Step I

Systematically describe the radiolucency (as outlined in Ch. 26) including its:

Step II

Decide whether or not the radiolucency is:

Step III

If the pathological radiolucency is acquired, decide within which of the following main disease categories it may be placed:

Step IV

Consider the classification and subdivision of cysts and other similar radiolucencies within each of the other main disease categories, as shown in Table 27.1. This resultant list includes most of the more likely diagnostic possibilities for the unknown radiolucent lesion.

Table 27.1 Classification of the main cysts and tumours and other bone-related conditions that can present as a cyst-like radiolucency (based broadly on the 2005 WHO Classification)

Step V

Compare the radiological features of the unknown radiolucency with the typical radiological features of these possible conditions. Then construct a list showing, in order of likelihood, all the conditions that the lesion might be. This list forms the radiological differential diagnosis.

Infection is described elsewhere (apical, Ch. 22, spreading, Ch. 32) and trauma is described in Chapter 30. The rest of this chapter is devoted principally to differentiating between the different cysts — the most common of the remaining categories — and the other lesions which often present as very similar radiolucencies.

Radicular (dental) cyst (Fig. 27.2)

This inflammatory cyst develops from the epithelial remnants of Hertwig’s root sheath — the cell rests of Malassez.

Fig. 27.2 A Static panoramic (Panoral) radiograph showing a typical radicular (dental) cyst (arrowed) associated with the non-vital . B Upper standard occlusal showing a large radicular cyst associated with the root-filled . C Part of a panoramic radiograph showing a typical unilocular radicular cyst associated with the non-vital .

Note: The term buccal bifurcation cyst is used to describe an inflammatory odontogenic cyst which develops on the side of a molar tooth in relation to a buccal enamel spur or pearl.

Residual radicular cyst (Fig. 27.3)

This term refers to a radicular (dental) cyst remaining after the causative tooth has been extracted.

Fig. 27.3 Part of a panoramic radiograph showing two residual radicular cysts (arrowed), one in the maxilla and one in the mandible.

Lateral periodontal cyst (Fig. 27.4)

The diagnosis of this rare developmental cyst should be reserved for a cyst in the lateral periodontal region that is not an inflammatory cyst or an atypical odontogenic keratocyst. It is thought to develop from either the cell rests of the dental lamina or from remains of the reduced enamel epithelium on the lateral surface of the root.

Fig. 27.4 Periapical showing a typically small lateral periodontal cyst (arrowed) between the and . Although the adjacent premolar was restored, it was vital and symptom free.

(Kindly provided by Mr N. Drage.)

Dentigerous (follicular) cyst (Fig. 27.5)

This cyst develops from the remnants of the reduced enamel epithelium after the tooth has formed.

Fig. 27.5 A Oblique lateral of the right side of the mandible showing a typical circumferential dentigerous cyst (arrowed) associated with the unerupted and displaced . B Part of a panoramic radiograph showing a unilocular central dentigerous cyst (arrowed) associated with the unerupted and inferiorly displaced . C Right side of a lower 90° occlusal of the same patient showing the typical buccal expansion (arrowed).

Note: The term eruption cyst is used to describe a dentigerous cyst when it is in the soft tissues overlying the unerupted tooth.

Odontogenic keratocyst (keratocystic odontogenic tumour) (Fig. 27.6)

Somewhat controversially in 2005 the WHO Working Group recommended that the odontogenic keratocyst be renamed the keratocystic odontogenic tumour as they felt this name better reflected its neoplastic nature. The WHO now define this lesion as a benign uni- or multicystic intraosseous tumour of odontogenic origin with a histologically characteristic lining of parakeratinized stratified squamous epithelium with a potentially aggressive, infiltrative behaviour. It is believed to develop from the epithelium of the dental lamina — the cell rests of Serres — instead of the normal tooth which is therefore typically missing from the series. Lesions are typically solitary but multiple odontogenic keratocysts are a feature of nevoid basal cell carcinoma syndrome (Gorlin’s syndrome), which also includes multiple basal cell carcinomas, and skeletal anomalies, e.g. bifid ribs and calcification of the falx cerebri.

Fig. 27.6 A Oblique lateral of the left side of the mandible showing a typically extensive pseudolocular odontogenic keratocyst (arrowed) which has apparently developed instead of . B PA jaws of the same patient showing that it has caused minimal mediolateral expansion (arrowed). CLeft side of a panoramic radiograph showing a very large multilocular odontogenic keratocyst (arrowed) occupying almost all the left side of the mandible.

• Age: Very variable, peak incidence between second and third decades.

• Frequency: Rare.

• Site: — Posterior body/angle of the mandible extending into the ramus

— Anterior maxilla in canine region.

• Size: Variable, but often large in the mandible.

• Shape: — Oval, extending along the body of the mandible with little mediolateral expansion

— Pseudolocular or multilocular.

• Outline: — Smooth and scalloped

— Well defined and corticated.

• Radiodensity: Uniformly radiolucent.

• Effects: — Adjacent teeth — minimal displacement, rarely resorbed

— Extensive expansion within the cancellous bone.

— May cause cortical perforation.

— May include crown of . by enfolding so resembling a dentigerous cyst.

Nasopalatine duct / incisive canal cyst (Fig. 27.7)

This cyst develops from epithelial remnants of the nasopalatine duct or incisive canal.

Fig. 27.7 A Periapical showing a typical nasopalatine duct cyst (solid arrows) in the midline between the upper central incisors. Note the superimposed shadow of the anterior nasal spine (open white arrows). B Upper occlusal showing a very extensive nasopalatine duct cyst (arrowed) occupying nearly the entire palate. C Lateral view of the same patient showing the expansion of the cyst into the nasal cavity and palate (arrowed).

Note: Differentiation is sometimes required between a nasopalatine duct cyst and a large normal nasopalatine foramen. Several features need to be considered including:

Bone cysts or pseudocysts

Despite their names — simple bone cyst and aneurymal bone cyst — these entities are no longer categorized as cysts. In the new WHO Classification they come under the heading of bone-related lesions. They more commonly affect the skeleton and only relatively rarely affect the jaws.

Simple (solitary) bone cyst (Fig. 27.8)

Defined as an intra-osseous pseudocyst, devoid of an epithelial lining and either empty or filled with serous or sanguinous fluid. The aetiology is unknown.

Fig. 27.8 A Oblique lateral of the right side of the mandible of a teenager showing a typical solitary bone cyst (solid arrows) in the body of the mandible. Note the upper border arching up between the roots of the molar teeth (open arrows). B Oblique lower occlusal of the same patient showing no apparent buccolingual expansion (arrowed).

• Age: Children or young adults, peak incidence in second decade.

• Frequency: Rare.

• Site: — Mandible, particularly anteriorly and in the premolar/molar region.

• Size: Variable, up to several centimetres in diameter.

• Shape: — Unilocular

— Irregular, but the upper border arches up between the roots of the teeth.

• Outline: — Smooth and undulating

— Moderately well defined

— Moderately well or poorly corticated.

• Radiodensity: Uniformly radiolucent.

• Effects: — Adjacent teeth — minimal or no displacement, very rarely resorbed

— Minimal or no expansion of the jaw.

Aneurysmal bone cyst (see Fig. 27.21)

This rare lesion is defined as an expansile osteolytic lesion, often multilocular with histologically blood filled spaces separated by fibrous septa containing osteoclast type giant cells and reactive bone. It is categorized as a giant cell lesion and described later.

Fig. 27.21 A Left side of a panoramic radiograph showing a very large multilocular aneurysmal bone cyst in the ramus (arrowed). Note the marked expansion and the displacement of . B PA jaws of the same patient showing ballooning expansion (arrowed).

Ameloblastoma (Fig. 27.9)

An aggressive but non-metastasizing tumour originating from remnants of the odontogenic epithelium of the enamel organ or dental lamina. Four main types include:

Fig. 27.9 A Part of a panoramic radiograph showing the typical multilocular appearance of a large ameloblastoma at the angle of the mandible, with extensive expansion (solid arrows) and resorption of adjacent teeth (open arrow).

B Right side of a panoramic radiograph showing a very extensive ameloblastoma (arrowed) with a less multilocular appearance but still causing considerable expansion and displacement of . C Left side of a panoramic radiograph showing bilocular ameloblastoma (arrowed) distal to the molar. D Part of a panoramic radiograph showing an ameloblastoma in a more unusual anterior position causing displacement of the adjacent teeth. E Lower occlusal of the same patient showing the bucolingual extent of the lesion (arrowed).

Ameloblastic fibroma (Fig. 27.10)

A rare, benign, mixed odontogenic tumour originating from both the odontogenic epithelium and the connective tissue of the developing tooth germ. Histologically, it consists of odontogenic ectomesenchyme resembling dental papilla and epithelial strands and rests resembling dental lamina and enamel organ. Radiographically these tumours closely resemble ameloblastomas but develop in a younger age group.

Fig. 27.10 A Part of a panoramic radiograph of a 4-year-old showing a large ameloblastic fibroma in the right maxilla, causing marked expansion (solid arrows) and displacement of the developing first molar (open arrow). B Oblique lateral of another small child showing a multilocular ameloblastic fibroma (arrowed) in the left body of the mandible causing displacement of the developing premolars and expansion of the lower border.

C Oblique lateral showing a very extensive ameloblastic fibroma (arrowed) of the right side in a 17-year-old.

(Kindly provided by Mrs J. E. Brown.)

Calcifying epithelial odontogenic tumour (CEOT), Pindborg tumour

This rare odontogenic tumour usually presents in the premolar/molar region of the mandible in 20–60 year-old adults. They can be either unilocular or multilocular, but tend to remain relatively small although they can cause expansion of surrounding cortical bone. They are often associated with an unerupted tooth particularly . The outline of the lesion tends to be of variable definition and cortication but is frequently scalloped. They are often radiolucent in their early stages; then numerous scattered radiopacities usually become evident within the lesion, often most prominent around the crown of any associated unerupted tooth. This appearance is sometimes described as driven snow. Adjacent teeth can be either displaced and/or resorbed (see Fig. 28.8).

Ameloblastic fibro-odontoma

These rare, unilocular or multilocular odontogenic tumours resemble closely ameloblastic fibromas (see Fig. 27.10), and also affect children. However, they are often associated with an unerupted tooth and usually contain enamel or dentine, either as multiple small opacities or as a solid mass (see Fig. 28.9).

Adenomatoid odontogenic tumour (AOT)

Another rare odontogenic tumour, but unusually the most frequent site affected, is the anterior maxilla in the incisor/canine region. Young adults are usually affected. The lesion tends to be unilocular, round or oval, and often surrounds an entire unerupted tooth. When radiolucent in their early stages, they can closely resemble a dentigerous cyst. However, as the lesion matures, small opacities (snowflakes) within the central radiolucency may be seen peripherally. Adjacent teeth are often displaced as the lesion expands but are rarely resorbed (see Fig. 28.10).

Calcifying cystic odontogenic tumour (calcifying odontogenic cyst or Gorlin’s cyst)

The new name of this lesion reflects its classification by the WHO as an odontogenic tumour. It presents typically anteriorly in either the mandible or the maxilla as a unilocular, well-defined, well-corticated radiolucency resembling any other odontogenic cyst. It can affect any age group having been reported in patients from 5–92 years old. One third of cases are associated with an unerupted tooth or odontome. As the lesion matures, a variable amount of calcified material, of tooth-like density, becomes evident scattered throughout the radiolucency. The opacities can range from small flecks to large masses. Adjacent teeth are usually displaced and/or resorbed (see Fig. 28.11).

Odontogenic fibroma (Fig. 27.11)

Controversy still exists as to the concept and definition of the odontogenic fibroma as a distinct lesion. The WHO classify it separately and describe it as a rare neoplasm characterized histologically by varying amounts of inactive looking odontogenic epithelium embedded in a mature fibrous stroma. Two sub-types are described, thought to develop from different parts of the tooth germ:

Fig. 27.11 Part of a panoramic radiograph showing a round, unilocular, well-defined radiolucency (arrowed) at the apex of which was clinically vital. Histopathology confirmed an odontogenic fibroma.

Typically lesions present as cyst-like well defined, unilocular radiolucencies with dense corticated margin. Rarely calcified material may develop internally and adjacent teeth may be displaced.

Odontogenic myxoma (Fig. 27.12)

An intra-osseous neoplasm characterized histologically by stellate and spindle-shaped cells embedded in an abundant myxoid or mucoid extracellular matrix originating from the odontogenic connective tissue fibroblasts of the developing tooth germ.

Fig. 27.12 A Left side of a panoramic radiograph showing the typical multilocular appearance of an odontogein myxoma (arrowed) in the body of the mandible. B Right side of a panoramic radiograph showing an extensive odontogenic myxoma (arrowed) with final internal septa. C Part of an upper oblique occusal showing a multilocular almost honeycomb appearance of an odontogenic myxoma (arrowed) in the maxilla.

Intrinsic primary benign bone tumours

Central haemangioma (Fig. 27.13)

This is a rare, benign tumour that occasionally affects the jaws, particularly the mandible. It is usually regarded as a developmental malformation (hamartoma) of the blood vessels in the marrow spaces, rather than a true neoplasm.

Fig. 27.13 A Part of a panoramic radiograph of an 8-year-old showing a large central haemangioma occupying most of the body of the mandible (solid arrows). The typical honeycomb appearance is evident on the right (open arrows) and there is evidence of root resorption. B Part of a panoramic radiograph showing a unilocular cyst-like haemangioma (arrowed). These two examples highlight the very variable appearance of this important lesion. C Left side of a panoramic radiograph showing the multilocular honeycomb appearance of a large haemangioma in the posterior maxilla (arrowed).

(Kindly provided by Mr K. Hussain.)

Central haemangioma can present at any age but is usually discovered in adolescents. It can produce a very variable radiographic appearance. These variations are important because of the life-threatening nature of the lesion; they include:

• Most commonly a multilocular, expanding lesion which may be associated with displacement and resorption of associated teeth. The size and number of locules can vary considerably, and, if numerous, can present with a honeycomb appearance.

• A moderately well-defined zone of radiolucency within which the trabecular spaces are enlarged and the trabeculae themselves are coarse and thick and are said to be arranged like a hub or the spokes of a wheel.

• Rarely, a relatively well-defined, round, cyst-like radiolucency — not distinctive in any way.

• Large lesions may cause cortical expansion, occasionally producing the sunray or sunburst appearance.

Intrinsic primary malignant bone tumours

Osteosarcoma (Fig. 27.14)

Rare, rapidly destructive malignant tumour of bone. From a radiological viewpoint, there are three main types:

• Osteolytic — no neoplastic bone formation.

• Osteosclerotic — neoplastic osteoid and bone formed.

• Mixed lytic and sclerotic — patches of neoplastic bone formed.

• Age: Young adults under 30 years old.

• Frequency: Rare, but the most common primary malignant bone tumour.

• Site: Usually the mandible.

Fig. 27.14 A Periapical of showing a poorly defined ragged area of radiolucency (arrowed) with resorption of the lateral aspect of root. Biposy revealed an osteolytic osteosarcoma. B Periapical showing a similar smaller poorly defined area of bone destruction between (arrowed) which was again shown to be an osteosarcoma.

Early features:

• Non-specific, poorly defined radiolucent area around one or more teeth.

• Widening of the periodontal ligament space.

Later features:

• Osteolytic lesion:

– Unilocular, ragged area of radiolucency

– Poorly defined, moth-eaten outline

– So-called spiking resorption and/or loosening of associated teeth.

• Osteosclerotic and mixed lesions:

– Poorly defined radiolucent area

– Variable internal radiopacity with obliteration of the normal trabecular pattern

– Perforation and expansion of the cortical margins by stretching the periosteum, producing the classic, but rare sun ray or sunburst appearance (see Ch. 28)

– Spiking resorption and/or loosening of associated teeth

– Distortion of the alveolar ridge.

Extrinsic primary malignant tumours involving bone

Squamous cell carcinoma (Fig. 27.15)

Squamous cell carcinomas of the oral mucosa directly overlying bone, in their latter stages, often invade the underlying bone to produce a destructive radiolucency.

Fig. 27.15 A Part of a panoramic radiograph of a patient who presented with a large squamous cell carcinoma on the left ventral surface of his tongue and the floor of his mouth. The radiograph shows two areas of poorly defined radiolucency (arrowed) with a ragged or moth-eaten appearance. B Left side of a lower 90° occlusal of the same patient showing the bony destruction (arrowed) of the lingual surface of the mandible as the soft tissue tumour invades the bone. C Part of a panoramic radiograph of another patient who presented with a very large squamous cell carcinoma of the floor of the mouth that had penetrated through the mandible (white arrow) causing a pathological fracture. The ragged bone edges are marked with the black arrows.

• Age: Adults over 50 years old.

• Frequency: Rare, but the most common oral malignant tumour.

• Site: Mandible, or maxilla if originating in the antrum.

• Size: Variable.

• Shape: Irregular area of bone destruction often initially saucer-shaped.

• Outline: — Irregular and moth-eaten

— Poorly defined

— Not corticated.

• Radiodensity: Radiolucent, radiodensity dependent on degree of destruction.

• Effects: — Adjacent teeth may be displaced, loosened and/or resorbed or left floating in space

— Destruction of surrounding bone may lead to pathological fracture.

Secondary (metastatic) bone tumours (Fig. 27.16)

Carcinomas from the bronchus, breast, prostate, kidney and thyroid sometimes metastasize to the jaws and produce the typical destructive radiolucency of a malignant lesion (see Ch. 22).

Fig. 27.16 A Right side of a panoramic radiograph showing the typical destructive, moth-eaten radiolucency of a malignant lesion (black arrows). Overlying soft tissue involvement is also evident (white arrows). Subsequent investigation showed this to be a secondary metastatic tumour from the breast. B Left side of a panoramic radiograph showing a large irregular destructive secondary metastatic tumour in the ascending ramus (black arrows). There is an associated pathological fracture (white arrows). C Left side of a panoramic radiograph and D PA jaws of the same patient showing a poorly defined radiolucent secondary metastastic deposit, from the lung, presenting centrally in the ramus (arrowed).

Note: The radiographic appearance, while strongly indicating a destructive malignant lesion, does not enable the distinction between a primary or secondary tumour to be made.

Lymphoreticular tumours of bone (Fig. 27.17)

Multiple myeloma (Fig. 27.17)

Multifocal proliferation of the plasma cell series within the bone marrow, resulting in overproduction of immunoglobulins.

Fig. 27.17 A True lateral skull showing the typical multiple punched-out lesions (arrowed) of the skull vault of multiple myeloma. B Oblique lateral of the left side showing two similar lesions in the mandible (arrowed). C Upper oblique occlusal showing the typical appearance of destructive malignancy of Burkitt’s lymphoma. Almost all normal anatomical structures have been destroyed.

• Age: Adults, middle-aged.

• Frequency: Uncommon.

• Site: Multiple lesions affecting:

— Skull vault

— Posterior parts of the mandible

— Other parts of the skeleton.

• Size: Variable, individual lesions may be several centimetres in diameter.

• Shape: — Round

— Unilocular, though multifocal.

• Outline: — Punched-out

— Well defined, not corticated.

• Radiodensity: Radiolucent.

• Effects: Enlargement and/or coalescence of lesions may lead to pathological fracture.

Langerhans cell disease (histiocytosis X)

Langerhans cell disease is used as a broad grouping of three different clinical manifestations of the same disease. All three manifestations produce tumour-like lesions in bone, caused by proliferation of Langerhans cells and eosinophilic leucocytes:

Fig. 27.18 A Oblique lateral of the left side of the mandible showing a well-defined, unilocular, punched-out, radiolucency (arrowed) beneath the inferior dental canal and therefore non-odontogenic, which proved to be an eosinophilic granuloma. B Left side of a panoramic radiograph showing an extensive punched-out destructive eosinophilic granuloma (arrowed) causing the to appear to be floating in space.

(Kindly provided by Dr J. Luker.)

Radiographically, the bone lesions (in whatever parts of the skeleton are affected) are similar in all three diseases.

Note: Appearance not suggestive of malignant disease.

Central giant cell lesion (granuloma) (Fig. 27.19)

A relatively rare lozalized, benign but sometimes aggressive osteolytic proliferation consisting histiologically of fibrous tissue with haemorrhage and haemosiderin deposits, presence of osteoclast- like giant cells and reactive bone formation producing an expansile radiolucent lesion.

Fig. 27.19 Typical appearance of central giant cell lesion. A Anterior portion of a static panoramic showing the multilocular appearance, expansion (arrowed) and considerable displacement of the adjacent teeth. B Lower 90° occlusal showing the gross buccal and lingual expansion (arrowed) and the scalloped cortical border. C Lower 45° occlusal of another patient showing the appearance of a similar but much smaller central giant cell lesion (arrowed).

Based on their clinical and radiological effects on adjacent structures, central giant cell lesions are sometimes subdivided into two categories:

Brown tumours in hyperparathyroidism

The general radiological features of hyperparathyroidism are discussed in detail in Chapter 32. A few patients with this disease, in addition to the generalized decrease in bone density, also develop circumscribed, cyst-like radiolucencies. Histologically and radiologically these individual lesions (so-called brown tumours) are indistinguishable from central giant cell lesions (see earlier).

Cherubism (Fig. 27.20)

This rare disease of the jaws is inherited, usually as an autosomal dominant, but some cases appear spontaneously. Radiologically the lesions resemble closely other giant cell-containing lesions.

Fig. 27.20 Panoramic radiograph of a 5-year-old boy showing the typical bilateral multilocular lesions of cherubism affecting the mandible (arrowed).

Aneurysmal bone cyst (Fig. 27.21)

As stated earlier, despite its name this rare lesion is categorized as a giant cell lesion and is defined as an expansile osteolytic lesion, often multilocular with histologically blood-filled spaces separated by fibrous septa containing osteoclast-type giant cells and reactive bone.

Periapical osseous dysplasia (Fig. 27.22)

Florid osseous dysplasia (Fig. 27.23)

Stafne’s bone cavity (Fig. 27.24)

A bone cavity or depression on the lingual aspect of the mandible near the lower border, frequently said to contain aberrant salivary gland tissue.

Fig. 27.24 Right side of a panoramic radiograph showing the typical cyst-like appearance of Stafne’s bone cavity at the angle of the mandible, below the inferior dental canal (arrowed).