An untapped resource: characteristics of thrombus recovered from intermediate or high risk pulmonary embolus patients.

INTRODUCTION:Response to anticoagulation varies during management of acute hospitalized pulmonary embolism. We aimed to study thrombus histology in pulmonary embolism samples removed during acute surgical embolectomy to evaluate whether thrombus morphology was similar between patients and whether there was an association with duration of symptoms and/or resolution on follow up imaging. METHODS:This was a retrospective observational single center study at the University of Rochester Medical Center. We evaluated patients that underwent acute surgical embolectomy and followed up in our clinic 2 - 4 months after the event with Ventilation/Perfusion (V/Q) scan obtained for all regardless of symptoms. Thromboemboli were formalin fixed and processed for light microscopy in the hospital histopathology laboratory. Four-micron thick sections were stained with hematoxylin and eosin, Masson trichrome, and Verhoeff elastic tissue stains. Immunohistochemistry was performed using anti-CD31 and anti-CD68. Slides were independently evaluated for time-dependent microscopic changes using Irniger's classification by two blinded pathologists. RESULTS:Sixteen patients underwent embolectomy with fifteen having V/Q imaging at follow up. The majority of patients were female. Samples showed a generally similar overall architecture that included a central core composed primarily of red blood cells and fibrin and an outer layer of platelets and monocytes. Two samples had evidence of fibrosis and recanalization. CONCLUSIONS:We found heterogeneous histopathology in samples obtained during acute embolectomy. Further prospective studies should systematically characterize clot morphology and evaluate treatment response and outcomes. Careful thrombus specimen measurement and consistent sampling for sections will be required to draw firm conclusions.