Chronic Constriction Injury of the Distal Infraorbital Nerve (DIoN-CCI) in Mice to Study Trigeminal Neuropathic Pain.

Animal models remain necessary tools to study neuropathic pain. This manuscript describes the distal infraorbital nerve chronic constriction injury (DIoN-CCI) model to study trigeminal neuropathic pain in mice. This includes the surgical procedures to perform the chronic constriction injury and the postoperative behavioral tests to evaluate the changes in spontaneous and evoked behavior that are signs of ongoing pain and mechanical allodynia. The methods and behavioral readouts are similar to the infraorbital nerve chronic constriction injury (IoN-CCI) model in rats. However, important changes are necessary for the adaptation of the IoN-CCI model to mice. First, the intra-orbital approach is replaced by a more rostral approach with an incision between the eye and the whisker pad. The IoN is thus ligated distally outside the orbital cavity. Secondly, due to the higher locomotor activity in mice, allowing rats to move freely in small cages is replaced by placing mice in custom-designed and constructed restraining devices. After DIoN ligation, mice exhibit changes in spontaneous behavior and in response to von Frey hair stimulation that are similar to those in IoN-CCI rats, i.e., increased directed face grooming and hyperresponsiveness to von Frey hair stimulation of the IoN territory.

Microglia and Inhibitory Circuitry in the Medullary Dorsal Horn: Laminar and Time-Dependent Changes in a Trigeminal Model of Neuropathic Pain.

Craniofacial neuropathic pain affects millions of people worldwide and is often difficult to treat. Two key mechanisms underlying this condition are a loss of the negative control exerted by inhibitory interneurons and an early microglial reaction. Basic features of these mechanisms, however, are still poorly understood. Using the chronic constriction injury of the infraorbital nerve (CCI-IoN) model of neuropathic pain in mice, we have examined the changes in the expression of GAD, the synthetic enzyme of GABA, and GlyT2, the membrane transporter of glycine, as well as the microgliosis that occur at early (5 days) and late (21 days) stages post-CCI in the medullary and upper spinal dorsal horn. Our results show that CCI-IoN induces a down-regulation of GAD at both postinjury survival times, uniformly across the superficial laminae. The expression of GlyT2 showed a more discrete and heterogeneous reduction due to the basal presence in lamina III of 'patches' of higher expression, interspersed within a less immunoreactive 'matrix', which showed a more substantial reduction in the expression of GlyT2. These patches coincided with foci lacking any perceptible microglial reaction, which stood out against a more diffuse area of strong microgliosis. These findings may provide clues to better understand the neural mechanisms underlying allodynia in neuropathic pain syndromes.

Revisiting major anatomical risk factors of maxillary sinus lift and soft tissue graft harvesting for dental implant surgeons.

The anatomical variations of the maxillary sinus septa, greater palatine artery, and posterior superior alveolar arteries might cause unexpected complications when they are damaged. Dentists who know these structures well might hope to learn more practical knowledge to avoid and assess injury preoperatively. Therefore, this review paper aimed to review the reported anatomy and variations of the maxillary sinus septa, greater palatine artery/nerve, and posterior superior alveolar artery, and to discuss what has to be assessed preoperatively to avoid iatrogenic injury. To assess the risk of injury of surgically significant anatomical structures in the maxillary sinus and hard palate, the operator should have preoperative three-dimensional images in their mind based on anatomical knowledge and palpation. Additionally, knowledge of the average measurement results from previous studies is important.

Frequency and location of the zygomaticofacial foramen and its clinical importance in the placement of zygomatic implants.

PURPOSE: Anatomical knowledge of the zygomatic region is important, because the zygomatic nerve and its branches may suffer lesions during surgical procedures in the periorbital region. The position and frequency of zygomaticofacial foramina (ZFF) may vary between individuals, and between one side and the other in the same individual. In the present study, we analysed the presence and location of ZFF, as well as the distance between them and the orbital cavity, in macerated skulls of adult individuals. METHODS: We examined 287 macerated skulls, of individuals of both sexes, analysing the frequency and location of ZFF and the distance from the ZFF to the margin of the orbital cavity (OC). RESULTS: Zygomaticofacial foramina are very frequent structures which tend to appear singly. They are generally located in the temporal process of the zygomatic bone, but in many cases, they may be located in the mid portion of the bone. They also tend to appear at the same distance from the OC when left and right sides are compared. Sex was an important factor in determining differences in ZFF; the distance from the ZFF to the margin of the OC was greater in males than in females. Sex, age, side and skin colour did not affect the frequency and location of the ZFF. CONCLUSION: We consider that the mid portion of the zygomatic bone is the safest place to anchor zygomatic implants (ZI), since ZFF are less frequently located there than in the temporal process of the zygomatic bone.

Complicaciones quirúrgicas de la elevación de seno maxilar en implantología / Surgical Complications Associated to Maxillary Sinus Floor Elevation in Implantology

RESUMEN La elevación de piso de seno maxilar ha sido sumamente documentada en implantología como una técnica segura y predecible en el procedimiento de ganancia vertical ósea, en el maxilar posterior atrófico. Sin embargo, conjuntamente se han reportado complicaciones en este procedimiento, las cuales podrían poner en peligro los resultados de la regeneración, y por consiguiente la colocación del implante. El propósito de esta revisión de literatura es exponer y analizar diferentes complicaciones que pueden presentarse en la elevación de piso de seno maxilar.

ABSTRACT Maxillary sinus floor elevation has been extensively documented as a safe and predictable procedure for gaining vertical bone height in the atrophic posterior maxilla. Even though, complications have been reported, which can potentially jeopardize the outcome of the regeneration and implant therapy. Therefore, the purpose of this literature review is to present, debate and analyze the different complications that can occur during a sinus floor elevation.

Pain threshold monitoring during chronic constriction injury of the infraorbital nerve in rats.

Background: The chronic constriction injury (CCI) of the infraorbital nerve (ION) has been used to establish an animal mode of trigeminal neuralgia (TN), but key parameters of the model have not been quantified until now. Objective: The aim of the study was to quantify a standard of pain threshold to evaluate a successful TN model in Sprague-Dawley (SD) rats. Methods: Forty-eight adult SD rats (200-220 g) underwent chronic constriction injury of the infraorbital nerve. The pain threshold was tested one day preoperatively (baseline) and day 1, 3, 7, 14, 28 postoperatively using the up-down method. At day 28, all the animals were killed by dislocation of the cervical spine and the trigeminal nerve specimens were removed for electron microscopy. Results: The baseline pain threshold was 14.40 ± 0.87 g. Postoperatively, all the rats presented an initial reduced sensitivity to mechanical stimulation from day 1 (15.63 ± 1.92 g) through 7 (17.39 ± 1.43 g) after the surgery. At day 14, 32 (66.7%) began to show significant mechanical allodynia (0.71 ± 0.43 g) which did not change significantly till day 28 (0.88 ± 0.54 g). These animals were regarded as successful TN models with a 95% confidence interval of the pain threshold of 0.58-1.27 at Day 14. The electron microscopy demonstrated homogeneously demyelinated changes in those successful TN model animals rather than severe or mild epineurial lesions in those unsuccessful model animals. Conclusion: Our study showed that an animal TN model could be established with a two-week chronic constriction injury of the infraorbital nerve. The mechanical allodynia index <1.27 at Day 14 was suggested as a criterion for a successful model.

Infraorbital Nerve Located Medially to Postoperative Maxillary Cysts: A Risk of Endonasal Surgery.

BACKGROUND/AIMS: This study aimed to examine variations in the location of the infraorbital nerve relative to postoperative maxillary cysts to assess the potential risk of nerve injury during endonasal marsupialization. METHODS: Coronal computed tomography images of 130 patients (162 sides) with postoperative maxillary cysts who visited our clinic between 2003 and 2014 were reviewed from the viewpoint of the anatomical relationship between the infraorbital nerves and cysts. RESULTS: The proportions of the six locations were as follows: upside 45.1% (n = 73), separate 13.0% (n = 21), medial 5.6% (n = 9), lateral 14.2% (n = 23), in-between 7.4% (n = 12), and unevaluable 14.8% (n = 24). The proportion of the cases with a potential risk of infraorbital nerve damage during endoscopic marsupialization, including medial, in-between, and unevaluable locations, was 27.8%. Retrospective chart review revealed that 2 patients with a postoperative maxillary cyst that were unevaluable complained of persistent postoperative hypoesthesia of the cheek. CONCLUSION: The anatomical relationship between the infraorbital nerve and postoperative maxillary cysts varied among patients, with approximately one-fourth of the patients being at risk of infraorbital nerve injury even during endoscopic procedures.

Does Dexamethasone Facilitate Neurosensory Function Regeneration After Zygomatic Fracture? A Randomized Controlled Trial.

PURPOSE: This study sought to clarify the rate of neurosensory disturbance (NSD) after zygomatic complex fractures in general, as well as the effect of perioperatively administered dexamethasone on neurosensory recovery. PATIENTS AND METHODS: This was a single-blinded randomized study aiming to clarify the benefits of perioperative dexamethasone after surgery. The patients were randomly assigned either to receive dexamethasone (up to a total dose of 10 or 30 mg) or to act as control patients (no glucocorticoid treatment). The outcome variable was NSD, the presence of which was established when patients had any sensory disturbance of the infraorbital nerve. Other predictor variables included in the analysis were age, gender, time span from accident to surgery, surgical approach to the fracture line, and relation of the fracture to the infraorbital foramen. The statistical significance of associations was evaluated with χ2 tests. RESULTS: We included 64 patients in the analyses. Of the patients in the dexamethasone group (either 10 or 30 mg), 58.3% had NSD at 6 months postoperatively, whereas in the control group, 66.7% of the patients had NSD. This finding was not statistically significant (P = .565). At the 1-month interval, the patients without a fracture through the infraorbital foramen had less NSD (P = .009); this finding was not significant at 3 and 6 months postoperatively. Age, gender, injury mechanism, surgical approach, and time span from accident to surgery were not significant predictors of NSD. In total, 64.4% of the patients still had NSD at 6 months postoperatively. CONCLUSIONS: This study showed no benefits of short-term, high-dose dexamethasone administration in the neurosensory recovery of patients with zygomatic complex fractures. The type of primary trauma is the main cause of NSD, but the precise predictors remain unknown.

Anterior superior alveolar nerve injury after extended endoscopic medial maxillectomy: a preclinical study to predict neurological morbidity.

BACKGROUND: Endoscopic medial maxillectomies (EMMs) are used to optimize exposure of the maxillary sinus and retromaxillary areas. Although in type D EMM (Sturmann-Canfield procedure) the anterior superior alveolar nerve (ASAN) is always at risk of injury, only 29% of patients complained of alveolar process and dental anesthesia. The purpose of this anatomical study is to assess the neural anastomotic network of the ASAN (ASAN-NAN) and describe different extensions of type D EMMs in a preclinical setting. METHODS: The ASAN and its medial anastomotic branches (MABs) and lateral anastomotic branches (LABs) were evaluated by cone-beam computerized tomography (CBCT). Five different extensions of type D (D1 to D5) EMMs were identified and nerves at risk of injury in each type were assessed by CBCT. Moreover, quantification of surgical corridors was performed on cadaver heads with a neuronavigation system. RESULTS: Fifty-seven CBCT scans were analyzed. The ASAN would be spared in 16.3% of cases with a type D1 EMM, while it would be injured in the majority of type D2 to D5 resections. At least 1 nerve of the ASAN-NAN was spared in 96.6%, 93%, 74.6%, 0%, and 65.8% of type D1 to D5 EMMs, respectively. Two cadaver heads were dissected and the incremental volume and number of maxillary subsites exposed was assessed in type D1 to D5 EMMs. CONCLUSION: ASAN function impairment is probably compensated by LABs and MABs. If this hypothesis will be validated in a prospective study on patients, preoperative CBCT evaluation could predict neurological morbidity after type D EMM, and allow tailoring the procedure to minimize impairment of the ASAN-NAN.

A Rare Complication of Infraorbital Nerve Hyperesthesia in Surgically Repaired Orbital Fracture Patients.

Injury to the peripheral sensory branches of the trigeminal nerve can follow a wide variety of craniofacial injuries. Many patients with facial fractures complain about the symptom of numbness to the distribution of injured nerve, which is indicative of hypoesthesia. Hyperesthesia involving the infraorbital nerve is rare in comparison to hypoesthesia secondary to facial trauma. The authors report on 2 patients with infraorbital nerve hyperesthesia in surgically repaired orbital fracture patients. Surgical decompression of the infraorbital nerve led to rapid resolution of hyperesthesia. To the best of our knowledge, these were rare cases of patients who presented with persistent hyperesthesia. Clinician should perform early surgical decompression of the infraorbital nerve in patient with persistent hyperesthesia of the infraorbital nerve.

Anatomical study of the internal nasal branch of the infraorbital nerve: Application to Minimizing Nerve Damage With Surgery In and Around the Nose.

The internal nasal branch of the infraorbital nerve (ION) runs down the nose and around the ala to be distributed to the nasal septum and vestibule. The aim of this study was to measure the internal nasal branch around the ala of the nose and discuss its possible relevance in clinical/surgical practice. Twelve sides from seven specimens derived from fresh frozen and embalmed Caucasian cadaveric heads were dissected. The specimens included three males and four females. The ages of the cadavers at death ranged from 65 to 84 years. The diameter of the internal nasal branch, horizontal distance from the lateral contour of the ala (Point A) to the branch (distance H) and vertical distance from the bottom part of the ala (Point B) to the branch (distance V) were recorded. Distance H ranged from -1.6 to 1.5 mm on right sides and -1.0 to 1.5 mm on left sides. The diameter of the nerves at Point A ranged from 1.3 to 1.8 mm on right sides and 1.3 to 1.6 mm on left sides. Distance V ranged from -1.5 to 1.0 mm on right sides and -2.3 to 1.1 mm on left sides. The diameter of the nerves at Point B ranged from 0.7 to 1.3 mm on right sides and 0.8 to 1.2 mm on left sides. The results of this study are the first to detail the topography of the internal nasal branch of the ION. Clin. Anat. 30:817-820, 2017. © 2017Wiley Periodicals, Inc.

Immunohistochemical comparison of astrocytic mGluR5 upregulation in infraorbital nerve- versus sciatic nerve-ligated rat.

The differential pharmacological responsiveness of cephalic and extra-cephalic neuropathic pain has been proposed to relate to distinct mechanisms that may involve neuroinflammatory reactions mediated by glial cells. Astrocytes are particularly important for neuronal sensitization in neuropathic pain, in part through modulation of glutamatergic transmission. Because the metabotropic glutamate receptor 5 (mGluR5) is involved in the astrocytic regulation of the glutamatergic system, we investigated modifications of its expression in models of cephalic versus extra-cephalic neuropathic pain. Adult male rats underwent unilateral chronic constriction injury (CCI) of either the infraorbital nerve (ION) or the sciatic nerve (SN). Seven days later, mGluR5 and the astrocyte marker GFAP (glial fibrillary acidic protein) were overexpressed and appeared localized mainly in the superficial lamina of the trigeminal nucleus in CCI-ION and the spinal cord dorsal horn in CCI-SN rats. In addition, colocalization of GFAP and mGluR5 strongly suggested an increase of astrocytic mGluR5 expression in nerve-injured rats compared to sham animals. The present data show an upregulation of astrocytic mGluR5 in central structures in both CCI-ION and CCI-SN. This suggests that the pharmacological modulation of mGluR5 could be a new approach to reduce both cephalic and extra-cephalic neuropathic pain.

Isolated unilateral upper alveolar numbness in silent sinus syndrome.

We present a case of a 59-year-old man with left upper alveolar numbness of 2 years' duration in the absence of sinonasal symptoms. On physical examination, he demonstrated mild left facial asymmetry and diminished sensation of his left upper alveolus from the left second upper incisor to first canine. CT imaging revealed chronic sinusitis changes of the left maxillary sinus, with reduced volume and depressed anterior wall. The patient underwent functional endoscopic sinus surgery to re-establish maxillary sinus ventilation. He was noted to have some improvement of his upper alveolar paraesthesia postoperatively. Silent sinus syndrome is part of the spectrum of chronic maxillary atelectasis. In the presented case, chronic osteitic bony sclerosis, as opposed to osteopenic change of the maxillary sinus, was seen. We postulate that bony encasement of the anterior superior alveolar nerve resulted in chronic nerve compression and the patient's unusual symptom of upper alveolar paraesthesia.

Female rat transcriptome response to infraorbital nerve transection differs from that of males: RNA-seq.

The effects of infraorbital nerve (ION) transection on gene expression in the adult female rat barrel cortex were investigated using RNA sequencing. After a 24-hour survival duration, 28 genes were differentially regulated by ION transection. Differentially expressed genes suggest microglial activity, increased retrograde ciliary transport, and a decrease in inhibition. These changes may be functionally comparable to changes in the male barrel cortex, where changes in genes related to morphology, neuronal activity, and neuronal excitability were observed. However, the patterns in changes in gene expression are vastly different between male and female rats. The results strongly caution against the practice of generalizing data from one sex to both sexes. This cautionary note has potentially profound implications for a range of research lines, including substance abuse and stress, both research domains in which subjects have been predominantly males. Future research needs to employ sex as a classification variable, as sex differences can generally be expected. Future research is also needed to confirm that changes in gene expression observed with RNA-seq correlate with changes in protein expression. J. Comp. Neurol. 525:140-150, 2017. © 2016 Wiley Periodicals, Inc.

Primary Infraorbital Foramen Decompression for the Zygomaticomaxillary Complex Fracture: Is It Essential?

PURPOSE: The frequency of zygomaticomaxillary fracture is second only to nasal bone fracture. Up to 30% to 80% of zygomaticomaxillary fracture patients complain of sensory disturbance results from infraorbital nerve injury. The objective of this study was to detect what factors are related to infraorbital nerve recovery and specifically to investigate decompression of infraorbital foramen improves sensory recovery. PATIENTS AND METHODS: A total of 257 patients were assessed with unilateral zygomaticomaxillary complex fracture, treated with open reduction and internal fixation with orbital floor reconstruction. Of these, 166 patients followed up over 6 months were included in this study. The data collected included age, sex, pre, and postoperative sensory score measured by visual analogue scale (range: 0-10). Sensory score was measured at the infraorbital nerve innervation. The impact of decompression operation on the change of sensory score was compared. Statistical analysis was performed using SPSS 18.0 software (SPSS Inc, Chicago, IL). RESULTS: In patients with preoperative hypoesthesia, difference between postoperative and preoperative sensory score was 3.2 (decompression group), 4.4 (nondecompression group), respectively, but not significant (P > 0.05). In patients without preoperative hypoesthesia, difference between postoperative and preoperative sensory score was -0.2 (decompression group), -0.3 (nondecompression group), respectively, and did not show significant association (P > 0.05). DISCUSSION: Based on this result, in patients with preoperative hypoesthesia, infraorbital decompression operation is not useful for sensory recovery. This result indicates infraorbital sensory disturbance occurs from not only pinched nerve injury at the infraorbital foramen but also traction nerve injury at the other part of the nerve.

Widespread pain sensitization after partial infraorbital nerve transection in MRL/MPJ mice.

Clinical studies show that chronic pain can spread to adjacent or even distant body regions in some patients. However, little is known about how this happens. In this study, we found that partial infraorbital nerve transection (p-IONX) in MRL/MPJ mice induced not only marked and long-lasting orofacial thermal hyperalgesia but also thermal hyperalgesia from day 3 postoperatively (PO) and tactile allodynia from day 7 PO in bilateral hind paws. Pain sensitization in the hind paw was negatively correlated with facial thermal hyperalgesia at early but not late stage after p-IONX. After a rapid activation of c-Fos, excitability and excitatory synaptic neurotransmission in lumbar dorsal horn neurons were elevated from day 3 and day 7 PO, respectively. In addition, microglial activation after p-IONX transmitted caudally from the Vc in the medulla to lumber dorsal horn in a time-dependent manner. Inhibition of microglial activation by minocycline at early but not late stage after p-IONX postponed and attenuated pain sensitization in the hind paw. These results indicate that neuropathic pain after p-IONX in MRL/MPJ mice spreads from the orofacial region to distant somatic regions and that a rostral-caudal transmission of central sensitization in the spinal cord is involved in the spreading process of pain hypersensitivity.

Transcriptome response to infraorbital nerve transection in the gonadally intact male rat barrel cortex: RNA-seq.

The effects of infraorbital nerve (ION) transection on gene expression in the adult male rat barrel cortex were investigated using RNA sequencing. After a 24-hour survival duration, 98 genes were differentially regulated by ION transection. Differentially expressed genes suggest changes in neuronal activity, excitability, and morphology. The production of mRNA for neurotrophins, including brain-derived neurotrophin factor (BNDF), was decreased following ION transection. Several potassium channels showed decreased mRNA production, whereas a sodium channel (Na(V)ß4) associated with burst firing showed increased mRNA production. The results may have important implications for phantom-limb pain and complex regional pain syndrome. Future experiments should determine the extent to which changes in RNA result in changes in protein expression, in addition to utilizing laser capture microdissection techniques to differentiate between neuronal and glial cells.

Chronic Constriction Injury of the Rat's Infraorbital Nerve (IoN-CCI) to Study Trigeminal Neuropathic Pain.

Animal models are important tools to study the pathophysiology and pharmacology of neuropathic pain. This manuscript describes the surgical and behavioral procedures to study trigeminal neuropathic pain in rats. To meet the specificity of trigeminal neuropathic pain syndromes, the infraorbital nerve (IoN) is subjected to a chronic constriction injury (CCI) by loosely ligating the nerve. An intra-orbital approach is presented here to expose and ligate the IoN in the orbital cavity. After IoN ligation, rats exhibit changes in spontaneous behavior and in response to von Frey hair stimulation that are indicative of persistent pain and mechanical allodynia. Two phases can be defined in the development of the behavioral changes. During the first week following IoN-CCI (phase 1), rats show an increased and asymmetric face grooming activity, i.e., with face wash strokes primarily directed to the nerve-injured IoN territory. A distinction is made between face grooming behavior that is part of a more general body grooming behavior, which remains largely unaffected by IoN-CCI, and face grooming that is neither preceded nor followed by body grooming, which is significantly increased after IoN-CCI. During this period, responsiveness to mechanical stimulation of the IoN territory is reduced. This hyporesponsiveness is abruptly replaced by an extreme hyperresponsiveness whereby even very weak stimulus intensities provoke nocifensive behavior (phase 2). The phenomenological similarities between these behavioral alterations and reported signs of facial pain (i.e., responses to noxious stimulation of the face) suggest the presence of dysesthesia/paresthesia and mechanical allodynia in the ligated IoN territory.

Surgical anatomy and variations of the infraorbital nerve.

OBJECTIVES/HYPOTHESIS: To assess relevant variations in the anatomical course of the infraorbital nerve (ION). This understanding may reduce the risk of surgical injury. METHODS: A total of 100 consecutive computed-tomography sinus studies obtained in a tertiary referral center were reviewed, and measurements were made of the 200 IONs. Anatomic variants were classified into three types based on the degree to which (if any) the nerve's course descended from the maxillary roof into the sinus lumen. RESULTS: A total of 60.5% of IONs were entirely contained within the sinus roof. In 27.0%, the nerve canal descended below the roof but remained juxtaposed to it. In 12.5%, the ION descended into the sinus lumen. The proportion of IONs descending into the sinus significantly increased to 27.7% when an infraorbital ethmoid cell was present (chi-square P < 0.001) and to 50% when the nerve was contained within a lamella of such a cell (chi-square P < 0.001). Descended nerves terminated in a foramen located an average of 11.9 ± 2.5 mm below the infraorbital rim, significantly further below the orbit than nondescended nerves (t test P < 0.001). Descended nerves were located a mean distance of 8.6 ± 2.9 mm below the sinus roof and traversed the sinus lumen diagonally for a mean length of 15.4 ± 3.1 mm. CONCLUSIONS: Descent of the ION into the maxillary sinus is a common anatomic variant that is more prevalent in the setting of an ipsilateral infraorbital ethmoid cell. Descended nerves are associated with the foramen significantly further below the inferior orbital rim than those of nondescended nerves. These observations may help surgeons avoid iatrogenic ION injury. LEVEL OF EVIDENCE: N/A.

Posttraumatic Midface Pain: Clinical Significance of the Anterior Superior Alveolar Nerve and Canalis Sinuosus.

BACKGROUND: Posttraumatic midface pain secondary to injury of the anterior superior alveolar nerve (ASAN) is characterized as pain localized to the central and lateral incisors, canines, and maxilla. This nerve is susceptible to injury and subsequent formation of neuromas after midface trauma. Surgical intervention requires an accurate and precise understanding of the course of the ASAN. METHODS: Dissections of 12 human cadaver heads were conducted to identify the course of the ASAN through the canalis sinuosus (CS). Fifty 1-mm slice face computed tomographic scans were evaluated to document the dimensions and course of the CS. RESULTS: The ASAN branched laterally from the infraorbital nerve before reaching the infraorbital rim in all cadavers. The bifurcation occurred 18 mm posterior to the infraorbital rim (range, 10-30 mm). At a point 25 mm inferior to the infraorbital rim, the ASAN is found 3.4 mm lateral to the piriform aperture (range, 3-4 mm). Radiographic analysis demonstrated a 12.9-mm horizontal length of the CS across the anterior maxilla (SD, 2.2 mm), a distance of 4.8 mm between the piriform aperture and the CS (SD, 1.2 mm), and 11.7 mm vertical length of the CS along the piriform aperture (SD, 3.0 mm). CONCLUSIONS: The ASAN maintains consistent coordinates at specific points along its course through the midface. An improved understanding of the course of the ASAN will guide future diagnosis of injury to this nerve and surgical intervention for patients with posttraumatic midface pain secondary to ASAN injury.