The black turbinate sign refers to the non-enhancement of nasal turbinates in a patient with acute invasive fungal rhinosinusitis.
Angioinvasive fungal infection (e.g. mucormycosis or aspergillosis) involves the nasal mucosa and causes infarction of the surrounding tissue. The infarcted tissue is non-enhancing on contrast-enhanced MRI and may show diffusion restriction 1,3. In comparison, non-infarcted inflamed mucosa shows contrast enhancement.
This sign is important for the early detection of invasive fungal rhinosinusitis 1. However, the sign is not entirely specific as it has been observed in immunocompetent individuals with essentially no chance of invasive fungal rhinosinusitis 2. Thus, correlation with clinical history is important for accurate interpretation. Features of benign black turbinates include progressive enhancement on delayed sequences, preserved thin peripheral mucosal enhancement, and thin internal septations 2.
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