Three-dimensional evaluation of the airway spaces in patients with and without cleft lip and palate: A digital volume tomographic study

Introduction

Patients with cleft lip and palate (CLP) suffer from several esthetic and functional challenges. Comprehensive treatment of these patients involves orthognathic surgery that may lead to velopharyngeal insufficiency or reduction in lower airway. Several cases of airway insufficiency, velopharyngeal incompetence, snoring, hypopnea, and obstructive sleep apnea have been reported in subjects with CLP. The aim of this study was to compare the anteroposterior dimensions of the oropharyngeal airway at 5 levels, the height of the oropharyngeal column, and the volume of the oropharyngeal airway in subjects with and without CLP.

Methods

The sample consisted of 62 patients with CLP and 42 subjects with Angle Class I malocclusion. Anteroposterior dimension, height, and volume of the oropharyngeal airway were measured using the midsagittal and axial slices obtained from 3-dimensional digital volume tomographic scans for both groups.

Results

The anteroposterior dimensions of the airway were significantly reduced in the study subjects compared with the control group at the level of the postnasal spine, the base of the tongue, and the epiglottis. The airway dimensions measured on the axial sections at the level of the palatal and epiglottic plane were also significantly lower in the study group. The height and volume of the oropharyngeal airway were also significantly smaller in patients with CLP compared with subjects without CLP.

Conclusions

Patients with CLP showed reduced dimensions and volumes of the oropharyngeal airway in all 3 planes compared with the control group.

Highlights

  • AP airway space dimension was significantly smaller in CLP patients than in controls.

  • Subjects with CLP had shorter oropharyngeal airway height than controls.

  • Oropharyngeal airway volume was lower in CLP patients than in controls.

  • A “compensation hypothesis” is suggested for oropharyngeal airway in CLP patients.

Clefts of the lip and palate (CLP) are the most common congenital anomaly affecting the craniofacial complex. Patients with CLP suffer from several esthetic and functional challenges. A patient with a cleft generally has a Class III profile, and the comprehensive treatment plan involves orthognathic surgery mainly in the form of maxillary advancement or mandibular setback. The former is associated with worsening of speech and velopharyngeal insufficiency, whereas the latter leads to reduction in the lower airway due to the retropositioned tongue and predisposes the patient to obstructive sleep apnea. Several cases of airway insufficiency, velopharyngeal incompetence, snoring, hypopnea, and obstructive sleep apnea have been reported in subjects with CLP.

The pharynx is a muscular tube suspended on a bony framework. It extends from the base of the skull to the cricoid cartilage. According to the counterpart hypothesis of Enlow and Hans, the growth activity in 1 region is invariably accompanied by complementary growth in other regions. The anterior displacement of the nasomaxillary complex during growth provides space for the developing pharynx. Hence, it may be surmised that the anatomic aberration in the nasomaxillary region in patients with CLP may lead to an anatomically smaller airway space and also result in functional respiratory challenges.

According to the functional matrix concept of Moss and Salentijn, craniofacial form and function are closely interlinked, and it follows that not only do the growth and morphology of the surrounding bony framework direct the enlargement of the pharynx, but also the converse may be true. Although there still is controversy regarding a relationship between impaired pharyngeal ventilation and malocclusion, several studies have shown a positive correlation.

Clefts of the lip and palate are a condition with several morphologic and functional aberrations. The diagnosis and management of patients with CLP pose a plethora of unanswered queries in the mind of an inquisitive clinician. Most of the literature available with regard to the airway problems in these patients is based on 2-dimensional (2D) studies. Several 3-dimensional (3D) imaging modalities such as magnetic resonance imaging, computed tomography scans, cone-beam computed tomography (CBCT), and digital volume tomographic (DVT) scans are currently available to evaluate the craniofacial structures. Three-dimensional DVT scans provides a clear and sharp visualization of the hard and soft structures of the craniofacial complex. Due to the large field of view, high resolution, and flat detector technology, the radiation dose of a DVT scan (1.8 mSv) is reduced compared with conventional computed tomography scans (2.1 mSv). A shorter scan time (4 seconds) is the greatest advantage of the DVT scan, which ensures less movement by the subject, hence reduced distortion and greater accuracy in the scanned images.

Not many 3D studies have been conducted to evaluate the impending airway challenge in patients with a repaired hard palate cleft. This retrospective study was planned at the Department of Orthodontics and Dentofacial Orthopaedics of Sharad Pawar Dental College in Sawangi, Wardha, India, to evaluate the variations in the anteroposterior dimensions of the oropharyngeal airway at 5 levels, the height of the oropharyngeal column, and the volume of the oropharyngeal airway in subjects with and without CLP.

Material and methods

The study was approved by the institutional ethical committee of Datta Meghe Institute of Medical Sciences (Deemed University). The institutional archives were searched for 3D data of patients who fulfilled the following inclusion and exclusion criteria. Inclusion criteria for the study group subjects were patients with repaired unilateral or bilateral CLP. All patients should have undergone the same surgical procedure, with no previous orthodontic treatment or orthognathic surgery. Patients suffering from any syndromes were excluded. Of the 252 available records, 62 patients who met these criteria were selected. Hence, the sample consisted of a study group of 62 patients with CLP (mean age, 15.09 years). The archives were also searched for the pretreatment records of subjects with Angle Class I dental malocclusion. Of the 65 records available, 42 records met the inclusion criteria. Therefore, the control group (mean age, 15.14 years) comprised scans of 42 subjects with Angle Class I dental malocclusion.

The study group comprised patients with unilateral CLP (39 patients), bilateral CLP (17 patients), and cleft palate only (6 patients). All patients with unilateral and bilateral cleft palate were treated by 2-flap push-back palatoplasty between 9 and 18 months of age; those with cleft palate only were treated by V-Y plasty. No subjects had undergone pharyngoplasty.

The control group scans were chosen for the study based on the following inclusion criteria: Angle Class I malocclusion, ANB between 0° and 4°, average growth pattern (FMA between 22° and 28°), and no previous surgeries or respiratory diseases. No subjects were exposed for research purposes; all scans were chosen retrospectively from pretreatment diagnostic records taken earlier. Written informed consent was obtained from all subjects (or parents in the case of minors) before using their records for the study.

The patients in both the groups were further divided into prepubertal and postpubertal groups based on the cervical vertebral maturation index status as seen on the 3D scans. The prepubertal group included cervical vertebral maturation index stages II through IV; subjects in stages V and VI on the 3D scans were included in the postpubertal group.

The DVT images for each subject were obtained using an Allura Xper FD20 3D RA Digital Subtraction Angiography unit (Philips, Eindhoven, Netherlands) with exposure parameters of 80 kVp, 10 mA, 4 to 5 seconds, field of view of 12 in, and 270° rotation. The voxel size was 0.3 mm 3 . The images were obtained with the patients positioned supinely, and the head was positioned so that the Frankfort horizontal plane was perpendicular to the floor. The patients were asked to place the tongue touching the mandibular anterior teeth so that the tongue and soft palate could be viewed separately. They were instructed not to swallow or move their head or tongue.

The acquired 3D data were converted to DICOM format, and the multiplanar reconstruction images were sectioned (slice thickness, 1 mm) using the 3D RA software (Philips) at the computer workstation. Three separate sections were obtained in different planes to carry out the measurements in all 3 dimensions. The Frankfort horizontal plane that was used to orient the scans was constructed by joining the right and left porions and the right orbitale. The midsagittal section was obtained by slicing the reconstructed image from glabella to the center of the third cervical vertebrae perpendicular to the Frankfort horizontal plane. The axial sections were obtained at the level of the palatal plane and at the lower border of the epiglottis, by sectioning the reconstructed images parallel to the Frankfort horozontal plane at these levels. These sections were then evaluated using Intruis Suite R2 software (Philips).

The dimensions of the oropharynx were measured between the palatal plane and the epiglottic plane. Since the pharyngeal tube is irregular in shape, the point at which the dimension of the tube is smallest may become the cause of the airway obstruction. Anteroposterior measurements at 5 levels (level of the postnasal spine [PNS], middle of the soft palate, tip of the soft palate, base of the tongue, and base of the epiglottis) ( Figs 1 A and B) and height ( Fig 2 ) of the oropharynx were made on the midsagittal section.

Fig 1
A, Anteroposterior measurements of the oropharyngeal airway space on the midsagittal section in a subject with a repaired hard palate cleft; B, color coding for anteroposterior measurements of the oropharyngeal airway space on the midsagittal section.

Fig 2
A, Height of the oropharyngeal airway measured on the midsagittal section; B, color coding for height of the oropharyngeal airway measured on the midsagittal section.

Transverse and anteroposterior dimensions of the airway tube were measured at the levels of the palatal plane and the epiglottis on the axial sections, and the average of these was calculated ( Fig 3 ). Volume of the airway column was calculated by using the above airway dimensions obtained in all 3 planes of space, and the values were reported in liters (cubic millimeters). Comparisons were drawn between the subjects with and without CLP (study and control groups). Comparisons were also made between the preputertal and postpubertal subjects in the 2 groups.

Fig 3
A, Dimension of the airway measured on the axial section; B, color coding for dimensions of the airway measured on the axial section.

Statistical analysis

The statistical analysis was carried out using statistical software (version 16.0; SPSS, Chicago, Ill). Descriptive statistics were carried out to calculate means and standard deviations. The study and control groups were balanced in terms of age and sex, shown in the frequency-based matching ( Tables I and II ). The normal distribution of the parameters was checked using QQ plots. The distribution of points about the diagonal line indicated the normality of the parameters; hence, the parametric t test was applied for testing the statistical significance between mean scores of the groups. Comparison of mean score in each group with respect to age was also carried out using the independent-sample t test. The confidence interval was set at 95%. A P value less than 0.05 was considered to be significant.

Table I
Distribution of the sample
Study group (mean or frequency) Control group (mean or frequency) P value
Male 31 (50%) 21 (50%) 1.00
Female 31 (50%) 21 (50%)
Age (y) 15.09 (3.95) 15.14 (4.22) 0.95

Table II
Distribution of subjects by age and sex in the groups
Age (y) Total sample Male Female
Cleft Control Cleft Control Cleft Control
≤11 24 (38.71%) 18 (42.86%) 10 (32.26) 8 (38.1) 14 (45.16) 10 (47.62)
12-15 8 (12.9%) 6 (14.28%) 7 (22.58) 4 (19.05) 1 (3.23) 2 (9.52)
16-18 24 (38.71%) 13 (30.95%) 11 (35.48) 6 (28.57) 13 (41.94) 7 (33.33)
19-22 6 (12.9%) 5 (11.9%) 3 (9.68) 3 (14.29) 3 (9.68) 2 (9.52)
Total 62 42 31 21 31 21
P value 0.8772 0.894 0.773

To determine the random error in the measurements, 30% of the sample (18 study group subjects, 12 control subjects) was randomly chosen, and the measurements were repeated. Intraclass correlation coefficients were performed to assess the reproducibility of the measurements. The intraexaminer reliability values were 0.73 to 0.87 for airway measurements in the midsagittal and axial planes.

Results

The statistical analysis between the study and control groups for the measurements on the midsagittal plane showed that the anteroposterior airway dimensions were significantly reduced in the study group compared with the control group at the level of the PNS ( P < 0.001), at the base of the tongue ( P < 0.001), and at the base of the epiglottis ( P < 0.001); these values were statistically significant. The airway dimension appeared to be slightly increased in the study sample compared with the control group at the level of the center of the soft palate ( P = 0.180) and at the tip of the soft palate ( P = 0.704). However, these values were not statistically significant ( Table III ). The evaluation of the height of the oropharyngeal airway on the midsagittal section showed that the length of the airway column was significantly reduced in the patients with CLP compared with the control group ( P = 0.014) ( Table III ).

Table III
Dimensions evaluating the oropharyngeal airway on the midsagittal section: comparison between groups
Parameter measured Group n Mean SD SE mean t value P value
PNS-post wall (mm) Study 62 18.51 4.67 0.59 −5.040 <0.001
Control 42 23.10 4.37 0.67
Middle of SP-post wall (mm) Study 62 13.20 4.07 0.51 1.350 0.180
Control 42 12.11 4.01 0.61
Tip of uvula-post wall (mm) Study 62 11.52 3.89 0.49 0.381 0.704
Control 42 11.22 3.98 0.61
Retroglossal (mm) Study 62 10.41 4.08 0.51 −3.748 <0.001
Control 42 13.41 3.88 0.60
Epiglottis (mm) Study 62 10.92 3.49 0.44 −4.417 <0.001
Control 42 15.18 6.30 0.97
Height: PNS- epiglottis (mm) Study 62 52.18 8.08 1.03 −2.496 0.014
Control 42 56.14 7.74 1.19
Post wall , Posterior pharyngeal wall; SP , soft palate.

Comparisons between the study and control group subjects for measurements on the axial section showed that the anteroposterior dimension of the airway was significantly shorter in the study group compared with the control group at the level of the palatal plane ( P = 0.02) and at the level of the epiglottis ( P < 0.001) ( Table IV ); these values were statistically significant. However, the transverse dimensions of the airway at the level of the palatal plane did not differ significantly among the 2 groups ( P = 0.79). The study group subjects showed a significantly smaller ( P < 0.001) transverse dimension of the airway at the level of the epiglottis compared with the controls; this was significant.

Table IV
Dimensions evaluating the oropharyngeal airway on the axial section: comparison between groups
Parameter Group n Mean SD SE mean t value P value
Level of palatal plane: AP (mm) Study 62 13.17 4.79 0.61 2.34 0.02
Control 42 16.02 7.62 1.18
Level of palatal plane: transverse (mm) Study 62 22.36 5.41 0.69 0.26 0.79
Control 42 22.05 6.21 0.96
Level of epiglottis: AP (mm) Study 62 11.27 3.59 0.46 3.91 <0.001
Control 42 14.70 5.36 0.83
Level of epiglottis: transverse (mm) Study 62 13.98 5.95 0.76 3.53 <0.001
Control 42 21.43 10.91 1.68
AP , Anteroposterior.

P < 0.05.

The study group subjects (13.98 + 5.95 L) had a significantly reduced ( P < 0.001) oropharyngeal airway volume compared with the control subjects (21.43 + 10.91 L) ( Table V ). The maximum values for the airway volumes were 27.06 L in the study group and 58.87 L in the control group. The minimum airway volumes were 4.24 L in the study group and 7.1 L in the control group.

Table V
Volume of the oropharyngeal airway: comparison between groups
Group n Mean SD SE mean t value P value
Volume (L) Study 62 13.98 5.95 0.76 4.49 <0.001
Control 42 21.43 10.91 1.68

P < 0.05.

On comparing the prepubertal and postpubertal subjects in each group, we found that the anteroposterior measurements of the airway column at the level of the PNS ( P = 0.01) and the tip of the uvula ( P = 0.01) were significantly reduced in the prepubertal subjects compared with the postpubertal subjects in the control group ( Table VI ). In the study group, the anteroposterior measurements of the airway at the PNS ( P = 0.001) and at the level of the epiglottis ( P = 0.02) were significantly reduced in the prepubertal group compared with the postpubertal group ( Table VII ). In the study group, the height of the oropharyngeal airway column differed significantly between the prepubertal and postpubertal subjects ( P = 0.002).

Table VI
Dimensions evaluating the oropharyngeal airway on the midsagittal and axial sections: comparison between prepubertal and postpubertal subjects in the control group
Parameter n Mean SD SE t value P value
Airway measurements on midsagittal section
PNS-post wall (mm)
Prepubertal 20 21.45 3.87 0.87 2.47 0.01
Postpubertal 22 24.60 4.34 0.93
Middle of SP-post wall (mm)
Prepubertal 20 12.13 4.81 1.08 0.03 0.97
Postpubertal 22 12.09 3.24 0.69
Tip of uvula-post wall (mm)
Prepubertal 20 12.73 4.28 0.96 2.48 0.01
Postpubertal 22 9.85 3.20 0.68
Retroglossal (mm)
Prepubertal 20 13.58 4.63 1.03 0.28 0.78
Postpubertal 22 13.24 3.16 0.67
Epiglottis (mm)
Prepubertal 20 15.34 7.72 1.73 0.16 0.87
Postpubertal 22 15.03 4.83 1.03
Height: PNS-epiglottis (mm)
Prepubertal 20 54.67 8.76 1.96 1.17 0.24
Postpubertal 22 57.48 6.61 1.41
Airway measurements on axial section
Level of palatal plane: AP (mm)
Prepubertal 20 13.19 6.59 1.47 2.43 0.01
Postpubertal 22 18.60 7.70 1.64
Level of palatal plane: transverse (mm)
Prepubertal 20 20.24 6.32 1.41 1.86 0.07
Postpubertal 22 23.71 5.76 1.23
Level of epiglottis: AP (mm)
Prepubertal 20 13.37 6.01 1.34 1.56 0.12
Postpubertal 22 15.92 4.49 0.96
Level of epiglottis: transverse (mm)
Prepubertal 20 26.35 4.41 0.99 0.15 0.87
Postpubertal 22 26.68 8.14 1.73
Volume (L)
Prepubertal 20 17.41 10.34 2.31 2.41 0.02
Postpubertal 22 25.09 10.30 2.20
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Dec 19, 2018 | Posted by in Orthodontics | Comments Off on Three-dimensional evaluation of the airway spaces in patients with and without cleft lip and palate: A digital volume tomographic study
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