We recently treated a patient with a bleeding nasal polyp that was localized in the nasal cavity. Since its histological features, such as an admixture of capillary congestion, dilated vessels, hemorrhage, and fibrin exudation, which resembled those of hematoma-like mass of the maxillary sinus (HLMMS), which we previously reported; the polyp was diagnosed as a hematoma-like mass of the nasal cavity. The finding that the most frequent site of attachment of the hematoma-like masses in our patients was near the ostium of the maxillary sinus suggests that the masses arose from in that site. The present findings led us to propose the following hypothesis to explain the pathogenesis of hematoma-like mass. Dysfunction of venous return at the ostium of the maxillary sinus leads to capillary and venous congestion in the mucosa, and the vessels become dilated and partially discontinuous. Despite leakage of red blood cells and fibrinogen from these discontinuous vessels, fibrin does not replace collagen, because these conditions do not mobilize inflammatory cells. These conditions cause a hematoma-like mass expansion in the maxillary sinus or the nasal cavity or the maxillary sinus.
