Mycetoma of the Sinuses (Fungal Ball): Understanding Your Pathology Report

Section Editor: Jason Wasserman MD PhD FRCPC
July 16, 2026

A mycetoma of the sinuses is a dense clump of fungus that builds up inside one of the paranasal sinuses, the air-filled spaces in the bones around the nose. It is now more commonly called a fungal ball, and you may see either term on your pathology report. The most important thing to understand about this diagnosis is that it is non-invasive, meaning the fungus remains within the sinus cavity without invading the surrounding tissue or blood vessels. This makes it very different from invasive fungal infections of the sinuses, which are far more serious. A fungal ball is not cancer, and it is usually cured by removal. This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.

A note on the name: the word “mycetoma” is also used for a completely different disease, a long-standing infection of the skin and deeper tissues of the foot or limb that occurs mainly in tropical regions. The two conditions are unrelated. To avoid this confusion, most doctors now prefer the term fungal ball for the sinus condition described here.

What causes a mycetoma of the sinuses?

A mycetoma of the sinuses forms when fungal spores, which are present everywhere in the environment and are breathed in every day, settle inside a sinus and begin to grow. Over time, the fungus builds up into a dense, tangled mass mixed with mucus and debris. The fungus most often responsible is Aspergillus, particularly the species Aspergillus fumigatus, although other fungi can also be involved.

This condition typically develops in people with normal immune systems; by contrast, invasive fungal infections of the sinuses usually occur in people with weakened immune systems. A fungal ball usually forms in a single sinus, often in people without any previous history of sinus disease, although it can also develop in people with chronic rhinosinusitis. Poor drainage of the sinus is thought to allow secretions to stagnate, creating conditions where fungus can grow.

Where does a mycetoma of the sinuses develop?

A mycetoma of the sinuses most often develops in the maxillary sinus, the largest of the paranasal sinuses, located in the cheek beneath the eye. Less commonly, it forms in the sphenoid, frontal, or ethmoid sinuses. It almost always involves only one sinus on one side.

The location influences the symptoms. A fungal ball in the maxillary sinus tends to cause facial pain or pressure over the cheek, while one in the sphenoid or frontal sinus is more likely to cause headache or pain felt behind the eyes or across the forehead. The location also shapes the surgical approach used to remove it, since each sinus requires the surgeon to navigate different nearby structures.

What are the symptoms?

The symptoms of a mycetoma of the sinuses often resemble those of ordinary chronic sinusitis, which is one reason the diagnosis can take time to reach. Many fungal balls cause no symptoms at all and are discovered incidentally on imaging performed for another reason, such as a dental scan.

Nasal congestion or blockage — Usually on one side only, corresponding to the affected sinus.
Facial pain or pressure — Often felt over the affected sinus.
Postnasal drip — A sensation of mucus dripping down the back of the throat.
Decreased sense of smell — Less prominent than with nasal polyps.
Foul-smelling discharge — An unpleasant odor or taste may occur, particularly if a bacterial infection develops alongside the fungal ball.

How is the diagnosis made?

A mycetoma of the sinuses is often first suspected on imaging. A CT scan typically shows a dense mass filling a single sinus, frequently containing flecks of calcium, a finding that strongly suggests a fungal ball. The condition may also be found unexpectedly on imaging performed for an unrelated reason. Nasal endoscopy, an examination using a thin scope passed through the nose, may also be used.

The diagnosis is confirmed after the material is removed and examined under the microscope by a pathologist. Under the microscope, a mycetoma appears as dense, tangled, matted clumps of fungal filaments called hyphae, surrounded by mucus and cellular debris. The fungal elements can be difficult to see on routine slides, so special stains such as Grocott (GMS) or PAS-D are used to highlight them against the surrounding inflammatory cells and sinus tissue.

The most important part of the pathologist’s examination is confirming that the fungus has not invaded the tissue. In a mycetoma, the fungal elements remain confined to the sinus cavity and do not penetrate the lining, the underlying tissue, or blood vessels. This non-invasive pattern is what separates a fungal ball from invasive fungal sinusitis, a much more serious condition that requires urgent treatment. Sending the tissue to pathology is what allows this distinction to be made with confidence. A sample may also be sent for fungal testing to identify the specific fungus, although the fungus in a mycetoma often fails to grow in culture, even when hyphae are abundant under the microscope.

How does this compare with other fungal conditions of the sinuses?

Doctors divide fungal conditions of the sinuses into two broad groups based on whether the fungus invades the tissue. Understanding where a mycetoma sits in this scheme explains why the outlook is generally good.

Non-invasive — The fungus does not grow into the tissue. This group includes mycetoma (fungal ball), allergic fungal rhinosinusitis (an allergic reaction to fungus, in which thick mucus contains fungus and eosinophils), and simple colonization of mucus crusts. These conditions are managed without urgency.
Invasive — The fungus grows into the tissue and can spread to the eye socket or brain. This group primarily affects people with weakened immune systems, and the acute form is a medical emergency.

A mycetoma belongs firmly in the non-invasive group. If your report confirms a mycetoma with no tissue invasion, this means the more serious invasive forms have been excluded.

What happens after the diagnosis?

A mycetoma of the sinuses is treated by removing the fungal mass, most often with endoscopic sinus surgery performed through the nose. In addition to removing the fungal ball and any associated debris, the surgeon usually widens the natural sinus opening to restore normal drainage and airflow, reducing the risk of recurrence. This is often how the material described in your pathology report was obtained.

Antifungal medication is generally not needed. Because the fungus is not invading the tissue, removing the fungal ball is usually curative on its own, and antifungal drugs also penetrate poorly into the dense, tangled mass. This is a meaningful difference from invasive fungal sinusitis, where antifungal therapy is essential. If a bacterial infection has developed alongside the fungal ball, antibiotics may be considered separately.

The outlook after surgery is excellent. Cure rates are high, and recurrence is uncommon, particularly when the sinus has been opened to drain properly. Your care is usually managed by an ear, nose, and throat (ENT) specialist, who will advise whether any follow-up is needed based on your symptoms and the sinus involved.

Questions to ask your doctor

Which sinus was affected, and was it only on one side?
Did my report confirm that the fungus had not invaded the tissue?
Was the fungus identified, and does it matter which type it was?
Was the entire fungal ball removed?
Do I need any antifungal medication?
Was there any sign of a bacterial infection alongside the fungal ball?
What is the chance that this will come back?
Do I have any underlying sinus problems that also need treatment?
Do I need any follow-up appointments or imaging?
What symptoms should prompt me to contact my doctor?