Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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January 2, 2025
Cerebral Aspergillosis Mimicking Aggressive Brain Neoplasm
- Background:
- Aspergillosis is very rare and difficult to diagnose clinically and on imaging as the classic neuroimaging findings of CNS aspergillosis described in immunocompromised patients are often not seen in immunocompetent individuals. Aspergillus flavus is the most common organism affecting immunocompetent hosts. Invasion of the central nervous system tends to occur as a result of hematogeneous dissemination among immunocompromised patients, and by local extension or direct inoculation secondary to trauma in immunocompetent hosts.
- Compromised sinus aeration and altered immune status could facilitate growth of the organism and eventual contiguous spread into the cranial cavity.
- Meningitis, cerebritis, abscess, granuloma, infarction, and mycotic aneurysms are among the varied involvement of cerebral aspergillosis. Among the reported cases of cerebral aspergillosis in immunocompetent hosts, only a small number of patients had large space-occupying lesions of the brain, as this patient did. We believe that straight extension from the sphenoid sinus is the most likely cause of infection in this case.
- Usually, neoplasm is the first diagnosis in a case of enhancing lesions with perilesional edema and mass effect seen on neuroimaging. However, certain nonneoplastic diseases, particularly infectious lesions, can also have comparable imaging features.
- Typically, culture and histologic examination of the brain biopsy specimen are done to establish the premortem diagnosis. Finding any particular neuroimaging abnormalities that would indicate the infection would be beneficial for an early diagnosis of aspergillosis because the disease is difficult to diagnose clinically.
- Clinical Presentation:
- Aspergillus invasion of the CNS may result in brain abscess, cerebritis, meningitis, cranial sinus thromboses, and ventriculitis. Therefore, patients may present with a variety of signs and symptoms, such as fevers, headaches, lethargy, altered mental status, seizures, abnormal gait, dizziness, or focal neurologic deficits
- Key Diagnostic Features:
- The MR imaging finding of a low T2 signal intensity zone surrounded by a thick surrounding enhancement should suggest the likely diagnosis of a fungal etiology. Aspergillosis and mucormycosis are the 2 fungi that are pathogenic in the hyphal form.
- T2-hypointense regions represent dense population of aspergillus hyphal elements and hypointensity is attributed to paramagnetic elements that are essential for the hyphal growth, especially iron and magnesium. Other elements including magnesium, zinc, calcium, chromium, and nickel are also present. Diffusion restriction is less compared with pyogenic infections.
- The discrepancy between the extensive mass effect and minimal neurologic deficit was likely due to accommodation of the brain to a slow-growing mass and compression of healthy brain rather than invasion or destruction.
- Differential Diagnosis:
- Aggressive primary brain neoplasms like glioblastoma: presence of T2 hypointensity showing blooming and tiny foci of diffusion restriction, absence of typical heterogeneous enhancement pattern, and long-standing history are features against.
- Treatment:
- The most effective treatment of cerebral aspergillosis is medical and surgical: Debridement of infected tissues along with systemic antifungal medication (current guidelines recommend the use of voriconazole [oral or IV]). Good outcome is expected with a combination of early diagnosis, prompt surgical removal, initiation of aggressive antifungal therapy, and the host immune response of the patient.
- Duration of antifungal treatment is not clearly established and typically continues for several months, depending on the clinical and radiologic response and ongoing immunosuppression.
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