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10 • Cysts and Odontogenic Tumours
Table 10.1 Clinical Features of Cysts
Cyst Type
Radicular 3rd and 4th M.F Tooth-bearing areas of jaws
Residual
radicular
Inflammatory
collateral
Dentigerous 3rd and 4th M.F Mandibular 3rd molar fol-
Eruption 1st and 2nd M.F Deciduous and permanent
Odontogenic
keratocyst
Lateral periodontal and
botryoid
Gingival Neonates and
Glandular
odontogenic
Calcifying
odontogenic
Orthokeratinised
odontogenic
Nasopalatine 4th to 6th M.F Nasopalatine canal Swelling anterior palate or floor of nose.
Nasolabial 4th and 5th F.M Nasolabial fold Swelling in soft tissue.
Solitary 2nd M5F Mandible Discovered on radiograph.
Aneurysmal 2nd F.M Posterior mandible Firm swelling, rapidly expanding.
Typical Age (Decade
at Presentation)
4th and 5th M.F Mandibular premolar area Slowly enlarging swellings, frequently symptomless.
1st to 3rd M.F Lower molars Paradental cysts associated with pericoronitis.
2nd and 3rd M.F Angle of mandible Frequently symptomless and discovered on dental
Wide range.
6th and 7th peak
adults
4th to 7th None Mandible Painless swelling, root resorption, and tooth
Wide range.
3rd peak
3rd and 4th M.F Posterior mandible Painless swelling or incidental finding on a radio-
Sex
Distribution Commonest Site Common Clinical Signs
especially anterior maxilla; most
common odontogenic cyst
lowed by maxillary canine
teeth, most frequently anterior
to first permanent molar
M.F Mandible, anterior to molars Asymptomatic, occasion buccal expansion.
F.M Buccal alveolus mandible.
maxilla
None Either jaw Painless swelling, unilocular radiolucency with
Slowly enlarging swellings, frequently symptomless
and often discovered by radiography of non-vital
teeth.
Mandibular buccal bifurcation cysts may present
as a painless swelling or, if infected, with pain and
suppuration.
May grow to large size before diagnosis and displace
the associated tooth; most discovered on radiograph
taken because of tooth eruption failure.
Smooth swelling of normal or blue-coloured mucosa
over erupting tooth.
examination or radiography; tooth displacement or
absence and occasional paraesthesia of lower lip.
Multiple small white nodules on buccal gingiva in up
to 80% of neonates. Adult type small dome-shaped
bluish swelling of buccal attached gingiva.
displacement common.
scalloped outline. Calcified material
often present and may be associated with an
odontome, particularly in anterior maxilla.
graph of a radiolucency with a corticated outline,
often associated with an impacted tooth.
153
F, Female; M, male.
Fig. 10.1 Photograph showing buccal swelling caused by residual cyst in maxilla.
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A
Fig. 10.2 Odontogenic keratocyst (A) Part of a panoramic radiograph showing displacement of the third molar and inferior dental canal to the lower
border of the mandible. (B) Axial cone beam computed tomography (CBCT) showing the scalloped margin and buccal perforation of an odontogenic
keratocyst.
10.3 Specific Cysts
B
Several features associated with inflammatory odonto-
genic cysts may be present in the cyst lumen, lining and
LEARNING OBJECTIVES
capsule: cholesterol clefts, foamy macrophages, haemosiderin and Rushton’s bodies.
You should:
• know the radiographic appearance of the more
common cysts affecting the jaw.
• understand the pathology of these cysts.
RADICULAR CYST
Radiology
A well-defined, round or ovoid radiolucency associated with
the root apex or, less commonly in the lateral position, of a
heavily restored or grossly carious tooth. A corticated margin is continuous with the lamina dura of the root of the
affected tooth. The appearances can be similar to those of
an apical granuloma, but lesions with a diameter exceeding
10 mm are more likely to be cystic (Fig. 10.3).
Pathology
The cyst lumen is lined by a layer of simple, non-keratinising,
squamous epithelium of variable thickness, which may
display areas of discontinuity where it is replaced by granulation tissue or mural cholesterol nodules. Arcades and
strands of epithelium may extend into the cyst capsule,
which is composed of granulation tissue infiltrated by a
mixture of acute and chronic inflammatory cells. This infiltrate reduces in intensity as the more peripheral areas of
the cyst capsule are approached, where mature fibrous tissue replaces the granulation tissue (Fig. 10.4).
Fig. 10.3 Radicular cyst arising from a non-vital maxillary first premolar.
In this CBCT the well-demarcated corticated outline is clearly shown
(green arrows). The cyst has elevated the floor of the maxillary sinus and
there is mucosal thickening in the antrum.
Fig. 10.4 Photomicrograph of a radicular cyst showing the nonkeratinising squamous lining arranged into arcades. A dense chronic inflammatory infiltrate is present in the capsule.
RESIDUAL RADICULAR CYST
Radiology
The residual cyst has a well-defined, round/ovoid radiolucency in an edentulous area (Fig. 10.5). Occasionally flecks
of calcification may be seen.
10 • Cysts and Odontogenic Tumours
155
known as paradental cyst and mandibular buccal bifurcation cyst.
Radiology
Intra-oral radiographs show a well-demarcated and often
corticated radiolucent cyst superimposed over the buccal
aspect of the tooth root. In mandibular buccal bifurcation cysts, the associated first or second molar may be
tilted; if infection is present, there may be a periosteal
reaction.
Pathology
Paradental cysts are mostly found around impacted third
molars and typically associated with a long history of
pericoronitis. The cyst is distinct from the follicular space
and is thought to arise from junctional epithelium driven
to proliferate by inflammation. They tend to form on the
mesial aspect with mesio-angular impactions, buccal aspect with vertical impactions and distal aspect with distoangular impactions. Mandibular buccal bifurcation cysts
are more common in childhood and arise in relation to
mandibular first and second molar teeth. Deep periodontal pockets are often present, and the tooth is tilted buccally. Inflammatory collateral cysts are really pouch-like
invaginations and the lining maybe attached to the
cemento-enamel junction or pericoronal gingival sulcus
epithelium. A squamous lining is present that resembles
that found in radicular cysts.
Pathology
Residual radicular cyst arises from a radicular cyst that is
left behind after tooth extraction. The squamous lining and
capsule are similar to the radicular cyst; however, both appear more mature, with the lining lacking the arcades and
strands of epithelium extending into the capsule.
INFLAMMATORY COLLATERAL CYSTS
These cysts arise on the buccal aspect of the roots of partially or recently erupted teeth. There are two types
DENTIGEROUS CYST
Radiology
The majority of dentigerous cysts are associated with unerupted third molars, but maxillary canines, maxillary third
molars and mandibular second premolars may also develop
dentigerous cysts. There is a pericoronal radiolucency
greater than 3–4 mm in width that is suggestive of cyst formation in a dental follicle. The well-defined, corticated radiolucency is associated with the crown of an unerupted
tooth. Classically the associated crown of the tooth lies centrally within the cyst, but lateral types occur (Fig. 10.6).
Pathology
The defining feature of a dentigerous cyst is the site of attachment of the cyst to the involved tooth. This must be at
the level of the amelocemental junction (Fig. 10.7). The
lining of the cyst is composed of a thin layer of epithelium,
either cuboidal or squamous in nature, some two to five
cells thick. This lining is of even thickness and may include
mucous cells along with focal areas of keratinisation of the
superficial epithelial cells. The cyst capsule is, classically,
free from inflammation and has loose, myxoid areas resembling dental follicles. Quiescent rests of odontogenic epithelium may also be present. However, the usual features of
the epithelial lining may be distorted when an inflammatory infiltrate is present.
Fig. 10.5 A residual radicular cyst in the mandible, showing a rounded
radiolucent lesion with a corticated outline.
ERUPTION CYST
Radiology
The extra-bony position of the eruption cyst means that the
only radiological sign is likely to be a soft tissue mass.
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A
Fig. 10.6 Dentigerous cyst. (A) A periapical radiograph showing an enlarged pericoronal space around an impacted lower right second molar. (B) The
corresponding coronal MRI showing the bright signal of the cyst arising from the neck of the displaced tooth that appears as a signal void.
B
appearance. Expansion is typically limited, with a propensity to grow along the medullary cavity (Fig. 10.8). Buccal
expansion of the mandible may occur, but lingual expansion is rare and more often found in odontogenic neoplasms.
Pathology
The odontogenic keratocyst is lined by a continuous layer of
stratified squamous epithelium of even thickness (5–10
cells), the surface of which tends to be corrugated. The
basal-cell layer is well defined, being composed of cuboidal
or columnar cells that display palisading. This epithelium
shows parakeratosis. The lumen of the cyst is filled with
shed terminally differentially squamous cells forming lamellated keratin that imparts a creamy white appearance to
the contents on opening the cyst. The cyst capsule is com-
Fig. 10.7 Dentigerous cyst showing origin from the amelocemental
junction.
posed of rather delicate fibrous tissue and is, classically, free
from inflammation (Fig. 10.9). However, should the cyst
become infected, then an inflammatory infiltrate may be
seen and the characteristic features of the epithelial lining
will be lost. The odontogenic keratocyst is a developmental
Pathology
An eruption cyst is basically a dentigerous cyst in soft tissue
over an erupting tooth. The histological features are similar
to those of the dentigerous cyst, though reduced enamel
epithelium is often seen.
cyst that is associated with mutation or inactivation of the
gene, PTCH1.
The presence of daughter cysts within the capsule is a
well-recognised finding, particularly in those odontogenic
keratocysts arising as a component of the basal-cell naevus syndrome, where there is a germ line mutation of
PTCH1. Multiple cysts may be found in Basal Cell Naevus
ODONTOGENIC KERATOCYST
Radiology
Around 80% of odontogenic keratocysts occur in the mandible with over 50% in the posterior body and ramus. There
is a well-defined radiolucency in odontogenic keratocysts,
often with densely corticated margins. The outline may be
“scalloped” in shape. Occasionally, there is a multilocular
Syndrome (BCNS). All odontogenic keratocysts have a
tendency to recurrence after enucleation.
LATERAL PERIODONTAL AND BOTRYOID CYSTS
The lateral periodontal cyst is a developmental cyst occurring on the lateral or inter-radicular aspects of the roots of
erupted teeth. The botryoid cyst is a multicystic variant.
10 • Cysts and Odontogenic Tumours
Fig. 10.8 Odontogenic keratocyst. The lesion is very well-defined with a corticated margin. The wisdom tooth appears displaced, as does the inferior
dental canal, visible at the inferior and posterior aspects of the cyst. The shape is not round or ovoid, but rather irregular with a separate locule below
the crown of the wisdom tooth.
157
Fig. 10.9 Photomicrograph of an odontogenic keratocyst showing the
epithelial lining of fairly uniform thickness, prominent basal cell palisading and parakeratosis.
Radiology
On intra-oral radiographs a well corticated radiolucency is
found juxtaposed to a tooth root. Most are less than 10 mm
in size. Lateral periodontal cysts are unilocular and botryoid cysts are typically multilocular.
Pathology
Both types of cyst are lined by a single or double layer
of non-keratinising epithelium with characteristic focal
plaques of whorled epithelial cells. Botryoid cysts have multiple anastomosing cystic spaces.
GINGIVAL CYSTS
Gingival cysts are commonly found in neonates but are
rarely encountered after 3 months of age. Many appear to
undergo spontaneous resolution. White keratinous nodules
are seen on the gingivae, and these are referred to as Bohn’s
nodules or Epstein’s pearls. Gingival cysts arise from the
dental lamina and histologically are keratin containing.
Many open into the oral cavity forming clefts from which
the keratin exudes. Gingival cysts are lined by stratified
squamous parakeratotic epithelium. In neonates and infants, the cysts are typically between 2 and 5 mm in diameter. They do not involve bone and no treatment is required.
Gingival cysts of adults are much less common and are
found mainly in the buccal gingivae in the mandibular
premolar–canine region. The cyst typically presents as a
solitary soft blue swelling within the attached gingivae,
seldom larger than 5 mm in diameter. Gingival cysts of
adults are lined by a thin cuboidal or flattened nonkeratinising epithelium that is between 1 and 3 cell layers in
thickness. Gingival cysts do not extend into bone although
they may rest in a shallow depression in the cortex. They
are usually removed by excision biopsy for diagnosis.
GLANDULAR ODONTOGENIC CYST
This developmental jaw cyst is also known as a sialoodontogenic cyst and it tends to occur mostly in the mandible and anterior maxilla.
Radiology
A well-defined radiolucency which may have a scalloped
border is typically found. A unilocular or multilocular appearance may be present. Tooth displacement and root resorption are common and a glandular odontogenic cyst is
characteristically associated with the roots of multiple teeth.
Pathology
The microscopic features are complex and not all features
are observed in any individual cyst. There is an epithelial
158
lining of variable thickness and a luminal layer of hobnail
cells can be a distinctive feature. Intra-epithelial microcysts
with glandular differentiation are found and the lumen
typically contains mucin. Clear cells, apocrine cells, mucous cells and papillary projections may be also present.
After enucleation, there is often recurrence and sometimes
multiple recurrences occur.
Master Dentistry
CALCIFYING ODONTOGENIC CYST
Radiology
This is a rare cyst and it most often arises in the anterior
parts of either jaw. Typically, there is a well-demarcated
unilocular radiolucency. Most cases contain calcified material that appears as radio-opaque flecks and sometimes an
odontome is closely associated with the cyst, especially
those in the anterior maxilla.
Pathology
The cyst is lined by epithelium of variable thickness with
basal cell palisading and areas resembling stellate reticulum. Dentinoid may be present. The characteristic finding is
the presence of ghost cells where is nucleus is obscured by
a distinctive type of eosinophilic keratinization. Ghost cells
may be present within the lining or the capsule and they
frequently initiate calcification. Recurrence is rare after
enucleation.
ORTHOKERATINISING ODONTGENIC CYST
Radiology
Most often a well-demarcated unilocular radiolucency is
found with a corticated outline, and only rarely is the cyst
multilocular. The posterior mandible is the most frequent
site and often an unerupted tooth is associated, resulting in
an appearance similar to a dentigerous cyst.
Pathology
An orthokeratinising odontogenic cyst is a distinct entity
and is not associated with PTCH1 abnormalities. The squamous epithelial lining is 5–8 cell layers in thickness. A
prominent granular layer is present and the luminal surface shows orthokeratosis. Keratinisation may be lost focally when inflammation is present. The cyst is treated by
enucleation and recurrence is very rare.
NASOPALATINE CYST
Radiology
The nasopalatine cyst appears as a well-defined, round radiolucency in the midline of the anterior maxilla (Figs. 10.10
and 10.11). Sometimes it appears to be “heart-shaped” because of superimposition of the anterior nasal spine. Radiological assessment should include examination of the lamina
dura of the central incisors (to exclude a radicular cyst) and
assessment of size (the nasopalatine foramen may reach a
width of as much as 6 mm).
Pathology
The cyst is lined by a layer of pseudostratified ciliated columnar epithelium and/or stratified squamous epithelium.
Fig. 10.10 Nasopalatine cyst. This small example could easily be mistaken for a radicular cyst, but the presence of the lamina dura of the
incisors indicates that this is not the case.
The capsule of the cyst is fibrous and may include the incisive canal neurovascular bundle.
NASOLABIAL CYST
Radiology
As the nasolabial cyst is a soft tissue lesion, radiography
may reveal nothing. However, radiography will be performed to exclude other causes of the swelling. “Bowing”
inwards of the anterolateral margin of the nasal cavity has
been recorded as a feature. Ultrasound examination would
be an appropriate investigation.
Pathology
The nasolabial cyst is lined by non-ciliated pseudostratified columnar epithelium, which is often rich in mucous
cells.
SOLITARY BONE CYST
Radiology
The solitary bone cyst appears as a well-defined but noncorticated radiolucency. Typically, it has little effect on adjacent structures and “arches” up between the roots of
teeth (Fig. 10.12). The inferior dental canal may not be
displaced, but the cortical margins of the canal may be lost
where it overlies the lesion. Expansion is rare.
10 • Cysts and Odontogenic Tumours
159
A B
Fig. 10.11 Nasopalatine duct cyst: (A) surface rendered and (B) axial CBCT. These images show perforation of palatal cortex and intact lamina dura of
the central incisors.
Fig. 10.12 Solitary bone cyst. There is a large radiolucency in the left
body of the mandible that arches up between the roots of the teeth,
which appear otherwise unaffected. The lower border cortex is very
thin. The inferior dental canal is not displaced.
Pathology
The cyst is lined by fibrovascular tissue that often includes
haemosiderin and multinucleate giant cells. On aspiration,
clear fluid may be found, or the cavity may appear empty.
ANEURYSMAL BONE CYST
Radiology
The aneurysmal bone cyst typically presents as a fairly welldefined radiolucency. Sometimes it has a multilocular appearance because of the occurrence of internal bony septa
and opacification. Marked expansion is a feature.
Pathology
The predominant feature of an aneurysmal bone cyst is the
presence of blood-filled spaces of variable size lying in a
stroma rich in fibroblasts, multinucleate giant cells and haemosiderin. Deposits of osteoid are also seen. Aneurysmal
bone cysts may be primary or secondary to another lesion
such as a vascular malformation or fibro-osseous lesion.
10.4 Surgical Management of Cysts
LEARNING OBJECTIVES
You should:
• know the general management of cysts.
• know the specific approach for the more common cysts
of the jaw.
Surgical management of cysts generally implies enucleation,
but occasionally marsupialisation is the technique of choice.
Some small radicular cysts do not require surgery and regress
once the root canal of the associated tooth has been effectively cleaned and filled. Antibiotic therapy may be required if
a cyst has become infected. Aspiration of fluid from a pathological cavity may be helpful in confirming the presence of a
cyst rather than the maxillary sinus (air) or a tumour (solid).
Biochemical analysis of the aspirate indicating protein content of less than 40 g/L and cytology showing parakeratinised
squames suggests an odontogenic keratocyst.
ENUCLEATION
Enucleation of a cyst involves the removal of the whole
cyst, including the epithelial and capsular layers from the
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bony walls of the cavity. This permits histopathological examination and ensures that no pathological tissue remains.
A large mucoperiosteal flap, usually buccal, is raised to ensure that closure will be over adjacent sound tissues and not
the bony cavity. Primary closure is nearly always undertaken unless the cyst is very infected, in which case this
may be delayed, and the cavity initially dressed with bismuth iodoform paraffin paste (BIPP) on ribbon gauze.
Enucleation of a nasopalatine cyst will require the raising of a palatal flap to provide surgical access and cyst removal. This inevitably damages the nasopalatine nerves
and vessels and results in a small area of paraesthesia,
which usually does not cause concern to the patient.
MARSUPIALISATION
Marsupialisation is a simple operation that may be performed under local anaesthesia in which a window is cut
and removed from the cyst lining. This allows decompression of the cyst, which then slowly heals by bone deposition
in the base of the cavity. However, this technique permits
histopathological examination of only a small and possibly
non-representative sample of tissue. Primary closure is not
undertaken but rather the cyst lining is sutured to the oral
mucosa to keep the cavity open (Fig. 10.13). The cavity
must be filled with a dressing such as BIPP, which must be
frequently replaced, to prevent food debris trapping during
the many months the cavity may take to heal. Alternatively,
an extension may be added to a denture to protect the cavity, which becomes reduced in size as the cavity heals.
Marsupialisation is advocated when the cyst is so large
that jaw fracture is the likely outcome of enucleation, although enucleation and simultaneous bone grafting may
be preferable. The technique may also be useful if there are
associated structures, such as the inferior alveolar nerve,
maxillary antrum or nose, that are at risk of damage during enucleation. Similarly, marsupialisation of an eruption
cyst will allow the eruption of a tooth without it being damaged by enucleation.
SURGICAL MANAGEMENT OF PARTICULAR CYSTS
Radicular Cysts
Large radicular cysts, or small ones that do not resolve following conventional endodontic treatment, require enucleation and surgical endodontic management to seal the root
canal of the associated tooth.
Access for apical surgery is gained via a three-sided or
a semilunar mucoperiosteal flap (Fig. 10.14A, B). The latter avoids involvement of the gingival margin, which may
be important where the tooth is restored with a crown
but does not offer adequate access or permit closure over
bone for larger cysts. Bone is removed with a rosehead
bur over the tooth root apex, which is then divided with a
fissure bur and removed so that the root face may be readily visualised from the buccal aspect (Fig. 10.14C). The
cyst is enucleated in the usual way and sent for histopathological examination. An access cavity is prepared in
the root face and restored with filler—the retrograde root
filling—to seal the root canal of the tooth. Following
irrigation of the surgical site, wound closure is achieved
with an appropriate suture material that will provide
adequate wound support. If the suture material is
absorbed too early, semilunar flaps are likely to show
dehiscence and three-sided flaps may cause gingival
recession. Follow-up with radiography to check bony
healing is indicated. See also Chapter 5.
Odontogenic Keratocyst
High recurrence rates are reported (up to 60%) because of
technical difficulty in removing all of the cyst lining, including projections into cancellous bone. Enucleation must
be thorough. Some advocate irrigating the cyst cavity with
chemical fixatives such as Carnoy’s solution (a fixative composed of ethanol, chloroform and acetic acid), to cause necrosis of any remaining remnants, and others suggest excision to include a bone margin about the cyst. Annual
radiographic review is recommended.
A
Fig. 10.13 Marsupialisation. (A) An incision is made over a large cystic lesion in the maxillary alveolus. (B) The flap is sutured to the margins of the cyst
lining following excision of a window of tissue for pathological examination.
B
10 • Cysts and Odontogenic Tumours
161
A
Fig. 10.14 Enucleation of a radicular cyst. (A) A three-sided incision. (B) A semilunar incision to gain access to a radicular cyst associated with a maxillary
lateral incisor. (C) Oblique sectioning of the apical root to permit good access to seal the root canal with amalgam.
Eruption Cysts
Reassurance of the parents is usually the only management
required as these cysts frequently fenestrate spontaneously
and require no surgical intervention. Occasionally, however, they may require marsupialisation to expose the tooth.
Solitary Bone Cyst
These bone cysts are often incidental findings on radiographs. Aspiration may reveal clear fluid or air indicating
that no further intervention is necessary.
Aneurysmal Bone Cyst
These cysts benefit from curettage. However, they may be associated with a second pathological lesion such as a vascular
malformation which may lead to profound haemorrhage.
B C
tumour forms in place of a tooth. The biological behaviour of
odontogenic tumours ranges from benign developmental
anomaly to malignant. An unusual feature of ameloblastoma
(the most common odontogenic neoplasm) is that it is locally
invasive but does not metastasise. This property is shared
with some other odontogenic tumours and is explained by
the biological ability of odontogenic ectodermal cells to
invade bone in order to form teeth.
Many classification schemes have been proposed. The
current WHO classification is based on whether the tumour
is benign or malignant, epithelial, mesenchymal or mixed
(Box 10.2). Only the mixed group can contain enamel or
dentine because odontogenic epithelial-mesenchymal interaction is necessary for dental hard tissue to form.
Odontogenic neoplasms are rare but are most likely to
present to the dentist. Many appear as chance findings on
Patients with this cyst need to be managed in hospital.
10.5 Odontogenic Tumours:
Origin, Behaviour, Classification
and Investigations
LEARNING OBJECTIVES
You should:
• understand the developmental origin of the cells that
give rise to odontogenic tumours.
• have knowledge of the WHO scheme of classification of
odontogenic tumours,
• know how odontogenic neoplasms are investigated and
diagnosed.
During foetal development, epithelium from the dental lamina invades the future jaw bones in order to form teeth and
their associated supporting structures. Odontogenic cells are
derived from the ectoderm of the first branchial arch and the
ectomesenchyme of the neural crest. Formation of dental
hard tissues requires their interaction. Odontogenic tumours
are mostly derived from tooth-forming cells that remain in
the jaws after tooth formation. Sometimes an odontogenic
Box 10.2 Odontogenic Tumours
Odontogenic carcinomas
n
Ameloblastic carcinoma
n
Primary intra-osseous carcinoma
n
Sclerosing odontogenic carcinoma
n
Clear cell odontogenic carcinoma
n
Ghost cell odontogenic carcinoma
Odontogenic carcinosarcoma
Odontogenic sarcoma
Benign epithelial odontogenic tumours
n
Ameloblastoma
n
Squamous odontogenic tumour
n
Calcifying epithelial odontogenic tumour
n
Adenomatoid odontogenic tumour
Benign mixed odontogenic tumours
n
Ameloblastic fibroma
n
Primordial odontogenic tumour
n
Odontoma, compound and complex
n
Dentinogenic ghost cell tumour
Benign mesenchymal odontogenic tumours
n
Odontogenic fibroma
n
Odontogenic myxoma
n
Cementoblastoma
Cemento-ossifying fibroma
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radiographs. Larger tumours may expand the jaw, particularly the lingual plate in the mandible, and may displace
teeth. Imaging plays an important role in defining the borders and extent of the tumour and cone beam CT with reconstruction is especially useful. While odontomes can be diagnosed radiographically, soft tissue odontogenic tumours
must be biopsied before removal is attempted. If partly cystic,
it is important to include a solid area in the biopsy sample.
10.6 Specific Odontogenic
Tumours
LEARNING OBJECTIVES
You should:
• have a good knowledge of ameloblastoma, the most
common odontogenic tumour.
• know the clinical features of odontomes.
• be aware of the other odontogenic tumours.
MALIGNANT ODONTOGENIC TUMOURS
These are extremely rare. Intraosseous squamous cell carcinoma arises from epithelial inclusions in the jaw and has a
poor prognosis. Malignant odontogenic neoplasms present
with expansion of the jaw, destruction of adjacent tissue,
displacement of teeth and sometimes pathological fracture.
Secondary deposits of cancer in the jaw are more common
than primary odontogenic cancer.
AMELOBLASTOMA
Ameloblastoma is the most common odontogenic neoplasm.
It arises mostly in the posterior mandible but can also occur
in the posterior maxilla and less commonly at other sites in
the jaws. The pattern of disease varies in populations. Ameloblastoma is most frequent in black Africans. The midline
mandible is often involved, which is a rare site in Caucasian
people. Ameloblastoma is slow growing and typically expands the jaw. Expansion of the lingual plate is a helpful diagnostic sign in the mandible, because cysts rarely expand
the plate. Adjacent teeth may be displaced or the roots may
undergo resorption. Pain may be a presenting feature. A
multilocular (“soap-bubble”) radiolucent cystic lesion is typically found on radiographs (Figs. 10.15 and 10.16). Patho-
logically ameloblastomas often show extensive cystic change
and biopsy of a solid area in the wall of the tumour is essential for diagnosis (Fig. 10.17). In the microscope, ameloblas-
toma contains islands of odontogenic epithelium. Columnar
cells resembling preameloblasts are found at the periphery
of the islands. The nuclei are located away from the basement membrane and there is abundant cytoplasm; this is
described as reversed nuclear polarity. Stellate reticulumlike cells are present in the centre of the islands. Cystic and
microcystic changes are seen microscopically. Follicular and
plexiform patterns are seen; often both patterns are present
(Fig.10.18).
Variants of ameloblastoma are recognised. The unicystic
type is noteworthy because, if no extramural islands are
present, it behaves as a cyst and can be treated by enucleation rather than resection. Other rare variants are the
metastasizing type and desmoplastic ameloblastoma. Peripheral ameloblastoma may occur outside the bone as a
red-white proliferation on the gingiva.
ODONTOMES
Odontomes are benign malformations, rather than true neoplasms and are very common, affecting up to 2% of the
population. Typical presenting signs are failure of eruption
of nearby permanent teeth or acute infection resembling a
dental abscess. Two types are recognised:
1. Complex odontome: a disorganised mass of dental hard
tissue, usually found in the posterior mandible.
2. Compound odontome: separate rudimentary teeth (denti-
cles) in a sac, usually found in anterior maxilla (Fig. 10.19).
Fig. 10.15 Ameloblastoma in the left lower molar region, displaying multilocularity and expansion of the bone.