Type A acute intramural hematoma (IMH) of the ascending aorta is defined as hemorrhage in the aortic wall in the absence of intimal disruption. Proximity to the adventitia may explain the higher incidence of rupture in IMH. We present a case of IMH, diagnosed by the presence of linear intense uptake of FDG on PET/CT, in a 70-year-old woman undergoing staging for colorectal cancer. There is no current role for FDG-PET in the diagnosis of IMH. This case demonstrates that incidental focal FDG activity in the wall of the aorta may indicate the life-threatening diagnosis of IMH.