The initial evaluation of an immunodeficient patient with symptoms of sinusitis should include a thorough head and neck examination, as well as nasal endoscopy, to identify any mucosal or structural abnormalities. Endoscopy-guided cultures should be obtained if discharge from the middle meatus or sphenoethmoid recess is identified. The diagnosis of IFS can pose a challenge, because physical examination findings may be very subtle. The endoscopic findings range from pale, ischemic mucosa to well-circumscribed necrotic plaques. Perforations of the nasal septum and hard palate may be present, and fungal infection may also be accompanied by suppuration, causing confusion with bacterial sinusitis.
Radiologic studies often play a key role in diagnosis, although debate exists regarding which imaging modality is the best for detecting IFS. Unilateral edema of the sinonasal mucosa with or without bony erosion on CT scan should lead to suspicion of fungal sinusitis or a neoplasm. The presence of bony erosion or changes in signal intensity of the soft tissue outside of the sinuses is highly suggestive of an invasive process. Whereas high-resolution CT imaging is the study of choice to identify bony erosion, MRI is superior in delineating the intracranial or orbital extent of disease. Changes seen on T1-weighted images are isointense in bacterial and fungal infections, but T2-weighted images demonstrate low signal intensity for fungal disease and high intensity for bacterial disease. Suspicious findings for IFS on MRI include obliteration or infiltration of periantral or orbital fat, inflammatory changes in the extraocular muscles, or leptomeningeal enhancement. A case-controlled study found that MRI had higher sensitivity than CT (85% vs. 63%) with similar specificity (83%) for detecting IFS. Regardless of which type of study is obtained, a low threshold for imaging patients with low neutrophil or CD4 counts is advised.

Invasive fungal sinusitis represents a diagnostic and therapeutic emergency, and any suspicion should be addressed as soon as possible. Consideration may be made for inferior and/or middle turbinate biopsy or diagnostic antral lavage with biopsy and histologic examination. A frozen section of a biopsy specimen is often used to accelerate initiation of treatment with antifungal agents. Biopsy tissue and drainage from the middle meatus should be collected and sent for bacterial and fungal culture. No uniform guidelines have been established for the diagnosis of IFS, although any suspicious lesions should undergo biopsy with silver staining, histopathology, and
culture.
Fungal sinusitis can extend via thrombophlebitic or hematologic spread and thus may enter into the orbit or intracranial cavity without histologic evidence of mucosal invasion. The angiocentric invasion pattern of Aspergillus may allow extension of disease without evidence of bony destruction on imaging. Thus in the clinical scenario consistent with fungal sinusitis and fungal elements identified on silver stain or culture, treatment of fungal sinusitis should begin regardless of the histologic confirmation of invasion.

Source: Cummings Otolaryngology, 6E (2015)