Anomalous intravascular casts with firm, rubber-elastic properties have been increasingly noted by embalmers and clinicians since 2021. To establish their structural characteristics, we performed blinded morphological and histological evaluations. Gross examination revealed elongated, lumen-filling casts up to 25 cm in length, frequently branching and demonstrating elastic resistance atypical of conventional thrombi. Histology demonstrated dense fibrinous lamination with intermittent Lines of Zahn and various cellular inclusions content, suggesting antemortem formation under atypical hemodynamic conditions. These structural features differ from both physiological thrombi and postmortem clots, indicating a distinct pathological phenotype. Further biochemical and molecular analyses will be required to determine the composition and mechanisms underlying these structures.