A 59-year-old man with a history of smoking and adult-onset asthma with recurrent eosinophilia presented with fatigue and weight loss, along with a progressive left facial swelling involving the cheek and infraorbital region. Laboratory tests revealed persistent eosinophilia and markedly elevated serum IgG4 levels (11.35 g/L). Antineutrophil cytoplasmic antibodies were negative. Facial MRI showed an infiltrative lesion extending into the masticator and pterygopalatine spaces, associated with submandibular lymphadenopathy (Fig.
