Presence of Residual Thromboemboli at Least Six Months after a First Episode of Symptomatic Pulmonary Embolism: DO Perfusion Scintigraphy and CT-Angiography Agree?

Introduction. The natural history of residual thromboembolic obstructions after pulmonary embolism (PE) and the clinical utility of imaging techniques at follow up are not completely known; in particular, to our knowledge, there are no clinical studies that compared the accuracy of angio-computed tomography (angio-CT) and perfusion scintigraphy (Q scan) in detecting residual thromboemboli after at least 6 months from a first episode of symptomatic PE.

Methods. Consecutive patients on anticoagulant treatment for a first episode of symptomatic PE diagnosed by angio-CT scan and/or Q scan underwent angio-CT and Q scan after 6 to 12 months from the index event. Exclusion criteria were previous PE, recurrent symptomatic PE or deep vein thrombosis (DVT) during the follow-up period. All diagnostic tests were independently assessed by one expert radiologist unaware of the clinical status of the patients. The results of the tests were classified as no signs of recanalization or reperfusion, partial resolution or complete resolution. The agreement beyond chance between tests was assessed by kappa statistics.

Results. Twenty-five patients (14 males, 56%, mean age 59.8) were included after a mean of 7.2 months (217 days, standard deviation 58 days) after acute PE. PE was diagnosed by CT alone in 13 cases, by high probability Q scan alone in 2 cases and by both CT and Q scan in 10 patients. Eleven episodes (44%) were considered idiopathic, 11 (44%) were secondary to transient risk factors, 3 (12%) patients had cancer; concomitant DVT was detected in 17 (68%) patients. At follow-up, Q scan showed no signs of reperfusion in 1 patient (4%), partial resolution in 13 patients (52%) and complete resolution in 11 (44%). Angio-CT showed no signs of recanalization in 0 patient, partial resolution in 17 patients (68%) and complete resolution in 8 (32%). Complete resolution was present in both tests in 1 patient (4%), partial resolution was present in both tests in 6 (24%) patients, with a k agreement between tests < 0.2 (slight).

Conclusions. Partial resolution of thromboemboli after a mean period of 7.2 months from a first episode of PE is present at Q scan or at angio-CT in more than 50% of patients, confirming the results of previous studies. However, the results of our study show for the first time that the agreement between these two tests is low. Thus, caution should be used when interpreting the results of either of these tests to monitor patients with previous PE.