Difference in interpretation of computed tomography pulmonary angiography diagnosis of subsegmental thrombosis in patients with suspected pulmonary embolism 1

The introduction of computed tomography pulmonary angiography (CTPA) as a diagnostic modality to diagnose pulmonary embolism (PE) has led to a significant increase in the incidence of PE diagnosis. Multidetector CTPA has improved the sensitivity for diagnosis of PE, allowing better visualization of segmental and subsegmental pulmonary arteries [1–4]. Concomitantly, the proportion of patients with suspected PE in whom isolated subsegmental pulmonary embolism (SSPE) is reported has increased [5]. Although the incidence of PE diagnosis has increased within the last few years, its case fatality rate and the mortality rates have remained unchanged, suggesting that the additional cases of PE might be associated with a lower severity of illness [6,7]. The management of PE isolated to the subsegmental pulmonary arteries (single or multiple vessels) without a concomitant deep vein thrombosis (DVT) is controversial among thrombosis experts and clinical equipoise exists regarding the use of anticoagulant therapy in the management of those isolated SSPEs [8]. Given how important it is for clinicians to have an accurate diagnosis in order to decide on the risk-benefit ratio of anticoagulant therapy to treatSSPE,we sought todetermine the proportion of agreement between radiologists on the diagnosis of isolated SSPE in patients presenting with suspected PE, and to report the management and 3-month outcome of patients who had been diagnosed with an isolated SSPE. We conducted a retrospective cohort study of consecutive patients with suspected acute PE who underwent CTPA at the Ottawa Hospital between January 2007 and December 2008. Computed tomography pulmonary angiography was performed using either GE LightSpeed Plus (4and 16-detectors), GE LightSpeed VCT (64-detectors) or Toshiba Aquilion One (320-detectors) CTdevices. SSPEwas defined as any number of pulmonary artery filling defects isolated to the subsegmental pulmonary arteries detected on CTPA. All included patients were followed for 3 months. The CTPA images of all patients with an index diagnosis of SSPE were reviewed by an experienced thoracic radiologist (RP). The examiner was blinded to the diagnosis and original filling defect location. The reviewing radiologist was also blinded to any other diagnostic test results (compressive lower extremity ultrasonography [US], etc.). The reviewing radiologist independently recorded findings on standardized forms. Normal CTPA (n = 4) studies and CTPA studies with index segmental filling defects (n = 2) interpretation were also included to ensure control and blindness of the reviewing radiologist. Disagreements were reviewed by a second experienced thoracic radiologist (CD). All clinical outcomes captured during follow-up were reviewed independently by two investigators (MK and MC). Disagreements on information were resolved by consensus or by retrieving further information from other medical records. The primary outcome was symptomatic objectively confirmed recurrent venous thromboembolism (VTE) during the 3-month follow-up period. Secondary outcomes included major bleeding episodes and overall mortality. Recurrent PE was defined as a new arterial filling defect on CTPA or high probability V/ Q-scan, and recurrent DVT was defined as a non-compressible venous segment on an ultrasound of the extremities. Major bleeding events were defined as per the Internal Society of Thrombosis and Haemostasis definition [9]. All study outcomes were adjudicated. Descriptive statistics were used to describe the patient characteristics and outcomes. We computed the proportion of cases, with its associated 95% confidence intervals (CI), in whom the second interpretation by the thoracic radiologist was concordant with the initial diagnosis of isolated SSPE. Agreement was determined using the most proximal level of filling defect detected on CTPA images. Analyses were performed using StatsDirect software version 2.7. 3 (StatsDirect Ltd, Altrincham, UK). Correspondence: Marc Carrier, Ottawa Hospital, General Campus, 501 Smyth Road, Box 201, Ottawa, Ontario K1H 8L6, Canada. Tel. : +1 613 737 8899 ext. 73034; fax: +1 613 739 6266. E-mail: mcarrier@toh.on. ca