General description

Aspergillus, a filamentous fungus, is known to cause invasive infections affecting the lungs and other body parts. It can lead to meningitis, encephalitis, and brain abscesses through the extension of sinusitis into the cranium or via hematogenous spread.

Aspergillus species naturally reside in the oral cavity, nasal cavity, and paranasal sinuses without being pathogenic under normal circumstances. They primarily cause disease in immunocompromised patients. However, in immunocompetent individuals, certain risk factors increase the likelihood of Aspergillus-related diseases. These risk factors include advanced age, diabetes mellitus, alcohol use, and liver failure.

Radiographic features

On T1WI, lesions typically exhibit hypointensity surrounded by peripheral patchy hyperintensity, which reflects the presence of iron, manganese, and methemoglobin. T2WI displays hypointensity in the corresponding areas, whereas T2WI shows inhomogeneous patterns of hyperintensity. The contrast enhancement of these lesions is minimal.

The lesions are commonly located at the corticomedullary junction of the brain, indicating hematogenous spread. This pattern of spread is also observed in brain abscesses; however, Aspergillus is notable for its vascular invasiveness. This leads to the obstruction of penetrating branches, resulting in the distribution of lesions within the basal ganglia, thalamus, corpus callosum, and brainstem—locations that are rarely affected in other infectious diseases.

Orbital apex syndrome

If aspergillosis spreads from the paranasal sinuses to the apex of the orbital cavity, it can affect the optic nerve, trochlear nerve, ophthalmic nerve, and abducens nerve.

CT imaging shows increased attenuation within the sphenoid and ethmoid sinuses, along with decalcification of the superior part of the sphenoidal bone.

MRI reveals a lesion in the apex of the orbital cavity that displays T1WI isointensity, comparable to cerebral white or gray matter, extending from the paranasal sinus. Owing to the iron component of Aspergillus, T2WI demonstrates hypointensity. DWI indicates restricted diffusion.