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Normal and Pathologic CT Anatomy of the Mandible
Abstract
The value of computed tomography (CT) in the diagnosis and management of a wide variety of facial lesions has been amply demonstrated. While a number of studies have focused on CT anatomy of the paranasal sinuses, nose, and nasopharynx, none has concentrated on the mandible. Although the mandible is difficult to image because of its complex, curving surfaces and the presence of artifact-producing amalgam fillings or restorations, CT of the mandible can nevertheless be highly informative in selected cases. This pictorial essay depicts normal gross and CT anatomy of the mandible and presents a series of cases that illustrate the utility of CT in examining mandibular lesions.
... Mandibular CT scans are obtained somewhat obliquely because the mandible has irregular contours; the gantry angle (+15 to +20) at the orbitomeatal line is important in CTs of the oral cavity and oropharynx to avoid dental artifacts and for improved visualization 6 ( Fig. 3A-G). ...
Introduction
There are few text resources to guide the otolaryngology resident systematically through the interpretation of Head and Neck CT Images. The residents struggle with the interpretation of CT Images. Our aim was to develop a comprehensive algorithmic technique for interpreting computerized tomography (CT) images of the head and neck using anatomic details and related CT images.
Methods
A prospective observational study conducted in an academic hospital.
Thorough literature search for descriptive articles regarding head and neck CT highlighted deficits in existing interpretation techniques. Systemic interpretation algorithm was constructed and used as a learning tool (lecture) for the junior Otorhinolaryngology and Head & Neck Surgery (ORL HNS) residents group of the Saudi Board. Questionnaire was formulated that emphasized the steps and skills involved in the interpretation of head and neck CT by investigating radiological and clinical anatomy in the CT images. The questionnaire was answered by the group of junior residents and by a group of senior residents and consultants (except for head and neck consultants).
Results
The results were analyzed and compared for both groups, revealing a higher score in the junior (algorithm) group compared with the other group.
Discussion
This structured comprehensive algorithm for the interpretation of head and neck CT scans is an effective and reliable reference tool that may enhance and refine ORL HNS resident training and knowledge.
... The practice of stripping the periosteum from the mandible at the site of tumor, before deciding between marginal and segmental mandibulectomy, is not recommended--it violates the fundamental principle of monobloc resection of cancer (which requires adequate threedimensional margins) and the risk of local failure by seeding or cutting through tumor (9). ...
Introduction
Marginal mandibulectomy (MM) is indicated for oral cavity squamous cell carcinomas (OCSCC) that abut or minimally erode the mandible without gross invasion. Successful implementation of MM is predicated on accurate patient selection and appropriate adjuvant treatment based on well-known host and tumor characteristics. The incidence of microscopically diagnosed bone involvement in MM specimens and its implications on outcomes have however not been reported in large contemporary series.
Purpose
To report the incidence of bone involvement and analyze its influence on oncologic outcomes in selected patients who underwent MM in treatment of OCSCC.
Method
A retrospective cohort study was performed on a consecutive series of previously untreated patients requiring MM, at a tertiary care cancer center, between 1985 and 2012 (n = 326). The median age was 64 years and 59% were male. The majority of patients (67%) had a primary tumor of the floor of the mouth or lower alveolus, 80% were clinically staged T1-2, and 31% were clinically N+. Postoperative radiation (PORT) was used in 27% and chemoradiation (POCTRT) in 8% of patients who had microscopic bone invasion. The median follow up period was 55 months and endpoints of interest were local and regional recurrence free (LRFS and RRFS) and disease specific (DSS) survival.
Results
Microscopic bone invasion was present in 15% of patients (n = 49). Among these, cortical invasion was present in 32, medullary in 13, and it was not specified in 4. Eight patients had microscopic positive bone margins. Positive bone margins were associated with medullary bone involvement (p < 0.001), floor of mouth and buccal mucosa primary site (p = 0.03), and positive soft tissue margins (p = 0.06). LRFS and DSS were similar in patients without versus with bone invasion (62.8% vs 79.7% and 76.2% vs 66% respectively, p = NS). LRFS were similar in patients with microscopic positive versus negative bone margins, as long as postoperative adjuvant treatment was administered.
Conclusion
Microscopic bone involvement does not adversely influence outcomes but medullary bone involvement does confer a higher risk of positive bone margins. MM and appropriate adjuvant treatment is an effective strategy for treatment of OCSCC in selected patients with primary tumors adherent to or in proximity to the mandible.
... Again in the case of osteosarcoma, unlike the radiographic findings, a "sunray" appearance with respect to the buccal and lingual cortex could be appreciated on the Dentascan images which envisaged its diagnosis. [18][19][20] ...
Background: Dental radiology has long played an exciting and critical diagnostic role in dentistry. The development of novel imaging modalities like computed tomography (CT) and magnetic resonance imaging (MRI) has revolutionized dental and medical diagnosis. However the role of conventional radiography in dentistry remains unparalleled. The current study was undertaken to evaluate the effectiveness of dental CT software compared to panoramic radiography in evaluation of the jaw lesions. Methods: Twenty cases of maxillary and mandibular jaw lesions were examined radiographically by digital panoramic radiography orthopantomography (OPG) and dental CT software. The radiographic images obtained with these two examination modalities were compared for visualization of antero-posterior extent of the lesion, dimension of the lesion, cortical bone involvement, tooth displacement, root resorption, involvement of the maxillary sinus, delineation of the neurovascular canal, presence or absence of calcification, imaging diagnosis of the lesion (cystic/solid). Results: The dental CT program rated significantly (P<0.001) higher in all points examined than the panoramic radiography. The dental CT program was found to be superior for detecting cortical bone involvement (P<0.02) and delineation of the mandibular canal (P<0.02) to the conventional CT program. Conclusions: Dentascan offers better characterization of the pathologic processes due to its ability to differentiate between different tissue types based on their Hounsfield units. Hence it can define the contents of the pathology as cystic or solid and thus predict the diagnosis of the lesion.
A prospective cross-sectional study was conducted to correlate clinically, radiologically, and pathologically the mandibular invasion in carcinoma bucco-alveolar complex. All biopsy-proven oral cavity cancer cases (64 patients) were assessed clinically and radiologically for involvement of the mandible. Preoperative clinicoradiological findings were compared with postoperative histopathological findings. In our study, oral cancer was 4 times more prevalent in males as compared to females and clinical evaluation was found to be highly sensitive in predicting mandibular invasion. Orthopantomogram showed sensitivity of 66.6% and specificity of 100%. CT scan showed sensitivity of 100% and specificity of 46% whereas MRI showed sensitivity of 54.5% and a specificity of 96%. MRI correlates well with final histopathology in predicting size of tumor. Prevalence of bony invasion in carcinoma oral cavity was 18%. We noted an inverse relation with tumor differentiation and mandibular invasion, and none of the verrucous carcinoma lesions showed mandibular invasion. Association of clinical T and N staging with postoperative histopathology was found to be statistically significant. Despite recent advances in molecular biology, radiological techniques, and newer modalities like visual surgical planning, exact measurement of bone invasion is still challenging. At present, CT scan and MRI along with clinical evaluation are widely used to evaluate mandibular invasion in carcinoma oral cavity, and all these are complementary to each other. The recent progress in tissue engineering technologies and stem cell biology has significantly promoted the development of regenerative reconstruction of jawbone defects.
The radiologic evaluation of head and neck neoplasms constitutes an important part in their diagnosis and treatment. The introduction of computerized tomography (CT) and the further development of this modality since 1972 have contributed significantly to the staging of these neoplasms. CT not only demonstrates soft-tissue densities, but also bony structures, muscles, facial planes, opacified vascular structures, and enlarged lymph nodes. CT, however, fails to differentiate the various histologic types of lesions in the majority of cases. Features such as size of the lesion, marginal definition, lytic bone destruction, sclerotic bony reaction, bony expansion, calcific densities, fat content, and obliteration of facial planes are utilized to delimit the spectrum of diagnostic possibilities.
MRI and CT are complementary modalities; neither is indisputably superior under all anatomic, pathologic, and clinical circumstances. MRI is the modality of choice for most malignant conditions relating to the jaw. MRI is able to detect subtle soft tissue lesions and to establish accurately cortical bone invasion, despite an apparent intact appearance on CT. The unparalleled visualization of bone marrow and the precise determination of perineural tumor spread are unique features of this modality. CT will continue as the most important modality to detect subtle calcifications and bone detail, for the foreseeable future. Ideally, all patients with malignant jaw disease should be evaluated by both CT and MRI.
The ultimate application of MRI and CT to malignant disease of the jaw will depend largely on logistic factors such as availability and cost as well as the experience of the radiologist and the familiarity of the clinician with the respective modalities. The future belongs to MRI.
Imaging is a crucial diagnostic tool in the assessment of acute and chronic osteomyelitis of the jaws. Before any cross-sectional imaging modality is applied, the orthopanoramic view is the first image to assess the status of dentition, recognize direct radiographic signs of osteomyelitis, narrow the differential diagnosis, and depict potential predisposing conditions such as a fracture or systemic bone disease. The orthopanoramic view is furthermore the first-line image when follow-up examinations are performed. In acute osteomyelitis the higher sensitivity of magnetic resonance imaging (MRI), with respect to detection of intramedullary inflammation, advocates its use as the imaging modality of choice to confirm the diagnosis and provide an estimate of the intraosseous extent and soft tissue involvement. In case surgical treatment is planned, high-resolution computed tomography (CT) is required to specify the degree of cortical destruction, delineate the presence of sequestra, and to define the extent of osseous removal required. In chronic osteomyelitis the higher sensitivity of CT with respect to detection of sequester and sclerotic bone changes renders CT the examination of choice to distinguish the usually more uniform and extensive primary chronic osteomyelitis from the more localized type of secondary chronic osteomyelitis. Magnetic resonance imaging is superior to detect periosteal inflammation and soft tissue involvement and thus aids in determining the persistence or recurrence of infection. Following surgery, CT is preferred as follow-up examination for a period of 6 months to distinguish postoperative and reparative changes from recurrent or persistent infection. Complimentary information is gained in particular situations by a combination of imaging modalities adapted to the individual patient’s course of disease and the panoramic view findings. An overview of the diagnostic imaging pathway in patients with suspected osteomyelitis of the jaws is given in Fig. 3.1.
Malignant tumours of the maxillary sinus and benign conditions including fibro-osseus dysplasia, mucocele, and different odontogenic cystic lesions may present with expansile maxillary masses. Odontogenic keratocystis in the maxilla is relatively rare and invasion of the maxillary sinus unusual. We describe a patient with odontogenic keratocyst of the maxillary sinus.
Differential diagnosis with expanding intrasinusal cyst can be assessed on the basis of CT findings: upward displacement of the inferior floor of the maxillary sinus is a peculiar finding in extrasinusal masses: as a consequence, the size of maxillary sinus is reduced, mimicking antral hypoplasia. The superiorly displaced maxillary sinus floor should not be misinterpreted as the calcified wall of an intrasinusal mucocele.
MRI is valuable in demonstrating the relation between the odontogenic keratocyst and surrounding structures. However, as the cyst may show high signal intensity on T1-weighted scans because of its contents (epithelial debris, blood degradation products), differential diagnosis of extrasinusal masses involving the sinus and intrasinusal mucocele may be difficult.
Although computerized tomography (CT) is valuable for evaluating head and neck pathology, it can be suboptimal when evaluating the presence or extent of mandibular and maxillary involvement by tumor, infection, or other pathology. The presence of dental restoration artifact, CT gantry positioning problems, and the inability to obtain cross-sectional images will diminish the accuracy of standard CT images.
A program, termed either DentaScan™ or multiplanar reformation (CT/MPR), eliminates these problems by processing axial CT scan information to obtain true cross-sectional images and panoramic views of the mandible and maxilla.
In this study, DentaScan imagery was used in 26 patients whose mandibles or maxillas were affected by tumor, osteomyelitis, or other pathology. CT scanning with multiplanar reformation proved useful in the precise location, assessment, monitoring, and treatment of various pathologies of the mandible and maxilla. Selected case studies illustrate the therapeutic implications and advantages of this new imaging technique.
To evaluate the mandibular canal using volume interpolated breath-hold examination (VIBE) sequencing in patients with cysts and tumors of the mandible.
Twenty-five patients with mandibular cysts and tumors were recruited for a study in the authors' institution to compare the role of multidetector row computed tomography with magnetic resonance imaging (MRI) in jaw lesions. Of these 25 patients, VIBE was performed in 12 patients (age range, 16 to 52 yrs; 11 male and 1 female patients) and formed the study group. The status (normal/destroyed/attenuated) and position of the inferior alveolar canal (normal/displaced) on panoramic reconstructed computed tomographic (CT) images and curved multiplanar reformatted (MPR) images reconstructed from VIBE images were analyzed. The contralateral normal mandibular canal was used as the control in these patients.
In all 12 patients, the inferior alveolar canal on the normal side was visualized as a hyperintense structure in relation to the hypointense bone on the curved MPR VIBE images. In 9 patients, the inferior alveolar canal was equally well visualized on panoramic CT and curved MPR VIBE images. In 2 patients, the inferior alveolar canal was better visualized on curved MPR VIBE images; in 1 patient, the course of the mandibular canal was better seen on panoramic CT images.
MR reconstructions with VIBE sequencing as source images provide images comparable to CT reconstructed images for evaluation of the mandibular canal. Three-dimensional (3D) VIBE sequencing can be added to the MR protocol to visualize the inferior alveolar neurovascular bundle. 3D VIBE sequencing increases the diagnostic capabilities of MRI when used to image mandibular cysts and tumors.
Although computerized tomography (CT) is valuable for evaluating head and neck pathology, it can be suboptimal when evaluating the presence or extent of mandibular and maxillary involvement by tumor, infection, or other pathology. The presence of dental restoration artifact, CT gantry positioning problems, and the inability to obtain cross-sectional images will diminish the accuracy of standard CT images. A program, termed either DentaScan or multiplanar reformation (CT/MPR), eliminates these problems by processing axial CT scan information to obtain true cross-sectional images and panoramic views of the mandible and maxilla. In this study, DentaScan imagery was used in 26 patients whose mandibles or maxillas were affected by tumor, osteomyelitis, or other pathology. CT scanning with multiplanar reformation proved useful in the precise location, assessment, monitoring, and treatment of various pathologies of the mandible and maxilla. Selected case studies illustrate the therapeutic implications and advantages of this new imaging technique.
Following radiation treatment, ablative surgery, and surgical flap reconstruction in cases of oral cancer, postoperative follow-up for oral cancer recurrence presents a difficult task. Computed tomography (CT) remains the most accessible method of postoperative assessment; however, it has yet to be conclusively shown to provide an advantage over an adequate history and physical examination. Twenty-four consecutive patients who had undergone flap reconstruction of the oral cavity for advanced or radiorecurrent disease were studied over an 18-month period. Eight patients showed no evidence of recurrent tumor either clinically or by CT scan. Eleven patients had evidence of recurrent disease clinically, which was confirmed by CT. In four patients, clinically unsuspected regional recurrent tumor was revealed by CT. One false negative scan was encountered. CT proved to be a sensitive modality for detecting clinically unsuspected recurrences, particularly regional recurrences.
Eleven of 57 tumours and cysts (19 per cent) seen at two major centres over a 4-year period were ameloblastomas, primary in eight and recurrent in three. Computed Tomography (CT) was the most sensitive imaging technique for detecting ameloblastomas. The radiological features were distinctive maxillary and mandibular pathology in primary cases and soft-tissue, maxillary sinus and asymmetrical deep tissue involvement in both primary and recurrent ameloblastomas. Following surgery and pathological confirmation, serial scans were combined with periodic clinical re-evaluation. We identified clinically occult recurrences in two cases and confirmed a clinically-suspected recurrence in one on the basis of the CT findings. Our protocol appears efficacious and is suggested for the necessary long-term follow-up in all pathologically verified ameloblastomas.
A case of chondrosarcoma of the maxilla with axial and coronal computed tomography is presented. The value of this new modality over conventional radiographs is discussed. A cartilagenous malignancy was suggested by a soft tissue mass with calcification. In addition there was lysis and osteoblastic bony reaction. Tumour extension into neighbouring structures is excellently demonstrated.
Due to the anatomical relationship of the jaws to the infratemporal fossa this area is readily involved in pathological processes of the jaw. Conventional radiographs play a limited role in demonstrating this region. A variety of primary diseases of the jaws, namely hereditary, developmental, infective, benign and malignant tumours with extension into the infratemporal fossa, are presented. Computed tomography is an excellent method for showing both osseous and soft-tissue components which include bony destruction, new bone formation, soft tissue calcification, inflammatory and malignant processes affecting the muscles and fat in the infratemporal fossa.
Over a period of 3 years, 18 patients with mandibular osteomyelitis were prospectively investigated by conventional radiograph, computed tomography (CT) and in 6 cases by magnetic resonance imaging (MRI). The diagnosis was based on histology in 17 patients operated upon.
Before application of any cross-sectional imaging modality, the orthopanoramic view is indispensable in assessing the status of dentition, in recognizing direct radiographic signs of osteomyelitis, or in determining the presence of predisposing conditions such as a fracture or systemic bone disease. The orthopanoramic view is the procedure of choice in follow-up examinations in patients who have osteomyelitis. In acute osteomyelitis, the higher sensitivity of MR imaging for detection of intramedullary inflammation advocates this imaging modality for confirmation of the clinical diagnosis. If surgical treatment is planned, high-resolution CT is required to specify the degree of cortical destruction, the presence of sequestra in particular, and to define the extent of osseous removal required. In chronic osteomyelitis, the higher sensitivity of MR imaging to detect periosteal inflammation and soft tissue involvement advocates this modality to reveal the presence, location, and extent of chronic inflammation. The assessment of persistence or recurrence of chronic inflammation after surgical treatment is by high-resolution CT for the first 6 months following surgery. Finally, scintigraphy is recommended when multi-focal systemic disease is suspected, such as in CRMO and SAPHO syndrome.
The role of plain skull radiography and pluridirectional tomography in determining anterior cranial fossa extension of paranasal sinus tumors is reassessed. The lateral wall of the olfactory fossa, a thin bony plate forming part of the roof of the ethmoid sinuses, is routinely visualized on plain skull radiography and pluridirectional tomography in the coronal plane and serves as an indicator of intracranial tumor extension. In a series of 47 patients with paranasal sinus tumors, 100% true positive and 3% false negative interpretations of the integrity of the lateral wall of the olfactory fossa were made with pluridirectional tomography. Interpretations with plain skull radiography were 90% true positive and 3% false negative. Assessment of the integrity of the lateral wall of the olfactory fossa by these techniques provides an accurate evaluation of the presence of intracranial tumor extension by this route. Computed tomography in the coronal plane with contrast infusion is a useful adjunct.
The physical characteristics of the fascial planes of the nasopharynx provide a basis for categorizing growth patterns of the more common benign nasopharyngeal masses. Lymphoid hyperplasias are confined to the surface by the very dense pharyngobasilar fascia that lies beneath the submucosa. It takes a very aggressive process to cross this fascial plane. More laterally throughout the paranasopharyngeal space the loose areolar nature of the buccopharyngeal fascia permits benign tumors in this space to assume a spherical configuration. The carotid sheath is also a loose areolar arrangement that permits free movement of the carotid artery in the neck. Juvenile angiofibromas permeate natural foramina, displace bony septa, and extend widely but do not invade the carotid sheath. Neurogenic tumors and paragangliomas are intimately associated with contents of the carotid sheath; therefore, they obliterate the low density regions surrounding the carotid vessels.
Analysis of anatomical features of the nasopharynx, nasal cavity, paranasal sinuses, and infratemporal fossa was carried out by retrospective review fo 50 CT scans. Conventional and axial anatomy are discussed, and normal size limits of selected structures are proposed on the basis of a series of measurements. Examples of early and advanced disease are shown.
Three patients with hypoplasia of the maxillary sinus were examined with standard radiography, linear or hyocycloidal tomography, and computed tomography (CT). The mucoperiosteal membranes and orbital contents were more clearly differentiated with CT than with conventional tomography. In most cases of maxillary sinus hypoplasia, the diagnosis can be made from the plain radiographs. However, CT can confirm the diagnosis and provide direction for a surgeon to perform a biopsy or to surgically approach the area.
In 52 normal nasopharyngeal computed tomographic (CT) scans the various tissue planes deep to the mucosa were always seen and appeared symmetric. The superficial structures were more often asymmetric; however, by using physiologic maneuvers, coronal scanning, and this very reliable deep plane anatomy, a highly accurate interpretation is possible. A knowledge of these simple scanning techniques and of the range of normal anatomy will help radiologists avoid the equivocal and false-positive interpretations that plague other radiographic studies of this area. Because of its deep plane information, CT best complements the clinical evaluation of the nasopharynx, and should be the radiographic examination of choice.