Imaging description

Invasive fungal sinusitis occurs predominantly in immunocompromised patients or patients who are on chronic steroid therapy or have diabetes. The most dreaded acute invasive form is seen in severely immunocompromised patients, while the chronic form is more common in diabetics.

In acute invasive fungal sinusitis, there is rapid invasion of mucosa, submucosa, and blood vessels with neutrophilic infiltrates. On CT, there is complete or partial soft tissue opacification of the paranasal sinus with mucosal thickening. Areas of bone erosion are common, with infiltration of adjacent fat and soft tissues (Fig. 69.1), but can be subtle. Intraorbital and intracranial extension takes place along the perivascular or perineural spread [1] or through direct bony invasion (Fig. 69.2). On MRI, the sinus secretions exhibit low T1 and high T2 signal [2]; however, high T1 signal may suggest proteinaceous content or fungal aggregation [3]. Fungal elements may also cause low T2 signal, which can look analogous to air within the sinuses (Fig. 69.3). When the sphenoid sinus is involved, there is a high incidence of cavernous sinus thrombosis and obliteration of the internal carotid artery (Fig. 69.2). Intracranial extension through cribriform plate and orbital invasion is common when ethmoidal sinuses are involved. Involvement of the maxillary sinus results in encroachment of retroantral fat or premaxillary soft tissue. Mucormycosis is more commonly associated with acute invasive fungal sinusitis, while in more than 50% of cases with chronic invasive fungal sinusitis Aspergillus fumigatus is the culprit.