|Year : 2015 | Volume
| Issue : 1 | Page : 27-33
Area and volume of the pharyngeal airway in surgically treated unilateral cleft lip and palate patient: A cone beam computed tomography study
Shailendra Singh Rana, Ritu Duggal, Om Prakash Kharbanda
Department of Orthodontics and Dentofacial Deformities, Centre for Dental Education and Research, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||4-Feb-2015|
Dr. Om Prakash Kharbanda
Division of Orthodontics and Dentofacial Deformities, Centre for Dental Education and Research, All India Institute of Medical Sciences, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
Background: Area and volume of the pharyngeal airway in surgically treated unilateral cleft lip and palate (UCLP) patient: A cone beam computed tomography (CBCT) study. Context: Surgical repair of cleft causes restriction of maxillary growth and mid face but the effect of this reduced growth on volume of the pharyngeal airway has not been investigated thoroughly. Aims: The aim of the study was to assess the area, volume and smallest cross-sectional area of the pharyngeal airway in individuals with UCLP using CBCT and compare with age and sex matched noncleft controls. Settings and Design: Retrospective study. Materials and Methods: The study was carried out on 20 surgically treated UCLP patients and compared with 40 normal non cleft subjects with Class I skeletal relation within age group of 7-14 years. CBCT image processing and analysis were performed using Dolphin Imaging software (11.7 version premium; Dolphin Imaging and Management Solutions, Chatsworth, Calif) and volumetric rendering was done for airway analysis. Statistical Analysis Used: All statistical analyses were performed with SPSS software (version 15.0J for Windows; SPSS, Inc., Chicago, IL). An independent sample t-test was used to determine the significance of the difference between the means. Results: No significant difference was found in the area and volume of nasopharynx, oropharynx, hypopharynx, total pharyngeal volume (P = 0.86) and minimum axial area (P = 0.69) of the pharynx between the groups. Conclusions: Using CBCT, this study found that there was no significant difference in the pharyngeal area and volume between UCLP and noncleft groups. Further investigations are necessary to clarify the relationship between pharyngeal structure and airway function in patients with CLP.
Keywords: Cleft lip and palate, cone beam computed tomography, pharyngeal airway
|How to cite this article:|
Rana SS, Duggal R, Kharbanda OP. Area and volume of the pharyngeal airway in surgically treated unilateral cleft lip and palate patient: A cone beam computed tomography study. J Cleft Lip Palate Craniofac Anomal 2015;2:27-33
|How to cite this URL:|
Rana SS, Duggal R, Kharbanda OP. Area and volume of the pharyngeal airway in surgically treated unilateral cleft lip and palate patient: A cone beam computed tomography study. J Cleft Lip Palate Craniofac Anomal [serial online] 2015 [cited 2019 Jul 17];2:27-33. Available from: http://www.jclpca.org/text.asp?2015/2/1/27/150741
| Introduction|| |
Cleft lip and palate (CLP) is a congenital birth defect which is characterized by complete or partial clefting of the lip and/or the palate.  The incidence of CLP is reported to be highest in Afghans (4.9/1000 live births) and lowest in Negroid (0.4/1000 live births) population. 
The pharynx traverses three regions: The nasopharynx which extends from the posterior nasal choanae to the hard palate; the oropharynx which comprises the retro palatal and retro glossal segments - the former extends from the level of the hard palate to the caudal margin of the soft palate and the tip of the uvula, and the latter from the soft palate margins to the base of the epiglottis; the laryngopharynx, which is the segment from the base of the tongue to the larynx. Narrowing of the posterior nasal choanae occurs in patients with craniofacial abnormalities. Pharyngeal airway narrowing or collapse is common at the retro palatal and the retro glossal aspects of the pharynx, with the majority of patients having more than one site of obstruction. ,,,,,,
The oropharyngeal airway is usually narrowed in obstructive sleep apnoea (OSA). ,, Reduced size of the posterior airway space and increased distance of the hyoid bone to the mandible are also associated with OSA. Two cephalometric parameters that are used as indicators of OSA are: Posterior airway space of <11 mm and a hyoid to mandible distance of >15.4 mm.  Severe respiratory disturbance indices are associated with a posterior airway space of <5 mm at the base of the tongue and a distance of the hyoid bone to the lower border of the mandible of 24 mm or greater.  There is a low probability of OSA if the airway cross-sectional area is >110 mm 2 , but a high probability of severe OSA if the area measures <52 mm 2 . Most constrictions are located in the oropharynx. ,, The upper airway has always been an area of interest because the oropharyngeal and nasopharyngeal structures play an important role in the growth and development of the craniofacial and orodental complex. Anatomical abnormalities associated with CLP increase the risk of airway complications. 
Lateral cephalometric films of children with CLP were compared with noncleft controls and showed a reduction in the nasopharyngeal bony framework and pharyngeal airway.  Furthermore, a reduction in the upper airway in juveniles with CLP was found when compared to gender and age matched noncleft controls and was found to persist through adolescence when lateral cephalometric films were compared.  According to Imamura et al. the anteroposterior dimension of the pharyngeal airway was smaller in adolescent patients with CLP than in those without CLP and significantly larger in the upper airway of adolescent patients with CLP than in juveniles with CLP. 
Three-dimensional techniques like computed tomography (CT) or cone beam CT (CBCT) data provide a reliable three-dimensional assessment of the airway in all three planes; coronal, sagittal and axial.  However, the radiation dose for standard CT scan of the maxillofacial region is high and repeated scanning is a concern. Medium field-of-view (FOV) CBCT radiation ranged from 69 to 560 microsieverts (mSv); whereas, a similar FOV medical CT produced 860 mSv.  Previous studies have shown that three-dimensional imaging using CBCT is a simple and effective method to analyze the airway accurately.  Advantages of CBCT include X-ray beam limitation, image accuracy, rapid scan time, dose reduction, display modes unique to maxillofacial imaging, and reduced image artefact. 
| Materials and Methods|| |
A retrospective study was performed. This study was approved by the research ethics committee. Informed consent was signed by all subjects or parents. The study was carried out on 20 surgically treated unilateral CLP (UCLP) patients and compared with 40 normal non cleft subjects with Class I skeletal relation within age group of 7-14 years. The mean ages of the UCLP and control groups were 11.2 and 10.5 years, respectively. The mean age of the patient at cleft lip surgery and at first palatal surgery was 7.8 and 18 months respectively. Out of 20 patients, Goslon index was three for most of the patients (n = 14) and remaining four patients were in Goslon four and two patients were in Goslon index five. The exclusion criteria included clefting associated with diagnosed syndromes and no prior adenoidectomy and/or tonsillectomy and prior orthodontic treatment.
The noncleft group included individuals who were age matched with the experimental group. The inclusion criteria were Angle's Class I malocclusion with beginning CBCT records for starting orthodontic treatment and no prior orthodontic treatment, no habitual mouth breathing recorded and no prior adenoidectomy and/or tonsillectomy. CBCT scans of subjects were obtained using one system i-CAT (i-CAT; Imaging Sciences International, Hatfield, Pa) according to a standard protocol (120 kV, 5 mA, 17 cm × 22 cm FOV, 0.4 mm voxel, and 26 s scanning time). The CBCT scans were made with the patient sitting in an upright position, Frankfort horizontal (FH) plane parallel to the floor and teeth in maximum intercuspation. The subjects were advised not to swallow, breathe or move their head while the scan was taking place.
The digital images files were exported in Digital Imaging and Communication in Medicine format and the basis images were imported into the Dolphin imaging software (version 11.7 premium; Dolphin Imaging and Management Solutions, Chatsworth, Calif). These images were rendered into volumetric images, and reconstructed sagittal, axial, coronal slices and the three-dimensional models were obtained.
Lateral cephalometric evaluations were carried out on two-dimensional lateral cephalograms obtained from CBCT image by software (ray sum technique) [Figure 1]. ANB angle was calculated to confirm the inclusion and cranio-cervical inclination was calculated as head posture had been reported to affect the airway volume. Only those patients with cranio-cervical inclination between 90° and 110° and cranial base angle between 120° and 140° were included in this study [Figure 2].
|Figure 1: Two-dimensional lateral cephalometric image with the use of a ray-sum technique (Dolphin Imaging software, version 11.7)|
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|Figure 2: Measurement of cranio-cervical inclination at level of second cervical vertebrae. Cv2ig: Tangent point at the superior, posterior extremity of the odontoid process of the second cervical vertebra. Cv2ip: Most infero-posterior point on the body of the second cervical vertebra. OPT: Line through Cv2ig and Cv2ip. NSL: Nasion-Sella line (N-S)|
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Before landmark identification, the three-dimensional volumetric images were oriented with the Dolphin imaging software as follows: The midsagittal plane was adjusted on the skeletal midline of the face, the axial plane was adjusted to show the FH plane (right porion to right orbitale), and the coronal plane was adjusted to pass through the level of the furcation point of the right maxillary first molar [Figure 3].
|Figure 3: Image orientations: Frontal (a) and sagittal (b) views. The mid sagittal plane was adjusted on the skeletal midline of the face, the axial plane was adjusted to show the Frankfort horizontal plane (right porion right orbitale), and the coronal plane was adjusted to pass through the level of the furcation point of the maxillary right fi rst molar|
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Landmark for different airway portions are defined in [Table 1]. After image orientation and landmark identification pretreatment airway area, volume and minimum cross-sectional area for nasopharynx and oropharynx were calculated using the airway tool of Dolphin software. The definitions for the airway parameters, volumetric analysis, and cephalometric measures are presented in [Figure 1], [Figure 2], [Figure 3], [Figure 4].
|Figure 4: Pharyngeal airway (nasopharyngeal airway, oropharyngeal airway, hypopharyngeal airway)|
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To obtain airway volume, Dolphin three-dimensional requires from the operator to define the airway part of interest by taking three actions. First, the user has to restrict the volume of interest from adjacent volumes by delineating the compartment borders in a two-dimensional view. Second, the user has to place seed points in the target compartment. Seed points denote densities that represent the airway. The target airway volume will "grow" from these seed points. Third, a threshold value must be determined. This threshold defines a density range that will be included in the measured airway volume. The volumes and minimum axial areas were measured with a tool for airway volume calculation in the three-dimensional mode of the software with a threshold value of 50. The limits for each portion of interest were defined in the sagittal slice, and the software automatically calculated the total volume and the most constricted airway area (minimum axial area) in the region previously set out.
| Results|| |
Statistical analyses were performed with SPSS software (version 15.0J for Windows; SPSS Inc., Chicago, IL). An independent sample t-test was used to determine the significance of the difference between the means. Pharyngeal airway measured as nasopharyngeal area, nasopharyngeal volume, oropharyngeal airway, hypopharyngeal airway, total pharyngeal volume (nasopharynx + oropharynx + hypopharynx) and minimal axial area did not show any significant difference between the groups [Figure 5] and [Table 2]. The comparative result shows that total pharyngeal volumes were not significantly different between the cleft and noncleft groups (P = 0.07). The cleft group showed an average volume of 18218.2 mm 3 with a standard deviation (SD) of 4374.9 mm 3 and the noncleft group showed an average volume of 18409.1 mm 3 with an SD of 3803.4 mm 3 .
|Figure 5: Comparison of mean nasopharyngeal, oropharyngeal, hypopharyngeal and total pharyngeal airway volume (mm3) in unilateral cleft lip and palate and noncleft groups|
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|Table 2: Comparisons of pharyngeal airway measurements in patients with UCLP and noncleft groups|
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The smallest cross-sectional area was not significantly different between the cleft and noncleft groups (P = 0.69). The cleft group showed an average cross-sectional area of 178.46 mm 2 with a SD of 60.9 mm 2 and the noncleft group showed an average of 184.7 mm 2 with a SD of 58.2 mm 2 [Figure 6] and [Table 2]. The location of the smallest cross-sectional area for the cleft and noncleft normal control group was the oropharynx.
|Figure 6: Depicting minimal axial area (mm2) in unilateral cleft lip and palate and noncleft groups|
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A linear regression was used to the relationship between total pharyngeal volume and minimal axial area for both UCLP and noncleft groups. The r2 value was + 0.75 and + 0.64 for CLP and non-CLP, respectively [Table 3]. The UCLP and noncleft both groups demonstrated a stronger (more linear) relation between volume and cross-sectional area. In both groups, a greater airway volume correlates to a proportionately larger cross-sectional area.
|Table 3: Relationship of minimal axial area with airway variables in UCLP and noncleft groups|
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| Discussion|| |
We used three-dimensional CBCT to quantitatively investigate the three-dimensional relationships between the pharyngeal morphology in patients with CLP and comparing the finding to the noncleft control group of similar age. In our study, we hypothesized that children with CLP had smaller pharyngeal airways compared to non-CLP control group.
Muto et al.  reported changes in airway dimensions related to the cranio-cervical inclination. The changes in cranio-cervical inclination produced by head extension were correlated with changes in the variables describing the posterior airway space. Kumar et al. found a greater dorsal inclination of the head in mouth breathing children 10-14 years old, compared with nose breathers.  Because the volume of the airway is influenced by head posture,  all patients were seated in the upright position with FH plane paralleled to the floor, maximum intercuspation and lips and tongue in position of filling the oral cavity. To offset these effects only those patients with cranio-cervical inclination between 90° and 110° and cranial base angle 120-140° were included in this study.
The patients were instructed not to swallow and not to move the head and tongue during the scanning. The subjects were asked not to breathe while the scan was taking place. Studies in airway imaging have emphasized that airway dimensions can change with the phase of respiration.  However, since scan time was relatively long (26s) and our sample comprised of young patients, chances are that this instruction might not have been followed leading to some errors in airway volumes. This remains the limitation of our study.
The Class I skeletal noncleft control group was selected according to the ANB angle because this is one of the most used criteria in the determination of the anteroposterior relationship between the maxilla and the mandible. ,
Two-dimensional representation of three-dimensional structures in lateral head films offers limited information about the airways. Information regarding axial cross-sectional areas and overall volumes can only be determined by three-dimensional imaging modalities. 
The accuracy and reliability of automatic airway segmentation by Dolphin three-dimensional were tested and proven to be reliable. It requires the user to initiate the calculation by selecting and limiting the specific airway part of interest. It has been qualified and used in several studies. It is considerably more accurate than or similar to another software in upper airway assessments. ,,
This study demonstrated that there was no significant difference in the pharyngeal area and volume of nasopharynx, oropharynx, hypopharynx and total pharyngeal volume in UCLP children when compared to noncleft children. The result in our study was similar to those reported by Cheung and Oberoi  and Aras et al.  who have reported no significant difference in pharyngeal volume of cleft and noncleft subjects. Aras et al. reported that the total airway volume of noncleft individuals was greater in their study, but the difference between the two groups was not statistically significant.  In our study, the mean airway volume was 18218 mm 3 (SD = 4374.9 mm 3 ) and 18409.1 mm 3 (SD = 3803.4 mm 3 ) for the cleft palate and noncleft palate groups, respectively. The findings of the present study were in agreement with the findings of Yoshihara et al.  who also found that the oropharyngeal and the oronasal pharyngeal airway volumes did not differ significantly when the cleft palate juvenile group was compared with the control juvenile group.
This study demonstrated that there was no significant difference in smallest cross-sectional area in UCLP children when compared to noncleft groups. However non cleft group had more minimal cross-sectional area than UCLP group, the mean smallest cross-sectional area for UCLP individuals was 178.4 mm 2 (SD = 60.9 mm 2 ) and for noncleft 184.7 mm 2 (SD = 58.2 mm 2 ). The large SDs signify a wide range of values for cross-sectional area. This may be attributed to the age range of patients and the varying levels of growth for each patient. Abramson et al.  found that the average smallest cross-sectional area in children age 6-11 years was 82.9 mm 2 (SD = 16.5 mm 2 ) and for adolescents 12-16 yrs was 122.2 mm 2 (SD = 39.3 mm 2 ). They did not find any significant differences in airway volume or minimum cross-sectional area between boys and girls. According to Tso et al. the range of the minimal cross-sectional airway in healthy adults varies from 90 to 360 mm.  However, there is evidence that subjects with OSA have smaller cross-sectional areas of the airway, implying a range in airway sizes in normal subjects, and that the cross-sectional areas of subjects with OSA can be below this range.  Cheung and Oberoi  also reported no significant difference in minimal axial area of cleft and noncleft subjects.
The outcome of cleft repair varies with the skill of the surgeon, timing of repair, protocol used for surgery and severity of the defect.
The UCLP patients in our study were treated at different centres, at different times with different protocols. Similarly, the patients had different Goslon index indicating varying severity of cleft defect. Hence, this might affect the overall area and volume of the pharyngeal airway, so the exact effect of surgery can only be ascertained using subjects treated with similar surgical protocol at same center with similar severity.
| Conclusions|| |
Using CBCT, this study found that there was no significant difference in the pharyngeal area and volume between surgically treated UCLP and noncleft groups. Further investigations are necessary to clarify the relationship between pharyngeal structure and airway function in patients with CLP.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]