Hyperdense Pulmonary Artery Sign on Noncontrast CT

A 75-year-old man with a history of renal cell carcinoma presented with dyspnea and an elevated D-dimer (4500 ng/mL). Clinical assessment suggested pulmonary embolism. Due to renal impairment (creatinine 2.1 mg/dL), CT angiography was contraindicated. Noncontrast chest CT revealed hyperdense intraluminal material in bilateral main pulmonary arteries, consistent with acute thromboemboli. Fresh clots appear hyperdense due to high hemoglobin concentration and reduced plasma content. Subsequent lung perfusion SPECT demonstrated multiple large bilateral perfusion defects, confirming high-burden pulmonary embolism. This case illustrates the diagnostic utility of the hyperdense pulmonary artery sign complemented by perfusion scintigraphy in patients where contrast angiography is contraindicated.