Answer: Invasive fungal sinusitis

Histology: This “mass” consists of necrotic bone and bone marrow. Within the necrotic marrow, one can appreciate ghosts of dead fungal hyphae on the H & E stain. The presence of hyphae is highlighted particularly well on the silver stain.

Discussion: Given the presence of necrosis, necrotic tumor would be the major differential diagnosis. Necrotic tumor is typically characterized by ghost cells marking the remnants of highly cellular foci. Occasionally, even a necrotic tumor can be characterized by immunohistochemistry to provide a definitive diagnosis, though this is fraught with pitfalls. A fungus ball is typically seen in an immune competent host, and does not show tissue invasion. Instead the fungus is a colonizer and is associated with a chronic clinical course. Allergic fungal sinus also is not characterized by tissue invasion, but instead by allergic mucin which is laminated, and replete with debris of eosinophils.

Acute fulminant (invasive) fungal sinusitis affects severely immuno-compromised patients who are usually neutropenic. This patient was neutropenic due to therapy for leukemia. The typical finding is that of tissue necrosis and vascular invasion without an associated inflammatory reaction. Treatment involves emergent radical debridement, along with systemic antifungal therapy. It is difficult to speciate fungi on histologic sections, as dying Aspergillus hyphae may become swollen and look like Zygomycetes like Mucor. Culture results should be correlated with the histologic findings.