The anatomical evolution of the thyroid cartilage from childhood to adulthood: A computed tomography evaluation

Gender Affirming Facial Surgery-Anatomy and Procedures for Facial Masculinization

For some patients, feminine facial features may cause significant gender dysphoria. Multiple nonsurgical and surgical techniques exist to masculinize facial features. Nonsurgical techniques include testosterone supplementation and dermal fillers. Surgical techniques include soft tissue manipulation, synthetic implants, regenerative scaffolding, or bony reconstruction. Many techniques are derived from experience with cisgender patients, but are adapted with special considerations to differing anatomy between cisgender and transgender men and women. Currently, facial masculinization is less commonly sought than feminization, but demand is likely to increase as techniques are refined and made available.

Virtual Reality Helps Describe the Progression of Thyroid Cartilage Calcification

OBJECTIVES

Thyroid cartilage (TC) calcifications may impact surgical planning and clinical management. However, few studies to date have implemented virtual reality (VR) to evaluate these calcifications. This study assessed the feasibility of evaluating TC calcifications in various regions and measuring their volumes through VR models generated from computed tomography scans. We also investigated age and gender-related differences in calcification patterns.

METHODS

Ninety-two participants were categorized into younger, middle-aged, and older age groups. Calcification patterns (degree in Hounsfield units and volume of calcification in cm3) in different TC regions were identified by VR analysis, which enabled comparisons between age groups and genders.

RESULTS

Significant differences in calcification patterns were observed between males and females, particularly in the middle right, middle left, bottom left, and vertex regions. Age-related differences in the vertex region showed increased calcification in the older age group.

CONCLUSION

This study points to the contribution of VR in the evaluation of complex anatomical structures. The findings revealed significant gender and age patterns in TC calcification. These insights can inform surgical planning and highlight the potential of using VR to gain a better understanding of TC calcification clinically.

Laryngeal cartilage calcifications on lateral cephalometric radiographs

The aim of this study was to determine the influence of age and gender on the incidence of calcification in laryngeal cartilage diagnosed on lateral cephalometric radiographs routinely taken for orthodontic diagnosis. The lateral cephalometric radiographs of 957 patients who met the study criteria were analyzed from among the 1000 lateral radiographs originally collected. The images were evaluated independently by two investigators. Given the dichotomous dependent variable (calcification or no calcification), a mixed logistic regression model was used to test how age and gender affected calcification. The effect of age and gender reliably determined the likelihood of laryngeal cartilage calcification. The greatest differences in the degree of calcification by gender were found at ages 20-25 years. The degree of calcification increased with age, reaching 100% in women at age 30 and in men at age 50. In women, the degree of calcification was higher than in men from the age of 13 years and levelled off at the age of 50 years. The interrater agreement was strong k = 0.97, z = 30.0, p < .001. Calcification can be detected by orthodontists trained in lateral cephalogram analysis and can be used as a screening or diagnostic tool to detect calcified areas in the larynx.

Two Cases of Atraumatic Laryngeal Fractures

INTRODUCTION AND AIM

Atraumatic laryngeal fractures are extremely rare and are most commonly provoked by sneezing or coughing. Only seven cases have been described in medical literature, and only one case described a fracture after swallowing. We present two cases of atraumatic laryngeal fracture after swallowing.

CASE REPORT

A 37-year-old male presented to the outpatient ENT clinic with severe dysphonia and odynophagia. He reported feeling a crack in the throat after swallowing with a flexed head. The patient's physical examination showed diffuse swelling and tenderness over the thyroid cartilage without subcutaneous emphysema. Flexible nasolaryngoscopy showed a large right true vocal fold hematoma with normal vocal fold movement. Computed tomography (CT) showed a fracture of the thyroid. Treatment consisted of corticosteroids and pantoprazole. Two years later he presented again at the emergency department with extreme odynophagia after suffering a knee punch on the larynx. CT showed a new fracture line, slightly off midline to the left in the thyroid cartilage. A 42-year-old male presented at the emergency department with odynophagia, dysphonia, and fever after feeling a crack in the throat during forceful swallowing in an extended neck position. Physical examination demonstrated a painful thyroid cartilage with subcutaneous emphysema. Flexible nasolaryngoscopy was normal but CT scan showed a slightly displaced fracture line of the median thyroid cartilage. Complaints gradually disappeared with conservative treatment with corticosteroids and antibiotics.

CONCLUSION

Congenital anomalies by abnormal mineralization and ossification could lead to focal weakness of the thyroid cartilage and thus predispose to non-traumatic fractures. The double triad of odynophagia, dysphagia, and dysphonia after sneezing, coughing or swallowing should raise the physician's attention to the possibility of thyroid cartilage fracture, especially after feeling or hearing a crack. Further investigation is obligatory with high-resolution CT of the neck and examination by an ENT specialist.

Laryngeal Framework Surgical Anatomy: A Radiological Study

PURPOSE

Awareness of variations in laryngeal anatomy among different age and gender groups is crucial during laryngeal framework surgery. The aim of this study is to demonstrate the relationship between gender and laryngeal radiologic morphometrics among different age groups and the applicability of important anatomical landmarks of laryngeal surgery.

METHODS

Laryngeal images of 180 adult patients older than 18 years of age were obtained by computed tomography and assessed. A total of 11 measurements of important laryngeal landmarks were taken from the patients' computed tomography images. Results were subgrouped according to gender and age, and these groups were compared for each measurement.

RESULTS

The majority of laryngeal measurements obtained in the study were higher in males than females, with the exception of the interlaminar angle. The mean interlaminar angle value was 88.27°± 14.99 for males and 103.04°± 14.81 for females (P <0.005). The distance from the anterior commissure to the inferior border of the thyroid cartilage was 10.46 ± 2.5 mm for males and 7.72 ± 1.9 mm for females. The anterior commissure locates slightly higher than the midpoint of the distance from the thyroid notch to the thyroid inferior border. The shortest distance between the muscular process of the arytenoid cartilage and the thyroid cartilage was found to be 9.60 ± 3.47 mm for males and 7.72 ± 2.33 mm for females (P <0.001).

CONCLUSION

Observation of obvious diversities in the size and distance of the important laryngeal structures between the gender groups is an important factor to be considered for successful laryngeal framework surgery. Also, using the midpoint of the thyroid cartilage as a landmark for anterior commissure is a practical method during surgery, especially for thyroplasty.

Chondrolaryngoplasty

Chondrolaryngoplasty is a surgical procedure that reduces the prominence of the thyroid notch. Although frequently performed on transgender (man to woman) women, anyone wishing to reduce the prominence of their thyroid notch for aesthetic purposes may consider undergoing a chondrolaryngoplasty. Direct visualization of the vocal cords with flexible laryngoscopy and intraoperative needle localization of the anterior commissure directs the extent of resection, helps increase safety, and avoids devastating postoperative voice complications. This procedure can be safely performed in combination with other facial feminization surgeries.

Bilateral Thyroid Foramina in a Completely Ossified Laryngeal Framework: A Case Report

The presence of a thyroid foramen in the thyroid cartilage of the larynx is not uncommon. It may be occluded by a fibrous layer, or it may be an abnormal path for the neurovascular bundle of the larynx. The superior laryngeal nerve and the superior laryngeal vessels are the most common contents of the thyroid foramen. During the observation of the skeleton of a 32-year-old female, we found a completely ossified laryngeal framework with bilateral double thyroid foramina. Three of the foramina were circular, and one was oval in shape. This is a very rare anatomical variation. Deep knowledge of the thyroid cartilage anatomy is mandatory during laryngeal and thyroid surgery. The meticulous dissection of laryngeal vessels and nerves is of paramount importance to control bleeding and avoid postoperative neurological sequelae due to nerve injury. The surgeon should be aware that in the whole length of the oblique line of the thyroid cartilage, a thyroid foramen may be detected.

Cervical ultrasound for the evaluation of the vocal cords: A pilot study in an endocrine surgery unit

INTRODUCTION

Cervical ultrasound (CE) has emerged as a promising tool in recent years for vocal cord (VC) assessment in patients undergoing thyroid surgery. Our aim is to assess the reliability of CE once implemented in an endocrine surgery unit and performed by the surgeons themselves.

MATERIAL AND METHOD

86 participants with no history of laryngeal pathology or cervical surgery underwent CE by three independent endocrine surgeons. Laryngeal structures and specifically the VCs were analysed. To consider the examination as diagnostic, the VCs had to be visualised statically and during phonation. The time taken to perform the technique and the interobserver variability were also analysed.

RESULTS

Of the 86 participants, 51.2% were male with a mean age of 43 years. The range of diagnostic examinations between surgeons was 60-68%, with substantial agreement between the 3 explorers (Fleiss's K-value = .714). Male sex and advanced age were factors associated with non-assessability of the technique. The mean procedure time was 72 s.

CONCLUSIONS

CE is a fast, non-invasive, feasible bedside tool useful for the assessment of VCs prior to thyroid surgery, mainly in young women.

Anatomic Characteristics of the Adolescent Cricothyroid Membrane on Computed Tomography Scans

BACKGROUND

The cricothyroid membrane (CTM) is the most important anatomic structure when performing emergency front-of-neck access (FONA) procedures. Adolescence is a period of rapid morphologic change in laryngeal structures, including the CTM. We hypothesized that the adolescent CTM would be sufficiently different from pediatric or adult anatomy to merit special consideration in FONA.

OBJECTIVE

The aim of the study was to define the procedurally relevant CTM anatomy in an adolescent population.

METHODS

This was a retrospective, multicenter cohort study composed of patients who underwent a diagnostic computed tomography scan during routine clinical care. Inclusion criteria were ages 16 to 19 years and a computed tomography of the neck with or without contrast. The primary outcome was CTM height measured in the midsagittal plane using electronic calipers.

RESULTS

One hundred thirty-four imaging studies met inclusion criteria. The average CTM height was strongly associated with age and ranged between 5.4 and 6.2 mm in male adolescents and 4.6 and 5.8 mm in female adolescents. We predicted that standard cuffed endotracheal and tracheostomy tubes recommended for FONA procedures (5.0- and 6.0-mm devices) could potentially fail for most patients in our cohort.

CONCLUSIONS

The adolescent CTM is smaller than previously recognized. We recommend having a variety of equipment sizes readily available at any site where airway management in adolescents may occur.

Transcutaneous Laryngeal Ultrasound for Vocal Cord Paralysis Assessment in Patients Undergoing Thyroid and Parathyroid Surgery-A Systematic Review and Meta-Analysis

Recurrent laryngeal nerve injury is an important complication following thyroid and parathyroid surgery. Recently, Transcutaneous laryngeal ultrasound (TLUSG) has emerged as a non-invasive alternative to laryngoscopic examination for vocal cord (VC) assessment. The aim of the systematic review and meta-analysis was to determine its diagnostic accuracy in reference to laryngoscopy. It was conducted in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. MEDLINE, Scopus, Cochrane library and Web of Science databases were searched to identify relevant articles. Sixteen studies were included in the review. Pooled diagnostic accuracy was calculated based on weighted arithmetic mean and plotting forest plot. The pooled visualization rate was 86.28% and 94.13% preoperatively and postoperatively, respectively. The respective pooled sensitivity and specificity was 78.48% and 98.28%, and 83.96% (CI 95%: 77.24-88.50%) and 96.15% (CI 95%: 95.24-96.88%). The diagnostic accuracy improved if transverse and lateral approaches, and valsalva maneuver were utilized. Male gender and older age were the most crucial risk factors for VC non-visualization. TLUSG is an efficacious screening tool for vocal cord palsy due to its high sensitivity. It is likely to prevent unnecessary laryngoscopic examination in around 80% of patients, with the potential for becoming a gold standard for specific (female/young) patient cohort through assimilative modifications use, increasing expertise and development of objective measurements in the future.

Emergency Front-of-Neck Airway Rescue Via the Cricothyroid Membrane: A High-Resolution Computed Tomography Study of Airway Anatomy in Adults

BACKGROUND

Emergency front-of-neck airway rescue is recommended in a can't intubate, can't oxygenate clinical scenario. Cannula cricothyroidotomy has been reported as having a high failure rate. Our primary aim was to estimate the angle of the trachea in relation to the horizontal axis in a simulated emergency front-of-neck airway rescue position. Our secondary aims were to estimate the optimal cannula angle of approach and evaluate the anatomical relationship of the cricothyroid membrane (CTM) to adjacent structures. We also assessed whether the CTM lies above or below the neck midpoint, a point equidistant from the suprasternal notch (SSN), and the chin surface landmarks. All measurements were compared between the male and female subjects.

METHODS

Subjects having elective computed tomography of their thorax were consented to have extension of the computed tomography to include their neck. A preliminary radiation dose and risk assessment deemed the additional radiation to be of very low risk (level IIa). Subjects were positioned supinely on the computed tomography table. Standard neck extension was achieved by placing a pillow under the scapulae and a rolled towel under the neck to simulate emergency front-of-neck airway rescue positioning.

RESULTS

Fifty-two subjects were included in this study: 31 men and 21 women. The mean angle of the trachea in relation to the horizontal axis was 25.5° (95% confidence interval [CI], 21.8-29.1) in men and 14.0° (95% CI, 11.5-16.5) in women. The mean minimum angles required for hypothetical cannula cricothyroidotomy for men and women were 55.2° (95% CI, 51.8-58.7) and 50.5° (95% CI, 45.4-55.6), respectively. The CTM was located lower in the neck in men compared to women. The CTM was located below the neck midpoint in 30 of 30 (100%) male subjects and 11 of 20 (55%) female subjects (P < .001).

CONCLUSIONS

The trachea angulates posteriorly in a simulated emergency front-of-neck airway rescue position in supine subjects and to a greater degree in men compared to women (P < .001). The minimum angle required for hypothetical cannula cricothyroidotomy was >45° in the majority (75%) of subjects studied. A steeper cannula angle of approach may be more reliable and warrants further clinical study. If airway anatomy is indistinct and performing a vertical scalpel cricothyroidotomy, consideration should be given to performing this incision lower in the neck in men compared to women.

The value of 1.5T MRI in the evaluation of vocal fold mobility in patients with goiter

The laryngoscopic examination remains the gold standard in the perioperative evaluation of the mobility of the vocal folds in patients with goiter. During the COVID-19 pandemic, many medical procedures, including laryngoscopy are optimized in terms of epidemiological safety. Therefore, it seems deeply justified to implement methods like i.e. ultrasound or MRI which can provide the diagnostic information usually obtained via laryngoscopic examination.

Aim of the study

To determine the value of dynamic MRI examination in the 1.5 T field in the assessment of the mobility of vocal folds in patients with goiter compared to healthy people and in relation to ultrasound examinations and routine laryngoscopy.

Materials and methods

35 healthy volunteers and 44 patients with goiter were subjected to videolaryngoscopy, dynamic examinations of the vocal folds during respiration and phonation using ultrasound and the MRI sequences: generic gradient echo (GRE) and true fast imaging with steady-state precession (TRUFI). The qualitative and quantitative data were analyzed, i.e. the angles of deviation from the midline of the vocal folds and the area of the right and left rima glottidis compartments.

Results

No statistically significant differences were found between the groups of healthy volunteers and patients with goiter in the values of the angles of deviation of the vocal folds with the use of ultrasound and two MRI dynamic sequences - GRE and TRUFI. There were also no statistically significant differences in the areas of the rima glottidis compartments between these two groups with the use of two MRI dynamic sequences - GRE and TRUFI. Among the analyzed parameters, the maximum size of each rima glottidis compartment was the only one to show features of sexual dimorphism and was significantly higher in men (GRE p < 0.001 and TRUFI p = 0.001). There was no correlation between the size of the minimum and maximum rima glottidis compartment and the total volume of the thyroid lobes in patients with goiter for the GRE and TRUFI sequences.

Conclusions

MRI is a promising tool for the objective assessment of the mobility of the vocal folds in patients with goiter, as well as for the qualification for treatment and monitoring its effects. It is particularly important during an epidemiological emergency due to its safety compared to laryngoscopy. The presence of the goiter and its volume do not limit the possibility of performing dynamic imaging studies of the vocal folds and do not affect the surface area of the glottis.

High-resolution magnetic resonance and mass spectrometry imaging of the human larynx

High-resolution, noninvasive and nondestructive imaging of the subepithelial structures of the larynx would enhance microanatomic tissue assessment and clinical decision making; similarly, in situ molecular profiling of laryngeal tissue would enhance biomarker discovery and pathology readout. Towards these goals, we assessed the capabilities of high-resolution magnetic resonance imaging (MRI) and matrix-assisted laser desorption/ionisation-mass spectrometry (MALDI-MS) imaging of rarely reported paediatric and adult cadaveric larynges that contained pathologies. The donors were a 13-month-old male, a 10-year-old female with an infraglottic mucus retention cyst and a 74-year-old female with advanced polypoid degeneration and a mucus retention cyst. MR and molecular imaging data were corroborated using whole-organ histology. Our MR protocols imaged the larynges at 45-117 μm² in-plane resolution and capably resolved microanatomic structures that have not been previously reported radiographically-such as the vocal fold superficial lamina propria, vocal ligament and macula flavae; age-related tissue features-such as intramuscular fat deposition and cartilage ossification; and the lesions. Diffusion tensor imaging characterised differences in water diffusivity, primary tissue fibre orientation, and fractional anisotropy between the intrinsic laryngeal muscles, mucosae and lesions. MALDI-MS imaging revealed peptide signatures and putative protein assignments for the polypoid degeneration lesion and the N-glycan constituents of one mucus retention cyst. These imaging approaches have immediate application in experimental research and, with ongoing technology development, potential for future clinical application.

A proposal for needle projections in transcutaneous injection laryngoplasty using three-dimensionally reconstructed CT scans

PURPOSE

This study aims to determine laryngeal dimension in relation to all three transcutaneous injection laryngoplasty (TIL) approaches (thyrohyoid, transthyroid and cricothyroid) using three-dimensionally reconstructed Computed Tomography (CT) scan and compare the measurements between sex, age group and ethnicity.

METHODS

CT scans of the neck of two hundred patients were analysed by two groups of raters. For thyrohyoid approach, mean distance from the superior border of the thyroid cartilage to the laryngeal cavity (THd) and mean angle from the superior border of the thyroid cartilage to mid-true cords (THa) were measured. For transthyroid approach, mean distance from mid-thyroid cartilage to mid-true cords (TTd) and Hounsfield unit (HU) at mid-thyroid cartilage (TTc) were measured. For cricothyroid approach, mean distance from the inferior border of the thyroid cartilage to the laryngeal cavity (CTd) and mean angle from the inferior border of the thyroid cartilage to mid-true cords (CTa) were measured.

RESULTS

There were statistically significant differences between males and females for all measurements except for CTa (p < 0.0001). No significant difference across age groups and ethnicities were found for all three approaches (p > 0.05). There was a significant fair positive correlation between age and TTc (p = 0.0002). For all measurements obtained, there were moderate to excellent inter-group consistency and intra-rater reliability.

CONCLUSION

This study demonstrated a significant sex dimorphism that may influence the three TIL approaches except for needle angulation in the cricothyroid approach. The knowledge of laryngeal dimension is important to increase success in TIL procedure.

Accuracy of pediatric cricothyroid membrane identification by digital palpation and implications for emergency front of neck access

BACKGROUND

Emergency front of neck access in a "can't intubate can't oxygenate" scenario in pediatrics is rare. Ideally airway rescue would involve the presence of an ear, nose, and throat surgeon. If unavailable however, responsibility lies with the anesthesiologist and accurate identification of anterior neck structures is essential for success.

AIM

We assessed anesthesiologists' accuracy in identification of the pediatric cricothyroid membrane by digital palpation in three predefined age groups (37 weeks to <1 year old, 1-8 years old, and 9-16 years old) and whether accuracy improved with repetition. We also investigated a novel hypothetical vertical skin incision strategy to successfully expose the cricothyroid membrane.

METHODS

We asked anesthesiologists to identify the location of the cricothyroid membrane of anesthetized children in the extended neck position. Accuracy was defined as a mark made within the margins of the cricothyroid membrane using ultrasound as a reference standard. The position of the cricothyroid membrane relative to the neck midpoint, between the suprasternal notch and mentum, was defined for each child. Using this neck midpoint, we determined the hypothetical vertical skin incision lengths required to successfully expose the cricothyroid membrane ("midpoint incision").

RESULTS

Ninety-seven patients were included in this study. There were 14, 58, and 25 patients recruited across the three predefined groups. Accurate anesthesiologist identification of the location of the cricothyroid membrane occurred in 29.4%, 28.6%, and 38.2% of attempts, respectively. The majority of inaccurate assessments (64.1%) were below the cricothyroid membrane. There was no improvement in accuracy with repetition. Hypothetical "midpoint incision" lengths of 20, 30, and 35 mm were required.

CONCLUSION

Significant anesthesiologist inaccuracy exists in locating the cricothyroid membrane in children of all ages. This has implications for the technical approach to emergency front of neck access and how we teach the management of "can't intubate can't oxygenate" in pediatric practice.

Exercise-induced laryngeal obstruction (EILO) in children and young adults: From referral to diagnosis

OBJECTIVE

To identify different presentations, referral patterns, comorbidities, and laryngoscopy findings in children and young adults with exercise-induced laryngeal obstruction (EILO).

METHODS

We performed a retrospective chart review of 112 patients, age <26 years, with EILO between 2013 and 2016.

RESULTS

Of the 112 patients who met criteria, 91 were female and 21 were male. Patients were most frequently referred by pulmonologists (60.7%). The majority of patients (93%) participated in organized sports, most of them at a competitive level. The mean age at symptom onset was 13.8 ± 3.3 years, and the mean age of diagnosis was 15.4 ± 3.0 years. Sixty-seven (59.8%) patients presented with a prior diagnosis of asthma, the majority of whom had failed asthma treatment. The most common symptoms reported were dyspnea (93.8%), wheezing/stridor (78.6%), and throat tightness (48.2%). Ninety-one (81.3%) patients had spirometry performed, with 46 (51.1%) showing inspiratory loop flattening. On flexible laryngoscopy, 87 (78.4%) of 111 patients had paradoxical vocal fold motion. Supraglottic involvement was observed to obstruct the airway in 26 (23.9%) patients, with patterns of obstruction similar to those observed in children with laryngomalacia.

CONCLUSION

Most patients participated in competitive sports, were female, and presented with exertional dyspnea. Most patients were diagnosed with exercise-induced asthma but treated unsuccessfully. Almost one-quarter of our patients showed supraglottic collapse obstructing the airway. Exercise-induced laryngeal obstruction is a more descriptive term than paradoxical vocal fold motion or vocal cord dysfunction, which only describe vocal fold involvement. The time to diagnosis of EILO was shorter than previously reported, suggesting that awareness of this condition is increasing.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:E400-E406, 2020.

Imaging of the age-related anatomical relationship between the innominate artery and the trachea

PURPOSE

To measure the age-dependent changes of anatomical positions and relations between the trachea, cricoid cartilage (CC), and innominate artery (IA) in adults by computed tomography (CT).

METHODS

A retrospective cohort reviewing images of 127 consecutive adult patients who underwent CT angiography (CTA) of the neck. The trachea-to-IA (T-IA) distance was measured as the minimal horizontal distance between them. The vertical distance between the CC and the IA was measured between the axial section, demonstrating the CC's inferior border to the axial section at the level of the T-IA measurement.

RESULTS

Images of 125 patients (median age 53 years, range 18-89; 74 males) were reviewed. The mean T-IA distance was 2.3 ± 1.1 mm for males and 1.7 ± 0.9 mm for females (P = 0.002). The vertical C-IA distance was 44.2 ± 11.4 mm and 49.5 ± 12.5 mm for males and females, respectively (P = 0.01). Age correlated negatively with the vertical C-IA distance (P < 0.0001) and positively with the T-IA distance (P < 0.0001). The rate of IA variants was 23.2%, with no significant difference between the measurements of distances among patients with or without IA variants.

CONCLUSIONS

This is the first description of the relationships between the trachea, CC, and IA distances in adults as depicted on CTA. The T-IA distance becomes larger while the T-CC distance becomes shorter with age.

Normal radiological anatomy of thyroid cartilage in 600 Chinese individuals: implications for anterior cervical spine surgery

Background

Thyroid cartilage is an important barrier in anterior cervical approach surgery. The objective of this study is to establish normative values for thyroid cartilage at three planes and to determine their significance on preoperative positioning and intraoperative traction in surgery via the anterior cervical approach.

Methods

Neck CT scans were collected from 600 healthy adults who did not meet any of the exclusion criteria. Transverse diameters (D1, D2, and D3) of the superior border of the thyroid cartilage (SBTC), inferior border of the thyroid cartilage (IBTC), and the trachea transverse diameters of the inferior border of the cricoid cartilage (IBCC) were measured on a horizontal plane.

Results

All measured variables had intra-class correlation coefficients (ICCs) of ≥ 0.7. The differences in transverse diameters on the same plane between males and females were significantly different (all p < 0.001). The SBTC is most often at C4 in women (59.5%) and C4/5 in men (36.4%), the IBTC is most often at C5 in women (48.1%) and men (46.2%), and the IBCC is primarily located at C6 in women (45.2%) and C6 or C6/7 in men (34.4%) (all p < 0.001).

Conclusion

We present normative values for thyroid cartilage at three planes of SBTC, IBTC, and IBCC in Chinese individuals. The individual and gender differences in the location of the thyroid cartilage and the size of the thyroid cartilage and the cricoid cartilage provide an anatomical basis to localize the skin incision, to predict the difficulty of intraoperative exposure and retractor pulling, and to identify that the thyroid cartilage protected the pharyngoesophageal wall.