Central nervous system aspergillosis caused by Aspergillus niger after implant cranioplasty in an immunocompetent patient: a case report

The human brain is a protected sanctuary, shielded by bone and a complex barrier that keeps most germs out. When this defense is breached, usually by surgery or injury, the risk of infection rises. Among the many organisms that can cause trouble, a group of common molds called Aspergillus is particularly dangerous when it invades the central nervous system. These fungi are typically found in the environment, on soil or decaying plants, and they rarely make healthy people sick. However, when they do enter the brain, they can cause severe damage, leading to seizures, weakness, or changes in mental status. While this condition is well-known in patients with weakened immune systems, such as those undergoing chemotherapy or taking strong steroids, it is considered an extreme rarity in people with normal immune defenses. Understanding how these infections take hold in healthy individuals is crucial, because the path to recovery often depends on recognizing the specific culprit and treating it with the right combination of surgery and medication.

This story begins with a sixty-one-year-old man who had survived a brain aneurysm rupture three years prior. That initial event required a major surgery where a portion of his skull was removed to relieve pressure, an operation that unfortunately opened a pathway from his frontal sinus into his brain cavity. Over the following years, doctors attempted to repair the missing bone in his skull twice: first using his own bone, and later using a synthetic implant. Two weeks after the second repair, the man began to feel unwell. He developed a headache and noticed weakness on the left side of his body. His surgical wound, located on the right side of his forehead, started leaking fluid, and a screw from the implant began to push outward. Although he was not running a fever, his condition was deteriorating, and he became drowsy.

When medical teams examined him, a scan of his brain revealed a troubling picture. There was a pocket of air trapped under the skin flap, and a strange, irregular mass of soft tissue with pockets of air was growing near the implant. The surgeons decided to reopen the wound immediately to clean out the area and remove the synthetic bone plate. As they worked, they saw something unusual beneath the artificial bone: the tissue looked unhealthy and was covered in black, soot-like deposits. This visual clue strongly suggested a fungal infection rather than a standard bacterial one. To confirm their suspicion, the team took samples of the tissue and sent them to the laboratory for analysis.

The laboratory results provided a definitive answer. Under a microscope, the samples revealed branching, thread-like structures typical of fungi. When these threads were grown in a petri dish, they produced colonies that started as white and fluffy but quickly turned into dense, black, powdery masses. Further testing using advanced mass spectrometry, a technique that identifies organisms by their chemical fingerprints, confirmed the specific species as Aspergillus niger. This was a significant finding because this particular type of fungus is rarely the cause of brain infections, especially in a patient who was not immunocompromised. The evidence pointed to the infection spreading directly from the man's frontal sinus, which had been exposed during his original aneurysm surgery, into the brain cavity where the implant now sat.

Treating this infection required a careful and precise approach. The medical team chose a powerful antifungal medication called voriconazole, known for its ability to cross the blood-brain barrier and reach the infected tissue. They started the patient on a high dose to quickly build up the drug in his system, but the journey was not straightforward. The patient's body reacted unpredictably; at one point, the level of the drug in his blood became dangerously high, causing nausea and confusion. The doctors had to lower the dose, but then the patient's changing physical condition, including a sunken area where the bone flap had been removed, made it difficult for his body to absorb the medicine through his stomach. This led to the drug levels dropping too low to be effective. To solve this, the team switched him to an intravenous form of the medication, ensuring a steady and reliable supply directly into his bloodstream.

After six weeks of this rigorous treatment, the infection was under control. The patient's symptoms improved, and follow-up tests showed that the fungus was no longer growing in the tissue samples. With the infection cleared, the surgeons were able to perform a final reconstructive surgery, placing a new, custom-made bone flap to restore the shape and protection of his skull. The man recovered well and continued on a lower dose of the medication to prevent the infection from returning. This case highlights a rare but critical lesson for medical practice: even in patients with healthy immune systems, brain infections can occur after neurosurgery, particularly when the surgery involves the sinuses. It demonstrates that early recognition of unusual signs, such as blackish tissue or persistent wound discharge, combined with aggressive surgical cleaning and carefully monitored drug therapy, can lead to a successful outcome where the odds might otherwise seem poor.