Pseudothrombus in the left ventricle due to microvascular obstruction

Imaging description A mass-like area of low signal intensity mimicking thrombus may be encountered in the setting of microvascular obstruction (MO) when cardiac MRI (CMR) is performed after acute myocardial infarction (MI). CMR is often used to assess viability after MI for prognosis and determining the need for possible revascularization. In the acute setting, large transmural MIs may demonstrate MO, which has been associated with poorer outcomes and adverse left venticular (LV) remodeling at follow-up imaging. MO is subendocardial in location and low in signal intensity on late gadolinium enhancement (LGE) images, characteristically surrounded by a zone of increased myocardial signal intensity due to LGE (Figure 5.1). MO represents a densely infarcted area of no-flow within the myocardium where gadolinium cannot reach due to severe micro-vascular damage. MO is recognized by its association with a wall motion abnormality, subendocardial decreased perfusion on dynamic post-contrast images, and a rim of delayed enhancement representing a zone of infarcted tissue with intact microvasculature that surrounds the infarct core with MO.Importance MO is important to recognize given the fact that it is associated with poorer outcomes after MI. MO must be correctly differentiated from thrombus, as this may require additional treatment such as anticoagulation therapy, which will expose the patient to additional bleeding risk in the inappropriate setting.Typical clinical scenario MO is encountered when viability MRI scans are performed in someone with recent MI. Differentiation of thrombus from MO is important as these patients with hypofunctioning myocardium in the setting of recent MI are at risk for thrombus due to blood stasis.Differential diagnosis Thrombus is the most important entity on the differential diagnosis of MO. The location of MO within the wall of the myocardium can help differentiate MO from thrombus. Myocardial location can be clarified by direct comparison of LGE and precontrast images (Figures 5.1, 5.2).