Hemophilic pseudotumor of the maxillary sinus in an inhibitor-positive patient with hemophilia A receiving emicizumab: a case report.

A 14-year-old inhibitor-positive male patient with severe hemophilia A and severe psychomotor disability was admitted due to left buccal swelling and impaired downward movement of the left eye. He had been on noninvasive positive-pressure ventilation (NPPV) through a nasal mask for upper airway obstruction. The patient began to have repeated epistaxis 16 months after initiation of treatment with 6 mg/kg Q4W of emicizumab, and was thus administered a bypassing agent. Left buccal swelling and impaired downward movement of the left eye appeared during the subsequent month. Imaging examination revealed a mass in the left maxillary sinus and bone destruction. Endoscopic tumor resection and tracheostomy were performed using recombinant activated factor VII. NPPV was discontinued thereafter. Pathological examination revealed that the mass was a hemophilic pseudotumor (HP). After discharge the emicizumab-regimen dose was changed to 3 mg/kg, Q2W to increase serum emicizumab levels. No recurrent HP or bleeding requiring treatment was observed. Pressure applied to the damaged nasal mucosa by NPPV was suspected as the main cause of HP development. If a mass is observed in a patient with hemophilia, HP should be considered as a possible diagnosis even if the patient is receiving emicizumab.