Anatomy of theMaxil lofacial Region in the

Three Planes of Section

Christos Angelopoulos, DDS, MS

KEYWORDS

� Cone beam computed tomography � Maxillofacial anatomy � Maxillofacial region� Multiplanar imaging

KEY POINTS

� Multiplanar imaging-reformatting (MPR) has significantly increased the diagnostic accu-racy and efficiency of the knowledgeable dental professional.

� Reviewing the dental and maxillo-facial structures in all perspectives may reveal hiddenaspects of relevant disease and may enhance diagnosis.

� The novelty of the diagnostic tool (CBCT) and the unfamiliarity of the generated sectionalimages make knowledge of the anatomy mandatory.

� Major anatomical structures, commonly seen in CBCT routine scans are reviewed as wellas related pathology, including the para-nasal sinuses, neck and cervical spine, skull baseand more.

INTRODUCTION

Multiplanar imaging has offered an unparalleled diagnostic approach when dealingwith an unknown entity (pathologic or not) that has stood as a diagnostic challenge.This concept is inherent to volumetric type of data (computed tomography [CT],cone beam computed tomography [CBCT], magnetic resonance imaging) and hasoffered the diagnostician the unique ability to generate images (sections) at differentplanes (flat or curved). Because a volume of data has been acquired and stored byCBCT, this data can be reformatted or realigned and several different types of imagescan be synthesized in any way the diagnostician requires,1 thus eliminating the super-imposition of the area or entity under investigation with other neighboring structuresand allowing its assessment from all perspectives. With multiplanar imaging, the diag-nostician/operator can re-create images in different planes (flat or curved) with verysimple functions, increasing the diagnostic efficiency in the hands of the knowledge-able individual in an unparalleled way (Fig. 1).2

Oral and Maxillofacial Radiology, College of Dental Medicine, Columbia University, 208 E, 51stStreet, Ste#121, New York, NY 10022, USAE-mail address: angelopoulosc@gmail.com

Dent Clin N Am 58 (2014) 497–521http://dx.doi.org/10.1016/j.cden.2014.03.001 dental.theclinics.com0011-8532/14/$ – see front matter � 2014 Elsevier Inc. All rights reserved.

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Undoubtedly, multiplanar imaging, as provided by cone-beam imaging, is a noveltyfor the dental professional: most dentists and specialists, with only a few exceptions,are not familiar with diagnostic imaging in different planes, although they are keen oninterpreting projectional images as those produced by traditional dental imaging mo-dalities (intraoral radiography and panoramic radiography). Sectional images (tomo-graphic images) reveal the spatial relationship of the various known anatomicstructures in the maxillofacial region, which was more or less lost in projectionalimaging.In this article the appearance of several anatomic structures of the maxillofacial re-

gion as well as the head and neck region in general is reviewed; these structures areanalyzed in all 3 basic tomographic planes (axial, coronal, sagittal). Additional recon-structed images may be used to view certain anatomic areas from all aspects. To re-view the anatomy of the maxillofacial region in a systematic way, the maxillofacialregion is divided into smaller areas of interest. Emphasis in this topographic anatomicreview is placed on areas that may demonstrate a higher incidence of occult disease.Emphasis is also on structures outside the dentoalveolar region. The anatomy ofdental and dentoalveolar structures has been thoroughly reviewed elsewhere.2

NOSE AND PARANASAL SINUSES

The paranasal sinuses are 4 pairs of air-filled osseous cavities that surround the noseand the orbits and that belong to the maxillary (maxillary sinuses), ethmoid (ethmoid aircells), frontal (frontal sinuses), and sphenoid (sphenoid sinuses) bones, respectively.Paranasal sinuses are best assessed in coronal sections; in fact, coronal images are

the most appropriate for the evaluation of anatomic structures that have a posteroan-terior orientation. The maxillary, ethmoid, and sphenoid sinuses as well as the nasalcavity and certain structures in the skull base will be optimally imaged in these views.In this review, the anatomic structures of interest ventrally to dorsally (or anterior toposterior) are reviewed (see Figs. 21–26).At the level of maxillary premolars, the coronal images section through the frontal si-

nuses, the orbits, the anterior aspect of the maxillary sinuses, the ethmoid air cells, andthe nasal cavity. The various anatomic structures of interest are addressed bymeans ofimportance to the dental professional (anatomic proximity to dental structures).The nasal cavity is seen as a pyramidal-shaped air cavity that is divided in 2 distinct,

fairly symmetric, noncommunicating air cavities by the nasal septum. Each one ofthem is separated further into smaller, blind (open) chambers by 3 elongated orarch-shaped osseous projections that originate from its lateral walls: these are theinferior, middle, and superior nasal conchae or turbinates, which border the inferior,middle, and superior nasal meatuses (chambers) (Fig. 2). Only the inferior concha isan independent facial bone; the rest are parts of the ethmoid bone. Although theyare lined by 2 to 3 mm of mucosa, there are identifiable air passageways that guidethe inhaled air to the paranasal sinuses. Shape alterations of the nasal chambers

Fig. 1. (A) The 3 standard planes of section: axial, coronal, and sagittal of the maxillofacialregion. These sectional images are the first to be reconstructed by any CBCT or MSCT (multi-slice CT) scanner and serve as the basis for numerous other reconstructions based on thediagnostic needs. Vertical and horizontal lines across the images guide the user at of theactual location of each section. (B) Panoramic reconstruction and related cross-sectional im-age. These images can be generated with very simple functions using the CBCT scanner’ssoftware applications. Their goal is to approach the region of concern from all perspectives.

Fig. 2. Coronal section of the face, approximately at the molar level, depicting the nasalcavity at its best. The nasal septum, in this case, is deviated to the left, causing a markedasymmetry between the right and left nasal cavities, this often affects the patency of thenasal passageways and may also be affected by the shape and size of the nasal turbinatesas well as the mucosal lining of the turbinates (seen as a dotted line). Thewhite arrow showsthe left maxillary sinus ostium (draining site of the sinus cavity). EB, ethmoid bulla, theinferior-most ethmoid air cell; INT, inferior nasal turbinate; MNT, middle nasal turbinate(in this case, this is pneumatized and called concha bullosa); O, orbits.

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and the septummay affect the flow of air through the nose andmay be associated withupper airway obstructive phenomena (ie, sleep apnea). In fact, a deviated nasalseptum is a common cause of sleep apnea (see Fig. 2). The nasal turbinates maysometimes be pneumatized; in this case, instead of a dense bony process, the nasalturbinate is presented as an extension of the ethmoid air cells, filled with air, and sur-rounded by a thin corticated border. This phenomenon is considered an anatomicvariant, and the pneumatized turbinate is best known as “concha bullosa,” and ismore frequently seen in the middle nasal turbinates; its incidence ranges between15% and 45%. Conchae bullosa may be inflamed because they are communicatingwith the ethmoid air cells; however, their presence does not seem to affect the path-ogenesis of sinus inflammation (sinusitis).3 Sometimes, conchae bullosa maycontribute to upper airway obstruction because they may obliterate the air passage-ways in the nasal cavity (see Fig. 2).Another prominent osseous canal is identified in the coronal sections through the

anterior third of the nasal cavity: the nasolacrimal duct, which originates at the floor/medial wall of the orbit, opens into the inferior nasal meatus (Fig. 3), and drains tearsform the orbit into the inferior meatus.Themaxillary sinuses are the largest among the variousparanasal sinuses (Figs. 4–6).

These air cavities belong to the maxillary bone. As all air cavities will be displayed asuniform dark or black because air is depicted as a very low density structure incomputed tomography (CTorCBCT). Thepresenceof any other appearance thanblackmay represent pathologic abnormality in the air cavity. Almost pyramidal in shape, withthe base of the pyramid being the medial wall or the wall that is shared with the nasalcavity and the tip of the pyramid being the zygomatic process of the maxilla (anteriorend of the zygomatic arch). The other sides of the pyramid are the superior wall (roofof the maxillary sinus), which is shared with the orbit, the lateral wall, the anteriorwall, and the posterior wall. CBCT images may provide a detailed evaluation of theintegrity of the walls of the maxillary sinuses as well as the presence of disease in theair cavities. The posterior superior alveolar neurovascular canals may be sometimes

Fig. 3. Coronal section of the face, at approximately the premolar level. The structures visu-alized at this level are the orbits (O), frontal sinuses (FS), the oral cavity (OC), the anteriorwalls of the right (R) and left (L) maxillary sinuses and nasolacrimal ducts, marked by thegreen arrows.

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be seen on the lateral wall of the maxillary sinus as a small, pinhead-size, low-densityareas (in coronal images) running almost parallel to the floor of the sinus and turningcephalad (superior) in the premolar region (in panoramic reconstructions). Its diameter,as with all vascular canals, may provide information as far as it concerns its bleedingpotential if injured during sinus grafting procedures (see Fig. 4).The draining sites of the maxillary sinuses (maxillary sinuses’ ostia) are likely to be

visualized in coronal images toward the anterior third of the sinus cavities (from frontto back) and may not be both identifiable in the same coronal plane. The ostium of themaxillary sinus is a small opening in the medial wall of the maxillary sinus (or lateral wallof the nasal cavity) toward the superior aspect, leading into the ethmoid infundibulum,a narrow passageway that opens into the middle nasal meatus; it is formed partially bythe ethmoid bone (ethmoid bulla-superior) and a thin pointy osseous process on thelateral wall of the nasal cavity known as the uncinate process. The maxillary sinusand the anterior ethmoid air cells drain into the middle nasal meatus through the infun-dibulum.4,5 The maxillary sinus ostium and the infundibulum are parts of the ostiomea-tal complex, a broader anatomic unit that serves as the draining site of the maxillary,anterior ethmoid, and frontal sinuses. Slightly higher, in the same sections, the drain-ing path of the frontal sinus is identified; this is known as the frontal recess. The narrowarch-shaped passageway between the ethmoid bulla and the middle turbinate just su-perior to the infundibulum is the hiatus semilunaris, named so because of its curved,almost semilunar shape, in the sagittal views (see Fig. 5). This hiatus semilunaris con-nects the ethmoid infundibulum to the frontal recess. The semilunar hiatus is the finalsegment of the drainage pathway from the maxillary sinus and ethmoidal infundibulumto the middle meatus.6 The narrow and delicate nature of the above-mentioned drain-ing sites makes them vulnerable to possible blockage when inflammation occurs intheir vicinity. Moreover, their close proximity to each other renders them possiblepaths for spread of infection. Identification of the draining sites and assessment oftheir integrity is important in patients who will undergo maxillary sinus grafting proce-dures. Blockage of the draining site may prevent the aeration of the sinus cavity andresult in accumulation of inflammatory products into the sinus (see Fig. 6). This fine

Fig. 4. (A) Panoramic reconstruction and related cross-sectional images of the right poste-rior maxilla for the assessment of the lateral wall of the maxillary sinuses before a graftingprocedure. The small, low-density (almost pinhead in size) area (red arrows) is the osseouscanal for the posterior superior alveolar (PSA) neurovascular bundle (artery, vein, andnerve). (B) Panoramic reconstructions along the lateral wall of the maxillary sinus illustrateclearly the course of neurovascular canal of PSA (red arrows) from posterior to anterior. Thebleeding potential of any vessel is proportional to its diameter.

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Fig. 5. (A, B) Coronal section of the face, at the level of maxillary sinuses/nasal cavity(approximate maxillary molar level) depicting the maxillary sinuses at best. These imagesare optimal for the evaluation of the integrity of the floor and walls of the sinuses and nasalcavities. The draining site of the maxillary sinus is known as ostium (red arrows) and is nar-row, opening on the medial wall of the maxillary sinus to the medial nasal meatus (cham-ber). The medial wall ends in a pointy osseous projection known as uncinate process(stars). The ostium opens into a narrow canal, the ethmoidal infundibulum (green dottedline). Part of the infundibulum is a thin curved canal, the shape of which is affected by itsproximity to the ethmoid bulla; this is the hiatus semilunaris (white dotted line). All ofthe above participate in a broader unit often identified as ostiomeatal complex or unit(green dash-marked cycle), including the draining sites of the maxillary sinuses, frontalsinuses, and anterior and middle ethmoid sinuses (all drain in the middle nasal meatus).EB, ethmoid bulla; INT, inferior nasal turbinate; MNT, middle nasal turbinate.

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and delicate anatomy of the ostiomeatal complex may be grossly altered if sinus sur-gery has occurred (Fig. 7).The ethmoid air cells or sinuses are numerous, small, mostly square, air cavities that

are separated by thin bony walls, grouped in 2 orthogonal prisms located on eitherside of the superior nasal cavities, and run parallel to the nasal cavities through theirentire length (from front to back). They are bordered from the orbits with the laminapapyracea, a paper-thin osseous wall, and from the nasal cavities with the superiorand middle nasal turbinates (Fig. 8). The anterior and middle ethmoid air cells draininto the middle nasal meatus, whereas the posterior ethmoid air cells drain into the su-perior nasal meatus (Fig. 9).

Fig. 6. (A) Coronal sections through the maxillary sinuses showing the presence of inflam-matory tissue (collection of soft tissue in density content) in the left maxillary sinus andthickening of the mucosal lining of the floor and walls of the right maxillary sinus. Notethe inflammatory tissue is rather extensive and has blocked draining passageway (ostium)(green arrow). (B) Coronal section through the sinuses showing extensive inflammatorychanges in the sinus cavities of the right and left maxillary sinuses. Flat surfaces on the(soft in density) content of sinuses may indicate coexistence of fluid in sinus cavity (air/fluidlevel) (red arrows). In this case, however, the evaluation of the maxillary sinuses is incom-plete and a more extended field of view should be used.

Fig. 7. Coronal section of the maxillary sinuses (approximate maxillary molar level): thenasal architecture as well as the ethmoid sinuses is dramatically altered; in addition, theostia of the right and left maxillary sinuses are widened to facilitate drainage, the resultof extensive sinonasal surgery.

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Fig. 8. (A–C) Axial (A), coronal (B), and sagittal (C) views of the ethmoid sinuses and sphe-noid sinuses (A, C). The ethmoid sinuses are composed of numerous, thin-walled air cells thecomplexity of which gave them the name of ethmoid labyrinth. Other structures visualizedincluded the sphenoid sinuses (SS), the lamina papyracea (thin wall separating the ethmoidsinuses from the orbit, green arrow), the inferior nasal turbinate (INT), and the middle nasalturbinate (MNT).

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Fig. 9. (A, B) The drainage path of the anterior ethmoid air cells (white dotted line) andmiddle ethmoid air cells (green dotted line) is depicted in coronal (A) and in sagittal (B) sec-tions of the anterior/middle ethmoid air cells. This path clearly opens to the middle nasalmeatus.

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The sphenoid sinuses are the posterior-most air cavities and belong to the sphenoidbone. Their shape is similar to that of a truncated pyramid with its base being the bonyroof of the nasopharynx; its roof, the sella turcica (pituitary fossa), and its lateral wallsborder the cavernus sinuses on either side of the body of the sphenoid bone. Thesphenoid sinuses drain to the superior nasal meatus through a small opening in theiranterior wall, the spheno-ethmoidal recess (Fig. 10).Important anatomic entities, such as the optic canal, the foramen rotundum, and the

vidian canal, are closely related to the sphenoid sinuses and will be addressed in laterdiscussion in the anatomic review of the skull base (see Figs. 25 and 26).The frontal sinuses are 2 funnel-shaped air cavities identified superior to the ethmoid

air cells and the nasal cavities and belong to the frontal bone. They demonstrate agreat deal of variation in shape and size. A septum, which is frequently deviated, sep-arates the right from the left and asymmetry between the 2 is not uncommon. Theydrain into the middle nasal meatus through the frontal recess, a thin passageway,part of the ostio-meatal complex (discussed earlier).The orbits are visualized toward the anterior third of the face as well as the ethmoid

air cells, the most anterior part of which is sectioned at this level. These views areexcellent for the assessment of the integrity of the osseous walls of the orbits and theirborders. A short osseous canal seen originating from the floor of the orbit and directedinferomedially to the anterior wall of the maxillary sinus is the infraorbital foramen,which accommodates the infraorbital nerve (Fig. 11). Lamina papyracea, a paper-thin osseous diaphragm that belongs to the ethmoid bone and serves as the medialorbital wall, stands as the boundary between the orbit and the ethmoid air cells (seeFigs. 6A and 8B).

Fig. 10. (A–C) Axial (A), coronal (B), and sagittal (C) views of the sphenoid sinuses (SS). Thegreen dotted line shows the draining path of the sphenoid sinuses to the superior nasalmeatus through a narrow opening on the anterior wall known as sphenoethmoidal recess(green arrow).

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Unfortunately, the soft tissue contrast of CBCT is inadequate for the assessment ofthe orbital content (eye globe, fat, and musculature of the eye globe).Inflammation is by far the most common pathologic entity among the ones affecting

the paranasal sinuses. Moreover, it seems that it is a frequent occult pathologic entityin CBCT scans prescribed for other diagnostic concerns.7,8

Fig. 11. (A, B) Coronal (A) and sagittal (B) views through the floor of the orbits and maxillarysinuses. Ovoid osseous canals seen on the floor of the orbits are the infraorbital foramina(green arrows). Also notice the inflammation in the left maxillary sinus. Nasolacrimal canal(stars).

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NECK AND CERVICAL SPINE

A considerable portion of the patient’s neck and cervical spine may be included in anextended field-of-view scan of the maxilla and mandible or of the mandible toward theinferior end of the scan. Axial images are best for the evaluation of the visible parts ofthe neck and cervical spine as well as the skull base, although a combination of recon-structed images in all 3 planes (axial, coronal, and sagittal) may be used to assess aregion of interest fully.Most times, the portion of the neck that is visualized in a CBCT includes the supra-

hyoid neck (above the hyoid bone). A few osseous structures and mostly soft tissuestructures are present at that level (Fig. 12). The inferior border of the anteriormandible may be sectioned at this level and may be visualized toward the upperborder of the image. The hyoid bone and the third or fourth cervical vertebra (thesevertebrae are almost indistinguishable at that level in axial sections) are the only otherbony structures seen toward the inferior end of the imaging volume. The sequentialaxial images of the neck are dominated by soft tissue structures, the visualization ofwhich is generally limited because of reduced soft tissue contrast in CBCT images.In fact, soft tissue structures often blend together in the various reconstructed images,a fact that renders CBCT inadequate for the diagnosis of soft tissue pathologic abnor-mality. However, sometimes, soft tissues are identifiable and this may vary in differentCBCT scanners.The soft tissue structures identified in that level include the sternocleidomastoid

muscle (SCMs) bilaterally, the geniohyoid muscles, as well as the submandibular sali-vary glands. Most of the time only the contour of these structures is discernible and,although their visualization is not adequate for possible disease involvement, they maybe used as anatomic landmarks for orientation. In the center of the neck lies the onlyreadily identifiable soft tissue structure: the airway; this is a semicircular, very low-density (dark) area bordered by the hyoid bone (ventrally) and the vertebral column

Fig. 12. (A) Axial CBCT image at the level of the hyoid/C3 vertebra. (B) The same axial imageas the one on the left with some identifiable neck anatomic structures outlined. (Despite thefact that the soft tissue contrast of cone-beam tomography is not optimal for the diagnosisof soft tissue pathologic abnormality, some of the neck anatomic landmarks are visualized.)The neck spaces, because they are mainly occupied by fat, appear of a lower density in com-parison to the neighboring musculature. Note that this is the approximate location of themajor blood vessels of the neck; their precise location cannot be clearly seen without theutilization of intravenous administration of contrast media. Knowledge of the topographiclocation of the major neck anatomic structures will assist the diagnostician to determine theorigin of the various pathologic entities that may develop on the neck. C3, an axial sectionof the third cervical vertebra; CA, carotid arteries; E, epiglottis; F, fatty tissue; GH, genio-hyoid muscle; H, hyoid bone (note the almost modular appearance of the hyoid bonethat can imitate a fracture); IJV, internal jugular vein; M, inferior border of the anteriormandible; S/M, submandibular salivary glands.

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(dorsally). The airway is separated almost in 2 halves by a soft tissue structure, cres-cent in shape (most often), the epiglottis.Approximately at this level, the common carotid artery bifurcates into 2 main

branches, the internal carotid and external carotid arteries, which supply the brainand face of each side, respectively. The most reliable reported landmarks to indicatethe level at which bifurcation occurs are the C3/C4 level and the superior border of thethyroid cartilage of the larynx; however, variation is not uncommon (see Fig. 12). Theblood vessel is accompanied by the internal jugular vein (the bigger blood vessel of theneck) and the vagus nerve to form the neurovascular bundle of the neck. The locationof the bundle in the axial images of the neck, at the level of C3-C4, is posterolaterally tothe airway and anteromedially to the sternocleidomastoid muscle (SCM) (Fig. 13). Su-perior to the bifurcation, the carotid artery branches are less distinguishable due theirreduced diameter.Despite that the major blood vessels of the neck discussed above are rarely distin-

guished from the rest of the soft tissues of the neck in CBCT images because of thelimited soft tissue contrast, familiarity of the course of the blood vessel on the lateralneck is crucial to identify pathologic conditions inside or in the vicinity of the bloodvessels, such as carotid artery atheromatosis, a pathologic condition in which calcifieddeposits (atheromas) accumulate on the internal wall of the blood vessel;9 this grad-ually reduces the flexibility and functionality of the blood vessel. Carotid artery athero-matosis demonstrates a fairly high incidence rate in older age groups and has been

Fig. 13. Axial section of the neck at the level of C3/C4 vertebral bodies with contrast-enhanced CT. The circulating contrast medium is depicted with a high-density fact thatmakes the blood vessels and other anatomic structures supplied by the blood with contrastwell-identifiable. ECA, external carotid arteries; EJV, external jugular vein; F, subcutaneousfat; GH, geniohyoid muscle; ICA, internal carotid arteries; IJV, internal jugular vein; MH,mylohyoid muscle; SMG, submandibular salivary gland; VA, vertebral arteries.

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associated with an increased risk of stroke. These calcifications most frequently occurwithin 10 to 15 mm of the bifurcation (above or below). Sometimes they have a cleartubular appearance that makes them more readily identifiable than not. Other timesthey look more like a cluster of calcifications in the region (Figs. 14 and 15).

Fig. 14. Axial section of the neck at the level of C3/C4 vertebral bodies showing an athero-matous plaque (green arrow) in the left common carotid artery almost tangential to the an-teromedial aspect of the left SCM (red dotted outline). The other smaller calcifications seenon either side of the airway are calcifications in the thyroid cartilage complex (yellowarrows).

Fig. 15. Axial section (A) and coronal section (B) of the neck at the level of C3/C4 vertebralbodies showing atheromatous plaques (green arrows) in the common carotid arteries bilat-erally. Variation as far as size and shape is frequent.

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Other types of neck calcifications may include calcifications in the thyroid cartilagecomplex, stylohyoid ligament calcifications, sialoliths, and tonsiloliths (Figs. 16 and17). Some may resemble carotid artery calcifications; however, the appearance andlocation most of the times will assist in determining the origin of the calcification.Apart from the visualization of the corresponding cervical vertebrae (depending on

the level of the axial sections) and the mandibular bone, axial images of the floor of themouth reveal minimal information about the soft tissue structures in the region(Fig. 18).Sagittal images of the neck are best for the assessment of the cervical spine and the

airway (Fig. 19A). The cervical spine is partially only visualized in CBCT scans (C1–C5).The normal (healthy) appearance of the vertebral bodies includes a fairly square body,a thin cortical outline, a cancellous component of homogenous density, and a fairlysymmetric spacing between the vertebrae visible in the scan. However, pathologic ab-normality associated with the cervical spine and other irregularities is not uncommon(see Fig. 19B). Often the above are incidental findings in scans that were prescribedfor different reasons.

Fig. 16. Bilateral calcifications at the level of the floor of the mouth (axial and coronal im-ages) (arrows). Note the superficial location of the calcifications in relationship to theairway. These were tonsilar calcifications or tonsiloliths and have been associated with recur-rent inflammation of the tonsils as well as halitosis.

Fig. 17. Single, round calcification in the left submandibular space (arrows); this was a silao-lith in the left submandibular salivary gland.

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Fig. 18. Axial cut of the mandible toward the lower half of the mandibular body. At thatlevel, the C3 vertebra is depicted. The red arrowsmark the right and left transverse foramen(or foramen transversarium). Contiguous transverse foramina form a canal that hosts thevertebral artery during its ascending course toward the endocranium. Note that due toinadequate soft tissue contrast, it is impossible to distinguish different soft tissue structuresin the mouth. FOM, floor of the mouth; VF, vertebral foramen.

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The airway is presented as a low-density (black), tubular-shaped structure, whichmay vary in width and lies just ventrally to the cervical part of the vertebral column.The position of the epiglottis, the laryngeal opening below the epiglottis, as well asthe position of the tongue may have an effect on the diameter of the airway in severallocations. CBCT images are very useful in the evaluation of the airway and the factorsthat may cause restrictions in the airflow in sleep-apnea cases (Fig. 20).10,11

Shape alterations of the airway in the various levels may trigger alerts for possibledisease. In fact, soft tissue pathologic abnormality around the borders of the airwaymay have an effect on the shape of the airway (Fig. 21).

MIDFACE AND SKULL BASE

The midfacial structures as well as the skull base are reviewed next in a series ofaxial sections (Figs. 22–27). This review starts at the level of the floor of the maxillarysinuses and the base of the maxillary alveolar bone. Apart from the apices of themaxillary teeth, the hard palate, and the floor of the maxillary sinuses, the superiorforamina (anteriorly) and the greater and lesser palatine foramina are visualized atthat level. The superior foramina are the entrance of the nasopalatine canal andare located on the floor of the nasal cavity (inferior meatus); they host the nasopala-tine nerve, which exists through the incisive foramen on the palatal aspect of themaxillary midline between the central incisor teeth. The greater and lesser palatineforamina serve as the passageways to the greater and lesser palatine nerves andvessels, which will run the hard palate from posterior to anterior just superior tothe palatal roots of the maxillary molars on the soft tissue in a palatal mucosa (see

Fig. 19. (A) Midsagittal cut of the face and neck. Sagittal sections are best for the evaluationof the visible portion of the cervical spine and the airway. C2, 2nd cervical vertebral axis;the superior end of C2 is the odontoid process, which is articulated with the atlas (C1) andthe skull base; C3, third; C4, fourth. FS, frontal sinus; NPC, nasopalatine canal; S, sella turcica;SS, sphenoid sinus. The yellow arrows mark the hard palate and the green arrows mark thesoft palate. The elongated, slightly curved, low-density area anterior to the cervical spine isthe airway. (B) Sagittal image of the cervical spine and the airway; large osseousmasses (greenarrows) on the ventral aspect of the C4, C5 are osteophytes, signs of degenerative joint diseasein the visible portion of the cervical spine. Other signs of degenerative joint disease (arthritis)include loss of intervertebral space, erosive changes, subchondral cyst formation, andsclerosis.

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Fig. 22). Their identification during palatal surgery and palatal flap elevation is impor-tant. Similarly to several other important anatomic structures, they will not always bevisualized in CBCT scans.The nasopharyngeal aspect of the airway dominates the center of the axial cuts of

the midface. Its shape and size vary and may be affected by neighboring anatomicstructures in the vicinity. A deep depression on the lateral walls of the nasopharynxbilaterally is the Eustachian tube, the tube that communicates and balances the air

Fig. 20. A thick sagittal cut visualized in 3 dimensions to assess the airway (blue). Severalsoftware programs (mostly third party) offer specific utilities that simplify airway evaluationas well as measurements, volume, and analysis.

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pressure between the inner ear and external ear (see Figs. 22 and 23). Just posterior tothe Eustachian tube, separated only by soft tissue projection (torus tubarius), lies thepharyngeal recess or fossa of Rosenmueller. This region almost always will appearinto the maxillary CBCT scans and it is imperative to be included in the evaluation.Further dorsally, an ovoid or ellipsoid structure is visualized toward the anterior aspectof the foramen magnum; this is the odontoid process of the axis (C2) (see Fig. 19A).Several very important anatomic structures are identified posterior to the midface, in

the skull base (see Figs. 24–27; Figs. 28 and 29). These structures are the mandibularcondyles, external auditory canals, mastoid processes (partially visualized), bilaterally,and the sphenoid sinus almost in the center of the axial image. Anteromedial to themandibular condyles lie 2 important foramina: the foramen ovale (larger one) andthe foramen spinosum (smaller one). The former hosts the third division of the trigem-inal nerve (V3), the mandibular nerve, and the latter, the middle meningeal artery.At the same level, simply by slightly changing the reformatting angle to make the

sections more parallel to the skull base, additional very important anatomic structureswill appear: one of the most important anatomic regions of the skull base is the pter-ygopalatine fossa (PPF), which is identified in contact with the posterior wall of theright and left maxillary sinuses. The PPF represents a major crossroad in the skullbase: in the PPF open 2 large osseous channels: the Vidian canal (or pterygoid canal),which hosts fibers of the petrosal nerves, and the foramen rotundum, which carries themaxillary nerve (V2). With the PPF as a passageway, the middle cranial fossa commu-nicates with the orbits (through the inferior orbital fissure), with the paranasal sinusesthrough the sphenopalatine foramen, the infratemporal fossa, and the nasal cavity.Through this crossroad, inflammation from the orbits, nasal cavity, sinuses, and oralcavity can be transferred into the middle cranial fossa and vice versa. The

Fig. 21. Axial (top) and coronal (bottom) sections of the airway showing marked asymmetrybetween the right and left lateral walls with the right posterolateral wall shifted medially.This shift is evident in the coronal view (arrows). Often, airway shape alterations may beassociated with soft tissue growths in the region and may require further investigation.

Fig. 22. (left) Axial section at the level of the roots of the maxillary teeth. (right) Axial sec-tion slightly superior to the other section, at the level of the floor of the maxillary sinus. Thegreen arrows show the pharyngeal opening of the Eustachian tube, which helps in equal-izing the pressure between the 2 sides of the eardrum. The red arrows mark the fossa Rose-nmuller. GLPF, greater and lesser palatine foramina; HP, hard palate; MS, maxillary sinus; OC,oral cavity; SF, superior foramina, the starting point of the nasopalatine canal; TT, torustubarius, a soft tissue process on either side of the nasopharynx (NF) separating the Eusta-chian tube from the fossa Rosenmuller.

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Fig. 23. Axial section at the level of the maxillary sinuses/mandibular rami demonstratingmajor structures of the maxillary sinus, nasal cavity, and nasopharynx at the axial plane.INT, inferior nasal turbinate; (L)MR, left mandibular ramus; MS, maxillary sinus; N/F, naso-pharynx; PP, lateral and medial pterygoid plates; ZP, zygomatic process of the maxilla. Thered arrowsmark the Eustachian tube, and the round shaded region, the general site of fossaRossenmuller and torus tubarius.

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identification of the PPF and assessment of the integrity of its margins are absolutelynecessary if this structure is demonstrated in the CBCT scan.12,13

Just posterior to the foramen ovale and medial to the mandibular condyle lies thecarotid canal, on either side of the skull base. The 2 canals converge toward thebase of the sphenoid, where they pass close to the cavernous sinus before theyascend.

Fig. 24. Axial section at the level of the maxillary sinuses (superior third) demonstrating ma-jor structures of the maxillary sinuses, nasal cavity, and skull base at the axial plane.Co, mandibular condyle; FO, foramen ovale; FS, foramen spinosum; IO, infraorbital canal;JF, jugular foramen (or jugular fossa); Ma, mastoid air cells; MNC, middle nasal concha;NL, nasolacrimal duct; SS, sphenoid sinus; ZA, zygomatic arch. The blue arrow indicatesthe external auditory canal.

Fig. 25. Axial section at the level of the maxillary sinuses (superior third) (same as Fig. 17,but slightly higher) demonstrating additional anatomic details about the skull base. MNC,middle nasal concha; SS, sphenoid sinus. The green arrows mark the walls of a thin channelknown as the “Vidian canal” or pterygoid canal. The yellow arrows mark the course of thecarotid canals that appear to be converging toward the base of the sphenoid bone. PPF is aregion of importance in the skull base. It is the passageway from the middle cranial fossa tothe orbit, face, sinuses, and vice versa. Disease processes may be transferred from the middlecranial fossa to other sites (mentioned above) through the PPF. Similarly, disease originatedextracranially may be transferred to the endocranium through the PPF.

Fig. 26. Axial image of the head at level of the orbits (inferior third). The section depicts theroof of the maxillary sinuses (MS) bilaterally and the ethmoid sinuses (ES), just medial to themaxillary sinuses. Note the fine and delicate air cells that form the ethmoid sinuses; this fineand complicated architecture has given the name of ethmoid labyrinth to the ethmoid aircells. The circular depressions toward the posterolateral walls of the sphenoid sinuses (SS),which can be seen in its magnitude in this image, represent the continuation of the carotidcanals (CC) as they are entering the cavernous sinus of the lateral border of the base of thesphenoid bone. Note the septations, present in the sphenoid sinus, seen in this image. Thesection very clearly illustrates the relationship between the PPF, the inferior orbital fissure(IOF), and the temporal fossa (yellow dotted area). Last, the green arrows mark the courseof the right and left foramen rotundum. IAC, internal auditory canal; MCF, middle cranialfossa; PCF, posterior cranial fossa.

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Fig. 27. Axial section of the head at the level of the orbits (superior half). The posterioropening of the orbits is divided by the superior orbital fissure (SOF) and the optic canal(yellow arrows). The orientation of the optic canals is toward the sella, where the opticchiasma takes place. ACP, anterior clinoid processes; PCP, posterior clinoid processes.

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At the same level, almost in contact with the posterior border of the external auditorycanals and medially to the mastoid air cells, the jugular foramina are located. Alsoknown as jugular fossae (due to their large size), they are well-defined, wide, corti-cated canals that serve as the passage points for the ninth (glossopharyngeal), tenth(vagus), eleventh (accessory) cranial nerves as well as the jugular vein, among others.Variation in their shape and size as well asymmetry is not uncommon.More cephalad axial sections (see Fig. 26) will show the orbits, the ethmoid sinuses,

and the sphenoid sinuses. The posterior opening of the orbits at that level is the inferiororbital fissure, which communicates with the PPF as mentioned earlier.The ethmoid sinuses are made up of numerous, small, thin-walled, air cells sepa-

rated by the vomer bone (nasal septum) in the midline. Their complicated anatomygave them the characterization of the ethmoid labyrinth. The larger sphenoid sinusesare located just posterior (dorsally) to the ethmoid sinuses. They occupy the base ofthe sphenoid bone (basisphenoid) and their thinned osseous walls are in contactwith some rather important anatomic entities: the carotid canals (posterolaterally)and the foramina rotunda/PPF (anterolaterally). Anatomic variation and the presenceof septations are often the rule rather than the exception.

Fig. 28. Coronal section through the sphenoid sinus (SS). CP, coronoid process of themandible; NP, nasopharynx. The yellow arrows show the Vidian canal (pterygoid canal)and the red arrows show the foramen rotundum.

Fig. 29. Coronal section through the sphenoid sinus (just posterior to section in Fig. 25). NP,naso-pharynx; SS, sphenoid sinus. The dotted lines mark the course of the foramen ovalebilaterally.

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The most superior (cephalad) axial sections will reveal the upper half of the orbits,the temporal fossa, and partially the middle and the posterior cranial fossae. The con-cavities seen toward the posterolateral orbital walls are the temporal fossae; they areanatomic depressions into the temporal bone and serve as the attachment point forthe temporalis muscle (see Fig. 27).At this level, the orbital apex (posterior opening of each orbit) appears to be splitting

into 2 distinct openings: a lateral opening, which is rather wide and opens into theanterior cranial fossa (superior orbital fissure), and a narrower medial opening, whichis longer and directed posteromedially toward the sella turica (optic canal). In fact, the2 optic canals are converging toward the sella turcica, where they finally unite. Theconvergence point is the optic chiasma where the 2 optic nerves (content of the opticcanals) cross each other’s course.The posterior clinoid processes (also identified at that plane) are 2 small osseous

tubercles, which demonstrate a transverse orientation form the dorsal boundary ofthe sella turcica. They show a great deal of variation in shape and size, deepen thesella, and serve as attachment points (see Fig. 27).The goal of the above anatomic review of themaxillofacial region was 2-fold: to shed

some light into structures and anatomic landmarks that were “lost,” in some ways, inprojectional imaging and discuss their location, course, and relationship with neigh-boring structures in 3 dimensions; and also to illustrate the effects of disease in knownanatomic boundaries (canals, foramina, osseous cavities, soft tissue contours) that,sometimes, may be the only signs of developing pathologic abnormality.The successful identification of an unknown entity lies in the ability of the observer to

approach it from all perspectives, using fully the potential of the multiplanar imaging. Itis strongly recommended that to take advantage of the CBCT images in full, the diag-nostician should be able to understand and apply the concept of multiplanar reformat-ting to the highest degree. It is in our hands to reveal the information related to eachdiagnostic task. In other words, our diagnostic efficiency is based on our sound knowl-edge of anatomy and on our skills to retrieve relevant diagnostic information.

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