Diagnosis of Isolated Sub-Segmental Pulmonary Embolism on Computed Tomography Pulmonary Angiography; How Sure Are We of the Diagnosis?
Authors: Kimpton Miriam , Fernandez Elena Pena , Dennie Carole , Peterson Rebecca , Carrier Marc 
Published: October 2019

Abstract
Abstract 714
Computed tomography pulmonary angiography (CTPA) has become the standard diagnostic modality for the detection of pulmonary embolism (PE). More recently, the advent of multidetector CT has allowed better visualization of segmental and sub-segmental pulmonary arteries. Hence, the proportion of patients with suspected PE, in whom an isolated sub-segmental pulmonary embolism (SSPE) is reported, has increased. The clinical importance of isolated SSPE diagnosis is unclear. The increased incidence of SSPE diagnosed by CTPA seems to be associated with a lower severity of illness and lower mortality in the CTPA era. Nonetheless, a large majority of patients with SSPE are treated with oral anticoagulant therapy. Current guidelines recommend to anticoagulate patients with unprovoked thrombosis for a minimum of three months and to consider long-term treatment in the absence of contra-indications. Therefore, accurate diagnosis of SSPE is important before exposing patients to potentially indefinite anticoagulant therapy and its associated complications. We sought to determine the rate of agreement between radiologists for the diagnosis of isolated SSPE in patients presenting with suspected PE, and report the three-month outcome of patients who had been diagnosed with an isolated SSPE.
A retrospective cohort study of consecutive patients with suspected acute PE who underwent CTPA between January 2007 and December 2008 was conducted. The CTPA images of all patients with a diagnosis of isolated SSPE were reviewed by a blinded thoracic radiologist. We reported the rate of agreement, with 95% confidence intervals (CI), of isolated SSPE diagnosis between radiologists. Other outcomes captured during follow-up included: recurrent venous thromboembolism (VTE), major bleeding episodes and overall mortality. All included patients were followed for three months.
A total of 70 patients with a diagnosis of isolated SSPE (single or multiple) on were included. The median age was 64 (range 15–92) and 55% (39/70) were female. Twenty-six percent had a prior history of VTE. Forty-five percent of patients had cancer. The blinded thoracic radiologist agreed with 44% (31/70; 95% CI: 32% to 56%) of the initial isolated SSPE diagnoses. A total of 12% of the included CTPA images were interpreted by the thoracic radiologist to be without evidence of PE. Out of the 70 patients, 18 (26%) did not receive any anticoagulation, and none of them suffered recurrent VTE (PE or DVT) during the three-month follow-up period. One patient in the group of 55 patients who received anticoagulation (2%) suffered a major bleeding. A total of 33% (24/73) of patients died during the follow-up period, most of them from cancer progression. There was no fatal PE.
The rate of agreement for the diagnosis of isolated SSPE on CTPA is moderate among radiologists. The risk-benefit ratio of anticoagulant therapy remains unclear in patients with SSPE, especially in the context of a modest agreement on the diagnosis. More prospective management studies and clinical trials are required to assess this very important clinical problem.

Disclosures:
No relevant conflicts of interest to declare.