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Head and Neck Imaging |
1 Department of Respiratory Medicine (J.L.D.P., D.V., P.M., P.A.L.)
2 Sleep Laboratory (J.L.D.P., P.M., P.A.L.)
3 Department of Radiology (G.R.F.), Centre Hôpitalier Universitaire de Grenoble, BP 217 X, F-38043 Grenoble 9, France
4 Department of Physiology, Faculty of Medicine, Preta Laboratoty, Joseph Fourier University, Grenoble, France (P.A.L.).
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Abstract |
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MATERIALS AND METHODS: One hundred thirty-one patients with snoring underwent cephalometric radiography, with which the posterior airway space, soft palate length and width, and distance between the hyoid bone and mandibular plane were measured, and/or pharyngeal CT, with which the luminal areas of the airway at the naso-, oro-, and hypopharyngeal levels were measured.
RESULTS: Of the 131 patients, 96 had OSAS, and 35 had snoring. Nine of 96 patients with OSAS had soft palate hooking on awake pharyngeal CT or cephalometric images. No patient with snoring alone had hooking. Patients with hooking had a larger posterior airway space than did patients with OSAS without hooking (P = .05), and an enlarged (
15-mm) posterior airway space was more frequent in patients with hooking (eight of nine patients) than in those without hooking (34 of 87) (P < .01). Oropharyngeal and hypopharyngeal areas were significantly larger in patients with hooking than in patients without hooking or in patients with snoring (P 
.04).
CONCLUSION: Cephalometric radiography and CT can demonstrate hooking of the soft palate in awake patients. This finding indicates a high risk for OSAS.
Index terms: Pharynx, abnormalities, 26.1492, 26.91 • Pharynx, CT, 26.12111 • Pharynx, stenosis or obstruction, 26.1492 • Sleep apnea, 26.827
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Imaging of the UA has been performed in patients with OSAS. Static techniques include cephalometric radiography (9), pharyngeal computed tomography (CT) (10,11), and magnetic resonance (MR) imaging (12–14); dynamic techniques include video fiberoptic pharyngeal studies (15), fast CT (16,17), and fast MR imaging (18,19). In a previous study (20), we used somnofluoroscopy and described a particular pattern of events that occurs during OSAS. In that series, hooking of the soft palate, which is defined as an angulation of 30° or greater between the distal part of the uvula and the longitudinal axis of the soft palate (Fig 1), occurred in 10 of 11 patients; this hooking caused abrupt narrowing of the airway, which led to occlusion of the oropharynx. There was then suction on the soft palate, with progression to occlusion of the hypopharynx. Thus, in some patients with OSAS, hooking of the soft palate is a key factor in UA obstruction (20).
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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UA Imaging
Definitions of pharyngeal segmentation.—The inferior border of the nasopharynx was defined as the lowest extent of the hard palate, and the lower margin of the oropharynx was identified as the tip of the uvula. The hypopharynx extends from the tip of the uvula to the upper limit of the epiglottis. This pharyngeal segmentation allowed us to clearly categorize the level of UA narrowing during the daytime. For example, an isolated reduction in UA size at the level we have called the oropharynx (ie, the level of the soft palate) is associated with a better outcome after uvulopalatopharyngoplasty (21). Conversely, OSAS with hypopharyngeal narrowing may necessitate maxillofacial surgery for cure (22). The division of the pharynx into these entities does not represent a formal anatomic classification but rather a descriptive paradigm that appears to have relevance in terms of functional and, therefore, surgical considerations.
Cephalometric radiographs.—Lateral cephalometric radiographs (Fig 2) were obtained, per our routine, by using the technique reported by Riley et al (9) and described in detail elsewhere (23). Briefly, the patient was seated with the head in a neutral position, the gaze parallel to the floor, and the teeth together. The x-ray plate was placed next to the left side of the face, and the collimator was placed 1.5 m from the patient. Exposures were performed while the patient remained still and slowly exhaled a moderately deep breath. Each radiographic study resulted in delivery of a skin dose of 4.7 mGy. The following measurements were made by using the radiographs (9): (a) distance from the mandibular plane (a plane constructed from gnathion through gonion) to the hyoid bone; (b) posterior airway space, measured between the posterior pharyngeal wall and the dorsum of the tongue on a line joining gonion to the supramentale (maximal concavity on the anterior surface of the mandible, with normal dimensions of 11 mm ± 2 [SD]); (c) distance from the posterior nasal spine to the tip of the palate, which provides a measure of the length of the soft palate and has a normal range of 34 mm ± 6; and (d) maximal width of the soft palate.
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Care was taken to ensure that all sections were perpendicular to the airway lumen to allow accurate assessment of the cross-sectional area. For each pharyngeal level (ie, naso-, oro-, and hypopharynx), the sections obtained every 10 mm were inspected to determine the single section on which the minimal cross-sectional area of the airway was present. The measurement of the cross-sectional airway was then performed on this image by determining the area with a cursor and the CT software. The window settings were standardized for all patients (window level, 100 HU; window width, 600 HU).
Identification of hooking.—The cephalometric image and the lateral scout view of the pharynx were closely examined for hooking of the soft palate. We arbitrarily decided that the angulation between the distal part of the uvula and longitudinal axis of the soft palate should be 30° or more for hooking to be present (Fig 1). The hooking of the palate by more than 30° increases the occlusive effect of the soft palate in the airway. In our experience, such an angle is not exhibited by healthy individuals during pharyngeal CT or cephalometric radiography. The cephalometric and CT images were examined and scored independently by two observers (J.L.D.P., P.A.L.).
All but two of the 131 patients underwent both cephalometric imaging and CT. These two patients had OSAS and showed hooking at cephalometric imaging. Pharyngeal CT was impossible in these patients because of massive obesity in one and claustrophobia in the other.
Sleep Studies
The patients underwent 1 night of monitoring to establish the diagnosis and measure the severity of the breathing disorder. We monitored the patients with polysomnography, which consisted of observation of electroencephalographic activity, eye movements, chin electromyographic activity, electrocardiographic activity, respiratory effort, airflow, and oxygen saturation, as previously described (23). Snoring was assessed qualitatively.
The polysomnogram was scored manually according to standard criteria (24). Episodes of apnea were defined as complete cessation of airflow for 10 seconds or longer, and hypopnea was defined as a decrease of more than 50% in oronasal airflow that lasted for at least 10 seconds. Apneic and hypopneic events were classified as central, obstructive, or mixed, according to the absence of breathing efforts. OSAS was defined in terms of a respiratory disturbance index (number of episodes of apnea or hypopnea per hour of sleep) score of 15 or higher. Snorers were defined as patients with fewer than 15 episodes of apnea or hypopnea per hour of sleep.
Statistical Analyses
The Kruskal-Wallis test was used for comparisons among patients with hooking, patients with snoring, and patients with OSAS; the Mann-Whitney U test or Student t test was used for comparisons of quantitative variables in patients with hooking versus all other patients. The 
2 test was used for comparisons of qualitative variables. A logistic regression analysis was used to determine if a UA enlargement was associated with a high probability of soft palate hooking.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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UA Imaging
Hooking of the soft palate.—Nine (9%) of the 96 patients, all with OSAS, showed hooking of the soft palate on awake cephalometric or CT images (Figs 4, 5). No snorer had hooking. Hooking of the soft palate was seen on CT scans alone in six of the nine patients and on cephalometric radiographs alone in two patients. Hooking was visualized on both types of images in the ninth patient. In two patients with hooking, it was not possible to perform pharyngeal CT: in one because of massive obesity (body mass index = 48 kg/m2) and in the other because of claustrophobia.
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2 test). Figure 5 shows CT measurements of the cross-sectional areas of the airway at the levels of the nasopharynx, oropharynx, and hypopharynx. Oropharyngeal areas were 171 mm2 ± 30 in patients with OSAS with hooking, 87 mm2 ± 62 in patients with OSAS alone, and 102 mm2 ± 62 in patients with snoring alone (P = .01, Kruskal-Wallis test). Hypopharyngeal areas were 324 mm2 ± 94 in patients with OSAS with hooking, 248 mm2 ± 144 in patients with OSAS alone, and 229 mm2 ± 147 in patients with snoring alone (P = .04, Kruskal-Wallis test). A logistic regression demonstrated that when a patient with OSAS had an oropharyngeal area greater than 150 mm2, the relative risk for soft palate hooking was increased 15 fold.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Hooking during Sleep and Reduced UA Dimensions
A substantial reduction in UA size while awake generally is found in patients with OSAS (9–13) and undoubtedly facilitates UA collapse during sleep. Indeed, in our study with somnofluoroscopy (20), hooking was seen in patients in whom the posterior airway space was normal or reduced in size. This hooking during sleep occurred at the beginning of the oropharyngeal occlusion and usually extended to the hypopharyngeal level. We hypothesized that soft palate hooking plays a key role in pharyngeal collapse in some patients, because hooking results in a sudden and major reduction in oropharyngeal dimensions, which therefore dramatically increases UA resistance and the transpharyngeal pressure gradient.
Hooking while Awake and Large UA Dimensions
In the present study, we found that 9% of the patients with OSAS had soft palate hooking while awake and that this was not evident in any patients with snoring.
These patients with hooking had a large UA while awake as assessed with cephalometric and pharyngeal CT images. Thus, we identified a particular subgroup of patients with OSAS with hooking of the soft palate when awake: In comparison with patients with ordinary snoring, these patients with hooking have a different UA anatomy and tend to be older and heavier and to have a greater soft palate length. In a previous report (23), we found that in young subjects or subjects with a low body mass index, static UA abnormalities explained most of the variance in the respiratory disturbance index and were likely to play an important physiopathogenic role. This was not the case in older and more obese subjects. In the subgroup of patients with a large UA, a dynamic abnormality such as hooking could be a key factor for the occurrence of UA collapse. Under ideal circumstances, we would have performed somnofluoroscopy in these patients, but they had been treated with nasal continuous positive airway pressure, which induces acute (12,14) and long-term (25) modifications of the UA. A prospective somnofluoroscopic study is needed to compare patients with large pharyngeal size who exhibited hooking when awake and a matched control group with OSAS alone.
Possible Mechanisms for Soft Palate Hooking
Hooking as an active phenomenon.—Knowledge about which UA muscles are most critical for UA patency has important implications. The retropalatal airspace is usually the site of minimal UA cross-sectional area, and UA collapse almost always occurs at the level of the palate during apnea. When compared with measurements in control subjects reported in the literature (11), there was no significant difference in the hypopharyngeal cross-sectional area in our study, but patients with awake hooking had significant oropharyngeal narrowing (171 mm2 ± 30 vs 259 mm2 ± 78; P < .02, t test). A reduction in oropharyngeal area was observed in the group of patients with OSAS, and this reduction was substantial in the subgroup of patients with OSAS with hooking of the soft palate, in whom hooking suddenly reduced the oropharyngeal area. Thus, in this latter condition, changes in the activity of the palatal muscles are likely to play an important role in triggering UA collapse.
Structural and functional changes in UA muscles have been demonstrated when studying uvular tissue obtained at uvulopalatopharyngoplasty (26–30). These modifications may be either an adaptive mechanism (ie, fiber type changes, increased muscle mass, enzymatic modifications) or a muscle injury (ie, damaged fibers, fibrosis) (31). The different patterns of muscle modifications are related to the severity of the disease (27,30) and could reflect the duration of the condition. These structural changes are consistent with a compensatory UA dilator muscle response leading to muscle injury (31–33) that ultimately may impair the ability of these muscles to maintain UA patency. This could explain why we found hooking only in patients with OSAS who were older and more obese. Thus, greater fat infiltration of the soft palate and greater muscular hypertrophy related to a longer duration of sleep apnea could also explain, at least in part, the particularity of this subgroup of patients.
In summary, the occurrence of hooking of the soft palate may represent an inappropriate activation of the palatal muscles. It has been shown (34) that the palatal muscles respond to smaller changes in UA pressure than do the tongue muscles. Thus, a slight variation in UA pressure may trigger palatal muscle activity and precipitate hooking and a dramatic secondary increase in UA resistance. Further studies are needed to identify with precision which palatal muscles are involved.
Hooking as a passive phenomenon.—Hooking may be a passive phenomenon generated by the interaction of airflow and variations in UA resistance. Huang (35) modeled snoring to examine its mechanical effects on the soft palate. In Huang's model, the oral and nasal pathways are separated upstream by a rigid barrier, the hard palate; downstream from the hard palate is attached a flexible "plate," the soft palate. In the model, the soft palate resembles an airfoil or flap with a control surface at its trailing edge. When the flap is displaced, the flow exerts a lifting force on it. It is unlikely, however, that a passive phenomenon can explain the upward displacement of the soft palate. In particular, the persistence of hooking when UA resistance is increasing implies palatal muscle activation, because the spontaneous passive mobilization would be downward.
Clinical Usefulness of Hooking Seen at UA Imaging
Our findings suggest that cephalometry and CT have 100% specificity for the determination of which patients have OSAS when hooking is observed; however, these tests are not sensitive, since only nine of 96 patients with OSAS also had hooking. Hooking is necessarily the transient phenomenon we implied it was in our discussion of mechanisms. It may be that we performed imaging in some people who may have hooking at other times than during the CT examination, which would lead to false-negative results and thereby reduce the sensitivity. We did not obtain repeated cephalometric or CT images to test the reproducibility of the phenomenon because of concern about the additional exposure to radiation in our study population. In addition, we did not include healthy control subjects in our study. In any case, this phenomenon has not, to our knowledge, been described in numerous reports of cephalometric and pharyngeal CT results that included healthy subjects. When hooking is seen, however, radiologists should suspect a high probability that the patient has OSAS. We observed hooking on CT scans alone, in most cases. Patients were supine in the scanner, whereas they were seated for cephalometry. Different levels of neck extension could also play a role in these two situations (36). Yildirim et al (37) obtained cephalometric measurements in subjects in supine and seated positions and found that the retroglossal hypopharynx widened in the supine position. This could explain the higher frequency of soft palate hooking on CT scans as compared with that on cephalometric images.
What are the implications of these findings for surgical intervention in cases of OSAS and in cases of snoring? The success rate of uvulopalatopharyngoplasty in patients with OSAS has been variable (38,39). Thus, there is a need to distinguish subgroups of patients with OSAS who might benefit from a definitive operation. We believe that the differentiation of subgroups of patients with particular anatomic features in the UA may be important for any future developments in surgical therapy for OSAS. A prospective study with a group of patients with large UAs and that includes patients with and patients without hooking is needed to determine if surgical intervention can provide any benefit.
In conclusion, we demonstrated the presence of soft palate hooking in awake patients with OSAS who had long soft palates, a wide oropharynx, and a wide hypopharynx. This pattern was present in 9% of patients with OSAS but in no patients with snoring. Radiologists who observe this finding of a hooked appearance of the soft palate on images of the UA should suspect the strong possibility of the presence of OSAS. Hooking of the soft palate while awake may facilitate pharyngeal collapse during sleep.
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Acknowledgments |
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Footnotes |
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Address reprint requests to J.L.D.P.
Abbreviations: OSAS = obstructive sleep apnea syndrome UA = upper airway
Author contributions: Guarantors of integrity of entire study, J.L.D.P., P.A.L.; study concepts and design, J.L.D.P., D.V., G.R.F., P.M., P.A.L.; definition of intellectual content, J.L.D.P., D.V., G.R.F., P.M., P.A.L.; literature research, J.L.D.P., D.V., G.R.F., P.M., P.A.L.; clinical studies, G.R.F.; data acquisition and analysis, J.L.D.P., D.V., P.M., P.A.L.; statistical analysis, J.L.D.P.; manuscript preparation, editing, and review, J.L.D.P., D.V., G.R.F., P.M., P.A.L.
Received July 16, 1997;
revision requested September 5, 1997; revision received July 9, 1998;
accepted August 14, 1998.
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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This article has been cited by other articles:
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  M You, X Li, H Wang, J Zhang, H Wu, Y Liu, J Miao, and Z Zhu Morphological variety of the soft palate in normal individuals: a digital cephalometric study Dentomaxillofac. Radiol., September 1, 2008; 37(6): 344 - 349. [Abstract] [Full Text] [PDF]
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 F. R B van Haute, G. F Taboada, L. L Correa, G. A B Lima, R. Fontes, A. P. Riello, M. Dominici, and M. R Gadelha Prevalence of sleep apnea and metabolic abnormalities in patients with acromegaly and analysis of cephalometric parameters by magnetic resonance imaging. Eur. J. Endocrinol., April 1, 2008; 158(4): 459 - 465. [Abstract] [Full Text] [PDF]
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 A. Yucel, M. Unlu, A. Haktanir, M. Acar, and F. Fidan Evaluation of the Upper Airway Cross-sectional Area Changes in Different Degrees of Severity of Obstructive Sleep Apnea Syndrome: Cephalometric and Dynamic CT Study AJNR Am. J. Neuroradiol., November 1, 2005; 26(10): 2624 - 2629. [Abstract] [Full Text] [PDF]
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