Spectrum of orbital fat necrosis in rhino-orbital-cerebral mucormycosis in post-COVID-19 patients

Purpose: Rhino-orbital-cerebral mucormycosis (ROCM) is the most common presentation of mucormycosis. Sinonasal–orbital debridement with exenteration is a life-saving procedure in ROCM patients in view of severe involvement of sinuses and the eyeball. Following the second wave of coronavirus disease 2019 (COVID-19), there was a massive surge in mucormycosis cases in India in post-COVID-19 patients. Of over 300 cases of mucormycosis admitted in our hospital, many underwent exenteration and these specimens were evaluated histopathologically, where fat necrosis was found to be a prominent finding. The spectrum of fat necrosis in ROCM in orbital fat has not been described in literature. Hence, we sought to evaluate the significance and spectrum of orbital fat necrosis in ROCM. Methods: This 3-month retrospective study included 15 cases of ROCM which underwent exenteration. Clinical data, radiologic details, and histopathologic findings were tabulated. Sections were also subjected to Periodic acid Schiff (PAS) and Gomori’s methenamine silver (GMS) stains for confirming the fungus. Results: All 15 cases showed fat stranding on computed tomography (CT) scan. On histopathologic examination, various tissue reaction patterns observed included acute/chronic inflammatory infiltrate, suppurative granulomas with giant cells, coagulative and fat necrosis, broad aseptate fungal hyphae with or without angioinvasion, and neural invasion. Fungal hyphae were confirmed with PAS and GMS stains. The spectrum of fat necrosis observed in all the cases included 1) acute necrotizing fat necrosis, 2) ghost adipocytes with or without saponification, and 3) crystalline/gouty fat necrosis. Conclusion: Fat necrosis is a significant finding in ROCM, both on CT scan and histopathology. All three patterns of fat necrosis may be observed simultaneously in a case of ROCM.