Background: The hyperdense lesion on non-contrast CT (NCCT) is a common postoperative phenomenon in acute ischemic stroke patients who are treated with endovascular therapy (EVT). Both contrast extravasation and hemorrhagic transformation presented hyperdense lesions on NCCT, which are sometimes difficult to distinguish them. Summary of Review: Radiographic findings are important for identifying contrast extravasation and hemorrhagic transformation. We recommended a standardized follow-up protocol involving imaging and clinical evaluation as it will allow neurologists and neuroradiologists to reveal the relationships between these hyperdensities and various clinical outcomes. Key Messages: Dual-energy CT and susceptibility-weighted imaging are capable of distinguishing contrast extravasation and hemorrhagic transformation at an early stage after EVT. However, in institutions without access to such technology, a follow-up protocol based on NCCT is crucial.