Mesiodistal extension with minimal buccolingual expansion
This appearance is almost pathognomonic for keratocysts in the mandible. Note however that glandular odontogenic cyst may also show this growth pattern (see below). Other cyst types and ameloblastomas show ballooning expansion. The feature is best visualised on computed tomography (CT) scans
A well‐demarcated unilocular radiolucency in the ascending ramus not associated with a tooth
Such a radiolucency is most likely to be an odontogenic keratocyst. If the cyst is associated with an unerupted tooth a dentigerous cyst cannot be excluded, and if it is multilocular an ameloblastoma must be considered. A keratocyst is even more likely if there is little buccolingual expansion (see above)
Figure 7.11
Lateral periodontal cyst
Well‐defined, round corticated radiolucency lateral to the tooth root. Periodontal space and lamina dura are intact
This feature is characteristic of lateral periodontal cyst. Lesions are rarely greater than 10 mm in diameter. If the lamina dura surrounds the cyst, or cannot be seen, a lateral radicular cyst must be considered. If the radiolucency is larger than 10 mm or is multilocular, an alternative diagnosis must be considered: possibly botryoid odontogenic cyst, keratocyst, or glandular odontogenic cyst
Figure 8.2
Glandular odontogenic cyst
Large multilocular radiolucency crosses the midline of the mandible in a symmetrical pattern
This is not diagnostic, but is typical of the glandular odontogenic cyst. In some reports up to 85% of cases are located in the anterior mandible. Keratocysts and ameloblastoma may be multilocular, but are more often located in the posterior mandible
Figures 10.3 and 10.4
Calcifying odontogenic cyst
A cystic radiolucency associated with irregular calcifications
About 25% of calcifying odontogenic cysts are associated with an odontoma and show irregular radiopacities either in or adjacent to the cyst. Note that simple bone cyst is occasionally associated with calcifications, but these are usually multiple and represent florid cemento‐osseous dysplasia (Chapter 17)
Figures 11.4 and 11.5
A cystic radiolucency with a peripheral band of calcifications
About 50% of calcifying odontogenic cysts contain dentinoid in the wall or show dystrophic calcification in the lining. A peripheral band of calcification is characteristic and is best seen on CT scans
Nasopalatine duct cyst
A radiolucency in the midline of the anterior maxilla
Almost diagnostic of nasopalatine duct cyst. Very rarely a radicular cyst may be in the midline. Occasional nasopalatine duct cysts are displaced laterally, in which case a radicular cyst must be considered. Note that the nasopalatine duct cyst is not associated with the periodontal ligament and the lamina dura may be intact
Figures 13.7 and 13.8
A heart‐shaped radiolucency in the midline of the anterior maxilla
This appearance is diagnostic of nasopalatine duct cyst and is seen in about 20% of cases
Figure 13.7
Nasolabial cyst
An upward or posterior convexity of the inferior margin of the nasal aperture or anterior floor of the nose
Nasolabial cyst is a soft tissue cyst, but it may distort the margin of the nasal aperture. This ‘distorted anchor appearance’ is diagnostic of nasolabial cyst. It is only seen on an anterior occlusal radiograph
Figure 14.3
Simple bone cyst
A scalloped margin at the superior aspect of a mandibular cyst, which rises up and embraces the roots of multiple teeth
This feature is typical and almost diagnostic of simple bone cyst and is seen in 50% or more of cases. It has been described as the tooth roots ‘hanging’ into the cyst cavity (Chapter 17)
Figure 17.1
A cone‐shaped margin at the anterior aspect of a mandibular cyst
This feature is specific to simple bone cyst. The margins converge at a 45° angle to form a cone. However, it is only seen in about 10% of cases
Figure 17.1
Stafne bone cavity
A corticated unilocular radiolucency at the angle of the mandible below the inferior dental (ID) canal
85% of Stafne bone cavities are located in the posterior mandible and are always below the ID canal. This excludes a lesion of odontogenic origin. The feature can be regarded as diagnostic
Figure 17.5
A radiolucency that, in a coronal view, is open on the lingual aspect of the mandible
This feature is best visualised on CT and is diagnostic of Stafne bone cavity
Figure 17.6
Figure 2.1 In the posterior region of the mandible, the course of the inferior dental (ID) canal (hashed lines) allows the tooth‐bearing areas (the alveolar bone) to be clearly distinguished from the basal bone of the mandible. Radiolucencies below the ID canal are not odontogenic in origin (see text for details).
In the first instance, the site of the cyst in the jaws can suggest an initial diagnosis. Odontogenic cysts arise in the tooth‐bearing areas of the jaws in the alveolar bone and in the mandible are always situated above the inferior dental (ID) canal (Figure 2.1). The cyst displaces the ID canal downwards towards, and sometimes beyond, the lower border of the mandible. Examples of this feature can be seen in Figures 5.5, 5.11 (dentigerous cyst), 7.6, 7.7 (odontogenic keratocyst), 10.4 (glandular odontogenic cyst), 11.3 (calcifying odontogenic cyst), 12.2, and 12.3 (orthokeratinised odontogenic cyst). A cystic radiolucency located below the ID canal is not an odontogenic cyst and when such a feature is seen, an alternative diagnosis must be considered. Figure 17.5 shows a Stafne bone cavity presenting as a radiolucency below the ID canal, excluding the possibility of an odontogenic origin. In the posterior region of the mandible, this judgement is easy to make (Figure 2.1), but in the anterior mandible and in the maxilla, the distinction between alveolar bone and basal bone is less clear. Although radiolucencies below the ID canal cannot be odontogenic, the converse is not true and a number of radiolucent lesions of non‐odontogenic origin may arise above the ID canal. Figure 17.1 shows an example
(odontogenic keratocyst), 12.3 (orthokeratinised odontogenic cyst)
