Incidence and Management of Isolated Subsegmental Pulmonary Embolism.

The use of computed tomographic pulmonary angiography (CTPA) in patients with suspected pulmonary embolism (PE) has improved the visualization of subsegmental pulmonary arteries. However, the clinical significance of subsegmental PE is unclear. In the PIOPED Study, PE limited to subsegmental pulmonary arteries was most prevalent among patients with low-probability ventilation/perfusion (V/Q) scans. Patients with non-diagnostic (low or intermediate) V/Q scans can be safely managed without anticoagulation. The incidence and clinical management of subsegmental PE remains uncertain.

To evaluate the incidence and clinical management of subsegmental PE in patients with suspected acute PE.

This is a retrospective cohort study of consecutive patients with suspected acute PE undergoing CTPA at the Ottawa Hospital from Jan 1, 2007 to Dec 31, 2008. Subsegmental PE was defined as one or more pulmonary artery filling defects located in the subsegmental level, with no filling defects visualized at more proximal pulmonary artery levels. All patients were followed for a minimum of 6 months after the index PE.

A total of 78 (10.4%, 95% CI: 8.4 to 12.8%) cases of subsegmental PE were identified out of 748 cases of PE diagnosed by CTPA. Forty-three (77%) of these had a single isolated subsegmental filling defect. Data could be extracted in 56 (72%) of the 78 cases. Among these 56 patients, 18 (32%) had unprovoked PE. Further investigations were performed in 50 patients (Ultrasonography (U/S) of legs (n=38), U/S and V/Q scan (n=11) or V/Q scan alone (n=1)). Deep vein thrombosis was detected in 12 patients and two patients had a high probability V/Q scan. Forty-eight (86%) patients were anticoagulated. All patients with concurrent DVT or high probability V/Q scan were started on anticoagulation therapy. Two patients experienced a major bleeding episode after anticoagulation. Out of the 8 patients left untreated, there were no recurrent VTE.

Isolated subsegmental PE represents approximately 10% of all acute PE diagnosed by CTPA. Patients with subsegmental PE diagnosed on CTPA are more commonly receiving anticoagulation than not. Further studies are needed to establish the risk benefit ratio of anticoagulation therapy in patients with subsegmental PE diagnosed on CTPA.

No relevant conflicts of interest to declare.