Predicting synkinesis caused by Bell's palsy or Ramsay Hunt syndrome using machine learning-based logistic regression.

Objective: To investigate whether machine learning (ML)-based algorithms, namely logistic regression (LR), random forest (RF), k-nearest neighbor (k-NN), and gradient-boosting decision tree (GBDT), utilizing early post-onset parameters can predict facial synkinesis resulting from Bell's palsy or Ramsay Hunt syndrome more accurately than the conventional statistics-based LR. Methods: This retrospective study included 362 patients who presented to a facial palsy outpatient clinic. Median follow-up of synkinesis-positive and -negative patients was 388 (range, 177-1922) and 198 (range, 190-3021) days, respectively. Electrophysiological examinations were performed, and the rate of synkinesis in Bell's palsy and Ramsay Hunt syndrome was evaluated. Sensitivity and specificity were assessed using statistics-based LR; and electroneurography (ENoG) value, the difference in the nerve excitability test (NET), and scores of the subjective Yanagihara scaling system were evaluated using early post-onset parameters with ML-based LR, RF, k-NN, and GBDT. Results: Synkinesis rate in Bell's palsy and Ramsay Hunt syndrome was 20.2% (53/262) and 40.0% (40/100), respectively. Sensitivity and specificity obtained with statistics-based LR were 0.796 and 0.806, respectively, and the area under the receiver operating characteristic curve (AUC) was 0.87. AUCs measured using ML-based LR of "ENoG," "difference in NET," "Yanagihara," and all three components ("all") were 0.910, 0.834, 0.711, and 0.901, respectively. Conclusion: ML-based LR model shows potential in predicting facial synkinesis probability resulting from Bell's palsy or Ramsay Hunt syndrome and has comparable reliability to the conventional statistics-based LR. Level of Evidence: 3.

Techniques in Staining of Rodent and Human Olfactory Tissue.

Staining of olfactory tissue allows for evaluation of the organization of specific cell types within the specimen and allows for assessment in abnormalities of function that may be related to changes in normal tissue architecture. Histochemical staining and immunohistochemical (IHC) techniques are the most common methods for visualizing olfactory epithelium and olfactory bulbs. Here we describe the method of IHC for olfactory tissue utilizing both fluorescent and peroxidase-based methods of visualization.

Intracranial aspergilloma mimicking metachronous meningioma following transsphenoidal removal of a tuberculum sellae meningioma: illustrative case.

BACKGROUND: Endoscopic transsphenoidal surgery (eTSS) is a well-established approach for resection of skull-based pathologies such as tuberculum sellae meningiomas; however, central nervous system (CNS) fungal infection is a potential complication, particularly in a patient with concomitant sinusitis. OBSERVATIONS: A 58-year-old woman with a tuberculum sellae meningioma causing progressive visual disturbance and concurrent asymptomatic chronic maxillary sinusitis underwent eTSS. Six months later, a de novo dura-based mass with peripheral edema, which was assumed to be an aggressive metachronous meningioma, developed in the middle cranial fossa. The patient underwent frontotemporal craniotomy for complete resection of the lesion, and subsequent histological examination revealed an aspergilloma. She was then treated with an antifungal agent and endoscopic sinus surgery to clear the sinusitis, and no recurrent fungal infection occurred thereafter. LESSONS: CNS fungal infections may appear as a dura-based mass mimicking meningioma. The current case reiterates the importance of the appropriate management of sinusitis prior to eTSS.

Clinical and electrophysiological findings of facial palsy in a case of hereditary gelsolin amyloidosis.

Hereditary gelsolin amyloidosis (HGA) is an autosomal dominant systemic amyloidosis, characterized by cranial and sensory peripheral neuropathy, corneal lattice dystrophy, and cutis laxa. We report a case of HGA presenting with bilateral facial palsy. A 70-year-old Japanese man presented with slowly progressive bilateral facial palsy and facial twitching, which had started in his 40s. His mother also had the same symptoms due to an unknown cause but rest of the family did not. He showed incomplete facial palsy with no frontal muscle movement and partial movement of the orbicularis oris and orbicularis oculi muscles. The patient showed no synkinesis. Electroneurography revealed symmetric low compound motor action potential amplitude of the orbicularis oris muscle, and a nerve excitability test showed a symmetric increase in the response threshold. Despite the partial voluntary movement of the orbicularis oculi muscle, bilateral blink reflexes were absent. He also showed facial spasms after contraction of the orbicularis oris muscle. Genetic testing revealed a heterozygous c.640G>A mutation (p. Asp214Asn); therefore, the patient was diagnosed with HGA. HGA related facial palsy showed moderate bilateral, upper blanch-dominant axonal degeneration of the facial nerve without reinnervation, and trigeminal nerve neuropathy.

Evidence for the spread of SARS-CoV-2 and olfactory cell lineage impairment in close-contact infection Syrian hamster models.

Objectives: Close contact with patients with COVID-19 is speculated to be the most common cause of viral transmission, but the pathogenesis of COVID-19 by close contact remains to be elucidated. In addition, despite olfactory impairment being a unique complication of COVID-19, the impact of SARS-CoV-2 on the olfactory cell lineage has not been fully validated. This study aimed to elucidate close-contact viral transmission to the nose and lungs and to investigate the temporal damage in the olfactory receptor neuron (ORN) lineage caused by SARS-CoV-2. Methods: Syrian hamsters were orally administered SARS-CoV-2 nonvariant nCoV-19/JPN/TY/WK521/2020 as direct-infection models. On day 3 after inoculation, infected and uninfected hamsters were housed in the same cage for 30 minutes. These uninfected hamsters were subsequently assigned to a close-contact group. First, viral presence in the nose and lungs was verified in the infection and close-contact groups at several time points. Next, the impacts on the olfactory epithelium, including olfactory progenitors, immature ORNs, and mature ORNs were examined histologically. Then, the viral transmission status and chronological changes in tissue damage were compared between the direct-infection and close-contact groups. Results: In the close-contact group, viral presence could not be detected in both the nose and lungs on day 3, and the virus was identified in both tissues on day 7. In the direct-infection group, the viral load was highest in the nose and lungs on day 3, decreased on day 7, and was no longer detectable on day 14. Histologically, in the direct-infection group, mature ORNs were most depleted on day 3 (p <0.001) and showed a recovery trend on day 14, with similar trends for olfactory progenitors and immature ORNs. In the close-contact group, there was no obvious tissue damage on day 3, but on day 7, the number of all ORN lineage cells significantly decreased (p <0.001). Conclusion: SARS-CoV-2 was transmitted even after brief contact and subsequent olfactory epithelium and lung damage occurred more than 3 days after the trigger of infection. The present study also indicated that SARS-CoV-2 damages all ORN lineage cells, but this damage can begin to recover approximately 14 days post infection.

High CT Attenuation Values Relative to the Brainstem Predict Fungal Hyphae Within the Sinus.

Objectives: There is currently no established objective diagnostic indicator for the differentiation of sinus fungal ball (SFB) from unilateral nonfungal chronic sinusitis (UCRS). This study evaluated whether computed tomography (CT) attenuation values relative to those of the brainstem (relative CT number) are useful for differentiating SFB from UCRS. Materials and Methods: Consecutive patients who were pathologically diagnosed with SFB or UCRS between 2013 and 2021 were retrospectively identified. The relative CT numbers of region of interest (ROIs) within the sinuses were compared between the two patient groups. Factors with predictive power for differentiating SFBs from UCRSs were identified by uni/multivariable logistic regression analyses. Results: One hundred and eighty-three patients with unilateral chronic sinusitis were finally analyzed (SFB, 86 cases; UCRS, 97 cases). Regardless of the presence or absence of calcified lesions, the relative CT numbers in SFB were significantly higher than those in UCRS. ROIs showing high relative CT numbers were those where fungal hyphae were present. In the uni/multivariable logistic regression analysis, age (p < 0.001), relative CT number (p < 0.001), and calcification (p = 0.002) had predictive value for distinguishing SFB from UCRS. Within those cases not showing calcification, age (p = 0.004) and relative CT number (p < 0.001) were predictive factors for differentiating SFB from UCRS. A relative CT number >1.5 was significantly associated with SFB (sensitivity, 70%; specificity, 91%), with a significantly larger area under the receiver operating characteristics curve than age. Conclusions: High relative CT numbers within the sinus are strongly associated with the presence of fungal hyphae, and measurement of relative CT number is a powerful adjunctive diagnostic method for distinguishing between SFB and UCRS.

Rapid fluorescent vital imaging of olfactory epithelium.

Olfactory epithelium (OE) undergoes degeneration in disorders such as age-related and post-viral olfactory dysfunction. However, methods for real-time in vivo detection of OE and assessment of total extent within the nasal cavity are currently unavailable. We identified two fluorescence probes for rapidly detecting and evaluating the entire extent of mice OE with topical application. Taking advantage of the differential expression of the enzymes cytochrome p450 (CYP) and γ-glutamyltranspeptidase (GGT) in OE relative to respiratory epithelium, we utilized the conversion of coumarin (a substrate of various CYP subtypes) and gGlu-HRMG (a substrate of GGT) by these enzymes to form metabolites with fluorescent emissions in the duct cells and sustentacular cells of neuron-containing OE. In depleted and regenerated OE model, the emission of these probes remained absent in respiratory metaplasia but appeared in regenerated OE. These substrates could be used to monitor OE degeneration and follow regenerative response to therapeutic interventions.

Traumatic facial nerve injury: A case of facial nerve avulsion at the cerebellopontine angle.

Post-traumatic facial nerve paralysis is a common disease, but intracranial facial nerve injury after blunt injury has rarely been reported. We report a case of facial nerve avulsion at the cerebellopontine angle. A 23-year-old female with incomplete right-sided facial nerve palsy and facial spasms presented to our hospital. She had a history of traumatic injury, having fallen off a table and hit her head at the age of 2 years. After the accident, she developed complete right-sided facial nerve palsy and underwent conservative treatment with steroids. A magnetic resonance imaging examination performed 21 years later showed avulsion of the facial nerve at the cerebellopontine angle. Magnetic resonance imaging targeting the facial nerves might provide additional information to computed tomography in cases with poor recovery with conservative treatment.

Odorant metabolism of the olfactory cleft mucus in idiopathic olfactory impairment patients and healthy volunteers.

BACKGROUND: It remains unclear whether the metabolic activity of nasal mucus in the olfactory and respiratory areas is different. Moreover, age- and olfaction-related changes may affect metabolism. METHODS: Hexanal, octanal, and 2-methylbutanal were selected for in vitro metabolism analysis and compared between the olfactory cleft and respiratory mucus of participants < 50-year-old with normal olfaction using gas chromatography mass spectrometry. The metabolic activity of hexanal in the olfactory cleft mucus was further compared between three groups, (1) normal olfaction, age < 50 years old, (2) normal olfaction, age ≥50 years old, and (3) idiopathic olfactory impairment. To characterize the enzyme(s) responsible for aldehyde reduction, we also tested if epalr22897estat and 3,5-dichlorosalicylic acid, types of reductase inhibitors, affect metabolism. RESULTS: Conversion of aldehydes to their corresponding alcohols was observed in the olfactory cleft and respiratory mucus. The metabolic production of hexanol, octanol, and 2-methybutanol was significantly higher in the olfactory cleft mucus than in the respiratory mucus (p < 0.01). The metabolic conversion of hexanal to hexanol in the mucus of the idiopathic olfactory impairment group was significantly lower than that in the age-matched normal olfaction group. Excluding the nicotinamide adenine dinucleotide phosphate (NADPH) regenerating system from the reaction mixture inhibited metabolism. The addition of either epalr22897estat or 3,5-dichlorosalicylic acid did not inhibit this metabolic conversion. CONCLUSIONS: The enzymatic metabolism of odorants in the olfactory cleft mucus is markedly higher than in the respiratory mucus and decreases in patients with idiopathic olfactory impairment.

Heterogeneous distribution of mature olfactory sensory neurons in human olfactory epithelium.

BACKGROUND: The olfactory cleft (OC) comprising the olfactory epithelium (OE) is the most important anatomical location for olfactory function. Endoscopic sinus surgery (ESS) is used to treat diseases related to the OC and improve olfactory dysfunction. However, iatrogenic OE injury occasionally occurs. Comprehensive knowledge of the olfactory region is required to avoid damage to the OE during endoscopic procedures. METHODS: Immunohistochemistry was performed on olfactory mucosa obtained from the unaffected side of olfactory neuroblastoma surgical specimens. The OE was defined as the epithelium containing mature olfactory sensory neurons (OSNs). The distribution and cell kinetics of the OE were examined. RESULTS: The OE was selectively localized to the anterior two-thirds of the superior turbinate (ST) and in the nasal septum (NS) just opposite to the ST; the OE was not detected within the mucosa of the superior meatus. The density of mature OSNs was high at the ethmoid tegmen but gradually decreased with distance from the ethmoid tegmen. The extent of cell death and proliferation was relatively even across the OE. Analysis of airflow profiles revealed that resection of inferior ST does not decrease airflow to the OC. CONCLUSION: The results indicate that the distribution and degree of differentiation of mature OSNs are heterogenous throughout the OE. Epithelial resection of the anterior or superior ST has the potential to damage olfactory function. Resection of the inferior or posterior ST or widening of the superior meatus is a safer alternative that does not damage mature OSNs or alter airflow to the OC.

Squamous and Respiratory Metaplasia After Olfactory Mucosal Resection.

Resection of the olfactory mucosa (OM) is sometimes unavoidable during surgery; however, it is not known whether the OM can completely recover thereafter. The aim of this study was to uncover whether the OM fully recovers after mucosal resection and describe the process of OM regeneration. 8-week-old male Sprague-Dawley rats (n = 18) were subjected to OM resection at the nasal septum; six rats were euthanized for histological examination 0, 30, and 90 days after surgery. Immunohistochemistry was performed to identify olfactory receptor neuron (ORN) lineage cells [mature and immature ORNs and ORN progenitors, and olfactory ensheathing cells (OECs)], as well as dividing and apoptotic cells. Squamous and respiratory metaplasia and inflammatory cell infiltration were also assessed. On day 30 after resection, the mucosa had regenerated, and mainly contained thin nerve bundles, basal cells, and immature ORNs, with a few mature ORNs and OECs. On day 90, the repaired nasal mucosa had degenerated into stratified squamous or ciliated pseudostratified columnar epithelia, with reducing ORNs. The lamina propria contained numerous macrophages. Partial regeneration was observed within 1 month after OM resection, whereas subsequent degeneration into squamous and respiratory epithelia occurred within 3 months. Given the poor persistence of ORNs and OECs, OM resection is likely to result in olfactory impairment. Overall, surgeons should be cautious not to injure the OM during surgery.

A Case of Huge Cutaneous Verrucous Carcinoma of the Neck.

Verrucous carcinoma (VC) is a rare subtype of squamous cell carcinoma. VC commonly occurs in the mucosa, but rarely occurs in the skin. The treatment for VC is surgical removal of the tumor. Because lymph node metastasis of VC is rare, the indications for prophylactic neck dissection for cutaneous VC of the neck are controversial. Here, we present the case of a 68-year-old man with a huge cutaneous VC of the neck and the long-term clinical course. The tumor occupied the entire right cervical skin, with suspected lymph node metastasis in the affected neck. Tumor resection and neck lymph node dissection were performed. Pathological examination revealed cutaneous VC with invasion to the adjacent tissues and no lymph node metastasis. Cutaneous VC of the neck is likely to grow locally without regional lymph node metastasis regardless of the long-term course and the size of the tumor.

Effects of Cigarette Smoke on the Nasal Respiratory and Olfactory Mucosa in Allergic Rhinitis Mice.

OBJECTIVE: Cigarette smoke (CS) exposure reportedly enhances allergic airway inflammation. However, some studies have shown an association between current cigarette smoke exposure and a low risk for allergic rhinitis. Thus, the impact of CS exposure on allergic rhinitis remains poorly understood. The purpose of this study was to investigate the effects of CS on the respiratory mucosa (RM) and the olfactory epithelium (OE) of mice with allergic rhinitis, as the effects may differ depending on the nasal histological compartments. METHODS: Eight-week-old male BALB/c mice were used for this study. We developed a mouse model of smoking by intranasally administering 10 doses of a CS solution (CSS), and a mouse model of allergic rhinitis by sensitization with intraperitoneal ovalbumin (OVA) injection and intranasal challenge with OVA. We examined the effects of CS on the nasal RM and OE in mice with or without allergic rhinitis using histological, serum, and genetic analyses. First, we examine whether CSS exposure induces allergic responses and then, examined allergic responses in the OVA-sensitized allergic rhinitis mice with or without CSS exposure. RESULTS: Short-term CSS administration intensified allergic responses including increased infiltration of eosinophils and inflammatory cells and upregulation of interleukin-5 expression in the nasal RM of OVA-immunized mice, although only CSS induced neither allergic responses nor impairment of the RM and OE. Notably, repetitive OVA-immunization partially impaired the OE in the upper-lateral area, but CSS administration did not reinforce this impairment in OVA-induced allergic mice. CONCLUSION: Short-term CSS exposure strengthened allergic responses in the nasal RM and did not change the structure of the OE. These results suggest that patients with allergic rhinitis could experience exacerbation of allergic symptoms after CS exposure.

Caloric restriction reduces basal cell proliferation and results in the deterioration of neuroepithelial regeneration following olfactotoxic mucosal damage in mouse olfactory mucosa.

The effects of caloric restriction (CR) on cell dynamics and gene expression in the mouse olfactory neuroepithelium are evaluated. Eight-week-old male C57BL/6 mice were fed either control pellets (104 kcal/week) or CR pellets (67 kcal/week). The cytoarchitecture of the olfactory neuroepithelium in the uninjured condition and its regeneration after injury by an olfactotoxic chemical, methimazole, were compared between mice fed with the control and CR diets. In the uninjured condition, there were significantly fewer olfactory marker protein (OMP)-positive olfactory receptor neurons and Ki67-positive proliferating basal cells at 3 months in the CR group than in the control group. The number of Ki67-positive basal cells increased after methimazole-induced mucosal injury in both the control and the CR groups, but the increase was less robust in the CR group. The recovery of the neuroepithelium at 2 months after methimazole administration was less complete in the CR group than in the control group. These histological changes were region-specific. The decrease in the OMP-positive neurons was prominent in the anterior region of the olfactory mucosa. Gene expression analysis using a DNA microarray and quantitative real-time polymerase chain reaction demonstrated that the expression levels of two inflammatory cytokines, interleukin-6 and chemokine ligand 1, were elevated in the olfactory mucosa of the CR group compared with the control group. These findings suggest that CR may be disadvantageous to the maintenance of the olfactory neuroepithelium, especially when it is injured.

Low CT Attenuation Values of Sinonasal Benign Tumours Relative to the Brainstem Identify Schwannomas.

OBJECTIVES: On computed tomography (CT), sinonasal schwannoma displays as a soft-tissue mass without any distinctive features. Our aim was to define the radiological criteria for distinguishing schwannoma from other sinonasal benign tumours. METHODS: We retrospectively identified consecutive patients who were pathologically diagnosed with benign sinonasal tumours between 2007 and 2016. CT attenuation values were compared between benign tumours and the brainstem. The utilities of demographic factors, clinical factors, and CT parameters for predicting the CT attenuation values of the brainstem were analysed by univariate and multivariate regression. RESULTS: Of the 111 identified cases of benign tumours, the CT attenuation values of tumours and the brainstem were analysed in 36 cases (schwannoma, 4 cases; inverted papilloma, 26; juvenile nasopharyngeal angiofibroma, 3; cavernous haemangioma, 3). The CT attenuation values of the schwannomas were significantly lower than in the brainstem, while those of the other tumours were significantly higher than in the brainstem. No factors affected the CT attenuation values of the brainstem. CONCLUSION: Low CT attenuation values of sinonasal benign tumours relative to the brainstem could distinguish schwannomas from other benign tumours.

Reduction of Proliferating Olfactory Cells and Low Expression of Extracellular Matrix Genes Are Hallmarks of the Aged Olfactory Mucosa.

Background: The incidence of olfactory impairment increases with age; however, the detailed molecular and cellular mechanisms underlying this increase are yet to be determined. Methods: We examined the influence of aging on olfactory receptor neurons (ORNs), which are maintained by a unique stem cell system, from olfactory progenitor cells to mature ORNs, by histological comparisons of the physiological status of the olfactory epithelium between young adult and aged mice. Furthermore, we clarified the expression of genes encoding inflammatory cytokines, neurotrophins, growth factors, and extracellular matrix proteins to reveal the molecular mechanisms underlying olfactory impairment caused by aging. Results: The numbers of mature and immature ORNs, but not olfactory progenitors, decreased in the aged olfactory epithelium, with a concurrent reduction in Ki-67-positive proliferating cells. Transcriptome analyses revealed an increase in Il6, encoding a component of senescence-associated secretary phenotypes (SASP), and a decrease in Igf1, encoding a growth factor for ORNs, in the aged nasal mucosa. Interestingly, expression levels of several extracellular matrix genes, including Col1a2, decreased in the aged nasal mucosa. Consistent with the transcriptional changes, the number of Col1a2-GFP-positive cells decreased in the aged lamina propria. Conclusions: Our data suggest that reduction in ORN number and cell proliferation, reduced extracellular matrix gene expression, and increased SASP contribute to olfactory impairment during aging.

Influence of the location of nasal polyps on olfactory airflow and olfaction.

BACKGROUND: Chronic rhinosinusitis with nasal polyps (CRSwNP) often results in decreased olfaction. In this study, we examined the relationship between nasal polyp location and olfactory airflow and odorant transport changes using virtual nasal polyp models at different locations and computational fluid dynamics (CFD) analysis. We also compared olfactory airflow and olfaction between patients with nasal polyps at different locations using CFD analysis and an olfactory test. METHODS: Nasal computed tomography images were used to generate a normal model and 4 virtual nasal polyp models based on polyp locations, including the olfactory region (all-olfactory model), the region anterior to the olfactory region (preolfactory model), the middle meatus (middle-meatus model), and the superior meatus (superior-meatus model). Various airflow parameters were compared between these models and a normal model without polyps. We then performed a similar comparison between the 3-dimensional (3D) reconstruction models of patients with nasal polyps, and retrospectively investigated the correlation between olfaction and nasal polyp location in those patients. RESULTS: Virtual nasal polyp analysis revealed dispersion of olfactory airflow in the all-olfactory model. Olfactory airflow and odorant transport showed maximum decrease in the preolfactory model and a slight decrease in the superior-meatus model. Olfactory airflow by polyps was further decreased by blockade of the olfactory airflow inlet than of the outlet. The findings obtained by patients corresponded well to those of the virtual polyp analysis. CONCLUSION: Olfactory airflow and olfaction are differentially affected by nasal polyp location. This finding is important for planning polyp-removal surgeries from the perspective of improving patient olfaction.

Environmental factors associated with allergic rhinitis symptoms in Japanese university students: A cross-sectional study.

OBJECTIVE: Numerous studies have reported that various environmental factors during early life are key determinants for developing allergic disease. Herein, we aimed to investigate the impact of environmental factors on allergic rhinitis. METHODS: This cross-sectional study was conducted in a single university in Japan (from April to June, in 2015 and 2016). Students voluntarily answered online questionnaires regarding their allergic rhinitis symptoms and their exposure to various environmental factors during preschool-age. RESULTS: Overall, 3075 students participated the questionnaire. After excluding those with incomplete datasets, 3016 students were eligible. Of these, 49% had allergic rhinitis symptoms. Female sex was associated with a lower risk of allergic rhinitis symptoms (odds ratio [OR], 0.82; 95% confidence interval [CI], 0.68-0.99). Comorbidity of asthma or atopic dermatitis and a family history of allergy (asthma, atopic dermatitis, or allergic rhinitis) were associated with higher risks of allergic rhinitis symptoms. Regarding the number of household members, compared with subjects with <3 people, those with 5 (OR, 0.74; 95% CI, 0.57-0.97) and ≥6 people (OR, 0.66; 95% CI, 0.49-0.88) in their household showed lower incidences of allergic rhinitis symptoms. No other environmental factors, including birth order, number of siblings, living environment, passive smoking, furry pet ownership, housing, bedding, breastfeeding, dairy product intake, preschool setting, and starting age of preschool, was associated with the incidence of allergic rhinitis symptoms. CONCLUSION: Sex, current asthma and atopic dermatitis symptoms, family history of allergies, and the number of people in the household at preschool-age were associated with the incidence of allergic rhinitis symptoms.

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.