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Multimodality Imaging of Mandibular and Maxillary Bone Infections

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Multimodality Imaging of Mandibular and Maxillary Bone Infections
Fitzhugh A 1, Chhabda S 1, Weller A 2, Lingam RK 2
1. Chelsea & Westminster Hospital NHS Foundation Trust, London; 2. Northwick Park Hospital, London North West University Healthcare NHS Trust

INTRODUCTION
Mandibular and maxillary osteitis and osteomyelitis may be secondary to a range of both odontogenic and non-odontogenic pathologies. Imaging plays a key role in detecting the source, mapping  osseous and extra-osseous spread, detecting complications and narrowing the differential. In addition, specialist clinical evaluation of oral mucosa is also vital in order to differentiate infection from pathologies that can radiologically mimic infection e.g. osteo(radio)necrosis and neoplasia.1

IMAGING ALGORITHM
The following modalities play a complementary role in the imaging of mandibular and maxillary bone infections.

PLAIN RADIOGRAPHY
Including dental radiographs and orthopantomographs (OPG). Simple low-dose examination. Can demonstrate apical (Fig. 2a) and carious (Fig. 1a) dental disease and osteomyelitis (Fig.4a)

CONE BEAM COMPUTED TOMOGRAPHY (CBCT)
A fast, low dose technique with high bony spatial resolution. Not affected by metal artefacts (e.g. dental amalgam) c.f. conventional CT (Fig.3b). Limitations are that soft tissues cannot be assessed.

COMPUTED TOMOGRAPHY
Initial cross sectional modality in the acute setting. Multiplanar can be used to image spread of infection to deep neck spaces. (Fig. 9 and 10) Better at depicting osseous changes c.f. MRI, but with lower sensitivity detecting early osteomyelitis.2

MAGNETIC RESONANCE IMAGING
HIGHEST SENSITIVITY (86-98%)2 for detecting early osteomyelitis. Sensitive in the assessment of extra-osseous spread, abscess formation, assessing joints (Fig. 13) and differentiating from neoplasia (diffusion weighted MRI sequences).

ULTRASOUND
Not frequently used but can detect superficial perimandibular extra-osseous spread / sinus tracts  (Fig. 11) and collections (e.g. submasseteric abscess).

SUMMARY
Odontogenic infection is the most common cause of maxillary and mandibular osteomyelitis
Maxillary and mandibular osteomyelitis may be acute, chronic or acute-on-chronic in nature
Multimodal imaging plays a key role in identifying the source of infection, characterising osteomyelitis and mapping both osseous and extra-osseous spread
CT is best for acute cases in identifying the source of infection and mapping spread to deep neck spaces
MRI is the most sensitive for detecting bone marrow and soft tissue changes  

ODONTOGENIC INFECTION
Osteomyelitis of the mandible and maxilla is often a complication of untreated odontogenic infection (up to 90% of cases)3; typically polymicrobial bacterial infection. The most common source is an infected tooth, which may present with periapicopathy and/or periapical abscess. The infection may spread into adjacent neck spaces.

The spectrum of odontogenic disease:
1: Carious disease on OPG (1a), and coronal CT (1b), appearing as focal lucency within crown (→).
2: Apical periodontitis manifesting as subtle apical lucency on OPG (2a) and CT (2b) (→)
3: Pericoronitis CT (3a) and CBCT (3b). CBCT shows large ‘arcuate’ zone of radiolucency in the bone posterior to LL8, indicating chronic distocoronal pericoronitis (→). There is minimal image degradation from dental amalgam on CBCT.

4. Chronic osteomyelitis left hemimandible OPG and CT: Diffuse bone sclerosis and expansion of the inferior dental canal on OPG.
CT (4b), highlights the asymmetry (→)

5. Chronic osteomyelitis with radicular cysts/periapical abscesses – sagittal CT:
Sclerotic and slightly expanded left hemimandible. Several radiolucent areas, likely radicular cysts / periapical abscesses (→) related to the roots of the remaining left premolar and molar teeth measuring up to 1.8 cm.

ODONTOGENIC INFECTION WITH EXTRA-OSSEOUS SPREAD
6. Dental infection with fistula tract on axial T2 weighted MRI
The fistulous tract  opens at left cheek / buccal space (with skin marker *)
7. Osteomyelitis of the mandible with masticator space abscesses.

Ultrasound (7a) shows pockets of fluid within the left masseter muscle (→) in keeping with collections. The bony cortex is thickened suggesting osteomyelitis.
CT soft tissue window (7b) demonstrates the extent of collections.

8a. Maxillary odontogenic sinusitis
Coronal CT showing mucosal thickening related to carious upper molar tooth with periapical lucency.
8b. Oro-antral fistula resulting in maxillary osteitis following tooth extraction on CT. There is a bony defect at the left maxillary alveolus/maxillary sinus floor in keeping with an oroantral fistula (→).

9 and 10. Dental infection with extra-osseous spread on CT
9. LR6 dental infection with abscess extending medially & above mylohyoid muscle into sublingual space. Mylohyoid (---) confines infection within the floor of mouth.
10. LR5 dental infection with spillage of infection lateral and below mylohyoid to reach the submandibular space. Note the defect in the buccal cortex of the mandible (→).

11. Periapical abscess with a fistula tract US and CT
CT (11a) shows lucency in the right hemimandible related to LR1-2 periapical abscess (→).
US of subcutaneous fluid tracking superiorly from chin (11b) to the right midline mandible (11c).

12. Osteomyelitis following dental extraction with spread
MRI axial STIR (12a) & T1 (12b) shows high and low signal respectively within the right hemimandible suggesting acute osteomyelitis. (→)

The extent of soft tissue inflammation within adjacent neck spaces is well characterised on T2 weighted imaging.

NON - ODONTOGENIC INFECTION
Whilst dental infection is the most common cause of bone infections of the maxilla and mandible, other sources of infection to consider include:

Direct pathogen inoculation e.g. from trauma or surgery
Systemic disease e.g. sickle cell disease or systemic immunosuppression (HIV infection, diabetes)
Spread of infection from a non-odontogenic contiguous process e.g. sinusitis, otitis, petrous apicitis or TMJ osteomyelitis
A radiological mimic of osteomyelitis such as:
Osteoradionecrosis, bisphosphonate related osteonecrosis, Garre sclerosing osteomyelitis, Langerhans cell histiocytosis and Ewing sarcoma

CT and MRI play a complementary role in assessment of the bone and spread of infection e.g. into the orbit and middle cranial fossa.

13: Necrotising otitis externa (NOE) on MRI
T1 weighted MRI with contrast and fat supression (13a) shows enhancing middle ear inflammation spilling into masticator space (arrows). Low T1 signal and enhancement of the mandibular condyle is in keeping with early osteomyelitis (13b). This demonstrates the sensitivity for detecting bone marrow changes in early osteomyelitis.

14: Temporomandibular septic arthritis CT + MRI
CT bone window (14a) of destructive mass centred at the TMJ, directly extending into middle ear and eroding into the cranium. (→)
MRI (14b) shows this inflammatory change extending into middle ear and skull base. (→), with potential for intracranial spread. Diagnosis was confirmed from cultured surgical specimen.

15: Maxillary osteitis CT. Bone thickening secondary to chronic maxillary sinusitis.
16: Acute on chronic osteomyelitis of the right hemimandible in an edentulous patient
Axial (16a) and sagittal (16b) CT bone windows demonstrate sclerosis and bony expansion of the mandible compatible with chronic OM. On the right there are lucent foci and cortical destruction of the lingual and buccal cortices in keeping with acute OM. (→) CT clearly depicts the chronic bony changes associated with chronic osteomyelitis

REFERENCES
1. Morag Y. et. Al. Bisphosphonaterelated Osteonecrosis of the Jaw: A Pictorial Review  RadioGraphics 2009; 29:1971–1986
2. Kothari N et. Al. Imaging of Musculoskeletal infections. Radiologic Clinics of North America. 39(4), 1 July 2001, 653-671
3. Andre C-V et. Al. Osteomyelitis of the jaws: A retrospective series of 40 patients. J. Stomatology, Oral and Maxillofacial surgery. 2017; 118(5): 261-264

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