Acute saddle pulmonary embolism on 18F-FDG PET/CT: diagnosis by functional imaging

F-18-labelled fluoro-2-deoxyglucose positron emission tomography/computed tomography (F-18-FDG PET/CT) is used extensively in the setting of cancer staging and in assessing cancer treatment response. Oncology patients have a sevenfold risk of developing pulmonary embolism (PE) due to underlying activation of the haemostatic system and anti-cancer therapy inducing a hypercoagulable state. The diagnosis of PE on F-18-FDG PET/CT is challenging, particularly in the absence of intravenous contrast. The case of a female patient undergoing treatment for advanced diffuse large B-cell lymphoma is presented. The ancillary signs of PE are illustrated on consecutive non-contrast-enhanced F-18-FDG PET/CT scans. The signs include the "rim sign" relating to regions of pulmonary infarction and abnormal cardiac uptake indicating right heart strain. The diagnosis was confirmed on CT pulmonary angiography which demonstrated extensive PE, including a saddle embolus.