Unusual cause of maxillary sinus mass with proptosis

We report a case of a 21-year-old Indian man with an 8-month history of left-sided headache, maxillary sinus mass, proptosis and swelling of the left temple, whose contrast-enhanced CT scans of the paranasal sinuses showed an enhancing, destructive soft tissue mass involving the left maxillary sinus, orbit, infratemporal fossa and anterior cranial fossa, suggestive of a malignancy or chronic granulomatous disease. Histopathological examination of the sinus mass, which was debulked and partially excised via an endoscopic approach, suggested a diagnosis of immunoglobulin G4-related sclerosing disease of the maxillary sinus. Subsequent immunohistochemical staining and biochemical tests confirmed the diagnosis. We highlight the importance of considering this increasingly recognised but rare entity that can mimic a malignant lesion with its clinical and radiological features but which, unlike the latter, has a very good prognosis with appropriate treatment.