Current diagnostic aspects on acute and chronic pulmonary embolism : MRI in acute pulmonary embolism, CT in chronic thromboembolic pulmonary hypertension and what the radiologists actually know

Abstract

Background: Acute pulmonary embolism (APE) is a potentially severe medical condition with blood clots obstructing the pulmonary arterial vasculature. In most cases the APE resolves without any sequelae after anticoagulation therapy. In some patients, however, the emboli do not resolve upon treatment and the remnants cause increased vascular resistance, a condition known as chronic thromboembolic pulmonary hypertension (CTEPH). Both APE and CTEPH have a non-specific clinical presentation and imaging is an important part of the diagnosis. In APE computed tomography pulmonary angiography (CTPA) is the diagnostic gold standard, although the method is not suitable for all patients. CTPA has a high specificity for CTEPH, but the sensitivity remains under debate. At present CTPA is not recommended as a first line test among patients with a clinical suspicion of CTEPH.

Purpose: To investigate unestablished imaging modalities in the diagnosis of APE (Study I) and CTEPH (Study III) including learning aspects (Study II) and knowledge (Study IV) of theses among radiologists. Regarding APE we studied magnetic resonance imaging (MRI) and in CTEPH we studied CTPA.

Material and methods: Studies I-II were based on a prospective collection of 70 unenhanced MRI exams with CTPA as the gold standard. In Studies III-IV we used a retrospective material based on 43 CTPA exams from patients with confirmed CTEPH referred for presurgical assessment at a specialist centre, with a matched control with suspected APE.

Results: All MRI exams were of diagnostic quality. Specificity was 100% for both readers and sensitivity 90% and 93% respectively with a nearly perfect inter-reader agreement (kappa 0.97) (Study I). Residents interpreting the MRI exams within the training program reached a clinically acceptable level after approximately 50 examinations and review time was halved during the training program (Study II). The sensitivity for CTEPH on CTPA reviewed by two experts was 100% and the specificity 100% (Study III), while the sensitivity based on the original reports from the same cases was 26% (Study IV).

Conclusions: Unenhanced MRI has a high sensitivity and specificity for APE (Study I) and residents can learn to interpret such exams by using a self-directed training program (Study II). Enhanced CTPA has a high sensitivity when reviewed by experienced radiologists (Study III), but among radiologists in general the sensitivity is low (Study IV).