Characteristic imaging findings in a patient with chronic expanding hematoma on the floor of the mouth.

Chronic expanding hematoma (CEH) is defined as chronic hematoma enlargement for more than 1 month. Although CEH rarely occurs on the floor of the mouth, the need to distinguish these cases from malignant disease is critical, given the need for potentially extensive resection in patients with malignancy. We report a case of CEH on the floor of the mouth, which required differentiation from malignant tumor. A 42-year-old woman was referred to our hospital for a submucosal mass on the right floor of the mouth, with a diagnosis of class 3 on aspiration cytology. Computed tomography revealed a submucosal mass with peripheral calcification on the floor of the mouth, which exhibited a hypointense rim on T2-weighted imaging and gradual nodular-like enhancement in the periphery on contrast-enhanced magnetic resonance imaging. Enucleation was performed to reach a definitive diagnosis, and CEH was confirmed pathologically. Well-defined morphology, presence of calcification, a hypointense rim on T2-weighted imaging, and weak peripheral nodular-like enhancement may be characteristic findings of CEH on the floor of the mouth. Accordingly, these imaging features may aid in differentiating CEH from low-grade malignancies and in determining the optimal management strategy.