THE DIAGNOSTIC IMAGING OF JAW LESIONS Radiologists are often called upon to perform a variety of imaging studies on themaxilla and mandible. Indications for these studies include evaluation of a known orsuspected jaw lesion, evaluation of a dental arch for dental implant placement, and theassessment of the temporomandibular joint (TMJ) in a patient presenting with chronic facialpain.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 occuron occasion via a number of different pathways. These include the direct extension of aneoplastic 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 andmargination on plain film studies. Jaw lesions can be described as having either aradiolucent radiopaque, or mixed appearance relative to the density of adjacent bone. Themajority of jaw lesions is radiolucent (> 80%), and includes a number of odontogenic andnonodontogenic lesions. Lucent cystic lesions may exhibit internal septae resulting in amulticystic or multiloculated appearance. Radiopaque lesions exhibit increased radiographicdensity 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. Amixed appearance can result from the presence of two or more tissues of normally differentradiographic densities, variation in the degree of maturation of a single or multiple tissueswithin the lesion. Another important criterion used in evaluating a jaw lesion is its margination. Jawlesions can be either well circumscribed (defined) or poorly circumscribed. Well-circumscribed lesions are usually benign, whereas poorly circumscribed lesions invariablyrepresent aggressive inflammatory or neoplastic processes. Involvement of a segment of ajaw by a poorly circumscribed or infiltrating radiolucent lesions may result in a permeativeof “moth eaten” appearance. Other important parameters that should be taken into account in arriving at adiagnosis or in formulating a differential diagnosis include anatomic location, relationship tothe cortex, and associated periosteal and soft tissue changes. In assessing a jaw lesion, itis 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 isimportant to remember that certain lesions occur exclusively in one area or site, whereasother lesions have no specific predilection. In addition, a number of other lesions can occuranywhere 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 thebone around two or more teeth, whereas odontogenic lesions typically involve only onetooth or a specific part of a tooth. If a lesion involves only one tooth, it is important to notethe 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 associatedwith the congenital or surgical absence of a tooth. The lesion’s relationship to the cortex should also be noted. Signs of corticalexpansion, destruction, or breakthrough should be looked for as well as evidence ofperiosteal or soft tissue involvement. Slow growing lesions often cause cortical bowing andpressure resorption with minimal if any periosteal or soft tissue involvement. Aggressiveinflammatory and neoplastic lesions often cause cortical destruction or breakthrough, whichmay 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 nonodontogeniclesions. The following sections examine a number of commonly encountered jaw lesionspresenting with each of these patterns.Well – Circumscribed Radiolucent Lesions: A number of odontogenic and nonodontogenic lesions can present as wellcircumscribed radiolucent lesions. Odontogenic lesions include periapical lesions,dentigerous cysts, odontogenic keratocysts, cysts of the globullomaxillary region, andameloblalstomas. 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 dentallamina or cells of the periodontal membrane. Odontogenic lesions presenting as well-
circumscribed radiolucent lesions include periapical lesions, dentigerous cysts, odoontogenickeratocysts, cysts of the globullomaxillary region, and ameloblastomas.Periapical Lesion: Periapical lesions include both the dental granuloma and the periapicalcyst. The earliest radiographic sign of a developing periapical lesion is widening of theperiodontal space around the apex of the tooth. As the lesion evolves and enlarges,osteolysis occurs resulting in a well – circumscribed, unilocular, radiolucent lesion aroundthe root apex. Lesions less than 1 cm in diameter is usually granuloma, whereas lesionsgreater than 1 cm are usually periapical cysts. Infected periapical lesions initially areradiographically indistinguishable from sterile lesions. Advanced lesions, however, maydemonstrate 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 toothassociated with periapical lesion is a key in making the diagnosis. On CT studies, a sterile periapical lesion presents as a well-defined low-density areaaround the apex (ices) of an involved tooth. Infected cysts may exhibit corticalbreakthrough and extension of the inflammatory process into the adjacent soft tissues.Radionuclide bone scans demonstrate discrete foci of increased uptake around the roots ofinvolved teeth. Uncomplicated periapical cysts on MR imaging studies demonstrate low tointermediate signal intensity on T1-weighted, intermediate signal intensity on proton densityon T2-weighted images.Dentigerous (Follicular Cyst.) The dentigerous or follicular cyst is the second mostcommon odontogenic cyst, resulting from the cystic degeneration of the enamel organ afterfull 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 crownOpacification and bowing of the walls of maxillary sinus can be seen in lesions involving themaxillary sinus. On CT studies and reformatted three-dimensional images, dentigerous cysts presentas expansile, low-density lesions associated with a full or partially formed unerupted crownor tooth. Cortical bowing and pressure resorption are well demonstrated on CT Associatedperiosteal and soft tissue reactions are absent. Direct coronal CT images are important inassessing 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 tointermediate signal intensity on T1and high signal intensity on T2- weighted images,whereas the crown appears devoid of signal intensity on all sequences. Dentigerous cystOdontogenic Keratocyst: Odontogenic Keratocyst is a relatively common developmentalodontogenic cyst constituting approximately 10% to 12% of all developmental odontogeniccysts. Approximately three quarters of all odontogenic keratocysts occur in the mandible,usually in the posterior body and ramus. Maxillary odontogenic keratocysts occur primarilyin the cuspid region. Odontogenic keratocysts can present as either single or multiplelesions. Multiple lesions are associated with the nevoid basal cell carcinoma syndrome(Gorlin’s syndrome). Components of this syndrome include multiple odontogenickeratocysts, early appearing basal cell carcinomas of the skin, skeletal developmentalanomalies, dyskeratotic pitting of the hands and feet, dural calcification, and ectopic softtissue calcification. Odontogenic keratocysts present on plain films as well circumscirbed and often wellcorticated radiolucent. Smaller odontogenic keratocysts, typically present as unilocularlesions, whereas larger lesions often exhibit a multilocular appearance. They can haveadditional radiographic or clinical features that may simulate or suggest other odontogeniclesions. These include small, well-corticated, radiolucent lesions associated with the absenceof a tooth (primodial cyst); radiolucent lesions associated with a tooth and indistinguishablefrom a dentigerous cyst (25% to 40% of cases); or as radiolucent lesions indistinguishablefrom either unicystic or multicystic ameloblastoma. A feature of many odontogenickeratocysts that can be useful in differentiating them from other lesions is the tendency forthem to grow within the medulary space in a predominantly anteroposterior direction while
causing minimal if any cortical expansion. Maxillary odontogenic keratocysts can extend intothe maxillary sinus, and present as a soft tissue density indistinguishable from a mucusretention cyst on plain film studies. CT can be helpful in assessing these intra sinus lesionsfrom uncomplicated mucus retention cysts. On CT examination, we have found odontogenickeratocysts to have higher CT numbers than uncomplicated retention cysts, and to causelocalized bowing of the sinus wall. On MR imaging studies, odontogenic keratocysts typicallydemonstrate low to intermediate signal intensity on T1 sequences, intermediate signalintensity on proton density sequences, and high signal intensity on T 2 sequences As a resultof the different radiographic appearances an odontogenic keratocyst can have, they shouldalways be considered in the differential diagnosis of cystic lesions of the jaw. Odontogenic keratocystCysts of the Globulomaxillary Region: The term globulomaxillary is used to denote thearea of fusion between the embryonic globular process of the median nasal process and themaxillary process. This region corresponds to the area between the maxillary lateral incisorand cuspid. Odontogenic cysts that can present with radiographic findings suggestive of theclassic globulomaxillary cyst include periapical cysts, odontogenic keratocysts, and lateralperiodontal cysts. In light of the histologic diversity of lesions presenting with similarradiographic findings in this area, it is more appropriate to refer to these lesions as cysts ofthe globulomaxillary region.
Radiographically, these lesions present as well circumscribed, often inverted pear-shaped, radiolucencies between the maxillary lateral incisor and cuspid. Large lesions canhave significant palatal extensions and are best appreciated on intraoral dental occlusalplain 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 lesionsbetween the lateral incisor and cuspid.Ameloblastoma: The ameloblastoma is the most common clinically significant odontogenictumor, constituting 1% of all tumors and cysts of the jaws, and approximately 11% of allodontogenic tumors Ameloblastomas arise from either the surface epithelium or remnants ofthe dental lamina, or from pluripotential epithelial cells lining dentigerous cysts. Approximately 80% of all ameloblalstomas occur in the mandible, with the ascendingramus and proximal body being the most common sites. Maxillary ameloblastomas occurmost 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 ofmulticystic 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 usuallypronounced buccal-lingual cortical expansion as well as the presence of internal osseousseptae between the low-density solid and cystic elements on plain film studies it isimpossible to differentiate between the solid and cystic elements of the tumor. Unicystic ameloblastomas are grossly cystic, and account for approximately 15% to20% of all ameloblalstomas. Radiographically, the unicystic ameloblalstoma presents as a well-circumscribed,unicystic, radiolulcent lesion, occurring most often in the mandibular molar region. On CTstudies both the unicystic and multicystic ameloblastomas present as well-circumscribedlow-density lesions. Cortical expansion with cortical pressure resorption is usually present inlarger lesions Associated periosteal and soft tissue reactions are absent. Multicystic lesionsalso demonstrate the presence of internal osseous septae. MR imaging, as a result of its greater soft tissue resolution, can provide importantpreoperative evaluation of a multicystic ameloblastoma. This information includesdifferentiating 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 ofsurgical resection. On T1-weighted images both solid and cystic components are usually oflow signal intensity. Areas of high signal intensity on T1 sequences usually denote thepresence of highly proteinaceous cystic fluids. Solid components, including soft tissueslining cyst walls, exhibit a homogeneous appearance on T1 sequences and significantenhancement following gadolinium administration. On T2 sequences solid tissuesdemonstrate low signal intensity, where as cystic areas demonstrate high signal intensityPostoperatively, MR imaging can demonstrate the presence of early recurrences, whichtypically exhibit high signal intensity on T2-weighted images. Ameloblastoma of the mandibleNonodontogenic LesionsNasopalatine Duct (Incisive Canal) Cyst. The incisive canal is located in the anteriorpalatal midline, extending between the nasal fossa and incisive foramen. Located within theincisive canal are remnants of the embryonic nasopalatine duct. The nasopalatine duct cystis the most common non-dental developmental lesion of the maxilla, and is believed toresult from the spontaneous degeneration and proliferation of remnants of the nasopalatineduct 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 themaxillary central incisors. Nasopalatine duct cysts are often incidental findings on CT andMR imaging studies performed for other reasons. On CT studies, there is focal or diffuse enlargement of the nasopalatine canal. OnMR imaging studies nasopalatine duct cysts demonstrate low signal intensity on T1- andhigh signal intensity on T2 weighted sequences.Traumatic Bone Cyst: The traumatic bone cyst is a pseudocyst, lacking a true epitheliallining. Although it is widely held that traumatic bone cysts result from the breakdown of anintramedullary hematoma following trauma, conclusive evidence in support of this or anyother mechanism is lacking. On plain film studies, the traumatic bone cyst presents as awell-defined radiolucent lesion in the posterior mandible, often extending between the rootsof adjacent teeth. Internal scalloping and preservation of the lamina dura arecharacteristic. On CT examination, traumatic bone cysts present as low-density lesions,demonstrating cortical expansion, thinning, and internal scalloping. Extension between theroots 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 froma localized vascular reactive process resulting in vascular proliferation and localizedosteolysis. Radiographically, aneurismal bone cysts present as a nonspecific, expansile,unilocular Radiolucency. Occasionally, aneurismal bone cysts may present as multilocularradiolucencies with slightly irregular internal margins.Central Giant cell granuloma central giant cell granulomas, formerly known as giant cellreparative granuloma, occur predominantly in children and young adults. These lesions areof uncertain etiology, and occur most often in the mandible. Mandibular lesions usually occurin the anterior mandible and often cross the midline .A characteristic feature of this lesion isits tendency to resorb the root tips of adjacent erupted teeth The radiographic findingsassociated with central giant cell granuloma are nonspecific, often consisting of anirregularly shaped, unilocular radiolucent lesion.Some lesions may present with a multilocular appearances. The lesions are usually welldelineated. Radiographically, smaller unilocular lesions may simulate periapical lesions,whereas larger multilocular lesions may simulate ameloblastomas or other multilocularlesions.
Poorly Circumscribed Radiolucent Lesions: Ill-defined radiolucent lesions can resultfrom acute osteomyelitis, the direct extension of a neoplasm arising in tissues bordering thejaw, a primary neoplasm arising in the jaw, or a distant metastasis. This section focusesprimarily on acute osteomyelitis. The remaining lesions are discussed in the section dealingwith lesions having a variable appearance.Acute Osteomyelitis: Acute osteomyelitis results from either the direct extension of anacute pulpal infection without the formation of a granuloma or from the acute exacerbationof a chronic periapical lesion. In the case of acute periapical abscesses developing in the absence of a pre-existingperiapical lesion, there are often no plain film findings present for the first 7 to 14 daysexcept for a possible widening of the periodontal space around the root apex or generalizedosteoporosis. 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, andloss of the lamina dura between the lucent lesion and tooth apex. Extension of the infectioninto adjacent soft tissues and fascial spaces is common and often the presenting clinicalsymptom for which a CT study may be ordered .CT studies on these patients should beperformed with intravenous contrast unless otherwise contraindicated, and images throughthe jaw should be obtained using both soft tissue and bone windows. Information gained byperforming 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 thatmight not be apparent on plain films CT findings that may be seen in these patientsinclude periosteal reactions, myositis, fascitis, cellulitis, abscess formation, and sinus tracts.Osseous changes that can be seen include localized osseous breakdown resulting fromabscess formation sequestrate & periosteal new bone formation. We have found MR imaginguseful in assessing patients presenting with acute osteomyelitis. On MR imagingexamination inflammatory changes involving both the marrow and soft tissues demonstrate
decreased signal on T1 sequences, intermediate signal intensity on proton density sequenChronic Osteomyelitis: Chronic osteomyelitis is a persistent infection of bone, resultingfrom either an untreated or inadequately treated acute infection or a long-term low-gradereaction to a sub-clinical infection. Three forms of chronic osteomyelitis occurring in thejaws 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-gradeinfection. Focal sclerosing osteomyelitis (condensing osteitis) usually occurs at the apex ofa tooth, and can have a variety of appearances. These include a well-defined area ofuniform opacity, a central opacity with a peripheral lucency; or a central lucency and aperipheral opacity. Diffuse sclerosing osteomyelitis is characterized by a generalized proliferation ofbone. Radiogrpahic findings initially consist of ill-defined osteolytic and osteoscleroticzones. In advanced stages the sclerotic component predominates, resulting in diffuse areasof sclerosis, poorly demarcated from noninvolved bone. Chronic suppurative osteomyelitis results from an inadequately treated acuteosteomyelitis 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 singleor multiple areas of bone destruction or abscess formation, and foci of increased densityrepresenting dead bone or sequestra that become more apparent as the surrounding bone
becomes osteoporotic. Sclerotic changes often are evident throughout the involved boneand around the abscess (es) On radionuclide bone scans, areas of involvement demonstrateintense uptake. Garre’s osteomyelitis or chronic osteomyelitis with proliferative periostitis is a chronicform of osteomyelitis occurring primarily in children and young adults. It typically occurs inthe 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 mostcommon non-dental developmental lesion of the maxilla, and is believed to result from thespontaneous degeneration and proliferation of remnants of the nasopalatine duct or mucouscells located within the incisive canal. On panoramic studies, nasopalatine duct cysts oftenappear as avoid or “heart-shaped” radiolucencies between the roots of the maxillary centralincisors. Nasopalatine duct cysts are often incidental findings on CT and MR imaging studiesperformed for other reasons.
Traumatic Bone Cyst: The traumatic bone cyst is a pseudocyst, lacking a true epitheliallining. Although it is widely held that traumatic bone cysts result from the breakdown of anintramedullary hematoma following trauma, conclusive evidence in support of this or anyother mechanism is lacking. On plain film studies, the traumatic bone cyst presents as awell-defined radiolucent lesion in the posterior mandible, often extending between the rootsof adjacent teeth. Internal scalloping and preservation of the lamina dura arecharacteristic. On CT examination, traumatic bone cysts present as low-density lesions,demonstrating cortical expansion, thinning, and internal scalloping. Extension between theroots 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 cellreparative granuloma, occur predominantly in children and young adults. These lesions areof uncertain etiology, and occur most often in the mandible. Mandibular lesions usually occurin the anterior mandible and often cross the midline .A characteristic feature of this lesion isits tendency to resorb the root tips of adjacent erupted teeth The radiographic findingsassociated with central giant cell granuloma are nonspecific, often consisting of anirregularly shaped, unilocular radiolucent lesion.Radiopaque Lesions: Discrete radiopaque lesions are nearly always benign, often representing anovergrowth of odontogenic or osseous tissues. These lesions are often incidental findingson both plain film and CT studies performed for other reasons. Odontogenic radiopacitiesinclude the odontoma and cementoblastoma. Nonodontogenic radiopacities includeosteoma, 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 typesbased on radiographic appearance. The compound odontoma appears as an accumulationof small, fully formed teeth, whereas the complex odontoma appears as an irregular radioopaque 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 fromthe periodontal ligament. The cementoblastoma typically presents as a well-circumscribed,radiopaque mass associated with the apex of a root. A radiolucent halo separating thecemental masses from normal bone is usually present. On occasion, a large maxillary lesionmay 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 almostexclusively on the skull or in the facial skeleton. Multiple osteomas are associated withGardner’s syndrome; an autosomal dominant disorder characterized by multiple osteomas,colonic adenomatous polyposis, fibromas of the skin, epidermal and trichilemmal cysts, andimpacted permanent and supernumerary teeth. A radiographic examination should suggest a possible diagnosis of Gardner’ssyndrome. 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 fromthe surface of the bone. Tori are named according to location. The torus palatinus occursin the midline of the hard palate in approximately 20% of the population, and is the mostcommon type of torus. On routine plain film studies, small tori palatini are often not welldemonstrated due to overlying bony structures; however, small asymptomatic lesions areoften incidentally encountered on CT studies performed for other reasons. Tori palatini onCT studies present as nodular midline osseous protuberances of varying sizes. Tori mandibulari are exophytic, usually bilateral lesions occurring on the lingualsurface of the mandible. Tori mandibulari occur in approximately 8% of the population andare usually of little, if any, significance. Large tori, however, may interfere with tonguemovement 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 superimposedover the roots of the mandibular premolars. Tori mandibulari on axial CT sections presentas 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 largetori involving both the palate and mandible by demonstrating the full extent of the lesion, aswell as the point of attachment between the torus and adjacent palate or mandible.