The black turbinate sign refers to an area of non-enhancing mucosa on MRI in a patient with angioinvasive fungal sinus infection.
Mucormycosis is caused by fungi that include Mucor, Rhizopus, and Absidia species. It is seen in diabetic and immunocompromised patients.
Fungal spores germinate to form angioinvasive hyphae that cause infarction of the surrounding tissue and invade the nasal mucosa.
The invaded tissue is nonenhancing on contrast-enhanced MR imaging and may show diffusion restriction. Non infarcted sinusitis shows T1 post contrast enhancement of the mucosa.
This sign is important for the early detection of mucormycosis so treatement may be initiated to reduce the chance of blindness and death which may occur within 2 weeks if left untreated.