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Keywords:

  • Dental radiology;
  • orthopantomograph

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Panoramic radiography has become a commonly used imaging modality in dental practice and can be a valuable diagnostic tool in the dentist’s armamentarium. However, the panoramic image is a complex projection of the jaws with multiple superimpositions and distortions which may be exacerbated by technical errors in image acquisition. Furthermore, the panoramic radiograph depicts numerous anatomic structures outside of the jaws which may create additional interpretation challenges. Successful interpretation of panoramic radiographs begins with an understanding of the normal anatomy of the head and neck and how it is depicted in this image type. This article will describe how osseous structures, soft tissues, air spaces and ghost shadows contribute to the final panoramic image. A systematic and repeated approach to examining panoramic radiographs, which is recommended to ensure that critical findings are not overlooked, is also outlined. Examples of challenging interpretations, including variations of anatomy, artefacts and disease, are presented to illustrate these concepts.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Panoramic radiography has become a commonly used imaging modality in dental practice and can be a valuable diagnostic tool in the dentist’s armamentarium. However, the panoramic image is a complex projection of the jaws with multiple superimpositions and distortions which may be exacerbated by technical errors in image acquisition. Furthermore, the panoramic radiograph depicts numerous anatomic structures outside of the jaws which may create additional interpretation challenges. Successful interpretation of panoramic radiographs begins with an understanding of the normal anatomy of the head and neck and how it is depicted in this image type. This article will describe how osseous structures, soft tissues, air spaces and ghost shadows contribute to the final panoramic image. A systematic and repeated approach to examining panoramic radiographs, which is recommended to ensure that critical findings are not overlooked, is also outlined. Examples of challenging interpretations, including variations of anatomy, artefacts and disease, are presented to illustrate these concepts.

Anatomy of a panoramic radiograph

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Although it is obvious that a panoramic radiograph depicts the teeth and jaws in a single convenient view, it may be less clear how the other structures of the head and neck become captured on the image. It is often these superimposing hard and soft tissues and airways that create confusing shadows which cause challenges in interpretation.

The panoramic perspective

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

The first step in understanding panoramic anatomy is to appreciate the perspective from which each part of the image is presented. Because the image is captured by an X-ray tube which rotates around the patient’s head, rather than from a stationary source, this perspective changes from the posterior regions of the jaws to the anterior area. The right and left posterior parts of the image represent lateral views, looking at the patient from the side; the anterior part of the image represents an anterior-posterior view, looking at the patient from the front (Fig. 1). The entire panoramic image is analogous to a composite of portions of two lateral and one anterior-posterior skull views, except without as many superimpositions.

image

Figure 1.  Top – composite photograph depicting the osseous anatomy of the maxilla and surrounding bones from the panoramic perspective. The anterior region is viewed from the front while the posterior regions are viewed from the side. Bottom – a panoramic radiograph divided to match the regions represented by the photograph above. a and black dotted outline = pterygoid plate; b = pterygomaxillary fissure; c = zygomatic process of maxilla; d = zygomatic arch; e = temporal component of temporomandibular joint; f = mastoid process of temporal bone (not imaged in panoramic radiograph); g = lateral and inferior orbital rim; h = infraorbital canal; i and white dotted outline = inferior concha/turbinate; j = hyoid bone.

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Osseous anatomy

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

With the panoramic perspective in mind, the osseous structures of the maxillofacial region can be reviewed. The structures around the posterior maxilla, which include the sphenoid, zygomatic and temporal bones, are likely the least familiar for many dental practitioners but contribute an important part of the panoramic image. The pterygoid plates of the sphenoid bone articulate with the posterior wall of the maxilla and, together, form the pterygomaxillary fissures (Fig. 1a and b). The zygomatic processes of the maxilla are thick buttresses of bone extending laterally from the maxilla bilaterally and are seen as J-shaped shadows superimposed over the maxillary sinuses (Fig. 1c). They articulate with the zygomatic bones which, in turn, articulate with the zygomatic processes of the temporal bones to form the zygomatic arches (Fig. 1d). The zygomatic arches can be followed posteriorly to where the temporal bones form the superior components of the temporomandibular joints (Fig. 1e). Sometimes the mastoid processes of the temporal bones, containing multiple radiolucent air cells, are imaged posterior and inferior to the temporomandibular joints (Fig. 1f). Occasionally, the mastoid air cells may extend anteriorly and pneumatize the roof of the temporomandibular joint (Fig. 2). This is a normal anatomic variation but may seem to mimic pathology due to the multilocular appearance produced. The lateral and inferior orbital rims of the orbits are seen as thick, curved, linear radiopaque structures superior to the maxillary sinuses (Fig. 1g). Each infraorbital canal may be seen as thin parallel cortices, extending inferiorly and medially from the floor of the orbit (Fig. 1h). The inferior turbinates of the nasal fossa create surprisingly large shadows across a large portion of the maxillary sinuses (as seen from the lateral perspective). They are also seen in the middle part of the image on either side of the nasal septum (seen from the anterior perspective) (Fig. 1i). The hyoid bone, which is normally seen inferior to the mandible, may create confusion when it becomes superimposed over the inferior border because of patient positioning (Fig. 1j).

image

Figure 2.  Mastoid air cells are seen bilaterally where they have pneumatized the articular processes of the temporal bones creating rounded, radiolucent loculations (black arrows). This is a variation of normal anatomy.

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Soft tissues and air spaces

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

The osseous structures of the maxillofacial region are surrounded by the soft tissues of the face, neck and oral cavity. These soft tissues create indistinct radiopaque shadows which superimpose over the osseous and dental structures. The external nose may be seen over the apices of the maxillary incisors with the ala curving laterally from the midline (Fig. 3a). The soft tissues of the external ear are often seen superimposed over the mandibular condyle with the earlobe forming a rounded radiopacity posterior to the ramus (Fig. 3b). The largest intraoral shadow is created by the tongue, whose dome-shaped image occupies a large proportion of the panoramic radiograph (Fig. 3c). In the posterior parts of the radiograph, the posterior region of the tongue may have a more irregular surface due to the lingual tonsils (Fig. 3d). The epiglottis can often be seen as a thin finger-like projection extending from the posterior tongue, below the angles of the mandible (Fig. 3e). The soft palate is seen from a lateral perspective on both sides of the panoramic image as an oval or inverted tear-drop shape extending off the hard palate (Fig. 3f). Its inferior surface is superior and approximately parallel to the tongue.

image

Figure 3.  Panoramic radiograph with major soft tissue structures (a–f) and airways (1–5) traced. a = external nose; b = external ear; c = tongue; d = lingual tonsils on posterior tongue; e = epiglottis; f = soft palate; 1 = nasal fossa; 2 = nasopharynx; 3 = oropharynx; 4 = oral cavity; 5 = oral orifice.

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The upper airway includes the nasal fossa, oral cavity and pharynx, all of which are imaged on the panoramic radiograph as radiolucent passages. These radiolucencies may be confused for bone destroying pathology or fractures (Fig. 4). The nasal fossa is seen in the midline, superiorly, and extends bilaterally across the region of the maxillary sinuses (Fig. 3,1). Posteriorly, it opens into the nasopharynx. The nasopharynx is seen posterior to the maxilla and superior to the soft palate (Fig. 3,2). It is continuous with the oropharynx inferiorly, which occupies the region anterior to the cervical spine and posterior to the tongue (Fig. 3,3). The oral cavity may be seen as a variably-sized radiolucent strip between the superior surface of the tongue and the palate (Fig. 3,4). The increased radiolucency of the oral cavity may obscure the roots of the anterior teeth due to overexposure. This effect may be minimized by having the patient place his or her tongue flat against the palate during imaging. The oral orifice, or space created between the upper and lower lips, may be seen as a ‘kiss-shaped’ radiolucency over the crowns of the maxillary and mandibular incisors (Fig. 3,5). Having the patient close his or her lips around the bite-stick can prevent overexposure of this area.

image

Figure 4.  The air shadow of the oral cavity may create a thin radiolucent line superimposed over the mandibular ramus, which may be mistaken for a fracture if not properly identified (open black arrows). Careful examination of the periphery of the radiograph is done to avoid missing findings in the tissues surrounding the jaws. An elongated styloid process (black arrow) and submandibular calcification (white arrow), most likely representing a submandibular gland sialolith, are detected in this patient.

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Ghost shadows

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Ghost shadows are shadows of structures imaged when they are not within the focal trough. Because these structures are outside the plane of focus, they appear increasingly magnified and blurry. For example, when the left side of the mandible is being imaged, the film or sensor is positioned close to this side. However, the X-ray source is positioned on the right side of the patient and the beam must pass through the right mandible in order to image the left side. Because the right side is at a greater distance from the film, its image is enlarged and indistinct. Hence there is a ghost shadow of the right mandible seen superimposed, in a slightly superior position and a reversed orientation, over the left mandible. Of course, the same is true for the contralateral side (Fig. 5a). The cervical spine may be seen in focus on a panoramic radiograph on the most posterior parts of the image. However, a ghost shadow of the cervical spine is formed when the anterior teeth are imaged because the X-ray beam originates from behind the patient’s head. This shadow may obscure a clear view of the anterior region of the jaws (Fig. 5b). Having a patient stand as tall as possible with his or her cervical spine extended maximally helps minimize this superimposition. Foreign objects, such as earrings or facial jewellery, may also create ghost shadows which can obstruct visualization of the underlying anatomy if they are not removed (Fig. 6).

image

Figure 5.  The ghost shadows produced by the contralateral mandible (a) and cervical spine (b) are traced on this panoramic radiograph. The shadows of these structures are indistinct because they are so far outside the focal trough when imaged.

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image

Figure 6.  Earrings worn by this patient during image acquisition have created ghost shadows. The right earring is seen superimposed over the left maxillary sinus (white arrow) and the left earring is projected over the right zygomatic arch (black arrow).

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An approach to reading panoramic radiographs

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

The interpretation of a panoramic image follows the same principles as with any other image or image series. A systematic and repeated process is used to ensure that all significant findings are identified. An observer cannot count on abnormalities to present themselves. Rather, one must be vigilant in assessing all anatomic structures to ensure they are present and normal. In the systematic approach recommended here the osseous structures and surrounding soft tissues are assessed first. Second, the alveolar processes are examined. Finally, the teeth are evaluated.

Osseous structures and surrounding soft tissues

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Compared to intraoral radiographs, the panoramic image depicts a much larger area of anatomic structures of the oral and maxillofacial region. More time will therefore be required to assess these structures, though once a routine is established a practitioner will find that this becomes a quick and natural process. It is critical to have a good understanding of the normal anatomy in order to identify the presence of any abnormalities. It is useful to compare the left and right sides of the image when deciding if a finding is normal, since structures appearing bilaterally are generally anatomic. Comparing the left and right sides may also allow detection of any asymmetries that may be indicative of disease or a developmental condition.

The following steps are an example of an approach to analysing the complex projection of the anatomic structures on a panoramic radiograph:

  • 1
    Assess the periphery and corners of the image
    • Start here to avoid zoning in on the teeth and neglecting important findings in the tissues surrounding the jaws (Fig. 4).
    • Structures that may be seen in this area include the:
    • orbits
    • articular processes of the temporal bones (at the temporomandibular joints)
    • cervical spine
    • styloid processes
    • pharynx
    • hyoid bone.
  • 2
    Examine the outer cortices of the mandible
    • Trace the periphery of the bone starting at one spot and completing a circuit which includes:
    • anterior and posterior rami
    • coronoid processes
    • condyles and condylar necks
    • inferior border.
    • Look for continuity and evenness of the cortices (Fig. 7).
  • 3
    Examine the cortices of the maxilla
    • This includes the posterior and medial walls and floor of each maxillary sinus.
    • While examining the posterior wall of the sinus, also look at the:
    • zygomatic process of the maxilla
    • pterygomaxillary fissure
      • -
        The thin radiopaque lines produced by these structures run roughly parallel to the posterior wall of the maxillary sinus, and may be confused with it. Destructive disease affecting the maxillary sinus may erode the posterior wall, which can be easily missed if all three lines are not identified (Fig. 8).
  • 4
    Examine the zygomatic bones and arches
    • Follow where they extend posteriorly from the zygomatic processes of the maxilla to the temporal bones.
  • 5
    Assess the internal density of the maxillary sinuses
    • Compare left and right sides.
    •  Opacification is most commonly a sign of inflammatory disease but could be a sign of more serious pathology.
  • 6
    Assess the structures of the nasal cavity and the palates
    • Examine the nasal floor/hard palate and conchae extending horizontally along both sides of the image.
    • Examine the nasal septum in the midline.
    • Note the soft palate seen bilaterally extending from the posterior aspect of the hard palate and into the oropharynx.
  • 7
    Examine bone the pattern of the maxilla and mandible
    • Assess the density and pattern of the trabeculae for abnormalities (Fig. 7).
    • Keep in mind that some metabolic conditions may present with a generalized alteration in bone pattern and therefore comparing left and right sides may not be helpful.
    • In the mandible examine the size, position, cortication and symmetry of the:
    • inferior alveolar nerve canals
    • mandibular foramina
    • mental foramina.
image

Figure 7.  Careful examination of this panoramic radiograph reveals that the inferior cortex of the mandible is not seen clearly on the left side, compared to the right. Assessment of the bone pattern also reveals increased trabecular bone density in the posterior left mandible. This has caused the mandibular nerve canal to appear relatively more prominent. The path of the nerve canal is also altered in a superior direction. These findings are consistent with fibrous dysplasia. This image cannot portray the buccal-lingual expansion that is characteristic of this condition.

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image

Figure 8.  Examination of the cortical lines in the posterior maxillary regions of this image would allow the observer to detect that the posterior wall of the left maxillary sinus is absent (open black arrows indicate where the cortex should be seen). This destruction was caused by a malignancy within the sinus. The white lines formed by the zygomatic process of the maxilla and posterior boundary of the pterygomaxillary fissure, which should be assessed at the same time as the posterior wall of the maxilla, are still visible.

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Alveolar processes and teeth

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

The spatial resolution of a panoramic image is much lower than intraoral radiographs, making detailed assessment of the alveolar processes and teeth more difficult. Nonetheless, full evaluation is required to avoid missing disease. These structures should be viewed in a systematic manner. A sequence from the posterior of the first quadrant to the posterior of the fourth quadrant in a clockwise direction, repeated for each finding to be evaluated, is recommended.

The following steps are suggested as an approach to this part of the interpretation: (1) assess the crestal bone position of the alveolar processes to identify any periodontal bone loss; (2) examine the periodontal ligament spaces and lamina duras around each tooth for signs of inflammatory disease; (3) don’t forget to examine the follicles and papillae of developing teeth for anything affecting their size, position or cortical boundaries. These changes could be indicative of developing pathology; (4) evaluate the teeth for presence/absence/eruptive or positional abnormalities, caries, inadequate restorations, calculus, developmental or acquired abnormalities.

Interpretation of pathology on panoramic radiographs

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

The panoramic radiograph is especially useful when examining regions of the jaws which cannot be imaged with intraoral radiographs, such as the temporomandibular joints and third molar regions. Due to distortion and a limited two-dimensional view, the temporomandibular joint cannot be assessed in detail, however, a general overview is provided which allows major abnormalities to be ruled out. When a lesion in the jaws needs to be studied, it is important to be able to examine its entire boundary, which may be best achieved on a panoramic image. Usually the location, periphery and shape, internal density and effects on the surrounding structures of lesions in the jaws can be appreciated on panoramic images. However, this modality is limited by the numerous superimpositions projected on the image, especially in the maxillary sinus and palate regions, and by its inability to demonstrate medial-lateral changes (Fig. 7). Advanced imaging, such as computerized tomography, cone beam computerized tomography or magnetic resonance imaging may be required to provide multidimensional views to supplement the information obtained from a panoramic radiograph.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Anatomy of a panoramic radiograph
  5. The panoramic perspective
  6. Osseous anatomy
  7. Soft tissues and air spaces
  8. Ghost shadows
  9. An approach to reading panoramic radiographs
  10. Osseous structures and surrounding soft tissues
  11. Alveolar processes and teeth
  12. Interpretation of pathology on panoramic radiographs
  13. Conclusions

Panoramic radiographs have many useful applications in dentistry but require diligence on the part of the observer to examine the image thoroughly. For this reason, a systematic approach is recommended for the interpretation of this image type. Understanding the perspective of the anatomy on a panoramic radiograph as well as the many superimpositions and distortions produced will help the practitioner to be more successful at this task.