by Jason Wasserman MD PhD FRCPC
May 14, 2024

A mycetoma of the sinus, also known as a fungal ball, is a type of fungal infection that occurs within the paranasal sinuses. It is typically non-invasive but can cause significant symptoms due to the mass effect of the fungal accumulation.

What causes a mycetoma?

Mycetoma of the sinus is caused by the accumulation of fungal hyphae, most commonly from fungi in the Aspergillus species, although other fungi can also be involved. It usually forms in a single sinus and develops when fungal spores are inhaled and then colonize the mucus lining of the sinus. This typically occurs in people with normal immune systems and without a history of sinus disease, although it can also develop in individuals with a history of chronic rhinosinusitis.

What are the symptoms of a mycetoma?

Symptoms of a mycetoma of the sinus often mimic those of chronic sinusitis and may include:

• Nasal congestion or blockage.
• Sinus pressure or pain.
• Postnasal drip.
• Decreased sense of smell.
• Occasionally, discharge may be foul-smelling if there is a secondary bacterial infection.

Commonly affected sites

Mycetomas typically develop in the maxillary sinus, which is the largest of the paranasal sinuses and is located under the eyes in the cheek area. This sinus is the most common site due to its larger size and more frequent exposure to inhaled air and particles, including fungal spores. However, mycetomas can also occur in other sinuses, such as the sphenoid, frontal sinuses, or ethmoid sinuses, although this is less common. The preference for the maxillary sinus may be related to its drainage pattern, allowing for the accumulation and stagnation of secretions where fungi can grow.

This location-specific tendency has implications for symptoms and treatment. For example, mycetomas in the maxillary sinus may cause more prominent symptoms of facial pain or pressure, whereas those in the sphenoid or frontal sinuses might lead to headaches or pain that is felt more diffusely across the forehead or behind the eyes. Surgical approaches to remove the fungal mass also vary depending on the affected sinus, with the need for careful navigation around critical anatomical structures.

Microscopic appearance

Under the microscope, a mycetoma appears as dense conglomerates of fungal hyphae, typically tangled and matted together, often surrounded by mucus and cellular debris. These fungal elements stain with special stains such as Grocott or PAS-D, helping to differentiate them from the surrounding inflammatory cells and sinus tissue. The non-invasive nature of mycetomas means that the fungal elements do not penetrate into sinus tissues or blood vessels.

Mycetomas are often diagnosed incidentally on imaging studies conducted for other reasons, or they may be suspected based on symptoms and then confirmed by endoscopic examination and imaging. Treatment typically involves surgical removal of the fungal mass, as these infections generally do not respond to antifungal medications due to the dense, compact nature of the fungal ball that prevents the medication from being absorbed.