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Magnetic resonance imaging MRI is the most sensitive imaging modality for further characterization of leptomeningitis, empyema, ventriculitis, or cerebral infarction. Acute or subacute fungal meningitis is often caused by yeast organisms, and cerebrospinal fluid CSF analysis serves as the diagnostic gold standard.

All patterns should be confirmed on more than three contiguous MRI. The inflammatory response in fungal disease results in deposits of thick gelatinous exudates containing inflammatory cells, fibrin, and hemorrhage leading to arachnoiditis. As fungal meningitis invites many differentials such as tuberculosis, sarcoid, or meningeal carcinomatosis, we emphasize that the imaging appearance of smooth and nodular leptomeningeal enhancement is often encountered in fungal infections but is nonspecific and needs to be correlated with CSF analysis and lab findings. Cerebritis is the earliest manifestation of brain infections and the precursor of abscess development.

On CT imaging, ill-defined intraparenchymal hypodense lesions resulting from edema and scattered areas of increased attenuation due to either hemorrhage or increased concentration of metal ions are indicative of fungal cerebritis. On T1WI, fungal cerebritis appears as an iso- or hypo-intense area with subtle mass effect, shift and minimal to no enhancement.

These lesions typically present with restricted diffusion on DWI. Britt and Enzmann defined early and late cerebritis, followed by early and late capsulitis as the four stages of abscess formation. Late cerebritis 4—5 days to 2 weeks can be differentiated from early cerebritis 3—5 days through the presence of a thick nodular enhancement on postcontrast MRI [ Figure 5 ]. On CT imaging, both stages demonstrate a low attenuation core with a contrast enhancing capsule.

Clinical symptoms include specific focal neurologic deficits and an increased intracranial pressure. While fungal abscesses are more likely to be multiple and can involve the basal ganglia, bacterial abscesses are often solitary lesions sparing the basal ganglia. On MR T1WI, fungal abscesses demonstrate a hypointense core with a surrounding iso- to mildly hyper-intense rim.

MR Imaging and Spectroscopy of Central Nervous System Infection - Semantic Scholar

T2WI shows increased signal intensity of the core of the lesion with a surrounding rim of hypointensity. Peripheral enhancement is seen on T1 weighted post contrast enhancement sequence. A dual-rim sign on DWI is a distinctive feature of a pyogenic abscess. Fungal abscesses may contain lipids 1. CNS involvement in a Cryptococcus infection usually leads to inflammation of the meninges, but abscess and granuloma formation may also occur [ Figure 7 ].

Metabolites released by Cryptococcus can inhibit the migration and function of leukocytes and promote survival as well as localized replication of the pathogen, facilitating chronic granulomatous inflammation and cryptococcoma formation.

Typical imaging findings include multiple T2 hyperintense masses with peripheral enhancement on T1 weighted post contrast enhanced images predominately found in the basal ganglia of immunocompromised individuals [ Figure 8 ], which may be mistaken for metastatic disease. Fungal infections can result in meningeal vasculitis with vessel thrombosis and localized brain infarctions and are often due to infections with Aspergillus species and Zygomycetes.

The induced inflammatory response in the vessel wall results in in situ thrombosis as a possible source of emboli [ Figure 9 ]. Disruption of the elastic laminae of the vessel wall may lead to its focal dilatation and formation of mycotic aneurysms.

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Fungal CNS infections present diagnostic challenges. Although neuroradiological manifestations of fungal CNS infections are often nonspecific, recognition of typical imaging patterns on CT and MRI are imperative to help refine the differential diagnosis and initiate early treatment.


In conclusion, our study provides additional data on the usefulness of DSC-MRI in correctly differentiating between infectious and neoplastic brain lesions and as a complementary tool to routine structural MRI. An exception in our study was low-grade gliomas, which, in our sample of patients, had rCBV values overlapping with those found in infectious lesions. Recently, with the more widespread availability of high-field MRI scanners at 3-T in the clinical practice, allowing valuable effects such as higher signal-to-noise ratio, better spatial resolution of images, shorter scan time and the concurrent acquisition of conventional structural imaging and advanced techniques such as PWI, DWI and spectroscopy [34] , it is expected an increasingly facilitated multiparametric approach to brain mass lesions, which may improve diagnostic accuracy.

Furthermore, arterial spin labeling ASL , an attractive non-invasive technique that measures blood flow by using arterial blood water as an endogenous contrast agent thus not requiring the administration of exogenous gadolinium-based contrast agent, which carries the risk of nephrogenic systemic fibrosis in patients with poor renal function , previously had limited clinical use in routine practice, but as 3-T MRI scanners have become more widely available addressing 1. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Background and Purpose Differentiating between infectious and neoplastic focal brain lesions that are detected by conventional structural magnetic resonance imaging MRI may be a challenge in routine practice.

Results Neoplastic lesions had higher rCBV values 4. Conclusion PWI is a useful complementary tool in distinguishing between infectious and neoplastic brain lesions; an elevated discriminatory value for diagnosis of infectious brain lesions was observed in this sample of patients when the rCBV cutoff value was set to 1.

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Funding: The authors have no support or funding to report. Introduction Differentiating between infectious and neoplastic focal brain lesions that are detected by imaging examinations is an important role usually expected from radiologists. Patients We retrospectively analyzed a total of consecutive patients mean age, MRI Acquisition We performed the brain examinations on a 1.

Download: PPT. Figure 1. Examples of rCBV maps of neoplastic and infectious lesions. Table 1. Univariate analysis of rCBV values for each group of lesions neoplastic and infectious and for the two subsets within the neoplastic group primary and metastatic lesions. Figure 2. Figure 3. ROC curve representing the discriminatory capability of rCBV in correctly classifying a lesion as infectious using a cutoff point of 1.

Figure 4. A cutoff point for rCBV values x- axis of 1. Table 3. Diagnostic performance of rCBV for the diagnosis of infectious lesions with a cutoff point of 1. Discussion Our results demonstrated statistically significant lower rCBV values in brain infectious lesions than in neoplastic lesions, and a good ability of PWI to successfully distinguish between these two conditions, with elevated sensitivity, specificity, positive and negative predictive, and accuracy values. References 1.

ECR 2010 / C-3394

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2-CNS infections

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Magnetic resonance imaging in central nervous system tuberculosis

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