48 year old man with history of hypertension and chronic kidney disease presents to the emergency department with chest pain and dyspnea. 2 days previously while walking up an incline he had sudden onset of pleuritic right chest pain, which has persisted.
Initial chest radiograph:
The chest radiograph demonstrates a rounded opacity at the lateral right lung base.
This was further evaluated with chest CT, which demonstrates a rounded region of mixed ground glass / solid attenuation in the lateral basal right lower lobe. Atelectasis is also present in the posterior basal lower lobes.
Because of his symptoms the patient also underwent a V/Q scan:
The VQ images show a large perfusion defect in the right lower lobe (green arrow) that is mismatched (ventilation images show normal initial/single breath ventilation in this region, with minimal xenon retention on washout images which is less extensive than the perfusion defect). There are additional small wedge-shaped perfusion defects in the right middle lobe and anterobasal right lower lobe (white arrows).
This case in an example of acute pulmonary embolism with hemorrhagic infarction, or “Hampton’s hump”. This sign was first described by radiologist Aubrey Hampton using postmortem examinations in 1940. Hampton AO, Castleman B. Am J Roentgenol Radium Ther 1940; 43:305-26. A peripheral rounded or wedge-shaped consolidation with ground glass attenuation on CT is the classic appearance.
There are no sensitive findings on chest radiograph for the diagnosis of pulmonary embolism, and the radiograph may frequently be normal. Atelectasis or alveolar opacity were the most common radiographic abnormalities in patients with acute PE included in the PIOPED study, however they were not more frequent than in patients without PE. Worsley DF, et al. Radiology 1993;189:133-136. If patients have no pre-existing cardiac or pulmonary condition, these radiographic findings are more common in PE, but still nonspecific. Stein PD, et al. Chest 1991;100:598-603. Hampton’s hump has an approximate sensitivity of 20% and specificity of 80% for pulmonary embolism. Other radiographic findings associated with pulmonary embolus such as decreased peripheral vascularity (Westermark sign), pleural effusion (usually small with PE), and prominent central artery (Fleischner sign) are similarly not sensitive (10-20%) and only moderately specific (70-90%).
The presence of hemorrhagic infarction or other pulmonary infiltrate may increase the chance of a “matched” ventilation abnormality, and can be a cause of false-negative VQ scan. Ziessman HA, O’Malley JP, Thrall JH, eds. Nuclear Medicine, the Requisites, 4th ed. Philadelphia: Elsevier, 2014. Note however when the ventilation abnormality is smaller than the corresponding perfusion defect (as in this case), this should be considered suspicious for pulmonary embolus.