Background: Fungi are ubiquitous microorganisms. Sinonasal fungal infections range from an acute fulminant to a chronic indolent clinical course. Fungal infections are common in immunocompromised patients, diabetics, and those with hematological malignancies. We present an unusual case of chronic invasive fungal sinusitis presenting as an anterior skull base lesion. Methods: A 42-year-old patient was referred with a history of right-sided proptosis. Prompt CT and MR imaging revealed a large right sinonasal erosive mass, predominantly T2 hypointense with heterogeneous enhancement. It extended into the right anterior skull base and invaded the right frontal lobe. The mass also invaded into the right extra-conal orbital fat, right pterygopalatine fossa, and right sphenopalatine foramen. Results: In view of the imaging findings, a biopsy was performed which confirmed fungal elements and chronic inflammation. Subsequently, a right-sided endoscopic endonasal resection of the sinonasal mass with resection of the right orbital component and debulking of the anterior skull base component was performed. Culture specimen grew aspergillosis. Conclusions: Extra-sinus invasion in fungal sinusitis is not uncommon. These cases may mimic other pathologies, e.g., tumors, with potential delay in treatment. Sound knowledge of the imaging appearances of this entity is imperative to ensure a good outcome.