Sinonasal Oxalosis due to Fungal Rhinosinusitis: A Unique Case of a Destructive Pseudotumor.

Oxalosis refers to the accumulation of calcium oxalate crystals in various organs and tissues, most commonly due to infection involving the lung or sinonasal tract. Both invasive and noninvasive forms of fungal rhinosinusitis can be associated with calcium oxalate crystal deposition. Here, we report a unique case of sinonasal oxalosis presenting as a destructive lesion in the absence of invasive fungal disease. Due to the clinical and pathologic significance of calcium oxalate crystals as seen in this patient, specimens from the sinonasal tract should be evaluated for the presence of these crystals, which may be a surrogate marker for fungal infection and may also independently cause tissue destruction.