The mandible typically demonstrates little or no metabolic activity. Its evaluation with PET/CT is limited by the exam’s large field of view and the prevalence of streak artifact from dental amalgam.

Dental/ Periodontal Disease:

• The vast majority of focal increased FDG uptake associated with the mandible represents dental/periodontal disease.  Unless an accompanying lesion is identified on the co-registered CT images (or unless a high clinical suspicion for a mandibular lesion exists), we presume such uptake to be odontogenic.

Malignant Lesions (Mets > primary lesions):

• If a focus of FDG uptake is associated with a lytic or sclerotic bone lesion on the co-registered CT images, it should be considered malignant until proven otherwise.

Osteoradionecrosis (ORN): 

• ORN (usually of the mandible) is a rare complication of high-dose radiation therapy. It can be intensely FDG-avid and can occur years after therapy, mimicking recurrent disease.
• Unfortunately, PET evaluation of metabolic activity is of limited utility in distinguishing ORN from recurrent disease (CT alone maybe useful, with a cystic or solid mass suggesting recurrent disease, while sclerosis suggests ORN).

False Positives:

• Physiologic Tongue Uptake: Physiologic uptake within the anterior tip of the tongue can be extremely intense and often abuts the mandible, mimicking a focal lesion.
• Mylohyoid Muscles: These muscles parallel the body of the mandible, often intensely avid.  When they demonstrate asymmetric uptake and abut the mandible, they can be mistaken for pathology.