Acute invasive fungal sinusitis

• Unilateral nasal cavity mucosal thickening (often the most common finding)
• Periantral fat stranding on CT/MRI (early sign of vascular invasion)
• Bone destruction or dehiscence on CT (may be subtle or inapparent)
• Fat stranding beyond the sinus perimeter or in masticator/pterygopalatine spaces

• CT demonstrates mucosal thickening (hypoattenuating), sinus opacification (soft tissue attenuation), and variable bone destruction that may be extensive, subtle, or inapparent due to vascular invasion
• CT findings include fat stranding outside the sinus, involvement of periantral fat, bone dehiscence, orbital invasion, nasal septal ulceration, pterygopalatine fossa involvement, and lacrimal duct/sac involvement
• MRI shows T1 intermediate-low signal within the fungal mass with T2 intermediate-to-low signal, often associated with fluid or blood elsewhere in the paranasal sinuses
• MRI with gadolinium shows absent sinus mucosal enhancement suggesting necrosis, while invasion beyond the sinus appears as increased enhancement
• Critical MRI findings for extrasinus extension include periantral fat stranding on T1 and STIR/T2 fat-saturated sequences, intraorbital fat involvement, masticator space stranding, and pterygopalatine fossa involvement
• Complications visible on MRI include subtle enhancement on T1 fat-saturated sequences, leptomeningeal enhancement, intracranial granulomas (low signal on T1 and T2), cavernous sinus thrombosis, carotid pseudoaneurysm, cerebritis, and brain abscess
• Early imaging findings may be mild, particularly in the initial phases, so imaging must be interpreted in context of high-risk immunocompromised status
• MRI is the modality of choice for assessing soft tissue extension and intracranial, intraorbital, or cavernous sinus involvement when clinically suspected

• Chronic invasive fungal sinusitis: distinguished by longer clinical history (>12 weeks), presence of hyperdense material in sinuses on CT, and sclerotic changes to bony sinus walls
• Complicated acute rhinosinusitis: lacks aggressive features of invasive fungal disease and typically responds to medical management without vascular invasion
• Sinonasal carcinoma: lacks the clinical context of immunosuppression and the pattern of periantral fat stranding with early vascular invasion
• Sinonasal non-Hodgkin lymphoma: can present similarly but typically has different clinical and imaging features on MRI
• Pott puffy tumor: frontal bone osteomyelitis presents differently with frontal swelling without the rapid invasive pattern
• Mucocele: benign retained secretion without acute inflammatory signs or tissue invasion

In an immunocompromised patient with acute sinusitis, always specifically evaluate for periantral fat stranding and check the extent of disease beyond the sinus boundaries (orbit, masticator space, pterygopalatine fossa, cavernous sinus) as these findings significantly impact urgency of management and prognosis; if any concerning features are present, recommend urgent MRI and immediate clinical correlation given the aggressive nature of this condition.

• Underestimating subtle early findings: mild periantral fat stranding may be the only sign of vascular invasion in early disease, requiring high suspicion in immunocompromised patients
• Assuming intact bony cortex rules out invasive disease: fungal organisms can spread through intact bone via vascular invasion, so imaging findings may be inapparent despite significant extension
• Missing extrasinus complications: failure to carefully evaluate for orbital, intracranial, and cavernous sinus involvement can delay recognition of life-threatening complications like abscess, thrombosis, or mycotic aneurysm
• Confusing acute with chronic invasive fungal sinusitis: chronic disease has longer history (>12 weeks), hyperdense material, and sclerotic bone changes; acute disease lacks these features and progresses over days to weeks