling within the trigeminal nucleus was significantly reduced. Cutting both AENs but not stimulating the nasal passages also produced some Fos labeling within the trigeminal nucleus. These findings suggest that a single AEN can provide sufficient afferent input to initiate the cardiorespiratory changes consistent with the nasopharyngeal response. We conclude that the AEN provides a unique afferent contribution that is capable of producing the diving response.

Brainstem projections from recipient zones of the anterior ethmoidal nerve in the medullary dorsal horn

Stimulation of the anterior ethmoidal nerve or the nasal mucosa induces cardiorespiratory responses similar to those seen in diving mammals. We have utilized the transganglionic transport of a cocktail of horseradish peroxidase conjugates and anterograde and retrograde tract tracing techniques to elucidate pathways which may be important for these responses in the rat. Label was seen throughout the trigeminal sensory complex after the horseradish peroxidase conjugates were applied to the anterior ethmoidal nerve peripherally. Reaction product was most dense in the medullary dorsal horn, especially in laminae I and II. Injections were made of biotinylated dextran amine into the recipient zones of the medullary dorsal horn from the anterior ethmoidal nerve, and the anterogradely transported label documented. Label was found in many brainstem areas, but fibers with varicosities were noted in specific subdivisions of the nucleus tractus solitarii and parabrachial nucleus, as well as parts of the caudal and rostral ventrolateral medulla and A5 (noradrenergic cell group in ventrolateral pons) area. The retrograde transport of FluoroGold into the medullary dorsal horn after injections into these areas showed most neurons in laminae I, II, and V. Label was especially dense in areas which received primary afferent fibers from the anterior ethmoidal nerve. These data identify potential neural circuits for the diving response of the rat.