Cysts and Cyst‐like Lesions Involving the Jaws










108
Atlas of Oral and Maxillofacial Radiology, First Edition. Bernard Koong.
© 2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.
ODONTOGENIC CYSTS ANDCYSTLIKE LESIONS
8.1 Radicular cyst
(Figures8.1–8.10)
Synonym: periapical cyst.
A true epithelium‐lined cyst related to a non‐vital tooth.
Most common jaw cyst.
Often asymptomatic until it causes swelling or is secondarily
infected.
Radiological features
Computed tomography (CT) is more sensitive in identifying the
presence of these lesions than 2D radiography. Multidetector CT
(MDCT) may demonstrate more features but cone beam CT
(CBCT) is likely to be sufficient for many, especially smaller lesions.
Corticated lucent lesion centred at the apical foramen of a
tooth root. Usually homogeneous fluid attenuation internally
(MDCT soft tissue window).
Occasionally centred upon the foramen of a lateral canal at
the ‘side’ (non‐apical surface) of a tooth root.
Often demonstrates a periapical ‘tear‐drop’ morphology in
relation to the offending tooth root apex.
The border can be more sclerotic if secondarily infected.
However, in acute secondary infection, there may be focal
regions of absent cortical borders.
Longstanding lesions may demonstrate internal dystrophic
calcifications.
Demonstrates mass‐type effect when sufficiently large.
Displacement and resorption of tooth roots.
Expansion with thinning of the jaw cortices.
Elevation of the maxillary sinus and nasal cortical floors.
Displacement and compression/flattening of the mandibu-
lar canal.
Post treatment, radicular cysts often demonstrate new bone
formation beginning at the periphery.
Occasionally, this bony infill of the cystic defect may
be incomplete, demonstrating a residual lucency related
to fibrous healing, more commonly seen with large
lesions.
At the maxillary sinus base, bony infill may result in the
appearance of an antral bony prominence centred in the
apical region (Figure 8.10) (the tooth may have been
extracted), similar to that seen with healed periapical
inflammatory lesions (see Figure5.15). These prominences
can occasionally be quite large.
Magnetic resonance imaging (MRI): internally homogeneous
low or intermediate T1 signal, homogeneous high T2 and
short T1 inversion recovery (STIR) signal. There may be thin
gadolinium rim enhancement.
Differential diagnosis
Key radiological differences
Periapical
inflammatory lesion
Radicular cysts usually
demonstrate a spherical ‘full’
appearance with corticated borders.
As a rule of thumb, a maximal
dimension larger than 10 mm is
considered by some to be more
likely a radicular cyst. However,
other radiological features are more
important and must be taken into
account.
Keratocystic
odontogenic tumour
(KCOT)
Rarely centred at the root apex.
However, it can be difficult to
identify the site of origin with larger
cysts. Relative lack of expansion is a
feature of the KCOT in the body of
mandible.
CHAPTER 8
Cysts andCystlike Lesions Involving theJaws

Cysts andCyst‐like Lesions Involving theJaws 109
Lateral periodontal
cyst
Can be difficult to differentiate from
the radicular cyst related to the
lateral canal.
Postendodontic
therapy apical fibrous
healing
Can be difficult to differentiate as
fibrous healing often demonstrates a
corticated border. However, a
radicular cyst tends to demonstrate a
more full spherical morphology and
the border of fibrous healing is
usually thick and denser, sometimes
with some irregularity.
Periapical osseous
(cemental) dysplasia
Immature lesions are essentially
lucent but the borders are usually
sclerotic rather than corticated.
These lesions are often multiple,
affecting more than one tooth.
Bony mass lesions at
the maxillary sinus
bases
A post‐treatment (extraction,
rootcanal therapy, enucleation)
healing/healed radicular cyst which
has expanded into the maxillary
sinus may infill with bone and
resemble a bony mass lesion. Antral
base prominences related to a
healing/healed radicular cyst may
be more hypodense centrally (new
bone formation begins at the
periphery). There may also be
evidence of postextraction new
bone formation within a tooth
socket or presence of an
endodontically treated tooth at the
base of this prominence.
Spherical/ovoid
expansile lucent
lesion
Absence of the
antral cortical floor
Superiorly displaced
cortical sinus floor
Figure8.1 Radicular cyst, 16: coronal CBCT image.

Internal homogeneous fluid density.
Note that this lesion has remained
well contained in spite of the focal
effacement of the labial cortex
(a) (b)
Well-defined corticated expansile lesion
centred at the apical foramen of 23.
Note the thinning of the expanded labial
cortex with focal effacement
(c)
Figure8.2 Radicular cyst, 23: axial bone (a), axial soft tissue (b) and corrected sagittal bone (c) MDCT images.
Labial expansion with
effacement of the cortex
The lesion is centred at the midroot region
mesiolabially, suggesting that this cyst is likely
to be related to a root fracture or lateral canal
(a)
(b)
Figure8.3 Radicular cyst related to the endodontically treated 11: axial (a) and corrected sagittal (b) CBCT images.

Cysts andCyst‐like Lesions Involving theJaws 111
Well-defined corticated lesion
centred at the root apex
Internal homogeneous
fluid attenuation
(a) (b) (c)
Figure8.4 Radicular cyst related to 31: axial soft tissue (a) and corrected sagittal (b) and axial (c) bone MDCT images.
Well-defined lesion expanding into
the left maxillary sinus. Note the
slightly collapsed appearance,
related to communication and
drainage into the oral cavity
Slightly thickened elevated sinus
floor reflects minor new bone
formation related to the exposure
of this lesion to the oral cavity
This border is more
than 3 mm from the
cementoenamel
junction of 28
Periapical relationship
with the root apex
Internally largely of fluid
attenuation, with focal slight
increased density related
to exposure to the oral cavity
(a)
(b)
(c)
Figure8.5 Radicular cyst related to 27: cropped panoramic radiograph (a), corrected sagittal bone (b) and axial soft tissue (c) MDCT images.

Expansile lesion centred at the apex of 13
elevating the sinus cortical floor. The slightly
lobulated appearance of this dome-shaped
lesion reflects some deflation related to
commencement of endodontic treatment
Figure8.6 Radicular cyst, 13: cropped panoramic radiograph.
Well-defined corticated expansile lesion.
Note the thinned and expanded
labial and palatal cortices
Elevated and thinned nasal
and sinus cortical floors with
focal effacements
Effacement of the
incisive canal border
(a)
(b) (c)
Figure8.7 Radicular cyst related to endodontically treated 23: axial (a), corrected sagittal (b) and coronal (c) CBCT images.
Well-defined corticated expansile lesion
centred at the apical foramen of 23,
extending labially and also inferiorly
over the labial aspect of the root
Internal homogeneous fluid
attenuation. This lesion is well
contained in spite of the focal
effacements of the labial cortex
Elevated cortical
floor of the left
maxillary sinus
Labial expansion with
cortical thinning and
focal effacements
(a) (b) (c)
Figure8.8 Radicular cyst, 23: corrected sagittal (a) and axial bone (b) and soft tissue (c) MDCT images.

Cysts andCyst‐like Lesions Involving theJaws 113
Medial bowing of the maxillary sinus
medial wall into the nasal cavity with
opacification of the right ostiomeatal
complex
Elevated sinus
cortical floor
Anterolateral expansion with
effacement of the sinus wall
Internally of
homogeneous fluid
attenuation
(a)
(b)
(c)
Figure8.9 Radicular cyst related to 16 almost fully occupying the right maxillary sinus: axial bone (a) and soft tissue (b) and coronal bone (c) MDCT
images.
Irregular bony prominence
at the antral base. Note the central hypodense
appearance related to fibrous healing
(a) (b)
Figure8.10 Healed radicular cyst, left maxilla (post extraction): axial (a) and corrected sagittal (b) MDCT images.

114 Atlas of Oral and Maxillofacial Radiology
8.2 Residual cyst (Figures8.11 and8.12)
Postextraction/surgery persisting radicular cyst.
The accepted term ‘residual’ for this lesion is not generic and
refers only to the postextraction persisting radicular cyst. To
avoid potential confusion, this author suggests consideration
for the use of the term ‘residual radicular cyst’.
Radiological features
Essentially the same as the radicular cyst, but with absent
tooth. The borders may appear thicker or slightly more scle-
rotic than those of the radicular cyst.
Differential diagnosis
Similar to the radicular cyst, in the absence of a related tooth.
Buccal expansion with cortical
thinning. Note the small focal
effacements superiorly
Well-defined
corticated lucent lesion
Internal
homogeneous
fluid attenuation
(b)
(c)
(a)
Figure8.11 Residual radicular cyst, right mandibular body: axial soft tissue (a) and corrected coronal (b) and axial (c) bone MDCT images.

Cysts andCyst‐like Lesions Involving theJaws 115
8.3 Dentigerous cyst (Figures8.13–8.23)
Synonym: follicular cyst.
A true epithelium‐lined pericoronal cyst associated with an
unerupted tooth.
Second most common jaw cyst.
Most commonly associated with the third molars.
Often asymptomatic until it causes swelling or is secondarily
infected.
Radiological features
These lesions are better demonstrated with CT than with 2D
radiography, although 2D radiography may be sufficient for
small lesions which do not impinge upon critical structures.
MDCT may demonstrate more features but CBCT may be
sufficient for many cases.
Presents as a corticated pericoronal lucent lesion or appearance
of an enlarged follicular space of a tooth crown (5 mm or
more – refer to the differential diagnosis). This pericoronal
lucency may evenly surround the entire crown or may be more
focal, centred at one region or limited to one side of the crown.
The border typically extends to the cementoenamel junc-
tion (CEJ) or at the root surface within 2–3 mm of the CEJ.
With larger lesions, this border relationship with the CEJ
may be difficult to appreciate (especially on 2D plain films)
as the lesion may ‘fold’ over the root.
This border can be sclerotic if exposed to the oral cavity and
is/was previously secondarily infected. When acutely sec-
ondarily infected, there may be focal regions of effacement
of this corticated border.
Demonstrates mass‐type effect when sufficiently large.
Displacement of teeth. The offending tooth can be dis-
placed substantially, depending on the size of the cyst, e.g.
a maxillary third molar can be displaced to the orbital
floor.
Resorption of adjacent tooth roots.
Expansion with thinning of the jaw cortices.
Elevation of the maxillary sinus and nasal cortical floors.
Displacement and compression/flattening of the mandi-
bular canal.
Internally, this lesion usually demonstrates homogeneous
fluid attenuation (MDCT soft tissue window). Longstanding
lesions may demonstrate internal dystrophic calcifications.
Deflated dentigerous cysts (exposed and drained into the
oral cavity) may not display the typical space‐occupying
expansile features and may also demonstrate more sclerotic
borders (secondary infection). Rarely, internal opacities can
be seen, which may be related to oral debris or dystrophic
calcifications.
MRI: often demonstrates internal pericoronal homogene-
ous low to intermediate T1 signal and homogeneous high
T2 and STIR signal. These lesions may sometimes demon-
strate more heterogeneous internal T1 and T2 signals, more
commonly seen if the lesion is longstanding or has been
exposed to the oral cavity. There may be gadolinium rim
enhancement.
Inferior deflection of the mandibular
canal with effacement of the
superior border
Lucent corticated lesion
centred at the apex of the
socket. Note absence of
new bone formation
New bone formation
within the apical aspect
of the distal socket
Internal fluid
density
(a)
(b)
(c)
Figure8.12 Residual radicular cyst post extraction of 36 with absence of healing of the mesial socket: corrected sagittal (a) and axial bone (b) and axial
soft tissue (c) MDCT images.

116 Atlas of Oral and Maxillofacial Radiology
Differential diagnosis
Key radiological differences
Normal follicular
space
Can be difficult to differentiate as an early
developing dentigerous cyst appears
similar. As a rule of thumb, a distance of
5 mm or more from the follicular cortex
to the crown surface is considered to be
more likely a cyst. Other features, such as
slight displacement of the affected tooth,
may be helpful.
Keratocystic
odontogenic
tumour
Usually non‐expansile in the mandible.
Likely to be attached 3 mm or more from
the CEJ. Less displacement and/or
resorption of tooth roots.
Unicystic
ameloblastoma
Can appear very similar but this is a
rarecyst and is usually substantially
expansile (more than most dentigerous
cysts).
Ameloblastic
fibroma
Can be difficult to differentiate. Rare.
Internally lucent
Pericoronal relationship, with the corticated
border attached to the tooth within 3 mm of
the cementoenamel junction
Effacement of the lamina dura. Note the
absence of root resorption, which is
typically not seen with smaller lesions
Posteriorly
displaced 48
(a)
(b)
Figure8.13 Dentigerous cyst, 48: panoramic radiograph (a) and axial MDCT image (b).

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108Atlas of Oral and Maxillofacial Radiology, First Edition. Bernard Koong. © 2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.ODONTOGENIC CYSTS ANDCYSTLIKE LESIONS8.1 Radicular cyst (Figures8.1–8.10)• Synonym: periapical cyst.• A true epithelium‐lined cyst related to a non‐vital tooth.• Most common jaw cyst.• Often asymptomatic until it causes swelling or is secondarily infected.Radiological features• Computed tomography (CT) is more sensitive in identifying the presence of these lesions than 2D radiography. Multidetector CT (MDCT) may demonstrate more features but cone beam CT (CBCT) is likely to be sufficient for many, especially smaller lesions.• Corticated lucent lesion centred at the apical foramen of a tooth root. Usually homogeneous fluid attenuation internally (MDCT soft tissue window). ◦Occasionally centred upon the foramen of a lateral canal at the ‘side’ (non‐apical surface) of a tooth root. ◦Often demonstrates a periapical ‘tear‐drop’ morphology in relation to the offending tooth root apex. ◦The border can be more sclerotic if secondarily infected. However, in acute secondary infection, there may be focal regions of absent cortical borders. ◦Longstanding lesions may demonstrate internal dystrophic calcifications.• Demonstrates mass‐type effect when sufficiently large. ◦Displacement and resorption of tooth roots. ◦Expansion with thinning of the jaw cortices. ◦Elevation of the maxillary sinus and nasal cortical floors. ◦Displacement and compression/flattening of the mandibu-lar canal.• Post treatment, radicular cysts often demonstrate new bone formation beginning at the periphery. ◦Occasionally, this bony infill of the cystic defect may be incomplete, demonstrating a residual lucency related to fibrous healing, more commonly seen with large lesions. ◦At the maxillary sinus base, bony infill may result in the appearance of an antral bony prominence centred in the apical region (Figure 8.10) (the tooth may have been extracted), similar to that seen with healed periapical inflammatory lesions (see Figure5.15). These prominences can occasionally be quite large.• Magnetic resonance imaging (MRI): internally homogeneous low or intermediate T1 signal, homogeneous high T2 and short T1 inversion recovery (STIR) signal. There may be thin gadolinium rim enhancement.Differential diagnosisKey radiological differencesPeriapical inflammatory lesionRadicular cysts usually demonstrate a spherical ‘full’ appearance with corticated borders. As a rule of thumb, a maximal dimension larger than 10 mm is considered by some to be more likely a radicular cyst. However, other radiological features are more important and must be taken into account.Keratocystic odontogenic tumour (KCOT)Rarely centred at the root apex. However, it can be difficult to identify the site of origin with larger cysts. Relative lack of expansion is a feature of the KCOT in the body of mandible.CHAPTER 8Cysts andCystlike Lesions Involving theJaws Cysts andCyst‐like Lesions Involving theJaws 109Lateral periodontal cystCan be difficult to differentiate from the radicular cyst related to the lateral canal.Postendodontic therapy apical fibrous healingCan be difficult to differentiate as fibrous healing often demonstrates a corticated border. However, a radicular cyst tends to demonstrate a more full spherical morphology and the border of fibrous healing is usually thick and denser, sometimes with some irregularity.Periapical osseous (cemental) dysplasiaImmature lesions are essentially lucent but the borders are usually sclerotic rather than corticated. These lesions are often multiple, affecting more than one tooth.Bony mass lesions at the maxillary sinus basesA post‐treatment (extraction, rootcanal therapy, enucleation) healing/healed radicular cyst which has expanded into the maxillary sinus may infill with bone and resemble a bony mass lesion. Antral base prominences related to a healing/healed radicular cyst may be more hypodense centrally (new bone formation begins at the periphery). There may also be evidence of postextraction new bone formation within a tooth socket or presence of an endodontically treated tooth at the base of this prominence.Spherical/ovoidexpansile lucentlesionAbsence of theantral cortical floorSuperiorly displacedcortical sinus floorFigure8.1 Radicular cyst, 16: coronal CBCT image. Internal homogeneous fluid density.Note that this lesion has remainedwell contained in spite of the focaleffacement of the labial cortex(a) (b)Well-defined corticated expansile lesioncentred at the apical foramen of 23.Note the thinning of the expanded labialcortex with focal effacement (c)Figure8.2 Radicular cyst, 23: axial bone (a), axial soft tissue (b) and corrected sagittal bone (c) MDCT images.Labial expansion with effacement of the cortexThe lesion is centred at the midroot region mesiolabially, suggesting that this cyst is likelyto be related to a root fracture or lateral canal (a)(b)Figure8.3 Radicular cyst related to the endodontically treated 11: axial (a) and corrected sagittal (b) CBCT images. Cysts andCyst‐like Lesions Involving theJaws 111Well-defined corticated lesioncentred at the root apex Internal homogeneousfluid attenuation (a) (b) (c) Figure8.4 Radicular cyst related to 31: axial soft tissue (a) and corrected sagittal (b) and axial (c) bone MDCT images.Well-defined lesion expanding intothe left maxillary sinus. Note the slightly collapsed appearance, related to communication and drainage into the oral cavitySlightly thickened elevated sinus floor reflects minor new bone formation related to the exposure of this lesion to the oral cavityThis border is morethan 3 mm from thecementoenameljunction of 28Periapical relationshipwith the root apexInternally largely of fluid attenuation, with focal slight increased density relatedto exposure to the oral cavity(a)(b)(c) Figure8.5 Radicular cyst related to 27: cropped panoramic radiograph (a), corrected sagittal bone (b) and axial soft tissue (c) MDCT images. Expansile lesion centred at the apex of 13 elevating the sinus cortical floor. The slightly lobulated appearance of this dome-shaped lesion reflects some deflation related to commencement of endodontic treatment Figure8.6 Radicular cyst, 13: cropped panoramic radiograph.Well-defined corticated expansile lesion.Note the thinned and expandedlabial and palatal corticesElevated and thinned nasal and sinus cortical floors with focal effacements Effacement of the incisive canal border(a) (b) (c)Figure8.7 Radicular cyst related to endodontically treated 23: axial (a), corrected sagittal (b) and coronal (c) CBCT images.Well-defined corticated expansile lesioncentred at the apical foramen of 23,extending labially and also inferiorlyover the labial aspect of the rootInternal homogeneous fluidattenuation. This lesion is wellcontained in spite of the focaleffacements of the labial cortexElevated corticalfloor of the leftmaxillary sinusLabial expansion withcortical thinning andfocal effacements(a) (b) (c)Figure8.8 Radicular cyst, 23: corrected sagittal (a) and axial bone (b) and soft tissue (c) MDCT images. Cysts andCyst‐like Lesions Involving theJaws 113Medial bowing of the maxillary sinus medial wall into the nasal cavity with opacification of the right ostiomeatalcomplex Elevated sinuscortical floor Anterolateral expansion witheffacement of the sinus wall Internally of homogeneous fluid attenuation (a)(b)(c)Figure8.9 Radicular cyst related to 16 almost fully occupying the right maxillary sinus: axial bone (a) and soft tissue (b) and coronal bone (c) MDCT images.Irregular bony prominenceat the antral base. Note the central hypodense appearance related to fibrous healing(a) (b)Figure8.10 Healed radicular cyst, left maxilla (post extraction): axial (a) and corrected sagittal (b) MDCT images. 114 Atlas of Oral and Maxillofacial Radiology8.2 Residual cyst (Figures8.11 and8.12)• Postextraction/surgery persisting radicular cyst.• The accepted term ‘residual’ for this lesion is not generic and refers only to the postextraction persisting radicular cyst. To avoid potential confusion, this author suggests consideration for the use of the term ‘residual radicular cyst’.Radiological features• Essentially the same as the radicular cyst, but with absent tooth. The borders may appear thicker or slightly more scle-rotic than those of the radicular cyst.Differential diagnosis• Similar to the radicular cyst, in the absence of a related tooth.Buccal expansion with corticalthinning. Note the small focaleffacements superiorly Well-definedcorticated lucent lesionInternalhomogeneous fluid attenuation (b)(c)(a)Figure8.11 Residual radicular cyst, right mandibular body: axial soft tissue (a) and corrected coronal (b) and axial (c) bone MDCT images. Cysts andCyst‐like Lesions Involving theJaws 1158.3 Dentigerous cyst (Figures8.13–8.23)• Synonym: follicular cyst.• A true epithelium‐lined pericoronal cyst associated with an unerupted tooth.• Second most common jaw cyst.• Most commonly associated with the third molars.• Often asymptomatic until it causes swelling or is secondarily infected.Radiological features• These lesions are better demonstrated with CT than with 2D radiography, although 2D radiography may be sufficient for small lesions which do not impinge upon critical structures. MDCT may demonstrate more features but CBCT may be sufficient for many cases.• Presents as a corticated pericoronal lucent lesion or appearance of an enlarged follicular space of a tooth crown (5 mm or more – refer to the differential diagnosis). This pericoronal lucency may evenly surround the entire crown or may be more focal, centred at one region or limited to one side of the crown. ◦The border typically extends to the cementoenamel junc-tion (CEJ) or at the root surface within 2–3 mm of the CEJ. With larger lesions, this border relationship with the CEJ may be difficult to appreciate (especially on 2D plain films) as the lesion may ‘fold’ over the root. ◦This border can be sclerotic if exposed to the oral cavity and is/was previously secondarily infected. When acutely sec-ondarily infected, there may be focal regions of effacement of this corticated border.• Demonstrates mass‐type effect when sufficiently large. ◦Displacement of teeth. The offending tooth can be dis-placed substantially, depending on the size of the cyst, e.g. a maxillary third molar can be displaced to the orbital floor. ◦Resorption of adjacent tooth roots. ◦Expansion with thinning of the jaw cortices. ◦Elevation of the maxillary sinus and nasal cortical floors. ◦Displacement and compression/flattening of the mandi-bular canal.• Internally, this lesion usually demonstrates homogeneous fluid attenuation (MDCT soft tissue window). Longstanding lesions may demonstrate internal dystrophic calcifications.• Deflated dentigerous cysts (exposed and drained into the oral cavity) may not display the typical space‐occupying expansile features and may also demonstrate more sclerotic borders (secondary infection). Rarely, internal opacities can be seen, which may be related to oral debris or dystrophic calcifications.• MRI: often demonstrates internal pericoronal homogene-ous low to intermediate T1 signal and homogeneous high T2 and STIR signal. These lesions may sometimes demon-strate more heterogeneous internal T1 and T2 signals, more commonly seen if the lesion is longstanding or has been exposed to the oral cavity. There may be gadolinium rim enhancement.Inferior deflection of the mandibular canal with effacement of the superior border Lucent corticated lesion centred at the apex of the socket. Note absence of new bone formation New bone formation within the apical aspectof the distal socket Internal fluiddensity (a)(b)(c) Figure8.12 Residual radicular cyst post extraction of 36 with absence of healing of the mesial socket: corrected sagittal (a) and axial bone (b) and axial soft tissue (c) MDCT images. 116 Atlas of Oral and Maxillofacial RadiologyDifferential diagnosisKey radiological differencesNormal follicular spaceCan be difficult to differentiate as an early developing dentigerous cyst appears similar. As a rule of thumb, a distance of 5 mm or more from the follicular cortex to the crown surface is considered to be more likely a cyst. Other features, such as slight displacement of the affected tooth, may be helpful.Keratocystic odontogenic tumourUsually non‐expansile in the mandible. Likely to be attached 3 mm or more from the CEJ. Less displacement and/or resorption of tooth roots.Unicystic ameloblastomaCan appear very similar but this is a rarecyst and is usually substantially expansile (more than most dentigerous cysts).Ameloblastic fibromaCan be difficult to differentiate. Rare.Internally lucent Pericoronal relationship, with the corticated border attached to the tooth within 3 mm of the cementoenamel junction Effacement of the lamina dura. Note the absence of root resorption, which is typically not seen with smaller lesions Posteriorlydisplaced 48 (a)(b)Figure8.13 Dentigerous cyst, 48: panoramic radiograph (a) and axial MDCT image (b). Cysts andCyst‐like Lesions Involving theJaws 117Corticated lucent lesion ina pericoronal relationshipwith the distallydisplaced 48Corticated lucent lesion in a pericoronal relationshipwith the impacted 48extending mesially and distally Lucent lesion ina pericoronal relationshipwith the impacted 48,centred inferiorly. Note thesclerotic margin related tosecondary infection(a)(b)(c) Figure8.14 Dentigerous cysts of three different cases, 48: cropped panoramic radiographs (a–c). 118 Atlas of Oral and Maxillofacial RadiologyInternally ofhomogeneous fluidattenuationCorticated lucent lesion in apericoronal relationship withthe displaced 38Effacement of the lamina of 37roots with apical resorption ofthe mesial rootEffacement of thesuperior border ofthe mandibular canal(a) (b)Figure8.15 Dentigerous cyst, 38: corrected sagittal bone (a) and axial soft tissue (b) MDCT images.Corticated lucent lesion ina pericoronal relationshipwith the displaced 38 Lingualexpansion(a)(b)Figure8.16 Dentigerous cyst, 38: axial (a) and coronal (b) CBCT images. Well-defined corticated expansile lucent lesion Expansion superiorly, withelevation of the nasal andmaxillary sinus corticalfloors Lateral expansion abuttingthe temporalis muscle. There is focaleffacement of the posterolateral wall of the sinus where the lesion remains contained. Note the pericoronal relationship with the displaced 28 Internal homogeneousfluid densityUnrelated sinonasalpolyposis(a)(b)(c)(d)Figure8.17 Dentigerous cyst, 28: axial soft tissue (a) and coronal (b), sagittal (c) and axial bone (d) MDCT images.Internally of homogeneousfluid attenuation Corticated lucent lesion in a pericoronalrelationship with the displaced 38.Note the effacement of the distallamina of the 37 distal root (a) (b)Figure8.18 Dentigerous cyst, 38: corrected sagittal bone (a) and axial soft tissue (b) MDCT images. 120 Atlas of Oral and Maxillofacial RadiologyCorticated lucent lesion in a pericoronal relationshipwith the impacted 48, centred distobuccally (a) (b)Figure8.19 Dentigerous cyst, 48: corrected sagittal (a) and axial (b) CBCT images.Corticated lucent lesion ina pericoronal relationship withthe impacted 38, centred distally Figure8.20 Dentigerous cyst, 38: corrected sagittal CBCT image.LingualexpansionCorticated lucent lesion in a pericoronalrelationship with the 37 contributing to theimpaction of this molar. Note the effacement ofthe overlying ridge cortex, distal lamina of the 36distal root and mesial follicular cortex of 38(a) (b)Figure8.21 Dentigerous cyst, 37: corrected sagittal (a) and coronal (b) CBCT images. LingualexpansionWell-definedcorticatedlucent lesionEffacement of the superiorcortex where there was drainage. The morphologydemonstrated here reflectsthe associated partialdeflation of the cystDisplaced 38Internalhomogeneousfluid density(a) (b)(c) Figure8.22 Partially deflated dentigerous cyst, 38: axial (a) and coronal bone (b) and axial soft tissue (c) MDCT images.Mixed intermediate and hyperintenseappearance. This heterogeneity isrelated to the secondary infectionHeterogeneous intermediatesignal related to thesecondary infectionPericoronal lucency withposterior displacementof 48. Slightly reactivesclerotic borders relatedto chronic secondaryinfectionEffacement of the superiorridge cortex where the cystcommunicates with the oralcavity. Note the effacementof the 47 distal lamina dura(a) (c)(b)(d)Figure8.23 Secondarily infected dentigerous cyst, 48: corrected sagittal MDCT image (a) and cropped panoramic radiograph (b). MRI images: corrected sagittal T1 image (c) and corrected sagittal STIR image (d). 122 Atlas of Oral and Maxillofacial Radiology8.4 Buccal bifurcation cyst (Figures8.24–8.26)• An epithelium‐lined true cyst arising from the buccal furca-tion of mandibular first or second molars, most frequently the first molars.• Similar lesions associated with the mandibular third molars are usually referred to as paradental cysts. Some consider these to be the same as the buccal bifurcation cyst.• Can be bilateral.• Usually seen in the younger child.• Clinically presents with swelling and/or delayed/non‐eruption of the molar.• Can be secondarily infected.• Postenucleation recurrence is rare and the affected tooth is usually preserved.Radiological features• Better examined with MDCT or CBCT than intraoral or panoramic radiography.• A well‐defined expansile corticated lucent lesion centred at the buccal furcation of a mandibular molar. There is often a tendency for this lesion to extend posteriorly from the bifurcation.• The root is usually displaced lingually, with the occlusal surface of the tooth directed superobuccally. Root resorption is not a feature.• If secondarily infected, periosteal new bone formation may be evident.• MRI appearances are often those of a typical true cyst. However, this cyst can be secondarily infected, with associated alteration in signal characteristics.Differential diagnosisKey radiological differencesDentigerous cyst The buccal bifurcation cyst is centred at the buccal furcation.Well-defined corticated lucent lesions. The appearance of a distal relationship to 47 reflects the tendency for these lesions to extend distally from the bifurcation, which is sometimes exaggerated by the typically oblique projection of these tomograms Figure8.24 Bilateral buccal bifurcation cysts, 37 and 47: panoramic radiograph. This border issclerotic, related tothe secondary infection Well-definedcorticatedlucent lesionSlight flattening ofthe mandibular canalCentred at thebifurcations. Note thetendency to extend distallyInflammatoryperiosteal responseInflammatory effacementof the buccal cortex. Thiscorresponds with thedraining fistula(a)(b)(c) (d)Figure8.25 Bilateral buccal bifurcation cysts, 36 and 46. The lesion associated with 46 is secondarily infected, with a draining fistula: cropped panoramic radiograph (a), coronal (b), axial (c) and left mandibular corrected sagittal (d) CBCT images.Well-defined corticated lucent lesion centred at the buccal bifurcation of 36. Note the tilt of this tooth, related to lingual displacement of the roots Figure8.26 Buccal bifurcation cyst, 36: cropped panoramic radiograph. 124 Atlas of Oral and Maxillofacial Radiology8.5 Keratocystic odontogenic tumour (Figures8.27–8.31)• Synonyms: KOT, KCOT, odontogenic keratocyst, OKC.• While considered an odontogenic tumour, this lesion demon-strates cyst‐like radiological features and is therefore discussed in this section.• Histologically, the parakeratinised epithelial lining demon-strates tumour‐like infiltrative behaviour. This lesion contains viscid keratinaceous material.• Most commonly seen in the posterior mandible.• Multiple KCOTs may be related to basal cell naevus (Gorlin–Goltz) syndrome.• High post‐treatment recurrence rate. Requires radiological review.• Surgical management often includes peripheral ostectomy and/or chemical treatment of the bony cyst wall. Occasionally, marsupialisation is considered for large lesions.• Usually asymptomatic unless large or secondarily infected.Radiological features• A suspected KCOT requires evaluation with CT: MDCT may demonstrate features which are not seen on CBCT. MRI may be useful.• Well‐defined corticated border which may demonstrate a scalloped appearance.• Most often unicystic and internally completely lucent on plain 2D radiographs and CBCT. With multislice CT (soft tis-sue algorithm) internal appearances may demonstrate slight heterogeneity, with regions of fluid density and regions of increased density related to the presence of keratinaceous material. However, the internal appearance of homogeneous fluid attenuation does not exclude the KCOT.• Larger lesions may demonstrate internal septa, usually one or a few, which are quite prominent.• Within the body of the mandible, it classically demonstrates little or no expansion, relative to the size of the lesion. It is usually expansile elsewhere within the mandible and in the maxilla. It can occupy much of the maxillary sinus.• There is often variable thinning of the jaw cortices, where there may be regions of cortical effacement.• While this lesion may displace teeth and contribute to root resorption, this occurs to a lesser degree than that usually seen with dentigerous cysts.• May displace or compress the mandibular canal.• When involving the posterior maxilla, evaluation of the integ-rity of the posterior wall of the sinus and possible extension of the lesion into the pterygopalatine fossa is important.• MRI: variable. May demonstrate regions of increased T1 signal (keratinaceous material) and regions of increased T2/STIR signal (fluid) internally. May also demonstrate intermediate T1 and T2 homogeneous signal internally. Usually demonstrates diffusion restriction (diffusion‐weighted imaging (DWI)). There may be variable gadolin-ium rim enhancement.Differential diagnosisKey radiological differencesDentigerous cyst A pericoronal cystic lesion with borders which are not at the CEJ or within 2–3 mm of the CEJ is more likely a KCOT than a dentigerous cyst. Dentigerous cysts are expansile, unless deflated, usually related to exposure to the oral cavity. KCOTs are more likely to demonstrate scalloped borders.Simple bone cyst (SBC)SBCs usually demonstrate a much thinner and delicate corticated border than KCOTs. May also be scalloped. Effacement of lamina dura and root resorption is less often seen with SBCs. SBCs essentially do not directly displace teeth.Odontogenic myxomaCan appear similar in the posterior body of the mandible, as both are often not expansile and KCOTs occasionally demonstrate internal septa.Radicular cyst The borders of a radicular cyst demonstrate a more acute angle to the root surface of the offending tooth, usually a ‘tear‐drop’ appearance. KCOT borders are usually at right angles or demonstrate obtuse angles in relation to the root surfaces of the apical aspect of involved roots. Radicular cysts are expansile and KCOTs are usually not expansile or minimally expansile within the body of mandible.Ameloblastoma The scalloped margins of KCOTs, when present, can be mistaken for a multi-locular lesion on plain 2D radiography. Ameloblastomas are expansile lesions, unless quite small. Cysts andCyst‐like Lesions Involving theJaws 125Well-definedcorticated lucent lesionInternal heterogeneous attenuation with fluid density regions and higher density regions compatible with keratinaceous material Minimal expansion for size.Note thinning of the buccalcortices with focaleffacements (b) (c) Extension betweenthe tooth roots (a)Figure8.27 Keratocystic odontogenic tumour within the right body of the mandible: corrected sagittal (a) and axial bone (b) and axial soft tissue (c) MDCT images.Well-defined corticated largely lucent lesion with two relatively prominent internal septa. Note the relatively minimal expansion for size Internal heterogeneous attenuationwith fluid density appearanceposteriorly and higher densityregions anteriorly, compatiblewith keratinaceous material(a) (b)Figure8.28 Keratocystic odontogenic tumour within the right body of the mandible: corrected sagittal soft tissue (a) and bone (b) MDCT images. Lucent corticated lesionexpanding into the leftmaxillary sinus with corticalfloor effacement. Noteeffacement of the 23lamina duraInternally heterogeneous with regions of fluid density andother regions of increaseddensity compatible with proteinaceous material (a)(b)Figure8.29 Keratocystic odontogenic tumour within the left posterior maxilla related to 23: corrected sagittal bone (a) and axial soft tissue (b) MDCT images.Internally homogeneousdensity compatible withproteinaceous fluid Substantial lateral expansionwith effacement of the cortex. The lesion remains well contained, abutting the temporalis and masseter musclesHomogeneous intermediatesignalExpansion into the left maxillary sinus, elevating the sinus cortical floor Preservation of the posterior wallof the sinus with no involvementof the pterygomaxillary fissureor the pterygopalatine fossa (a)(b)(c)(d)Figure8.30 Keratocystic odontogenic tumour within the left posterior maxilla: axial bone (a) and soft tissue (b) MDCT images. MRI images: axial T1 (c) and sagittal T2 fat‐saturated (d). Cysts andCyst‐like Lesions Involving theJaws 1278.6 Basal cell naevus syndrome (Figure8.32)• Synonyms: naevoid basal cell carcinoma syndrome (NBCCS), Gorlin–Goltz syndrome.• An inherited syndrome demonstrating abnormalities which include multiple skin naevoid basal cell carcinomas, skeletal, central nervous system and eye abnormalities as well as mul-tiple KCOTs of the jaws.Radiological features• Multiple KCOTs: refer to preceding section.• Early calcification of the falx cerebri.Differential diagnosisKey radiological differencesBuccal bifurcation cysts Often present bilaterally in a relatively symmetric pattern, unlike the basal cell naevus syndrome.Other cysts Examples include radicular, residual, dentigerous cysts. Morethan one of these cysts may be seen. These cysts demonstrate different radiological features.Well-defined corticated lucent lesion. Note that this recurrent lesion is not well demonstrated on the panoramic radiograph Postsurgical healing ofthe original lesion Internal fluid andproteinaceousfluid density(a)(c)(b)Figure8.31 Recurrent keratocystic odontogenic tumour, right mandibular ramus: panoramic radiograph (a) and axial soft tissue (b) and bone (c) MDCT images. 128 Atlas of Oral and Maxillofacial Radiology8.7 Lateral periodontal cyst (Figures8.33 and8.34)• Cyst arising from the odontogenic epithelium of the lateral surface(not at the apex) of the root, unrelated to the pulp status/vitality of the tooth.• Most often involving mandibular premolars, canines and lateral incisors. Also seen in the anterior maxilla, especially the canines and lateral incisors.Radiological features• MDCT may demonstrate more features but CBCT may be sufficient for most cases.• Well‐defined corticated unicystic lucent lesion centred upon the lateral (not at the apex) surface of a root surface. A multi-cystic variety (botyroid odontogenic cyst) has been described, but is thought to be extremely rare.• Internally of homogeneous fluid density (MDCT soft tissue window).• Effacement of the lamina dura of involved teeth is common. Large lesions demonstrate expansion and displacement of teeth.Well-defined corticated lucentlesions within the mandibleCystic density expansile opacitydisplacing 18Absence of the tuberosity andmaxillary sinus cortical floor confirmsthe presence of a lesion originatingfrom the alveolar process(a)Corticated borderEffacement ofthe lamina duraCalcificationof the falxcerebri(b) (c)Figure8.32 Multiple keratocystic odontogenic tumours and early falx cerebri calcification related to basal cell naevus syndrome: panoramic (a), posteroanterior skull (b) and periapical (33/34) (c) radiographs. Cysts andCyst‐like Lesions Involving theJaws 129Differential diagnosisKey radiological differencesRadicular cystRadicular cysts related to lateral canals can appear similar. However, there is often evidence to suggest a compromised/non‐vital pulp and there may be periapical inflammatory disease.Keratocystic odontogenic tumourKCOTs are relatively non‐expansile.Well-defined corticated lucent lesioncentred at the mesial surface of 43.Note the mesial displacement of 42 Labial expansion withcortical effacement Internal homogeneousfluid attenuation (a)(b) (c) Figure8.33 Lateral periodontal cyst, 43: coronal (a) and axial bone (b) and axial soft tissue (c) MDCT images.Well-defined expansile corticated lucent lesion centred at the mesial surface of 33, with effacement of the labial cortex. Note the mesiolabial displacement of 32 Internal homogeneousfluid density (a) (b)Figure8.34 Lateral periodontal cyst, 33: axial bone (a) and soft tissue (b) MDCT images. 130 Atlas of Oral and Maxillofacial Radiology8.8 Glandular odontogenic cyst (Figure8.35)• Synonym: sialo‐odontogenic cyst.• Odontogenic cyst demonstrating salivary gland‐type histo-logical features.• Rare.• Tendency for postsurgical recurrence.Radiological features• Unilocular or multilocular well‐defined lesion with corticated borders.• Expansile, with effacement of maxillary/mandibular cortices.• Displaces teeth.Differential diagnosisKey radiological differencesOther multilocular lesions Can be difficult to differentiate, e.g. ameloblastoma and central mucoepidermoid carcinoma.Keratocystic odontogenic tumourSmall lesions can appear similar.NONODONTOGENIC CYSTS ANDCYSTLIKE LESIONS8.9 Simple bone cyst (Figures8.36–8.45)• Synonyms: unicameral bone cyst, traumatic bone cyst, haemor-rhagic bone cyst, haemorrhagic cyst, solitary bone cyst, SBC, idiopathic bone cavity.• A pseudocystic cavity in bone with connective tissue lining. There is no epithelial lining and this is not a true cyst. Usually contains serosanguinous straw‐coloured fluid.• Common. Usually in those less than 20 years old. Almost all occur within the mandible.• Unknown aetiology.• Most are asymptomatic, and are often incidentally identified radiologically.• May be associated with cemento‐osseous dysplasias (Figure 8.44).• May spontaneously heal without intervention (Figure8.45).• Usually managed with conservative surgical exploration to exclude other cyst‐like conditions. Low recurrence.Well-defined multilocular lesion.Lobulated expansion with focaleffacements of the labial cortexInternal heterogeneous fluiddensity appearance with regionsof increased densityInternalseptum(a)(b)Figure8.35 Glandular odontogenic cyst, right mandible: axial bone (a) and soft tissue (b) MDCT images. Cysts andCyst‐like Lesions Involving theJaws 131Radiological features• When suspected, CT should be considered. MDCT demon-strates more features but CBCT may be sufficient for many cases, especially the smaller lesions. MRI may be useful.• Unilocular well‐defined corticated lucency. This corticated border is often delicate in appearance. Some regions may notdemonstrate the presence of a cortex but remain well defined. The borders may be scalloped. Usually no expan-sion, although larger lesions may demonstrate minimal expansion.• On 2D radiography, the margins may appear ill‐defined in some regions, usually where the periphery of the lesion does not occupy the entire thickness of the jaw or where there is less trabecular bone between the cortices (e.g. inferior mandi-ble with prominent submandibular fossae).• In lesions where the borders scallop the buccal or lingual corti-ces, 2D radiography may give the impression of a multilocular lesion.• While this lesion often scallops between the roots of teeth, most of the lamina dura is usually preserved. Tooth displace-ment and root resorption is rare.• Internally, it is usually of homogeneous fluid attenuation (MCDT soft tissue window).• MRI: homogeneous intermediate T1 signal. Homogeneous high T2 and STIR signal. May demonstrate minimal gadolin-ium rim enhancement.Differential diagnosisKey radiological differencesKeratocystic odonto-genic tumourKCOTs usually demonstrate more corticated margins and are more likely to cause root resorption and tooth displacement than SBCs. MRI DWI usually demonstrates diffusion restriction in KCOTs.Radicular cyst Apical lamina dura is effaced. Usually demonstrates a tear‐drop morphology of at the root apex. SBC borders often scallop between the roots. The radicular cyst, unless small or deflated, is expansile.Well-defined corticated lucent lesionextending superiorly between the 45and 46 roots. Most of the radicularlamina dura is preserved. No rootresorption or tooth displacementFigure8.36 Simple bone cyst, right posterior body of mandible: cropped panoramic radiograph. 132 Atlas of Oral and Maxillofacial RadiologyWell-defined corticated lucent lesionextending superiorly between the 48,47 and 46 roots. Most of the radicularlamina dura is preserved. No rootresorption or tooth displacementFigure8.37 Simple bone cyst, right posterior body of mandible: panoramic radiograph.Internal homogeneousfluid attenuation (a)(b)(c)Well-defined corticated lucentlesion extending superiorlybetween the roots of 48 and 47.The lamina dura is largelypreserved. No root resorptionor tooth displacement. There isthinning of the inferior cortex. The mandibular canal isnot deflected Figure8.38 Simple bone cyst, right posterior body of mandible: cropped panoramic radiograph (a), corrected sagittal bone (b) and axial soft tissue (c) MDCT images. Well-defined corticated lucent lesionthinning the inferior cortex. The 47 lamina dura and 48 follicular cortex are preserved. No root resorption ortooth displacementHomogeneouslow tointermediate signalHomogeneouslyhyperintenseRim enhancement(a)(b)(c)(d)Figure8.39 Simple bone cyst, right posterior body of mandible: corrected sagittal T1 (a), corrected sagittal STIR (b) and corrected sagittal postgadolinium fat‐saturated (c) MRI images and corrected sagittal MDCT image (d).Well-defined non-expansile lightly corticated lucent lesion with slight thinning of the labial cortex, which remains preserved. Note preservation of the incisor lamina dura (a) (b)Figure8.40 Simple bone cyst, right anterior mandible: axial (a) and sagittal (b) CBCT images. 134 Atlas of Oral and Maxillofacial RadiologyWell-defined non-expansile corticated lucent lesion. The slightly thinned labial cortex remains preserved (a) (b)Internal homogeneousfluid attenuationFigure8.41 Simple bone cyst, right mandibular parasymphysis: axial bone (a) and soft tissue (b) MDCT images.Well-defined non-expansile lucent lesion. Note scalloped thinning of the lingual cortex, which remains preserved Internal homogeneousfluid density (a) (b)Figure8.42 Simple bone cyst, left posterior body of the mandible: axial bone (a) and soft tissue (b) MDCT images. Cysts andCyst‐like Lesions Involving theJaws 135Well-defined expansile (expansion is not a typical feature) lucent lesion. Note thinning of the lingual cortex, which remains preserved. The lamina dura of the involved teeth are largely preserved. No root resorption or tooth displacement Internally of homogeneousfluid attenuation(a) (b)(c) Figure8.43 Simple bone cyst, right posterior body of the mandible: axial bone (a) and soft tissue (b) and coronal bone (c) MDCT images.Well-defined corticated lucent lesion. Note thinning of the buccal cortex, which remains preserved Internal homogeneousdensity is compatible with fluid Opacity related tocemento-osseous dysplasia (a) (b) (c)Figure8.44 Simple bone cyst associated with cemento‐osseous dysplasia, left posterior body of the mandible: corrected sagittal (a) and axial bone (b) and axial soft tissue (c) MDCT images. 136 Atlas of Oral and Maxillofacial Radiology8.10 Nasopalatine duct cyst (Figures8.46–8.48)• Synonyms: nasopalatine cyst, incisive canal cyst, median palatal cyst.• Arises from the epithelial remnants of the nasopalatine duct.• Usually asymptomatic until large, when swelling is the most common first clinical feature. This swelling is classically fluctuant.• Most often enucleated. Recurrence is low.Radiological features• MDCT may demonstrate more features but CBCT is likely to be sufficient, especially with smaller lesions.• Well‐defined, lucent, corticated lesion centred at the incisive canal.• Often asymmetric.• Expansile when sufficiently large. This can be seen labially and palatally. It may also expand into the nasal cavity and maxillary sinus, elevating the cortical floors.• The expanded maxillary cortices are often thinned with focal regions of effacement.• Displaces teeth and resorbs roots when sufficiently large.• Internally, it is usually of homogeneous fluid attenuation (MDCT soft tissue algorithm).• MRI: homogeneous intermediate to slightly hyperintense T1signal. Homogeneous high T2 signal.Differential diagnosisKey radiological differencesLarge incisive canalCan be difficult to differentiate as the normal incisive canal is not infrequently asymmetric, with focal region(s) of asymmetric corticated prominence(s). Symmetric focal corticated widened appearance can also reflect a normal variant. Some consider that a maximal transverse dimension of the canal/foramen of more than 6 mm is more likely to reflect a cyst. However, the normal incisive canal presents with a large variation in morphology and size. Evidence of expansion, tooth displacement or resorption favours the presence of a nasopalatine duct cyst.Radicular cystThe radicular cyst is centred upon a root, usually apically. This is more likely to be mistaken for a nasopalatine duct cyst on 2D radiography. If a nasopalatine duct cyst is suspected, pretreatment MDCT or CBCT should be considered.New bone formation with some remodelling relatedto spontaneous healing of a simple bone cyst.Note the minimal expansion and the thinnedpreserved cortices(a) (b)Figure8.45 Spontaneously healed simple bone cyst, right mandibular body: axial (a) and corrected sagittal (b) CBCT images. Cysts andCyst‐like Lesions Involving theJaws 137Well-defined corticated lucent focalwidening of the incisive canalEffacement of the 21 and 22 lamina dura with no resorption.Note that root resorption is usuallyeventually seen with larger lesions Accessory neurovascular canaland foramen, a normal variant(a) (b)(c)Figure8.46 Nasopalatine duct cyst, premaxilla: axial (a), coronal (b) and sagittal (c) MDCT images.Focal well-defined corticated lucent widening of the incisive canal and foramen (a) (b) (c) Figure8.47 Nasopalatine duct cyst, premaxilla: axial (a), coronal (b) and sagittal (c) CBCT images. 138 Atlas of Oral and Maxillofacial Radiology8.11 Nasolabial cyst (Figure8.49)• Synonym: nasoalveolar cyst.• Non‐odontogenic developmental cyst occurring in the naso-alar region.• Rare.• Low tendency for postsurgical recurrence.Radiological features• Not well demonstrated on 2D radiography. CBCT may be suf-ficient for the evaluation of bony involvement but MDCT usually demonstrates more features. Ultrasound or MRI could be considered.• Well‐defined spherical or ovoid lesion centred in the soft tis-sues of the nasoalar region, over the base of the premaxillary alveolar process. Most are unilateral but may be bilateral.• Internally, it is usually isodense with proteinaceous fluid (MDCT soft tissue algorithm).• Larger lesions may remodel the labial aspect of the alveolar process, resulting in a focal concave depression of the anterior surface usually at the level of the incisor root apices. This depression usually remains corticated. Where the depression extends to the tooth roots, there is usually associated root resorption.• MRI: variable T1 signal. High T2 signal. There may be focal regions of intermediate signal related to proteinaceous material.Differential diagnosisKey radiological differencesPeriapical lesion The focal depression at the labial surface of the maxillary alveolar process may present as a lucent appearance at the anterior root apices on 2D radiography. MDCT or CBCT usually clarifies.Minor salivary gland lesionsMucous retention/extravasation or cystic tumours related to minor salivary glands can appear similar.Well-defined corticated lucent lesion centred at the incisive canal, expanding into the nasal base with cortical effacementFluid density internally (a)(b)Figure8.48 Nasopalatine duct cyst, premaxilla: coronal soft tissue (a) and bone (b) MDCT images. Cysts andCyst‐like Lesions Involving theJaws 139Internal homogeneous fluid densityCorticated concave remodelling of the left premaxillaRoot resorption(a)(b)(c) (d)Figure8.49 Nasolabial cyst: axial soft tissue (a) and axial (b,c) and sagittal (d) bone MDCT images.

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