Prevalence and clinical significance of solitary pulmonary sub-segmental microembolism

BACKGROUND: Solitary pulmonary microembolism is rarely discussed as a distinct diagnostic entity. The purpose of this investigation was to determine the prevalence and clinical significance of embolism limited to subsegmental branches in a group of patients discharged from hospital on anticoagulants with a diagnosis of pulmonary embolism based on ventilation-perfusion imaging followed by selective angiography. MATERIAL AND METHODS: Of 29 consecutive patients with classic signs of pulmonary embolism at angiography, we identified a subgroup of 5 patients with sub-segmental embolism, which was solitary in all cases. RESULTS: Clinical presentation included chest pain (2/5), shortness of breath (2/5, or hypoxemia (1/5). Chest X-rays were normal (2/5), or showed pulmonary oedema (1/5) or atelectasis with (1/5), or without (1/5) pleural effusion. VQ imaging patterns included small subsegmental mismatch (1/5), one segment mismatch (1/5), single (1/5) or triple (2/5) match. The site and size of the microemboli found at angiography were incompatible with the location and severity of symptoms in 4/5 (80%) patients, and with location and extent of Chest X-ray findings and with VQ patterns in all patients. VQ abnormalities were either either disproportionably larger or were non congruent with the vascular territory compromised by the subsegmental embolus. CONCLUSIONS: Sub-segmental pulmonary micro-emboli were always solitary, and not uncommon, comprising 17% of all patients with pulmonary embolism. The location and size of the emboli were inconsistent with clinical, Chest X-ray and scintigraphic findings, suggesting that isolated microemboli are a serendipitous finding, of no clinical significance