Slow Flow Mimicking Pulmonary Embolism

A man in his 70s in a rehabilitation hospital, post cerebral infarct, became acutely short of breath with reduced oxygen saturations and an elevated d-dimer.Non-occlusive filling defects were noted on the CT pulmonary angiogram in the proximal left pulmonary arteries. There was associated hypoplasia of the distal pulmonary arterial tree in the left hemithorax with left pulmonary vein stenosis. Review of previous imaging suggested this oligaemia was longstanding.Although filling defects in the pulmonary arteries usually correspond to embolic material, in our patient they were too dense to represent thrombus and probably represented flow-related artefacts in the setting of chronic air trapping.Given the associated volume loss, bronchiectasis and bronchial wall thickening in the left hemithorax Swyer-James-McLeod syndrome was thought to be the most likely underlying cause.