A 30-year-old female patient with facial pain diagnosed as organizing hematoma of maxillary sinus by biopsy and imaging studies, and subsequently tumor was resected via an endoscope-assisted midfacial degloving approach. The tumor was histopathologically confirmed as organizing hematoma. In 3-week follow-up, asymptomatic emerging mass was observed at the same site, and needed a revision endoscopic resection. On pathologic examination, a low-grade angiosarcoma was identified, not organizing hematoma. After postoperative radiotherapy, she has been a status of no evidence of disease. This report emphasizes that complete and delicate resection of sinonasal tumor should be made to prevent recurrence and submerged malignant potential.