Purpose: The pathogenic mechanisms of antrochoanal polyps (ACPs) remain largely unknown. This study aimed to characterize inflammatory patterns and tissue remodeling features in ACPs. Methods: Inflammatory cell infiltration and tissue edema severity as well as fibrin deposition in ACPs and bilateral eosinophilic and noneosinophilic nasal polyps (NPs) were studied with immunohistochemical and immunofluorescence staining. Cytokine levels in sinonasal tissues were detected with the Bio-Plex assay. The expression of coagulation and fibrinolytic markers was measured using reverse-transcription polymerase chain reaction and enzyme linked immunosorbent assays. Results: Compared to control tissues and bilateral eosinophilic and noneosinophilic NPs, ACPs had higher levels of neutrophil infiltration and expression of myeloperoxidase (MPO), interleukin (IL)-8 and interferon (IFN)-gamma. In total, 94.4% of ACPs demonstrated an eosinophil cationic protein/MP O ratio of < 1, compared to 79.0% of noneosinophilic and 26% of eosinophilic NPs. Principle component and multiple correspondence analyses revealed a neutrophilic and type 1 inflammation pattern in ACPs. Compared to control tissues, edema scores and fibrin deposition were increased, whereas d-dimer and tissue plasminogen activator (tPA) levels were decreased in ACPs and bilateral NPs, with more prominent changes in ACPs even than in eosinophilic NPs. The tPA levels were negatively correlated with IFN-gamma, IL-8, and MPO levels in ACPs. Neutrophils were the major cellular source of IFN-gamma in ACPs, and the number of IFN-gamma(+) neutrophils was elevated in ACPs than in control tissues and bilateral eosinophilic and noneosinophilic NPs. Conclusions: ACPs are characterized by the neutrophilic and type 1 inflammation endotype. Neutrophil-derived IFN-gamma is associated with reduced tPA production in ACPs.