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Background
Medication-related osteonecrosis of the jaw (MRONJ) was first described relatively recently (2003) in patients who were taking bisphosphonates, and not soon after in patients taking denosumab. Since these first reports, MRONJ has become a well-established entity that can significantly affect the treatment course in patients with malignancy and osseous metastatic disease. Although a clinical diagnosis, radiologic evaluation of this process can play a key role in evaluating the extent of the disease, as well as any complications. The purpose of this exhibit is to explore the variety of imaging features associated with the condition in the context of the advantages and disadvantages of the utilized imaging modalities.

Educational Goals / Teaching Points
To evaluate MRONJ in an appropriate context, the first goal of this exhibit is to review the epidemiology, risk factors, pathogenesis, and clinical setting related to this entity. The imaging findings are then discussed, including common findings of the condition on radiographs, CT, MRI, bone scintigraphy, and PET/CT. There is a focus on the role of imaging, especially when evaluating for complications. Lastly, treatment options are described.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Though it is understood that the medications associated with MRONJ function by limiting osteoclast activity, the pathology underlying the condition itself is not completely understood. It is thought to be multifactorial, with the decrease in bone resorption that occurs with osteoclastic inhibition playing a key role in pathogenesis. The diagnostic criteria do not rely on imaging features and include exposure of either the maxilla or mandible for more than 8 weeks with current/previous use of anti-resorptive therapy, and without a history of metastatic disease/radiation therapy to the area. The disease can be classified into 3 stages based on patient symptomatology and complications. The role of radiological analysis is to assess the extent of the disease, assist with staging, and in some cases evaluate the findings prior to surgery. Although the mandible tends to be involved more frequently than the maxilla, both can be involved simultaneously. In earlier stages, radiographic and CT imaging can have broad characteristics including sclerosis, lucency, or a combination of both – though findings as periosteal reaction and sequestrum formation have been reported as the process advances. Complications such as pathologic fractures, fistula formation, or paranasal sinus disease can be present. Nuclear medicine imaging can also be useful for the initial detection of the disease due to its high sensitivity.

Conclusion
MRONJ, though not dependent on imaging for the diagnosis, often requires imaging evaluation to gauge the extent of the disease, development of complications, and in pre-surgical planning. In patients who have a history of metastatic cancer and are receiving anti-resorptive agents, MRONJ should be kept high on the differential when evaluating osseous lesions of the jaw.