Upper Airway Size Analysis by Magnetic Resonance
Imaging of Children with Obstructive Sleep
Raanan Arens, Joseph M. McDonough, Aaron M. Corbin, Nathania K. Rubin, Mary Ellen Carroll, Allan I. Pack,
Jianguo Liu, and Jayaram K. Udupa
Division of Pulmonary Medicine, Children’s Hospital of Philadelphia, and Division of Sleep Medicine and Department of Radiology,
Hospital of the University of Pennsylvania, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Detailed analysis of the upper airway has not been performed in The three-dimensional relationship between the upper air-
children with obstructive sleep apnea. We used magnetic resonance way, adenoid, and tonsils has not been previously studied in
imaging and automatic segmentation to delineate the upper airway children with OSAS. The aim of the present study was to
in 20 children with obstructive sleep apnea and in 20 control sub- characterize the differential contribution of the adenoid and
jects (age, 3.7 1.4 versus 3.9 1.7 years, respectively). We mea- tonsils to airway restriction along the upper airway by de-
sured mean and minimal cross-sectional area, length, and volume termining the cross-sectional airway area in planes orthogo-
of: (1 ) the total airway; (2 ) regions along the adenoid, tonsils, and nal to the upper airway axis. To this end, we used a new
where adenoid and tonsils overlap; and (3 ) 10 segments at 10% methodology, developed on the basis of fuzzy connectedness-
increments along the airway. The mean cross-sectional area of the
based automatic segmentation (7–9), that enabled us to visu-
total airway of the obstructive sleep apnea group was significantly
alize and analyze the upper airway in a correct anatomic
smaller in comparison with the control group, 28.1 12.6 versus
47.1 18.2 mm2, respectively (p 0.0005). Minimal cross-sec-
orientation as it relates to airﬂow and further delineate the
tional area and airway volume were smaller in this group, 4.6 upper airway changes that occur in children with OSAS.
3.3 versus 15.7 12.7 mm2 (p 0.0005), and 1,129 515 versus
1,794 846 mm3 (p 0.005), respectively. Regional analysis sug- METHODS
gested that the upper airway in children with obstructive sleep
Subjects with OSAS
apnea is most restricted where adenoid and tonsils overlap. Seg-
mental analysis demonstrated that the upper airway is restricted Twenty children were recruited from the pool of patients evaluated for
throughout the initial two-thirds of its length and that the nar- sleep-disordered breathing at the Children’s Hospital of Philadelphia
rowing is not in a discrete region adjacent to either the adenoid (Philadelphia, PA). After OSAS was conﬁrmed by polysomnography,
or tonsils, but rather in a continuous fashion along both. parents provided consent for the sedation and upper airway MRI of
their child; children older than 6 years provided their own consent. The
Keywords: magnetic resonance imaging; obstructive sleep apnea syn- study was approved by the Institutional Review Board.
drome; upper airway
Obstructive sleep apnea syndrome (OSAS) in children is a Twenty children with normal growth and development were matched
common disorder and may affect as many as 2% of children to subjects with OSAS by age, sex, ethnicity, weight, and height. Control
(1, 2). Both anatomic and physiologic factors affecting upper subjects were selected from among patients who underwent head MRI
airway size, shape, and function may play a role in the causa- at the Children’s Hospital of Philadelphia for other medical indications.
tion of OSAS in children. Frequently, OSAS is associated Exclusion criteria included the following: (1 ) likelihood of OSAS
(scores of 1 or more; assessed by a standard questionnaire ), (2 )
with adenotonsillar hyperplasia; however, abnormalities in evidence of a brain tumor or a seizure disorder requiring therapy,
craniofacial anatomy, neuromotor tone, or airway compli- (3 ) genetic disorders associated with any craniofacial anomaly, and
ance should be considered as possible causes in children with (4 ) chronic respiratory disease such as asthma or bronchopulmonary
the disorder when no apparent adenotonsillar hyperplasia is dysplasia.
Magnetic resonance imaging (MRI) allows visualization Overnight Polysomnography
and accurate measurement of the upper airway as well as of For subjects with OSAS, polysomnography was performed 0–4 weeks
the various soft tissues and skeleton comprising it (3–6). before MRI. Subjects were studied in the Sleep Disorders Center at
Using MRI, we have previously shown that children with the Children’s Hospital of Philadelphia. Scoring of respiratory variables
OSAS and no apparent craniofacial or neurologic disorder was performed on the basis of standards set by the American Thoracic
have decreased upper airway volume and increased adenoid Society and previously published data on children (11, 12). Flow was
measured with an oral/nasal thermistor and a nasal end-tidal Pco2 cathe-
and tonsillar volume in comparison with control subjects (5).
ter. We used the deﬁnition of obstructive apnea as absence of oral/
nasal thermistor signal for at least two respiratory cycles associated
with out-of-phase movement of the rib cage and abdomen. Hypopnea
was deﬁned as a decrease of 50% or more in oral/nasal thermistor
(Received in original form June 26, 2002; accepted in final form October 4, 2002) signal and a concurrent fall of 4% or more in basal oxygen saturation.
Sleep stages were determined by the criteria of Rechtschaffen and
Supported by grants HL-62408 and MO1-RR00240 from the National Institutes
Correspondence and requests for reprints should be addressed to Raanan Arens, Sleep Questionnaire
M.D., Division of Pulmonary Medicine, Children’s Hospital of Philadelphia, 34th
Street and Civic Center Blvd., Philadelphia, PA 19104-4399. E-mail: arens@email. A questionnaire regarding symptoms of sleep-disordered breathing
chop.edu based on the questionnaire developed by Brouillette and coworkers
Am J Respir Crit Care Med Vol 167. pp 65–70, 2003
(10) was used to assess the likelihood of OSAS in control subjects and
Originally Published in Press as DOI: 10.1164/rccm.200206-613OC on October 11, 2002 subjects with OSAS. On the basis of the questionnaire, no subject with
Internet address: www.atsjournals.org a score less than 1 would be expected to have OSAS; a score between
66 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 167 2003
1 and 3.5 is considered indeterminate, and a score greater than 3.5 RESULTS
is considered highly predictive of obstructive sleep apnea.
We studied 20 children with OSAS, mean age 3.7 1.4 years
Magnetic Resonance Imaging (range, 1.9–7.9 years), and 20 matched control subjects, mean
MRI studies were performed in the Department of Radiology at the age 3.9 1.7 years (range, 1.9–7.8 years). Children with OSAS
Children’s Hospital of Philadelphia. All studies were performed while were not signiﬁcantly different from control subjects with respect
subjects were sedated. Sedation consisted of intravenous pentobarbital to age, sex, ethnicity, height, or weight (Table 1). All control
(2-mg/kg increments) until sleep was achieved. A maximum of three subjects had normal development and cognitive function, intact
doses or 200 mg was administered. All subjects were monitored continu- tonsils and adenoid, and no respiratory disorders or craniofacial
ously by pulse oximetry and were observed by an intensive care unit anomalies. The primary indications for head MRI of control
attending physician until recovery (about 1 hour). subjects were as follows: single seizure/febrile convulsion (10
All MR images were obtained as part of a larger ongoing study subjects), migraine/headache (6 subjects), head concussion (2
(unpublished data), using a comprehensive MR protocol. Images of 15 subjects), limping (1 subject), and dizziness (1 subject). Thus,
of the 40 subjects in this study (9 subjects with OSAS and 6 control none of these clinical indications would be expected to affect
subjects) were used in a previous study (5), and were now processed upper airway anatomy.
for the ﬁrst time according to the new methodology (see below) to
further delineate airway anatomic characteristics. Polysomnography
MRI was performed with a 1.5-T Vision System (Siemens, Iselin,
NJ). Images were acquired with an anterior–posterior volume head For subjects with OSAS the mean total sleep time during polys-
coil. The patient’s head was positioned supine in the soft tissue Frank- omnography was 7.6 0.6 hours. The mean respiratory variables
fort plane (tragus of the ear to orbital ﬁssure) perpendicular to the values during this period were as follows: apnea index, 2.6
table. Sequential T2-weighted spin-echo axial sections were obtained, 4.1; apnea/hypopnea index, 8.4 9.5; baseline peripheral oxygen
spanning from the orbital cavity to the larynx. Mean acquisition time saturation (SpO2), 96 1%; SpO2 nadir, 85 7%. Thus, these
was 2 minutes, spin-echo repetition time (TR) 650 milliseconds, echo data suggest mild–moderate OSAS in this group.
time (TE) 14 milliseconds, 192 256 matrix, slice thickness 3 mm
with distance factor 0, one acquisition, ﬁeld of view (FOV) 20 to Sleep Questionnaire
24 cm, rectangular FOV 6/8. All control subjects had an apnea score of less than –1, indicating
unlikelihood of obstructive sleep apnea (10), and as a group had
Image Processing and Anatomic Measurements
a mean apnea score of 3.3 0.6. This score was signiﬁcantly
The MR images were transferred to a SUN workstation. Images were lower than the apnea score noted in the OSAS group of 2.9
processed and segmented automatically to compute the airway includ- 1.5 (p 0.0005).
ing its surface description, centerline, and volume (Figure 1A), using
a software program we have developed utilizing fuzzy connectedness Magnetic Resonance Imaging
segmentation (7–9) and based on 3DVIEWNIX (14).
Representative three-dimensional display of the upper airway,
Upper airway centerline. We computed a centerline through the
airway that passes through all points that are maximally distant from its centerline, and cross-sectional images orthogonal to the cen-
the perimeter of the airway at sequential planes orthogonal to the terline at levels of the adenoid, the region of overlap between
airway axis. The centerline was bounded by the upper nasopharynx adenoid and tonsils, tonsils, and the superior portion of the
(deﬁned as the posterior edge of the vomer) and the lower oropharynx epiglottis of a control subject and a subject with OSAS are
(deﬁned as the most superior part of the epiglottis). Centerline length presented in Figures 1 and 2, respectively.
was deﬁned as the distance along the centerline between the two bound- Airway analysis. The mean cross-sectional area of the total
aries. Airway regions adjacent to adenoid, tonsils, and the overlap upper airway of the OSAS group was signiﬁcantly smaller in
region between adenoid and tonsils were measured along the centerline. comparison with the control group, 28.1 12.6 versus 47.1
Because the lower poles of the tonsils extend at times below the oro- 18.2 mm2 (p 0.0005). Similarly, the minimal cross-sectional
pharynx, measurement of the airway length, area, and volume adjacent area and upper airway volume were smaller in this group, 4.6
to the tonsils was performed along an extended airway centerline as 3.3 versus 15.7 12.7 mm2 (p 0.0005) and 1,129 515 versus
deﬁned above. 1,794 846 mm3 (p 0.005), respectively. The upper airway
Upper airway cross-sectional area measurements. Cross-sectional ar-
centerline length was similar in subjects with OSAS and control
eas at planes orthogonal to the centerline were computed every 0.2 mm
subjects, 40.2 5.8 versus 37.1 8.2 mm (p NS), respectively.
after interpolation, ﬁltering, and thresholding of the original axial slices
(9). We measured the mean and minimal cross-sectional area of the Regional analysis. Analysis of the airway along the adenoid,
total airway; the mean cross-sectional area in regions adjacent to the the region of overlap between adenoid and tonsils, and tonsils
adenoid, adjacent to the overlap region between the adenoid and tonsils, in subjects with OSAS and control subjects is shown in Table 2.
and adjacent to the tonsils; and the mean and minimal cross-sectional Accordingly, we noted a signiﬁcantly smaller mean cross-sec-
area for 10 consecutive segments at 10% increments of the centerline. tional area in subjects with OSAS in all three regions and signiﬁ-
Upper airway volume measurements. The total airway volume was cantly smaller mean volume and a longer mean airway centerline
computed as the product of centerline length and mean cross-sectional
area. Similarly, regional airway volumes adjacent to the adenoid, adja-
cent to the overlap region between the adenoid and tonsils, and adjacent
to the tonsils were computed as the product of mean airway cross- TABLE 1. DEMOGRAPHICS
sectional areas along these regions and the corresponding centerline
Subjects with OSAS Control Subjects
lengths. Finally, volumes for 10 consecutive segments at 10% increments
(n 20) (n 20)
of the centerline were computed.
Age, yr 3.7 1.4 3.9 1.7
Data Analysis Sex, male/female 8/12 8/12
Ethnicity, black/white 13/7 13/7
Mean and standard deviation were used to summarize continuous vari-
Height, cm 101 13 101 13
ables. For comparisons between the groups for MRI data, demograph- Weight, kg 17.4 5.2 16.8 5.6
ics, and questionnaire data, we used a two-tailed unpaired t test, the
Wilcoxon rank test, or the 2 test as appropriate. A p value of 0.05 or Definition of abbreviation: OSAS obstructive sleep apnea syndrome.
less was considered to indicate statistical signiﬁcance. Values represent means SD.
Arens, McDonough, Corbin, et al.: Upper Airway Size Analysis 67
Figure 1. Left: three-dimensional display of an upper airway and its centerline in a control subject. Top right: gray-level two-dimensional scene of
the cross-section of the airway orthogonal to the centerline at marker locations: A adenoid; A T adenoid and tonsil overlap; T tonsils;
E epiglottis. Bottom right: plot of the cross-sectional area function.
in regions adjacent to the adenoid and where adenoid and tonsils noted in subjects with OSAS in the upper 60–70% of the upper
overlap, but not in the region adjacent to the tonsils. The smallest airway, whereas in the lower regions of the upper airway, these
mean cross-sectional area and volume were noted for both OSAS parameters were similar in both groups.
and control subject groups in the airway region where adenoid
and tonsils overlap. DISCUSSION
Segmental analysis. Airway length is dependent on height
and age. To normalize our measurements along the upper airway We used MRI to study the size of the upper airway in children
nasopharynx and oropharynx, we performed a similar analysis with OSAS. Our ﬁndings suggest that the upper airway of chil-
throughout the airway centerline based on 10 segments repre- dren with OSAS is restricted along the upper two-thirds of its
senting 10% total length increments; this is shown graphically length and predominantly in the region where the adenoid and
in Figures 3A–3C. Accordingly, signiﬁcantly smaller mean cross- tonsils overlap.
sectional area, minimal cross-sectional area, and volume were Some methodological issues need initial comment. The upper
Figure 2. Left: three-dimensional display of an upper airway and its centerline in a subject with OSAS. Top right: gray-level two-dimensional scene
of the cross-section of the airway orthogonal to the centerline at marker locations: A adenoid; A T adenoid and tonsil overlap; T tonsils;
E epiglottis. Bottom right: plot of the cross-sectional area function.
68 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 167 2003
TABLE 2. UPPER AIRWAY DIMENSIONS AND REGIONAL ANALYSIS IN SUBJECTS WITH
OBSTRUCTIVE SLEEP APNEA SYNDROME AND CONTROL SUBJECTS
Subjects with OSAS Control Subjects
Measurement (n 20) (n 20)
Total upper airway Mean cross-sectional area, mm2 28.1 12.6* 47.1 18.2
Minimum cross-sectional area, mm2 4.6 3.3* 15.7 12.7
Airway centerline length, mm 40.2 5.8 37.1 8.2
Volume, mm3 1,129 515† 1,794 846
Airway region adjacent Mean cross-sectional area, mm2 19.2 10.1* 44.7 24.5
to adenoid Length, mm 22.6 5.5‡ 19.5 3.8
Volume, mm3 440 240* 840 403
Airway region where adenoid Mean cross-sectional area, mm2 11.7 5.7* 34.7 23.9
and tonsils overlap Length, mm 15.4 4.5‡ 12.5 3.1
Volume, mm3 188 119† 403 235
Airway region adjacent Mean cross-sectional area, mm2 27.0 15.9‡ 37.9 15.2
to tonsils Length, mm 34.9 6.8 32.6 7.5
Volume, mm3 946 574 1,197 425
For definition of abbreviations, see Table 1.
Values represent means SD.
* p 0.0005.
airway has a complex shape formed by various tissues with het- In the present study we conﬁrm our previous ﬁnding (5),
erogeneous compositions that surround the air column. This, suggesting that the size of the upper airway in children with
along with airway boundary motion, results in some MR signal OSAS is smaller compared with normal children. However, the
gradation and blurring. This was true in the present study when current study was more comprehensive because it was designed
data were collected during a 2-minute period throughout numer- to identify the actual site(s) of restriction along the upper airway
ous respiratory cycles. Fuzzy connectedness is a computational path and the role of the adenoid and tonsils in airway restriction
method of object segmentation that takes into account the effects in these subjects, using a new methodology.
of tissue heterogeneity, imaging noise, and blurring. This method In the previous study, we used T1 images for airway analysis.
determines voxels that comprise an object by assigning weights The airway measurements included a single axial cross-sectional
to each voxel on the basis of its spatial nearness, similarity of area at the midtonsillar level, an airway volume derived from
intensity, and pathwise relationship to all other voxels. The resul- sequential 3-mm axial slices, and a single nasopharyngeal cross-
tant fuzzy object is a pool of voxels with a membership value sectional area obtained from a midsagittal image. All measure-
that represents its strength as a member of the object (7, 8). ments were made manually with the program VIDA and no
Fuzzy connectedness is a robust tool for airway segmentation. airway reconstruction was performed.
It achieves an intraoperator and interoperator variation of less In the present study, we reconstructed the airway using T2
than 0.87% and the accuracy of volume and delineation was images with a new algorithm in a program 3DVIEWNIX. This
found to be 97% as compared with expert manual segmentation method is a multistep process, including nonmanual fuzzy con-
(9). In addition, when applied to the airway, fuzzy connectedness nectedness delineation, interpolation, ﬁltering, and thresholding
was performed in less than 10% of the time required for manual that results in a three-dimensional display of the airway, center-
segmentation (9). line, area proﬁle, and cross-sectional images (9). This method
For the most reliable comparison of the OSAS group with enables accurate representation of the airway as it relates to
the control group, we performed a case–control study and airﬂow and surrounding tissues and is signiﬁcantly more efﬁcient
matched each subject with OSAS by age, height, weight, sex, than manual segmentation.
and ethnicity. All could inﬂuence the airway by affecting size, In the present study, we found that the upper airway cross-
shape, and function of the surrounding tissues, including muscle, sectional area varies along the airway centerline in a similar
lymphoid, fat, and bone (5, 15, 16). Our control subjects did not form in both normal children and in children with OSAS, with
undergo polysomnography and were screened only by history the OSAS group being about one-half smaller in the upper two-
and a standardized questionnaire. No obstructive events were thirds of the airway. In both groups, about 20 to 60% of the
observed in the control subjects during imaging. airway represents a region where adenoid and tonsils overlap
To obtain optimal MR images in young children, mild seda- (Figure 3, bottom); this region corresponds to the lowest mean
tion to avoid body movement is necessary and is routinely used and minimal airway cross-sectional areas. It is possible that air-
in our institution. Sedation can reduce upper airway muscle way obstruction in children with OSAS occurs in this region.
activity compared with wakefulness and could have affected our However, our study could not prove this speculation because of
airway measurements (17). It is possible that sedation had a the relatively long MR acquisition time, and further investigation
bigger effect on upper airway muscle activation in subjects with in another study using faster MR sequences will be needed to
OSAS compared with control subjects, amplifying the differ- visualize dynamic changes of the airway during respiration.
ences between the groups in our study. Moreover, sedation could Isono and coworkers (18) assessed the collapsibility and mini-
have caused partial or complete airway obstruction during data mal cross-sectional area of the passive airway in children with
acquisition, leading to increased motion and resulting in more OSAS (age, 7.6 3.5 years). These children were studied under
blurring of our images in the OSAS group. Hence, the limitation general anesthesia and measurements were performed by endos-
of sedation in our study should be recognized. copy at discrete levels including the adenoid, soft palate, tonsils,
Arens, McDonough, Corbin, et al.: Upper Airway Size Analysis 69
and tongue. These investigators noted the mean highest closing
pressure and minimal cross-sectional area to occur mostly at the
levels of adenoid and soft palate. These ﬁndings suggesting that
higher airway segments are more involved in children with OSAS
support our ﬁndings showing restriction in the upper two-thirds
of the airway.
Although the total centerline length was similar in OSAS
and control groups, in regions adjacent to the adenoid and where
the adenoid and tonsils overlap, the lengths were signiﬁcantly
longer in the OSAS group (22.6 5.5 versus 19.5 3.8 mm,
p 0.05, and 15.4 4.5 versus 12.5 3.1 mm, p 0.05,
respectively). This could be related to the increased extension
of lymphoid tissue in OSAS and the more tortuous path along
the centerline in these narrowed regions. In addition, segmental
analysis along the entire centerline suggests that the upper air-
way of children with OSAS is restricted compared with control
subjects over the initial 60–70% of its length. The narrowing is
not a discrete region adjacent to either the adenoid or tonsils,
but rather occurs in a continuous fashion along both. These
observations suggest that ﬂow resistance is higher in these re-
gions, and complete obstruction during inspiration in sleep may
be more likely where narrowing occurs and high negative pres-
sures are developed.
Interestingly, segmental analysis suggests that airway mea-
surements below the region of maximal restriction (i.e., region
of overlap between adenoid and tonsils) are similar in both
groups (Figure 3). This could explain to some extent why clinical
assessment of the tonsils and airway that are below this region
of restriction do not predict the existence or severity of OSAS
In summary, we used MRI to analyze the size of the upper
airway in children with OSAS. Our results suggest that the upper
airway in children with OSAS is signiﬁcantly smaller with respect
to airway volume, mean airway cross-sectional area, and minimal
cross-sectional area compared with matched control subjects.
We also noted that the upper airway in children with OSAS is
restricted along the initial 60–70% of its length and most affected
in regions where adenoid and tonsils overlap.
1. Ali NJ, Pitson DJ, Stradling JR. Snoring, sleep disturbance, and behavior
in 4–5 year olds. Arch Dis Child 1993;68:360–366.
2. Redline S, Tishler PV, Schluchter M, Aylor J, Clark K, Graham G. Risk
factors for sleep-disordered breathing in children: associations with
obesity, race, and respiratory problems. Am J Respir Crit Care Med
3. Schwab RJ, Gupta KB, Gefter WB, Hoffman EA, Pack AI. Upper airway
soft tissue anatomy in normals and patients with sleep disordered
breathing: signiﬁcance of the lateral pharyngeal walls. Am J Respir
Crit Care Med 1995;152:1673–1689.
4. Schwab RJ, Pack AI, Gupta KB, Metzger LJ, Oh E, Getsy JE, Hoffman
EA, Gefter WB. Upper airway and soft tissue structural changes in-
duced by CPAP in normal subjects. Am J Respir Crit Care Med
5. Arens R, McDonough JM, Costarino AT, Tayag-Kier CE, Mahboubi S,
Schwab RJ, Pack AI. Magnetic resonance imaging of the upper airway
structure in children with obstructive sleep apnea. Am J Respir Crit
Care Med 2001;164:698–703.
6. Arens R, McDonough JM, Corbin AM, Hernandez EM, Maislin G,
Figure 3. Segmental analysis—percent airway centerline length versus Schwab RJ, Pack AI. Linear dimensions of the upper airway structure
(A ) mean airway cross-sectional area, (B ) minimal cross-sectional area, during development: assessment by magnetic resonance imaging. Am
and (C ) volume. Data points represent mean values SD along 10% J Respir Crit Care Med 2002;165:117–122.
segments. Dotted lines represent estimated measurements between data 7. Udupa JK, Samarasekera S. Fuzzy connectedness and object deﬁnition:
points; solid circles subjects with OSAS; open circles control subjects. theory, algorithms, and applications in image segmentation. Graphical
Models Image Processing 1996;58:246–261.
*p 0.05; **p 0.005; ***p 0.0005. Regions of the adenoid and
8. Udupa JK. Three-dimensional visualization and analysis methodologies:
tonsils adjacent to the airway are shown by horizontal bars. Note overlap a current perspective. Radiographics 1999;19:783–803.
regions for tonsils and adenoid. 9. Liu J, Udupa JK, Odhner D, McDonough JM, Arens R. Upper airway
segmentation and measurement in MRI using fuzzy connectedness.
SPIE Proc 2002;4683:238–247.
70 AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 167 2003
10. Brouillette R, Hanson D, David R, Klemka L, Szatkowski A, Fernbach 16. Fujioka M, Young LW, Girdany BR. Radiographic evaluation of adenoi-
S, Hunt C. A diagnostic approach to suspected obstructive sleep apnea dal size in children: adenoidal–nasopharyngeal ratio. Am J Roentgenol
in children. J Pediatr 1984;105:10–14. 1979;133:401–404.
11. American Thoracic Society. Standards and indications for cardiopulmo- 17. Litman RS, Weissend EE, Shrier DA, Ward DS. Morphologic changes
nary sleep studies in children. Am J Respir Crit Care Med 1996;153:866– in the upper airway of children during awakening from propofol ad-
878. ministration. Anesthesiology 2002;96:607–611.
12. Marcus CL, Omlin KJ, Basinski DJ, Bailey SL, Rachal AB, Von Pech- 18. Isono S, Shimada A, Utsugi M, Konno A, Nishino T. Comparison of
mann WS, Keens TG, Ward SL. Normal polysomnogram values for static mechanical properties of the passive pharynx between normal
children and adolescents. Am Rev Respir Dis 1992;146:1235–1239. children and children with sleep disordered breathing. Am J Respir
13. Rechtschaffen A, Kales A. A manual of standardized terminology, tech- Crit Care Med 1998;157:1204–1212.
niques and scoring systems for sleep stages on human subjects. Wash- 19. Fernbach SK, Brouillette RT, Riggs TW, Hunt CE. Radiologic evaluation
ington, DC: National Institutes of Health; 1968. Publication No. 204. of adenoids and tonsils in children with obstructive sleep apnea: plain
14. Udupa JK, Odhner D, Samarasekera S, Goncalves R, Iyer K, Venugopal ﬁlms and ﬂuoroscopy. Pediatr Radiol 1983;13:258–265.
K, Furuie S. 3DVIEWNIX: an open transportable, multidimensional, 20. Mahboubi S, Marsh RR, Potsic WP, Pasquariello PS. The lateral neck
multimodality, multiparametric imaging software system. SPIE Proc radiograph in adenotonsillar hyperplasia. Int J Pediatr Otorhinolaryn-
1994;2164:58–73. gol 1985;10:67–73.
15. Jeans WD, Fernando DC, Maw AR, Leighton BC. A longitudinal study 21. Brooks LJ, Stephens BM, Bacevice AM. Adenoid size is related to sever-
of the growth of the nasopharynx and its contents in normal children. ity but not the number of episodes of obstructive sleep apnea in
Br J Radiol 1981;54:117–121. children. J Pediatr 1998;132:682–686.