Year : 2006 | Volume
: 16 | Issue : 4 | Page : 749--752
S Singh, V Chowdhury, R Dixit
Department of Radiodiagnosis, Maulana Azad Medical College and associated Lok Nayak Hospital, Jawahar Lal Nehru Marg, New Delhi - 110002, India
212, SFS Flats, Phase IV, Ashok Vihar, Delhi - 110052
|How to cite this article:|
Singh S, Chowdhury V, Dixit R. CNS aspergillosis.Indian J Radiol Imaging 2006;16:749-752
|How to cite this URL:|
Singh S, Chowdhury V, Dixit R. CNS aspergillosis. Indian J Radiol Imaging [serial online] 2006 [cited 2020 Apr 8 ];16:749-752
Available from: http://www.ijri.org/text.asp?2006/16/4/749/32339
Aspergillosis of the central nervous system tends to occur most often in immunosuppressed patients. Its incidence has increased with the practice of intensive chemotherapeutic regimens, use of corticosteroids and transplantation procedures. Manifestations include meningitis, meningoencephalitis, granulomata formation, abscess, vasculitis, aneurysm formation, infarct and intracranial haemorrhage. Unlike some saprophytic opportunistic pathogens that decimate immunocompromised patients, aspergillus infection is treatable. The survival of patients depends on early diagnosis and prompt initiation of therapeutic measures.
A high index of clinical suspicion and familiarity with the imaging findings may ensure an earlier diagnosis and consequent early onset of therapy.
A 35 year old male with non- Hodgkin's lymphoma on chemotherapy presented to the emergency room with sudden onset of seizures. He was suffering from headache, slurred speech and inability to walk. He also had history of productive cough of 4 weeks duration. On examination the patient was febrile with normal vital signs. Chest X-ray revealed extensive pulmonary infiltrates. MRI examination was performed which showed multiple focal lesions of T2 hyperintensity with hypointense rim with extensive perilesional edema and mass effect in the right basal ganglia, right parietal and bilateral temporal regions.Few interspersed foci of hypointensity were also seen. (Fig. 1). Similar findings were seen on FLAIR coronal MR images (Fig. 2). Gradient echo FLASH images revealed extensive blooming of the interspersed foci of low signal seen on T2 and FLAIR images suggesting haemorrhagic foci. Diffusion weighted images (Fig. 4a) and ADC maps (Fig. 4b) revealed evidence of restricted diffusion in the focal lesions. Postgadolinum T1W axial MR image (Fig. 5a) and postgadolinium T1W coronal MR images (Fig. 5b) revealed ring and nodular enhancement of the focal lesions s/o multiple abscesses.
The sudden onset of neurological symptoms in a febrile immunocompromised patient with extensive pulmonary infiltrates and multiple abscesses with mass effect on MR suggested the diagnosis of cerebral aspergillosis. The patient's sputum culture was positive for Aspergillus. Medical antifungal therapy was instituted resulting in clinical improvement.
Aspergillosis is a ubiquitous mold normally found in soil, water or decaying vegetation. Although this species may exist in the mycelial or hyphal form, the hyphal form predominates at room temperature. It is an opportunistic infection affecting mainly those with immunodeficiency .
The typical route of entry by aspergillus organisms is through inhalation of spores. Once within the pulmonary tree, the organism is usually contained as a result of the host's normal immune response with a resultant hypersensitivity reaction. Lapses in the host's immune defenses result in superinfection, haematogenous spread and dissemination through the body, including the CNS with the formation of granuloma, brain abscess or meningitis. Less commonly it is caused by direct extension of disease in the nasal cavity and paranasal sinuses known as the rhinocerebral form ,.
The hyphal elements lodge in intracerebral blood vessels, grow through the vessel walls causing occlusion resulting in infarct which is commonly haemorrhagic . This sterile infarct is converted into a septic infarct when the fungus erodes through the vessel wall resulting in fungal vasculitis and subsequently mycotic aneurysm . Aspergillosis is the most common cause of fungal mycotic aneurysms. The apparent affinity of CNS aspergillosis for perforating artery distribution is due to the invasive nature of the aspergillus within the walls of larger patent arteries to which it has spread haematogenously subsequently compromising the origin of the perforating arteries.
Early diagnosis of CNS aspergillosis in an immunocompromised patient can be achieved by diffusion weighted MR imaging, where conventional CT and MRI are not of much help . Diffusion weighted images are of value in identifying early lesions as these lesions represent septic infarction. The finding of cerebral infarction on imaging in a patient with known risk for cerebral aspergillosis should suggest the diagnosis. The presence of ring or nodular enhancement consistent with granuloma or abscess formation indicates that the host defence system is able to encapsulate the offending organism. MRI reveals a hyperintense lesion with hypointense rim on T2-weight images. The lesions show vasogenic oedema and contrast enhancement.
Invasive or rhinocerebral aspergillosis results from involvement of the orbit, paranasal sinuses, base of skull, anterior and middle cranial fossae or parasellar regions with direct extension to the brain. Imaging findings related to aspergillosis are most noted within the paranasal sinuses. CT scan findings typically show significant sinusitis with areas of hyperattenuation within the sinuses. MR imaging findings may show markedly hypointense signal on the T1-weighted and T2-weighted images which might be mistaken for aerated sinuses. Post-gadolinium study shows rim enhancement. Analysis of the washings from diseased sinuses have shown increased concentrations of calcium, magnesium, manganese and iron which may account for the decreased signal intensity on T2-weighted images .
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