Mucormycosis

Why Mucormycosis is correct

• Mucormycosis is caused most commonly by Rhizopus and Mucor; major risk factors include uncontrolled diabetes with ketoacidosis (acidic pH releases iron from transferrin, fueling fungal growth), hematologic malignancy, and transplant.
• KOH preparation shows broad (6-25 micron) aseptate hyphae with wide-angle (90-degree) branching — exactly as described — distinguishing Mucorales from Aspergillus.
• Angioinvasion leads to thrombosis, rapidly progressive necrosis, and black eschar with the orbital extension seen here.

Why the others are wrong

• Candidal sinusitis — Candida forms narrow, septate pseudohyphae or true hyphae, not the broad aseptate wide-angle hyphae shown (confused-with fungal morphology).
• Invasive aspergillosis — produces septate hyphae with 45-degree acute-angle branching on KOH, not broad aseptate wide-angle hyphae (confused-with mold morphology).
• Fusarium sinusitis — Fusarium is also an angioinvasive mold, but it produces narrow hyaline septate hyphae rather than the broad aseptate hyphae shown, and invasive fusariosis occurs mainly in patients with hematologic malignancy or stem cell transplant, especially with profound neutropenia, rather than in uncontrolled diabetes (confused-with angioinvasive mold).
• Maxillary fungus ball — the maxillary sinus is the most common site of a fungus ball, which opacifies the sinus on CT, but a fungus ball is a noninvasive mass of densely packed septate hyphae, usually Aspergillus, that typically forms in an immunocompetent host; it does not invade tissue, so it does not produce the orbital extension, proptosis, and rapid necrosis of angioinvasive disease in uncontrolled diabetes (confused-with noninvasive fungal sinusitis).

Additional high-yield points

• Treatment: (1) aggressive surgical debridement (mainstay of cure); (2) liposomal amphotericin B 5-10 mg/kg/day; (3) isavuconazole as an alternative or in combination; (4) control diabetes; (5) reduce immunosuppression.
• Voriconazole must be AVOIDED — all Mucorales have intrinsic resistance to voriconazole.

Why Rhino-orbital mucormycosis is correct

• Rhino-orbital-cerebral mucormycosis is the classic presentation in a patient with diabetic ketoacidosis: acidosis impairs phagocytosis and frees iron, and hyperglycemia plus available iron promote rapid growth of Mucorales molds.
• The Mucorales are angioinvasive, causing vascular thrombosis, tissue infarction, and necrosis — producing the pathognomonic black eschar on the nasal turbinate or hard palate.
• Proptosis, ophthalmoplegia, and a fixed dilated pupil reflect orbital and cavernous sinus extension, a surgical emergency requiring immediate liposomal amphotericin B and aggressive debridement.

Why the others are wrong

• Bacterial orbital cellulitis causes periorbital swelling and proptosis but is not angioinvasive and does not produce a necrotic black eschar; it typically responds to antibiotics, which failed here.
• Invasive sinus aspergillosis shares the immunocompromised host and angioinvasion, but galactomannan and beta-D-glucan are positive (negative in mucormycosis), and a palatal black eschar in a DKA patient points to Mucorales (broad non-septate hyphae with 90-degree branching) rather than Aspergillus (septate, 45-degree branching).
• Sinonasal squamous carcinoma is a chronic, slowly infiltrative process diagnosed by biopsy; it does not cause acute fever, rapid necrosis, and a black eschar over days.
• Granulomatosis with polyangiitis — bloody nasal discharge, sinus disease that fails antibiotics, and orbital inflammation with proptosis can all occur in this ANCA vasculitis, but it typically evolves over weeks to months, is usually PR3-ANCA (c-ANCA) positive, and often involves the lungs (nodules) and kidneys (glomerulonephritis); it is not angioinvasive and does not produce a black necrotic eschar over days in a patient with diabetic ketoacidosis.