This patient most likely has acute Aspergillus rhinosinusitis. Invasive fungal infections, such as sinusitis, are uncommon except in immunocompromised persons with prolonged neutropenia, such as this patient who has an underlying hematologic malignancy and is undergoing chemotherapy. His clinical symptoms (sinus pain), examination and radiographic findings (sinusitis and exophthalmos), and laboratory studies (positive result on galactomannan antigen immunoassay and characteristic histopathologic findings) support the diagnosis of Aspergillus rhinosinusitis. Direct invasion into the palate can occur from infection of the maxillary sinus. Infection of the ethmoid sinus may extend into the cavernous sinuses and cause cranial nerve deficits and internal carotid artery thrombosis. Central nervous system (CNS) involvement may also occur as a complication. Additionally, periorbital infection with subsequent loss of vision may occur. The mortality rate of Aspergillus rhinosinusitis is high. Definitive diagnosis requires a tissue biopsy demonstrating hyphae and a positive culture for Aspergillus. The appearance of septate hyphae with acute angle branching on histopathologic testing can be diagnostic. The galactomannan assay is an important non-culture-based tool for the diagnosis of invasive aspergillosis. Detection of galactomannan in serum has a high sensitivity and specificity in patients at high risk; galactomannan can also be detected in cerebrospinal fluid specimens from patients with CNS aspergillosis and in bronchoalveolar lavage fluid from those with invasive pulmonary aspergillosis. It is useful in early detection and in therapeutic monitoring. Voriconazole is the therapy of choice for most patients with invasive aspergillosis because of its potent fungicidal activity against Aspergillus species. Culture confirmation is important to distinguish Aspergillus from other filamentous fungal infections.

Candida and Cryptococcus are yeasts that are unlikely causes of rhinosinusitis and do not result in a positive finding on galactomannan assay or have the characteristic morphologic features of Aspergillus.

Although rare in otherwise healthy patients, Pseudomonas rhinosinusitis is encountered most frequently in immunocompromised or severely traumatized patients. Pseudomonas is a gram-negative, bacillary bacterium that also does not cause a positive galactomannan test result.