Aim: Inflammatory myofibroblastic pseudotumor (IMT), part of the inflammatory pseudotumor (IPT) family, shares many presenting features with more common expansile sinonasal masses and is unlikely to be diagnosed without clinical suspicion. Background: Inflammatory myofibroblastic pseudotumor (IMT) is histologically characterized by myofibroblasts with prominent small lymphocytes and plasma cells, often initially mistaken for other inflammatory processes. These lesions share characteristics of pseudotumors and neoplasms with possible malignant potential. Case description: We present the case of a 57-year-old woman who was eventually properly diagnosed with IMT. She initially presented with several month histories of severe right-sided headache, facial pain, blurry vision, and right lid ptosis. The patient was diagnosed with invasive fungal sinusitis by another provider but proved nonresponsive to intravenous antifungal therapy. Repeat biopsy revealed an inflammatory process consistent with IMT. The lesion was rapidly responsive to intravenous steroid therapy. Conclusion: A destructive sinonasal mass necessitates a wide differential diagnosis that should include IPT. Both medical and multimodal treatment strategies have proven highly efficacious with a high cure rate and a higher rate of tumor stabilization. Clinical significance: IMT is an example of a commonly misdiagnosed pathology even with permanent section analysis by several pathologists. Early identification of this condition can lead to better treatment with medical therapeutic options and minimize unnecessary interventions.