Acute invasive fungal sinusitis (AIFS) is a rare but rapidly progressive infection affecting immunocompromised patients and carrying high morbidity and mortality. Early diagnosis is challenging, as clinical and radiological features may be subtle or overlap with other inflammatory conditions. Histopathology remains the diagnostic gold standard, underscoring the need to recognise early imaging cues. Aims: To evaluate radiological features of histologically confirmed AIFS and identify early markers that may raise clinical suspicion. Retrospective review of CT and MRI studies assessed patterns including bone erosion, extrasinus extension, periantral fat stranding and mucosal changes, with correlation to histopathology. Results: Four patients with confirmed AIFS underwent retrospective imaging review. Imaging appearances were variable, reflecting differences in pathogen virulence and host immune status. Abnormal soft tissue changes, particularly perisinus inflammation, were the most consistent findings. Bone erosion and mucosal hypoenhancement were not universal but were useful when present. Diffusion restriction on MRI aided detection of necrotic or purulent areas, though caution is required as proteinaceous or haemorrhagic material may appear similar. Non-contrast MRI remained informative, demonstrating soft tissue inflammation more clearly than CT, though oedema was still appreciable on CT. Conclusion: AIFS shows variable imaging features, and this case series highlights key correlating findings across MRI and CT. These preliminary observations provide proof of concept for a larger study aimed at more precisely defining the complex radiological presentation of AIFS. 1. Voruz F, Neofytos D, Van Delden C, Lobrinus J, De Vito C, Macario S, et al. The Importance of MRI in the Early Diagnosis of Acute Invasive Fungal Rhinosinusitis. Diagnostics (Basel). 2025;15(3).