|Year : 2015 | Volume
| Issue : 1 | Page : 2-8
A lateral cephalogram study for evaluation of pharyngeal airway space and its relation to neck circumference and body mass index to determine predictors of obstructive sleep apnea
Sandeep Kaur1, Shalu Rai2, Abhishek Sinha3, Vikas Ranjan2, Deepankar Mishra2, Sapna Panjwani2
1 Department of Oral Medicine and Radiology, Indira Gandhi Government Dental College and Hospital, Jammu, Jammu and Kashmir, India
2 Department of Oral Medicine and Radiology, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
3 Department of Orthodontics and Orthopedics, Mithila Minority Dental College and Hospital, Darbhanga, Bihar, India
|Date of Submission||14-Jan-2014|
|Date of Acceptance||02-Aug-2015|
|Date of Web Publication||12-Oct-2015|
Department of Oral Medicine and Radiology, Institute of Dental Studies and Technologies, Kadrabad, Modinagar, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: The airway is assumed to play a role in dentofacial development. So, several studies tried to correlate patients with normal nasorespiratory functions with different malocclusions and airway dimensions. A narrow upper airway is associated with obstructive sleep apnea (OSA). Currently neck size and obesity are considered to be the most important physical characteristics of patients with sleep apnea. Aim: To study the interaction between craniofacial structures and pharyngeal airway space along with soft palate and tongue in patients with different anteroposterior skeletal patterns using lateral cephalogram. The correlation of upper airway and soft-tissue measurements with neck circumference (NC) and body mass index (BMI) was elucidated to evaluate the predictors on lateral cephalogram, in order to determine the etiology of OSA. Materials and Methods: Lateral cephalograms of 45 subjects were used to measure the pharyngeal airway and were divided into three groups (each group included 15 subjects) according to ANB angle: Class I (ANB angle 2°-4°), Class II (ANB angle >4°), and Class III (ANB angle <2°). Velar morphology along with its length was also analyzed and categorized into different types. The NC and BMI of all the patients were also calculated. Student's t-test for paired samples was used to compare the mean values of the study variable vital parameters. Results: Significant reduction was found in pharyngeal airway in ANB group II. The soft palate and tongue size increased with increasing BMI and NC. Conclusion: Sagittal skeleton pattern had a close association with the dimensions of pharyngeal airway passage. The correlation of NC with increase in soft-tissue size (soft palate and tongue) suggested that obesity mediates its effects in OSA through fat deposition in the neck.
Keywords: Airway space, BMI, lateral cephalogram, malocclusion, NC, OSA, soft-tissue area
|How to cite this article:|
Kaur S, Rai S, Sinha A, Ranjan V, Mishra D, Panjwani S. A lateral cephalogram study for evaluation of pharyngeal airway space and its relation to neck circumference and body mass index to determine predictors of obstructive sleep apnea. J Indian Acad Oral Med Radiol 2015;27:2-8
|How to cite this URL:|
Kaur S, Rai S, Sinha A, Ranjan V, Mishra D, Panjwani S. A lateral cephalogram study for evaluation of pharyngeal airway space and its relation to neck circumference and body mass index to determine predictors of obstructive sleep apnea. J Indian Acad Oral Med Radiol [serial online] 2015 [cited 2020 Jan 19];27:2-8. Available from: http://www.jiaomr.in/text.asp?2015/27/1/2/167062
| Introduction|| |
Normal respiration is dependant on sufficient anatomic dimensions of the airway. Many studies demonstrated a significant relationship between various pharyngeal structures and both dentofacial and craniofacial structures at varying degrees.  It suggests that variation in skeletal pattern could predispose to upper airway obstruction.
Lateral cephalometry is a simple and well-standardized imaging technique consisting of a radiograph of the head and neck with specific emphasis on bony and soft-tissue structures. It has demonstrated various abnormalities of the craniofacial and upper airway soft-tissue anatomy in patients with upper airway obstruction during sleep which is related to the severity of obstructive sleep apnea (OSA). Craniofacial abnormalities such as mandibular deficiency, bimaxillary retrusion, steep occlusion plane, increased mandibular plane angle, and a more caudally positioned hyoid bone result in narrowing of the pharyngeal airway passage. , Morphometric assessment of the nasopharynx or the configuration of adjacent structures including oropharynx and hypopharynx can be defined in terms of depth and height in the median sagittal plane on this radiograph. The dimensional analysis of the soft palate and tongue and its interaction with upper airway size can be reviewed in depth. It remains unclear whether craniofacial abnormalities or upper airway soft-tissue changes are the more important determinants of OSA in most patients.
Obesity occurs in most patients with OSA and is considered to be a major risk factor for its development. Neck circumference (NC) is a simple clinical measurement that reflects obesity in the region of the upper airway. Patients with OSA have been shown to have big necks when compared with both nonapneic snorers and weight-matched controls.  Also, in OSA patients, upper airway morphology seems to differ according to neck size or body mass index (BMI). Furthermore, NC correlates with several soft-tissue variables measured from lateral cephalometry and correlates better than body mass index with apnea severity,  suggesting that obesity mediates its effects in OSA through fat deposition in the neck. However, not all patients with OSA are obese and some of these nonobese patients have obvious abnormal craniofacial structure.  The aim of this study was, therefore, to evaluate the relationship of craniofacial structures and upper airway soft-tissue measurements on a lateral cephalogram along with BMI and NC to evaluate the predictors of sleep apnea.
| Materials and Methods|| |
The study was carried out on patients reporting to the Institute of Dental Studies and Technologies who were diagnosed with Class I, II, and III malocclusion and were advised for lateral cephalogram. A total of 45 patients in the age range of 18-25 years were selected for the study. All the subjects who were not undergoing orthodontic treatment were included in the study. However, the patients who were edentulous, had cross bite (posterior), and were suffering from airway problem, large adenoids, and tonsils were excluded from the study. Written consent was taken from each patient and ethical clearance was obtained from the ethical committee of the institution.
Based on the saggital skeleton pattern, all the patients were divided into three groups with each group containing 15 subjects: Class I group (ANB angle 2°-4°), Class II group (ANB angle >4°), and Class III group (ANB angle <2°). Subjects were exposed with teeth in centric occlusion and lips relaxed, and a fixed anode midsaggital plane distance was used using a standarized technique. Magnification of machine was also taken into consideration. The dorsum of the tongue and pharyngeal airway were coated with radiopaque dye IOHEX (i.e. iodine 300 mg, tromethamine 1.2 mg, edetate calcium disodium 0.1 mg, and water) to enhance the outline of tongue and pharyngeal soft tissue. The patient was asked to swish the dye for 1 s and then swallow. The radiographs were obtained with Kodak model no. 8000C (Kodak Dental System, France). All the radiographs were traced manually by the same investigator. Various cephalometric landmarks and the linear and angular parameters used for the measurement of pharyngeal airway passage and soft-tissue (soft palate and tongue) dimensions were traced manually with 0.5 mm lead pencil on acetate paper to the nearest 0.1 mm. The area of the airway and soft tissue, i.e. nasopharynx, oropharynx, hypopharynx, soft palate, and tongue, was calculated with Image Tool 3.00 software in pixel square. The pixel square was converted into millimeter square by multiplying the value with 0.264.
Angular measurement [Figure 1]
- SNA: Angle formed between the plane constructed from Nasion (N) to Sella and Point A.
- SNB: Angle formed between the plane constructed from Nasion (N) to Sella and Point B.
- ANB: Difference between SNA and SNB angles.
|Figure 1: Cephalometric landmark: Hard tissue linear and angular measurement|
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Hard tissue linear measurement [Figure 1]
- Upper anterior facial height (UAFH): Plane constructed from N to the anterior nasal spine (ANS).
- Lower anterior facial height (LAFH): Plane constructed from ANS to menton.
- Posterior facial height (PFH): Plane constructed from Sella (S) the center of the hypophyseal fossa (sella turcica) to the Gonion (Go).
- Position of hyoid bone: The distance from anterior hyoid (AH) to the cervical column measured parallel to Frankfort horizontal plane (FH), the horizontal position of the hyoid bone.
Linear measurement of upper airway space and soft tissue [Figure 2]
- Superior posterior airway space (SPAS): It is measured from a point on the posterior outline of the soft palate to the closest point on the pharyngeal wall. This measurement is taken on the anterior half of the soft palate outline.
- Middle airway space (MAS): It is measured from the point of intersection of the posterior border of the tongue and the inferior border of the mandible to the closest point on the posterior pharyngeal wall.
- Inferior airway space (IAS) (mm): It is measured between the posterior pharyngeal wall and the point of intersection of the tongue with hyoid bone, i.e. the point of intersection of epiglottis and base of the tongue (V) to lower pharyngeal wall (LPW).
- Tongue length (TGL) (mm): It is measured between the tip of the tongue (TT) and the base of the epiglottis (Eb), the deepest point of the epiglottis.
- Tongue height (TGH) (mm): It is the linear distance between a point on the most superior curvature of the tongue dorsum and the base of a line drawn perpendicular to the TT-V line.
- Soft palate length (PNS − P) (mm): The linear distance between posterior nasal spine (PNS) and P.
Measurement of upper airway and soft-tissue area [Figure 3]
- Nasopharynx (mm 2 ): The area outlined by a line between R and PNS, an extension of the palatal plane to the posterior pharyngeal wall, and the posterior pharyngeal wall.
- Oropharynx (mm 2 ): The area outlined by the inferior border of the nasopharynx, the posterior surface of the soft palate and tongue, a line parallel to the palatal plane through the point Et, and the posterior pharyngeal wall.
- Hypopharynx (mm 2 ): The area outlined by the inferior border of the oropharynx, the posterior surface of the epiglottis, a line parallel to the palatal plane through the point C4, and the posterior pharyngeal wall.
- Tongue (mm 2 ): The area outlined by the dorsal configuration of the tongue surface and lines that connect TT, retrognathion (RGN), hyoidale (H), and Eb.
- Soft palate (mm 2 ): The area confined by the outline of the soft palate that starts and ends at PNS through P.
The NC was measured at the cricothyroid level with the measuring tape and was divided into three groups:
Group A: NC less than or equal to 30 cm;
Group B: NC 31-34 cm; and
Group C: NC greater than or equal to 35 cm.
The population was stratified by BMI using cut-off points as follows:
Group I: <23 - lean
Group II: 23-25 - normal
Group III: >25 - obese
During routine clinical assessment, patients were weighed on health scale weighing machine. Height was measured with a wall-fixed height rule (Sterling, an ISO-certified unit health scale). The BMI of the subjects was calculated using the following formula:
Student's t-test for paired samples was used to compare the mean values of the study variable vital parameters. The statistical test, Chi-square test, was used for calculating the difference between proportions. All the statistical analyses were performed using appropriate software (SPSS for Windows, Release 16.0; SPSS, Mumbai, India). The probability value P < 0.05 was considered as significant and probability value equal to or less than ≤0.01 was considered as highly significant.
| Results|| |
The study sample consisted of 25 males with a distribution of 9 (36%), 4 (15%), and 12 (48%) and 20 females with a distribution of 6 (30%), 11 (55%), and 3 (20%) in each ANB group, respectively [Table 1]. Upper airway space and area were measured and compared in the three different ANB groups [Table 2], which showed a statistically significant difference in oropharynx (P < 0.05) and highly significant difference in SPAS and nasopharynx (P < 0.01). Statistically significant difference was found among the groups for PFH (P < 0.05). There was a statistically significant difference in SNA, SNB, and ANB angles (P ≤ 0.01), suggesting a positive association between sagittal maxillomandibular relationship and the dimensions of pharyngeal structures. Larger dimension of soft palate length (PNS − P) was found in Class II; however, the statistical difference was found to be insignificant (P > 0.05). Skeletal configuration (ANB) showed a correlation with the anteroposterior position of the hyoid bone in relation to C3 [Table 3]. Demographic data based on BMI was calculated, i.e. less than or equal to 23 (n = 16, 35.6%), between 23 and 25 (n = 19, 42.2%), and more than or equal to 25 (n = 10, 22.2%) [Table 4]. Comparison of upper airway space and soft-tissue variables in different BMI groups showed a statistically significant difference for the tongue area (P < 0.05) and a highly significant difference for the soft palate area (P ≤ 0.01) [Table 5]. The subjects in our study were also divided into three groups according to NC, i.e. less than or equal to 30 (n = 12, 26.7%), between 31 and 34 (n = 16, 35.65%), and greater than or equal to 35 (n = 17, 37.8%) [Table 6]. Highly significant statistical difference was found for NC and BMI (P < 0.01) in the BMI group [Table 4] and for NC (P ≤ 0.01) and BMI (P < 0.01) in the NC group [Table 6], suggesting that BMI increased progressively with increasing NC and NC increased progressively with increasing BMI. Comparison of upper airway soft tissue in different NC groups showed corelation to the size of tongue and the soft palate [Table 7]. Highly significant statistical difference was found for the tongue area when compared with NC (P ≤ 0.01).
|Table 2: Comparison of facial height, soft-tissue linear measurements, upper airway space and area, and soft tissue in different ANB groups on the lateral cephalogram|
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|Table 3: Comparison of level of hyoid bone in three different ANB groups|
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|Table 4: Demographic data of patients depending on BMI with NC, gender, and age|
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|Table 5: Mean and standard deviation of cephalometric upper airway space and area along with soft tissue according to three different BMI groups|
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|Table 6: Demographic data of patients depending on NC with BMI, gender, and age|
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|Table 7: The mean and standard deviation of cephalometric upper airway space and area according to three different NC groups|
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| Discussion|| |
Cephalometric radiographs have been used for many years to evaluate facial growth and development. Cephalometry enables analysis of dental and skeletal anamolies as well as soft-tissue structures and form. A normal nasal airway is dependent on sufficient anatomical dimensions of the airway. The ANB angle was used to classify the subjects according to their skeletal configurations. Bhad et al.'s  classification regarding ANB angle was used, i.e. Class I group (ANB angle 2°-4°), Class II group (ANB angle >4°), and Class III group (ANB angle <2°).
When the airway dimensions were compared, significant difference was found between Class I, Class II, and Class III groups at the nasopharynx and oropharynx levels. It was found that with increase in ANB angle (>4°), i.e. Class II group, there was an overall lesser dimension of upper airway area, i.e. nasopharynx, oropharynx, and hypopharynx, and with decrease in ANB angle (<2°), i.e. Class III group, there was an overall larger nasopharyngeal and oropharyngeal area dimension. The finding that oropharyngeal airway area became smaller with the increase in ANB angle (Group II) was in accordance with Ceylon and Otkay who measured the pharyngeal size of subjects with different ANB angles. The fact that the larger the ANB angle, the lesser is the oropharyngeal area may be attributable to the different location of tongue and mandible in Class II malocclusion than in other skeletal configurations, as stated by Balters' philosophy.  The respiratory function is impeded in the region of larynx and there is faulty deglutition and mouth breathing. Class III malocclusions are due to more forward position of the tongue and the cervical overdevelopment. 
There was a positive correlation between SNA, SNB, and ANB angles and pharyngeal airway, i.e. nasopharynx, oropharynx, and hypopharynx (P ≤ 0.01). Our results are in accordance with those of Alves et al.  The upper airway space was measured and compared between the three different ANB groups. It was found that with increase in ANB angle (>4°), i.e. Class II group, there was decrease in MAS and IAS; in ANB group (2°-4°), i.e. Class I group, there was increase in upper airway space, i.e. SPAS, MAS, and IAS. The finding that patients with Class II malocclusion had narrower oropharynx and hypopharynx spaces, i.e. MAS and IAS, than the patients in Class I group was in accordance with the findings of Kirjavainen and Kirjavainen. 
The relationship of facial height of patients with upper airway, soft palate, and tongue size was determined. It was found that with increase in PFH, the tongue area increased, which was in accordance with Hwang et al.  Patients with increase in UAFH showed larger nasopharyngeal area, which was in partial accordance to the finding of Kerr (1985),  confirming that when the function is normal, the relationship between changes in nasopharyngeal morphology and anterior facial height is weak. The finding that nasopharyngeal area is of smaller dimension in the Class II group is completely in accordance with the author. With increase in PFH, there was an increase in airway space, i.e SPAS, MAS, and IAS. Thus, our study concludes that facial height has an influence on nasopharynx and tongue area.
The finding of larger dimension of soft palate length in Class II group is in aggrement with Jena et al.,  who evaluated the effects of sagittal mandibular development on the dimensions of the pharyngeal airway passage in awake patients and suggested that the backward position of tongue results in compression of the soft palate and, therefore, decrease in thickness and increase in length of the soft palate. Class II malocclusion group had a narrower upper airway associated with decreased PFH than in the Class I malocclusion group. This finding was in accordance with Hong et al. 
Cephalometric upper airway space and soft-tissue variables were compared in different BMI groups and it was found that there was a decrease in SPAS, MAS, and IAS with an increase in BMI, and in patients with BMI <23, there was narrower nasopharynx and hypopharynx. Soft palate and tongue size increased with increasing BMI and were different among groups, and no relationship was found between upper airway size and BMI, which was in accordance with Lowe et al. The fact that upper airway abnormalities do not correlate significantly in more obese subjects suggests that other pathophysiological mechanisms such as increased upper airway collapsibility, fragmented sleep, ventilatory instability, and neurological mechanisms (changes in upper airway dilator muscle activity) may be more important factors.
The NC was correlated with BMI and it was found that BMI increased progressively from group A to C, which was in accordance with Ferguson et al.  Tongue and soft palate area increased as NC increased and the difference was highly significant, which was in accordance with Ferguson et al. Our study also concluded that there was reduction in MAS, IAS, and oropharyngeal airway area with increasing NC and the difference was statistically insignificant (P < 0.05). However, cross-sectional upper airway measurements of the SPAS, nasopharynx, and hypopharynx did not relate to NC. Ferguson et al.  evaluated the relationships between NC, BMI, apnea severity, and craniofacial and upper airway soft-tissue measurements from upright lateral cephalometry and found that obese patients showed increased upper airway soft-tissue structures, nonobese patients showed abnormal craniofacial structure, and an intermediate group of patients had abnormalities in both craniofacial structure and upper airway soft-tissue structures.
Obesity occurs in most patients with OSA and is considered to be a major risk factor for its development. The mechanisms whereby obesity contributes to the pathogenesis of OSA are poorly understood. Various studies have used upper airway imaging to examine the relationship between obesity and OSA. Our data are consistent with that of Partinen et al.,  where they demonstrated that upper airway soft-tissue structures increase in size with increasing obesity; however, they did not demonstrate a similar relationship between obesity and craniofacial measurements, which is in accordance with our study. The evidence that OSA patients with a low BMI may have a higher incidence of upper airway abnormalities is not in accordance with Partinen et al. Although the limitations of an awake upright two-dimensional image of a three-dimensional structure are obvious, lateral cephalogram used in the assessment of sleep apnea and craniofacial form have advantages of wide availability, simplicity, and low cost. But scans obtained in supine position are recommended for individuals with OSA, as this position results in changes in the dimensional measurements of the upper airway space due to gravitational changes.
| Conclusion|| |
Sagittal skeleton pattern may be a contributory factor in variations in the upper airway dimension. The fact that the larger the ANB angle, the lesser is the oropharyngeal area may be attributable to a different location of tongue and mandible in Class II malocclusion than in other skeletal configurations. Comparison of the relationship of facial height of patients with upper airway soft tissue suggested that PFH has an influence on pharyngeal airway space and tongue area. Changes in position of hyoid bone tend to be related to changes in mandibular position and retrognathic mandible in Class II patients which leads to inferior posterior displacement of the hyoid bone.
Patients with increasing NC have large dimensions of upper airway soft tissue (increased soft palate and tongue size) providing predictive information about the severity of OSA and insights into the possible underlying cause of OSA. It has been hoped that these findings may be used not only as references for the normal soft palate, but also for etiological research of OSA syndrome (OSAS). Further investigation using both static and dynamic imaging techniques would further clarify the pathogenesis of OSA in obese and nonobese patients.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]