THE DIAGNOSTIC IMAGING OF JAW LESIONS

Radiologists are often called upon to perform a variety of imaging studies on the

maxilla and mandible. Indications for these studies include evaluation of a known or

suspected jaw lesion, evaluation of a dental arch for dental implant placement, and the

assessment of the temporomandibular joint (TMJ) in a patient presenting with chronic facial

pain.

DIAGNOSTIC IMAGING OF JAW LESIONS:

Lesions occurring primarily in the jaws arise in either odontogenic or non-

odonotogenic tissues located within the jaw. Secondary involvement of the jaw may occur

on occasion via a number of different pathways. These include the direct extension of a

neoplastic or inflammatory process involving the soft tissues bordering the jaw, a blood-

borne metastatic process, or as a result of an underlying systemic process.

Jaw lesions are often classified according to their radiographic densities and

margination on plain film studies. Jaw lesions can be described as having either a

radiolucent radiopaque, or mixed appearance relative to the density of adjacent bone. The

majority of jaw lesions is radiolucent (> 80%), and includes a number of odontogenic and

nonodontogenic lesions. Lucent cystic lesions may exhibit internal septae resulting in a

multicystic or multiloculated appearance. Radiopaque lesions exhibit increased radiographic

density due to the presence of normal or dysplastic calcified odontogenic tissues (e.g.,

dentin or cementum), or the apposition of new bone on an existing osseous matrix. A mixed

appearance can result from the presence of two or more tissues of normally different

radiographic densities, variation in the degree of maturation of a single or multiple tissues

within the lesion.

Another important criterion used in evaluating a jaw lesion is its margination. Jaw

lesions can be either well circumscribed (defined) or poorly circumscribed. Well-

circumscribed lesions are usually benign, whereas poorly circumscribed lesions invariably

represent aggressive inflammatory or neoplastic processes. Involvement of a segment of a

jaw by a poorly circumscribed or infiltrating radiolucent lesions may result in a permeative of

“moth eaten” appearance.

Other important parameters that should be taken into account in arriving at a

diagnosis or in formulating a differential diagnosis include anatomic location, relationship to

the cortex, and associated periosteal and soft tissue changes. In assessing a jaw lesion, it is

important to note its precise anatomic location within the jaw, its relationship to the

dentition in general, and any specific relationship to a tooth or portion of a tooth. It is

important to remember that certain lesions occur exclusively in one area or site, whereas

other lesions have no specific predilection. In addition, a number of other lesions can occur

anywhere in the jaws but occur with greater frequency in a given site or area. Non-

odontogenic lesions usually have no specific relations to the dentition & can involve the

bone around two or more teeth, whereas odontogenic lesions typically involve only one

tooth or a specific part of a tooth. If a lesion involves only one tooth, it is important to note

the degree of tooth development present; the lesion’s location with respect to the tooth

(crown versus root versus entire tooth); and any signs of root resorption or displacement. If

assessing a lesion in an edentulous area, it is important to know if the lesion is associated

with the congenital or surgical absence of a tooth.

The lesion’s relationship to the cortex should also be noted. Signs of cortical

expansion, destruction, or breakthrough should be looked for as well as evidence of

periosteal or soft tissue involvement. Slow growing lesions often cause cortical bowing and

pressure resorption with minimal if any periosteal or soft tissue involvement. Aggressive

inflammatory and neoplastic lesions often cause cortical destruction or breakthrough, which

may be accompanied by periosteal reactions or soft tissue masses.

In general, jaw lesions exhibit one of the following radiographic patterns.

1. Well – circumscribed radiolucent lesions

2. Poorly circumscribed radiolucent lesions.

3. Mixed lesions.

4. Radiopaque lesions.

Included in each of these groups are a number of odontogenic and nonodontogenic

lesions. The following sections examine a number of commonly encountered jaw lesions

presenting with each of these patterns.

Well – Circumscribed Radiolucent Lesions:

A number of odontogenic and nonodontogenic lesions can present as well

circumscribed radiolucent lesions. Odontogenic lesions include periapical lesions,

dentigerous cysts, odontogenic keratocysts, cysts of the globullomaxillary region, and

ameloblalstomas. Nonodonstogenic lesions include nasopalatine duct cysts, traumatic cysts,

aneurismal bone cyst, and central giant cell granuloma.

Odontogenic Lesions:

Odontogenic cysts are derived directly or indirectly from remnants of the dental

lamina or cells of the periodontal membrane. Odontogenic lesions presenting as well-

circumscribed radiolucent lesions include periapical lesions, dentigerous cysts, odoontogenic

keratocysts, cysts of the globullomaxillary region, and ameloblastomas.

Periapical Lesion: Periapical lesions include both the dental granuloma and the periapical

cyst.

The earliest radiographic sign of a developing periapical lesion is widening of the

periodontal space around the apex of the tooth. As the lesion evolves and enlarges,

osteolysis occurs resulting in a well – circumscribed, unilocular, radiolucent lesion around the

root apex. Lesions less than 1 cm in diameter is usually granuloma, whereas lesions greater

than 1 cm are usually periapical cysts. Infected periapical lesions initially are

radiographically indistinguishable from sterile lesions. Advanced lesions, however, may

demonstrate loss of smooth margination and osseous destruction.

Residual cysts are radiographically indistinguishable from a number of other well-

circumscribed radiolucent lesions. Therefore a clinical history of the extraction of a tooth

associated with periapical lesion is a key in making the diagnosis.

On CT studies, a sterile periapical lesion presents as a well-defined low-density area

around the apex (ices) of an involved tooth. Infected cysts may exhibit cortical

breakthrough and extension of the inflammatory process into the adjacent soft tissues.

Radionuclide bone scans demonstrate discrete foci of increased uptake around the roots of

involved teeth. Uncomplicated periapical cysts on MR imaging studies demonstrate low to

intermediate signal intensity on T1-weighted, intermediate signal intensity on proton density

on T2-weighted images.

Dentigerous (Follicular Cyst.) The dentigerous or follicular cyst is the second most

common odontogenic cyst, resulting from the cystic degeneration of the enamel organ after

full or partial completion of the crown (an unerupted tooth).

Radiographically, dentigerous cysts present as well-circumscribed, expansible,

radiolucent lesions, associated with a partially or completely formed, unerupted crown

Opacification and bowing of the walls of maxillary sinus can be seen in lesions involving the

maxillary sinus.

On CT studies and reformatted three-dimensional images, dentigerous cysts present

as expansile, low-density lesions associated with a full or partially formed unerupted crown

or tooth. Cortical bowing and pressure resorption are well demonstrated on CT Associated

periosteal and soft tissue reactions are absent. Direct coronal CT images are important in

assessing possible ostium obstruction by a displaced crown in the case of lesions involving

the maxillary sinus. On MR imaging studies, the cystic fluid usually exhibits low to

intermediate signal intensity on T1and high signal intensity on T2- weighted images,

whereas the crown appears devoid of signal intensity on all sequences.

Dentigerous cyst

Odontogenic Keratocyst: Odontogenic Keratocyst is a relatively common developmental

odontogenic cyst constituting approximately 10% to 12% of all developmental odontogenic

cysts.

Approximately three quarters of all odontogenic keratocysts occur in the mandible,

usually in the posterior body and ramus. Maxillary odontogenic keratocysts occur primarily

in the cuspid region. Odontogenic keratocysts can present as either single or multiple

lesions. Multiple lesions are associated with the nevoid basal cell carcinoma syndrome

(Gorlin’s syndrome). Components of this syndrome include multiple odontogenic

keratocysts, early appearing basal cell carcinomas of the skin, skeletal developmental

anomalies, dyskeratotic pitting of the hands and feet, dural calcification, and ectopic soft

tissue calcification.

Odontogenic keratocysts present on plain films as well circumscirbed and often well

corticated radiolucent. Smaller odontogenic keratocysts, typically present as unilocular

lesions, whereas larger lesions often exhibit a multilocular appearance. They can have

additional radiographic or clinical features that may simulate or suggest other odontogenic

lesions. These include small, well-corticated, radiolucent lesions associated with the absence

of a tooth (primodial cyst); radiolucent lesions associated with a tooth and indistinguishable

from a dentigerous cyst (25% to 40% of cases); or as radiolucent lesions indistinguishable

from either unicystic or multicystic ameloblastoma. A feature of many odontogenic

keratocysts that can be useful in differentiating them from other lesions is the tendency for

them to grow within the medulary space in a predominantly anteroposterior direction while

causing minimal if any cortical expansion. Maxillary odontogenic keratocysts can extend into

the maxillary sinus, and present as a soft tissue density indistinguishable from a mucus

retention cyst on plain film studies. CT can be helpful in assessing these intra sinus lesions

from uncomplicated mucus retention cysts. On CT examination, we have found odontogenic

keratocysts to have higher CT numbers than uncomplicated retention cysts, and to cause

localized bowing of the sinus wall. On MR imaging studies, odontogenic keratocysts typically

demonstrate low to intermediate signal intensity on T1 sequences, intermediate signal

intensity on proton density sequences, and high signal intensity on T2 sequences As a result

of the different radiographic appearances an odontogenic keratocyst can have, they should

always be considered in the differential diagnosis of cystic lesions of the jaw.

Odontogenic keratocyst

Cysts of the Globulomaxillary Region: The term globulomaxillary is used to denote the

area of fusion between the embryonic globular process of the median nasal process and the

maxillary process. This region corresponds to the area between the maxillary lateral incisor

and cuspid.

Odontogenic cysts that can present with radiographic findings suggestive of the

classic globulomaxillary cyst include periapical cysts, odontogenic keratocysts, and lateral

periodontal cysts. In light of the histologic diversity of lesions presenting with similar

radiographic findings in this area, it is more appropriate to refer to these lesions as cysts of

the globulomaxillary region.

Radiographically, these lesions present as well circumscribed, often inverted pear-

shaped, radiolucencies between the maxillary lateral incisor and cuspid. Large lesions can

have significant palatal extensions and are best appreciated on intraoral dental occlusal

plain film or on CT studies. On axial CT and reformatted panoramic images of the maxilla,

cysts of the globulomaxillary region appear as well-circumscribed low-density lesions

between the lateral incisor and cuspid.

Ameloblastoma: The ameloblastoma is the most common clinically significant odontogenic

tumor, constituting 1% of all tumors and cysts of the jaws, and approximately 11% of all

odontogenic tumors Ameloblastomas arise from either the surface epithelium or remnants of

the dental lamina, or from pluripotential epithelial cells lining dentigerous cysts.

Approximately 80% of all ameloblalstomas occur in the mandible, with the ascending

ramus and proximal body being the most common sites. Maxillary ameloblastomas occur

most often in molar premolar region.

Grossly and radiographically ameloblalstomas are divided into two subtypes: (1)

multicystic and (2) unicystic .The multicystic ameloblastoma constitutes approximately 85%

of all ameloblastomas and contains both solid and cystic elements. The majority of

multicystic ameloblastomas occur in the distal ramus and proximal body of the mandible

(85%). Occasionally, a multicystic ameloblastoma may occur in the posterior maxilla.

The multicystic ameloblastoma is often described as having a “soap bubbly”

appearance on various plain film examinations; this appearance results from its usually

pronounced buccal-lingual cortical expansion as well as the presence of internal osseous

septae between the low-density solid and cystic elements on plain film studies it is

impossible to differentiate between the solid and cystic elements of the tumor.

Unicystic ameloblastomas are grossly cystic, and account for approximately 15% to

20% of all ameloblalstomas.

Radiographically, the unicystic ameloblalstoma presents as a well-circumscribed,

unicystic, radiolulcent lesion, occurring most often in the mandibular molar region. On CT

studies both the unicystic and multicystic ameloblastomas present as well-circumscribed

low-density lesions. Cortical expansion with cortical pressure resorption is usually present in

larger lesions Associated periosteal and soft tissue reactions are absent. Multicystic lesions

also demonstrate the presence of internal osseous septae.

MR imaging, as a result of its greater soft tissue resolution, can provide important

preoperative evaluation of a multicystic ameloblastoma. This information includes

differentiating between solid and cystic elements, and the demonstration of soft tissues

lining cyst walls. This information is important for the surgeon in planning the level of

surgical resection. On T1-weighted images both solid and cystic components are usually of

low signal intensity. Areas of high signal intensity on T1 sequences usually denote the

presence of highly proteinaceous cystic fluids. Solid components, including soft tissues

lining cyst walls, exhibit a homogeneous appearance on T1 sequences and significant

enhancement following gadolinium administration. On T2 sequences solid tissues

demonstrate low signal intensity, where as cystic areas demonstrate high signal intensity

Postoperatively, MR imaging can demonstrate the presence of early recurrences, which

typically exhibit high signal intensity on T2-weighted images.

Ameloblastoma of the mandible

Nonodontogenic Lesions

Nasopalatine Duct (Incisive Canal) Cyst. The incisive canal is located in the anterior

palatal midline, extending between the nasal fossa and incisive foramen. Located within the

incisive canal are remnants of the embryonic nasopalatine duct. The nasopalatine duct cyst

is the most common non-dental developmental lesion of the maxilla, and is believed to

result from the spontaneous degeneration and proliferation of remnants of the nasopalatine

duct or mucous cells located within the incisive canal. On panoramic studies, nasopalatine

duct cysts often appear as avoid or “heart-shaped” radiolucencies between the roots of the

maxillary central incisors. Nasopalatine duct cysts are often incidental findings on CT and

MR imaging studies performed for other reasons.

On CT studies, there is focal or diffuse enlargement of the nasopalatine canal. On MR

imaging studies nasopalatine duct cysts demonstrate low signal intensity on T1- and high

signal intensity on T2 weighted sequences.

Traumatic Bone Cyst: The traumatic bone cyst is a pseudocyst, lacking a true epithelial

lining. Although it is widely held that traumatic bone cysts result from the breakdown of an

intramedullary hematoma following trauma, conclusive evidence in support of this or any

other mechanism is lacking. On plain film studies, the traumatic bone cyst presents as a

well-defined radiolucent lesion in the posterior mandible, often extending between the roots

of adjacent teeth. Internal scalloping and preservation of the lamina dura are characteristic.

On CT examination, traumatic bone cysts present as low-density lesions, demonstrating

cortical expansion, thinning, and internal scalloping. Extension between the roots of

adjacent teeth with preservation of the lamina dura also can be seen on CT studies.

Aneurysmal Bone Cyst. The aneurismal bone cyst is a pseudocyst believed to result from

a localized vascular reactive process resulting in vascular proliferation and localized

osteolysis. Radiographically, aneurismal bone cysts present as a nonspecific, expansile,

unilocular Radiolucency. Occasionally, aneurismal bone cysts may present as multilocular

radiolucencies with slightly irregular internal margins.

Central Giant cell granuloma central giant cell granulomas, formerly known as giant cell

reparative granuloma, occur predominantly in children and young adults. These lesions are

of uncertain etiology, and occur most often in the mandible. Mandibular lesions usually occur

in the anterior mandible and often cross the midline .A characteristic feature of this lesion is

its tendency to resorb the root tips of adjacent erupted teeth The radiographic findings

associated with central giant cell granuloma are nonspecific, often consisting of an

irregularly shaped, unilocular radiolucent lesion.

Some lesions may present with a multilocular appearances. The lesions are usually well

delineated. Radiographically, smaller unilocular lesions may simulate periapical lesions,

whereas larger multilocular lesions may simulate ameloblastomas or other multilocular

lesions.

Poorly Circumscribed Radiolucent Lesions: Ill-defined radiolucent lesions can result

from acute osteomyelitis, the direct extension of a neoplasm arising in tissues bordering the

jaw, a primary neoplasm arising in the jaw, or a distant metastasis. This section focuses

primarily on acute osteomyelitis. The remaining lesions are discussed in the section dealing

with lesions having a variable appearance.

Acute Osteomyelitis: Acute osteomyelitis results from either the direct extension of an

acute pulpal infection without the formation of a granuloma or from the acute exacerbation

of a chronic periapical lesion.

In the case of acute periapical abscesses developing in the absence of a pre-existing

periapical lesion, there are often no plain film findings present for the first 7 to 14 days

except for a possible widening of the periodontal space around the root apex or generalized

osteoporosis. Definitive plain film findings usually become evident between 7 and 14 days.

These include ill definition of trabeculae, single or multiple ill-defined radiolucent areas, and

loss of the lamina dura between the lucent lesion and tooth apex. Extension of the infection

into adjacent soft tissues and fascial spaces is common and often the presenting clinical

symptom for which a CT study may be ordered .CT studies on these patients should be

performed with intravenous contrast unless otherwise contraindicated, and images through

the jaw should be obtained using both soft tissue and bone windows. Information gained by

performing studies in this manner can have a definite impact on patient management.

Intravenous contrast is essential in demonstrating the presence of soft tissue abscesses,

whereas images obtained using bone windows may demonstrate a periapical abscess that

might not be apparent on plain films CT findings that may be seen in these patients

include periosteal reactions, myositis, fascitis, cellulitis, abscess formation, and sinus tracts.

Osseous changes that can be seen include localized osseous breakdown resulting from

abscess formation sequestrate & periosteal new bone formation. We have found MR imaging

useful in assessing patients presenting with acute osteomyelitis. On MR imaging

examination inflammatory changes involving both the marrow and soft tissues demonstrate

decreased signal on T1 sequences, intermediate signal intensity on proton density sequen

Chronic Osteomyelitis: Chronic osteomyelitis is a persistent infection of bone, resulting

from either an untreated or inadequately treated acute infection or a long-term low-grade

reaction to a sub-clinical infection. Three forms of chronic osteomyelitis occurring in the jaws

are (1) chronic sclerosing osteomyelitis, (2) chronic suppurative osteomyelitis, and (3)

Garre’s osteomyelitis (chronic osteomyoelitis with proliferative periostitis).

Chronic sclerosing osteomyelitis is an osseo-proliferative response to a low-grade

infection. Focal sclerosing osteomyelitis (condensing osteitis) usually occurs at the apex of a

tooth, and can have a variety of appearances. These include a well-defined area of uniform

opacity, a central opacity with a peripheral lucency; or a central lucency and a peripheral

opacity.

Diffuse sclerosing osteomyelitis is characterized by a generalized proliferation of

bone. Radiogrpahic findings initially consist of ill-defined osteolytic and osteosclerotic

zones. In advanced stages the sclerotic component predominates, resulting in diffuse areas

of sclerosis, poorly demarcated from noninvolved bone.

Chronic suppurative osteomyelitis results from an inadequately treated acute

osteomyelitis or from a low-grade infection that never evoked an acute phase.

The radiographic and CT appearance.

These include a loss of trabeculation a “moth-eaten” appearance representing single

or multiple areas of bone destruction or abscess formation, and foci of increased density

representing dead bone or sequestra that become more apparent as the surrounding bone

becomes osteoporotic. Sclerotic changes often are evident throughout the involved bone

and around the abscess (es) On radionuclide bone scans, areas of involvement demonstrate

intense uptake.

Garre’s osteomyelitis or chronic osteomyelitis with proliferative periostitis is a chronic

form of osteomyelitis occurring primarily in children and young adults. It typically occurs in

the posterior mandible resulting either from periapical abscess, a post extraction infection,

or an infection associated with a partially erupted tooth. Radiographically, one sees ill-

defined intraosseous lesions as well as a distinctive periosteal reaction resulting in onion-

skin reduplication of the cortex.

Nasopalatine Duct (Incisive Canal) Cyst. The nasopalatine duct cyst is the most

common non-dental developmental lesion of the maxilla, and is believed to result from the

spontaneous degeneration and proliferation of remnants of the nasopalatine duct or mucous

cells located within the incisive canal. On panoramic studies, nasopalatine duct cysts often

appear as avoid or “heart-shaped” radiolucencies between the roots of the maxillary central

incisors. Nasopalatine duct cysts are often incidental findings on CT and MR imaging studies

performed for other reasons.

Traumatic Bone Cyst: The traumatic bone cyst is a pseudocyst, lacking a true epithelial

lining. Although it is widely held that traumatic bone cysts result from the breakdown of an

intramedullary hematoma following trauma, conclusive evidence in support of this or any

other mechanism is lacking. On plain film studies, the traumatic bone cyst presents as a

well-defined radiolucent lesion in the posterior mandible, often extending between the roots

of adjacent teeth. Internal scalloping and preservation of the lamina dura are characteristic.

On CT examination, traumatic bone cysts present as low-density lesions, demonstrating

cortical expansion, thinning, and internal scalloping. Extension between the roots of

adjacent teeth with preservation of the lamina dura also can be seen on CT studies.

Central Giant cell granuloma central giant cell granulomas, formerly known as giant cell

reparative granuloma, occur predominantly in children and young adults. These lesions are

of uncertain etiology, and occur most often in the mandible. Mandibular lesions usually occur

in the anterior mandible and often cross the midline .A characteristic feature of this lesion is

its tendency to resorb the root tips of adjacent erupted teeth The radiographic findings

associated with central giant cell granuloma are nonspecific, often consisting of an

irregularly shaped, unilocular radiolucent lesion.

Radiopaque Lesions:

Discrete radiopaque lesions are nearly always benign, often representing an

overgrowth of odontogenic or osseous tissues. These lesions are often incidental findings on

both plain film and CT studies performed for other reasons. Odontogenic radiopacities

include the odontoma and cementoblastoma. Nonodontogenic radiopacities include

osteoma, osteochondroma, torus palatinus, and torus mandibulate.

Odontoma: Odontomas are hamartomas, and the most common odontogenic neoplasm.

Odontomas occur primarily in children and young adults, and are divided into two types

based on radiographic appearance. The compound odontoma appears as an accumulation

of small, fully formed teeth, whereas the complex odontoma appears as an irregular radio

opaque mass learning no resemblance to formed teeth. Odontomas are typically small,

asymptomatic lesions, usually incidentally discovered on routine radiographic examination.

Treatment is surgical excision, and there is a zero recurrence rate.

Cementoblastoma: The cementoblastoma is a benign odontogenic neoplasm derived from

the periodontal ligament. The cementoblastoma typically presents as a well-circumscribed,

radiopaque mass associated with the apex of a root. A radiolucent halo separating the

cemental masses from normal bone is usually present. On occasion, a large maxillary lesion

may extend into the adjacent maxillary sinus.

Osteoma: Osteoma is the most common osseous tumor of the jaws. They are slow-

growing benign tumors occurring most often in the second to fifth decade and almost

exclusively on the skull or in the facial skeleton. Multiple osteomas are associated with

Gardner’s syndrome; an autosomal dominant disorder characterized by multiple osteomas,

colonic adenomatous polyposis, fibromas of the skin, epidermal and trichilemmal cysts, and

impacted permanent and supernumerary teeth.

A radiographic examination should suggest a possible diagnosis of Gardner’s

syndrome. Radiographically, an osteoma normally appears as a small, dense, well-

delineated, radiopaque mass on both plain and CT studies.

Torus: A torus is a benign, reactive hyperplasia of osseous tissue extending outward from

the surface of the bone. Tori are named according to location. The torus palatinus occurs in

the midline of the hard palate in approximately 20% of the population, and is the most

common type of torus. On routine plain film studies, small tori palatini are often not well

demonstrated due to overlying bony structures; however, small asymptomatic lesions are

often incidentally encountered on CT studies performed for other reasons. Tori palatini on

CT studies present as nodular midline osseous protuberances of varying sizes.

Tori mandibulari are exophytic, usually bilateral lesions occurring on the lingual

surface of the mandible. Tori mandibulari occur in approximately 8% of the population and

are usually of little, if any, significance. Large tori, however, may interfere with tongue

movement or mastication. On frontal views of the mandible (Waters and Caldwell views), tori

appear as dense, exophytic lesions arising on the medial aspect of the anterior mandible,

whereas on lateral views mandibular tori appear as radiopacities superimposed over the

roots of the mandibular premolars. Tori mandibulari on axial CT sections present as osseous

protuberances on the medial aspect of the anterior mandible. CT, with three-dimensional

reconstruction if possible, can be useful in the preoperative evaluation of large tori involving

both the palate and mandible by demonstrating the full extent of the lesion, as well as the

point of attachment between the torus and adjacent palate or mandible.