Obstructive Sleep Apnea and the Use of ConeBeam Computed Tomography in AirwayImJo ceDo A

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Osleasa levemosnabdurisrivvardiagawaFactors bearing on this challenge include thedifficulty in visualizing the airway in three di-mensions, the difficulty of visualizing the airwaythrough its entire length, and the inability to

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Den402The upper airway has three major functions:ventilation, swallowing, and speech. For ventila-tion, the upper airway must remain patent, butfor the other functions, it must narrow or close.In addition, ventilation must be maintainedwhen the nose is occluded or, alternatively,when the mouth is closed. Integration of theseconflicting functions in one anatomical region iscomplicated, and it is not surprising that inter-mittent failure of ventilation occurs.6 Addition-ally, the nose and mouth are the source of largevolumes of secretions that must be cleared viathe pharynx.

Private Practice, Louisville Dental Sleep Medicine, Louisville,. Dental Student, School of Dentistry, The University of Louis-e, Louisville, KY. Graduate Orthodontics Student, School oftistry, The University of Louisville, Louisville, KY. Anatomage,Vivo Dental, San Jose, CA. Department of Radiology, School oftistry, University of Louisville, Louisville, KY.Address correspondence to: John M. McCrillis, DMD, Louisvilletal Sleep Medicine, 2902 Taylorsville Road, Louisville, KY05. Phone: 502-458-7476; E-mail: drmcf_jm@insightbb.com 2009 Elsevier Inc. All rights reserved.1073-8746/09/1501-0$30.00/0doi:10.1053/j.sodo.2008.09.008

63Seminars in Orthodontics, Vol 15, No 1 (March), 2009: pp 63-69aging: A Reviewhn M. McCrillis, Jennifer Haskell, Bruuglas Chenin, William C. Scarfe, and

The use of cone beam computed tomvisualization of the airway is describedrelation to associated anatomy. Worktion of airway changes using one trvancement device, is discussed. (SeElsevier Inc. All rights reserved.

bstructive sleep apnea (OSA) can be de-fined as a cessation of breathing during

ep because of a mechanical obstruction sucha retropositioning of the tongue in the airway,arge amount of tissue in the upper airway, orn a partially collapsed trachea. OSA is a com-n respiratory sleep disorder characterized byoring and episodes of breathing cessation orsence of respiratory airflow (10 seconds)ring sleep and despite respiratory effort.1 Aing occurrence rate in the general populationaling that of asthma and diabetes has beeniously credited to increased awareness, bettergnostics, and a pandemic of obesity.2-4 Re-rdless of etiology, identifying the area of air-y obstruction has often proven challenging.S. Haskell, Michelle Brammer,llan G. Farman

phy to permit three-dimensionalstructive sleep apnea is defined inrogress examining the visualiza-ent modality, a mandibular ad-Orthod 2009;15:63-69.) 2009

ualize the anatomical changes of various treat-nt methods.Cone beam computed tomography (CBCT)nners have been available for craniofacial imag-since 2001 in the United Sates. Their compact

e and relatively low radiation dosage make theCT scan an imagingmodality that helps addresspreviously stated challenges effectively and ef-

iently.5 The resulting volume of digital datan be manipulated to allow the clinician three-ensional (3D) images that can be rotated inee axes, can be selectively contrasted, empha-ed, or reduced to visualize certain anatomicaluctures such as the airway, and can be sharedctronically among any number of remotees.

Patency of the pharynx is vital to the ventila-tioofanynrat19qutiodu

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64 J.M. McCrillis et al.n (respiratory) function. With the exceptionthe two ends of the airway, that is, the naresd the small intrapulmonary airways, the phar-x is the only collapsible segment of the respi-ory tract. What became apparent only in the70s is that some individuals possess an ade-ate pharyngeal lumen for all respiratory func-ns while awake but have an obstructed lumenring sleep.7,8

atomical Terms

atomical structures describing the variousrtions of the pharyngeal airway, superiorly toeriorly, include:Nasopharynx. The uppermost portion of theway, mainly the nose. It begins with the nares,ere air enters the nose, and extends back tohard palate at the superior portion of the

t palate. This includes, then, the nasal septumd the nasal turbinates.Velopharynx (also known as the retropalatalea). Extends from the hard palate to the infe-r tip of the soft palate. Includes the uvula anduppermost segment of the posterior pharyn-

al wall. Major muscles include the tensor pala-i and levator pallatini, which elevate the softlate, and the musculous uvulae providing ele-ion of the uvula.Oropharynx (also known as the retroglossalea). Includes the oral cavity, beginning with theck portion of the mouth and extending rear-rd to the base of the tongue. This segment ofposterior pharyngeal wall includes the tonsils.this area are many muscles, both extrinsic andrinsic, that control tongue posture: genioglos-, palatoglossus, and the superior longitudinald transverse muscles of the tongue as examples.Hypopharynx. Extends from the tip of the epi-ttis to the lowest portion of the airway at theynx. A large number of muscles affect thisrtion of the airway, often acting in concerth or opposition to other related muscles.9

ep Apnea Events and Terms

A events are often described as follows:Apnea (obstructive apnea), literally no bre-. Cessation of airflow for 10 or more sec-ds.Hypopnea (partial obstructive apnea), literallyw breath. Reduction of airflow below 70%od oxygen desaturation. Alternatively de-ed as reduction of airflow below 50% for 10onds or longer with a 3% desaturation, or thent is associated with arousal.10

Respiratory effort-related arousals (RERAs). Anusal from sleep that follows a 10-second orger sequence of breaths that are character-d by increasing respiratory effort but whiches not meet criteria for an apnea or hypop-a.11

Upper airway resistance syndrome (UARS). A formsleep disordered breathing (SDB) in whichetitive increases in resistance to airflowhin the upper airway lead to brief arousalsd daytime somnolence.12 There may be few, ify, obvious apneas or hypopneas with desatu-ion, but snoring may be a very prominentding.13

Apnea/hypopnea index (AHI). An index of theerity of the OSA, the AHI is calculated byding the total number of apneas and hypop-as observed and dividing by the number ofurs observed.14

Respiratory disturbance index (RDI). Many sleepgnostic centers use AHI and RDI inter-angeably. While similar, the RDI also includespiratory events such as RERAs that do nothnically fit the definitions of apnea or hypop-a but do disrupt sleep.14

Mild, moderate, and severe OSA. Severity of OSAenerally defined using the AHI/RDI (mild o 15; moderate 16 to 25; severe 26 andre). Exact boundaries are somewhat fluid,ding to terms such as mild to moderate andforth, to better describe clinical reality. Addi-nally, it should be noted that the level ofvere is quite open ended with AHI/RDIsceeding 100 being well known.

thophysiology

A events occur when the pharyngeal airwayrrows or closes with respiratory effort duringep. Several concepts, among them a balancepressures, a modification that adds transmu-pressure, and a tube law have been de-ibed in explanation of the many and variedanges in the airway leading to these apneasd hypopneas.15,16 This challenging and oftenredibly detailed work permits a summary de-iption as follows.

The pharyngeal airway is unique in having norigmeneDugelapgraretres

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65CBCT in Airway Imagingid support, instead being muscle and liga-nt formed and supported. During wakeful-ss, muscle tensions keep the lumen patent.ring sleep, as the muscles relax, the pharyn-al walls become more flexible and more col-sible. In the reclined position, the effects ofvity distort the pharyngeal walls, especially byropositioning the tongue mass when supine,ulting in a narrowed lumen.As the desired volume exchange of air re-ins the same, a higher velocity is requiredough the smaller passageway. This flow is tur-lent17 and tends to produce vibration andtter of the flexible walls and soft palate, pro-cing (often loud) snoring.The narrower the lumen, the faster the veloc-and the lower the pressure.18 At some criticalint, this combination of physical conditionsl result in an occluded airway (sucked shut).though breathing effort will continue, withdiaphragm contracting downward forcefully

ough that the chest walls may be drawn in-rd, no air will be exchanged until there isfficient arousal (lighter level of sleep) to re-in some muscle tension and reopen the pha-geal airway.This sequence of loud snoring, sudden si-ce, and loud resuscitative snort is not onlytually pathognomonic for OSA, but is fre-ently the last straw that drives the offendersily to force the individual to seek care.

mptoms and Consequences

Symptoms

Loud irregular snoringSnorts, gasps, and other unusual breathingsounds during sleepLong pauses in breathing during sleepExcessive daytime sleepinessFatigueObesityChanges in cognitive functions such as alert-ness, memory, personality, or behaviorImpotenceMorning headaches19

Consequences

Cardiovascular.

Systemic hypertensionCoronary heart diseaseSudden nocturnal deathOther (stroke, pulmonary hypertension)

Social/behavioral.

Drowsy driving/accidentsDecreased work performancePoor quality of life19

Increased mortality20-22

e of CBCT in Airway Imaging

chnology

CT provides, in a single rotation much like antal panoramic radiograph unit, precise, es-tially immediate, accurate 3D radiographicages (Figs 1 and 2). Collimation of the CBCTimary x-ray beam allows limitation of exposurethe region of interest or field of view (FOV).using megapixel solid state detection devices,nimal voxel (3D pixel) sizes of 0.09 mm 5 mm are achieved, exceeding the highestde multislice CT in terms of spatial resolu-n. Reconstruction of the digital data for view-is accomplished on a PC in close to real time.ndard viewing layouts include the display ofronal, sagittal, and axial data sets concur-tly. The views can be rotated on all three

ure 1. Segmentation of airway in relation to hardue using midline cone beam computed tomogra-y ray-sum volume of Digital Imaging and Commu-ations in Medicine data set and Anatomage InVi-ental software (San Jose, CA). (Color version of

ure is available online.)

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66 J.M. McCrillis et al.es. Cursor-driven measurement algorithmsovide the clinician with an interactive capabil-for real-time dimensional assessment.23

simetry

CT provides a lower dose, lower cost alterna-e when compared with conventional medicalscans although somewhat more than typical

ntal panoramic exposures.24 As noted byrman, ALARA (as low as reasonably achiev-le) still applies.25

Ludlow and coworkers looked at dosimetry ofBCT devices for oral and maxillofacial radi-gy: CB Mercuray (Hitachi Medical Systemserica, Twinsburg, OH), NewTom 3G (QR,rona, Italy), and i-CAT (Imaging Sciences In-national, Hartfield, PA).Utilizing thermoluminescent dosimeter chipsLDs) in a tissue-equivalent phantom (RANDO-iation analog dosimetry system; Nuclear Asso-tes, Hicksville, NY), Ludlow and coworkers re-rted widely varying exposure levels dependingnot only the exposure settings but also the fieldview (FOV), which can range from 6 to 12.se levels reported were 4 to 77 times greatern comparable panoramic examination doses.ductions in dose were seen with reduction inld size and with mA and kV technique factors.24

ure 2. Airway and facial soft tissue surface seg-nted from 3D volume (Anatomage InVivoDentaltware, San Jose, CA). (Color version of figure isilable online.)a review of medical therapy for OSA, Veaseyd coworkers state: OSA is a highly prevalentdrome that is associated with substantial mor-ity and increased mortality. Positive air pres-re (PAP) is the most uniformly effective ther-y . . . However, approximately 25-50% oftients with OSA will either refuse the offer ofP therapy, or will not tolerate it. Oral appli-ces and surgical procedures to improve upperway patency are successful in certain subsetspatients, but a notable proportion of patientsnot receive adequate clinical benefit fromse approaches.26

Any technology that would enhance clini-ns ability to visualize where in the airwaystruction occurs would help identify thosebsets of patients who may or may not benefitm a choice of treatment modalities. CBCT,h its 3D presentation of the airway and itsrrounding structures, offers this increased vi-alization of both untreated obstruction ten-ncies and potentially of changes in the airwaytreatment modality.Ogawa and coworkers demonstrated the util-of diagnosis of anatomy with the 3D airwayaging with CBCT. They noted the ability toscribe significant group differences in totalway volume and the anteroposterior dimen-n of the oropharyngeal airway between OSAd gender-matched controls.27

The same group published additional find-s notable in the use of a CBCT capable ofpine position imaging (Newtom QR DVT00; QA sri, Via Silvestrini 20, 37,135 Verona,ly). In this study of 10 OSA and 10 non-OSAtients, statistically significant differencesre reported in: the anterior-posterior di-nsion of the minimum cross-section seg-nt; the minimum cross-section area; and ine percentage incidence of location of thenimum cross-section above or below the oc-sal plane. The OSA group presented a con-ve or elliptic shaped airway and the non-A group presented a concave, round, oruare-shaped airway.28

Shi and coworkers utilized anonymousCT data sets from subjects imaged for con-ions unrelated to the airway to evaluateth a manual segmentation and an auto-ted segmentation algorithm in measuring

certain airway dimensions and airway volume.Thinopsis

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67CBCT in Airway Imagingey found no clinical significant differencethe manual versus automated algorithms,ening the door to further automated analy-of CBCT data sets.29

In a follow-up article, Farman and coworkersmonstrated the immense flexibility of CBCTa highly visible Education in the Roundting at the 148th American Dental AssociationDA) Annual Session in San Francisco, Sep-ber 26-30, 2007. Image production, process-, and export to third-party software was per-med in real time. Multiple add-on services,luding model and positioning stent prepara-n from CBCT data sets, and 3-D photographoduction (3dMD, Atlanta, GA) were alsoown.30

ure 3. Subtraction radiography using Anatomage Iprovement in airway patency following placement ofure is available online.)amine the possibilities of using different soft-re packages to analyze changes in the upperway with and without placement of a mandib-r advancement device (MAD). Image J, ancommercial software (National Institutes ofalth, Bethesda, MD), was used to look at hor-ntal plane file sets for cross-sectional areaanges. Anatomage (InVivoDental, San Jose,) used the entire Digital Imaging and Com-nications in Medicine (DICOM) multifileta sets to produce a color-contrasted blendedw of the airway changes with and without theD in place (Figs 3 and 4). Excellent segmen-ion was achieved and it was possible to makeway minimum cross-sectional area and volu-tric assessment.31

oDental software (San Jose, CA) to demonstrateandibular advancement device. (Color version ofexwaairulanoHeizochCAmudavieMAtatairme

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CT technology provides 3D images that pro-e the third dimension in dental/airway imag-. The rapid growth in numbers of new CBCTaging units being readied for the marketplacedences the interest of industry in this sector ofdical imaging.32 Further studies are requiredcorrelate the visualized airway characteristicsh clinical outcomes by treatment modality,nce then to the possibility of treatment mo-lity choice based on predictable outcomes.

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69CBCT in Airway Imagingmaintaining exothoracic airway patency. J Appl Physiol46:772-779, 1979Sung S, Jeong S, Yu Y, Hwang C, Pae E, et al: Customizedthree-dimensional computational fluid dynamics simula-tion of the upper airway of obstructive sleep apnea.Angle Orthod 46:791-799, 2006Fajdiga I: Snoring imaging: could Bernouilli explain itall? Chest 128:896-901, 2005Pascualy RA, Soest SW: Snoring and Sleep Apnea: SleepWell, Feel Better. 3rd ed. New York, Demos MedicalPublishing, Inc, 2000Carden KA: The cardiovascular effects and metabolicsyndrome. Presented at the annual meeting of the Amer-ican Academy of Dental Sleep Medicine, Minneapolis,MN, June 8-10, 2007Partinen M, Bliwise D, Bliwise N, Partinen M, Pursley A,Dement W, et al: Sleep apnea and mortality in an agedcohort. Am J Public Health 78:544-547, 1988Technol Inform 2005; 111:365-368Ogawa T, Enciso R, Shintaku W, Clark G, et al: Evalua-tion of cross-section airway configuration of obstructivesleep apnea. Oral Surg Oral Med Oral Pathol Oral Ra-diol Endod 103:102-108, 2007Shi H, Scarfe WC, Farman AG: Upper airway segmenta-tion and dimensions from cone-beam CT datasets. IntJ Comput Assist Radiol Surg 1:177-186, 2006Farman A, Levato C, Scarfe W, Mah J, et al: Education inthe round: multidimensional imaging in dentistry. In-side Dentistry, pp 82-86, January 2008McCrillis J, Farman A, Scarfe W, Brammer M, Chenin D,et al: Analysis of Airway Changes Using CBCT With andWithout Placement of a Mandibular Advancement De-vice. Louisville, KY, University of Louisville School ofDentistry, 2008Farman A, Levato C, Scarfe W: 3-D x-ray: an update.Inside Dentistry, June 2007, pp 70-74

Obstructive Sleep Apnea and the Use of Cone Beam Computed Tomography in Airway Imaging: A ReviewObstructive Sleep ApneaAnatomical TermsNasopharynxVelopharynx (also known as the retropalatal area)Oropharynx (also known as the retroglossal area)Oropharynx (also known as the retroglossal area)

Sleep Apnea Events and TermsApnea (obstructive apnea), literally no bre-ath.Hypopnea (partial obstructive apnea), literally low breath.Respiratory effort-related arousals (RERAs)Upper airway resistance syndrome (UARS)Apnea/hypopnea index (AHI)Respiratory disturbance index (RDI)Mild, moderate, and severe OSA

PathophysiologySymptoms and ConsequencesSymptomsConsequencesCardiovascularSocial/behavioral

Use of CBCT in Airway ImagingTechnologyDosimetryApplication

SummaryReferences