CNS INFECTIONS

Acute Bacterial Meningitis

In uncomplicated cases of purulent meningitis, early CT scans and MRIs usually

demonstrate normal findings or small ventricles and effacement of sulci.

This axial nonenhanced computed tomography scan shows mild ventriculomegaly and sulcal effacement

Acute bacterial meningitis. This axial T2-weighted magnetic resonance image shows only mild ventriculomegaly.

This contrast-enhanced, axial T1-weighted magnetic resonance image shows leptomeningeal enhancement (arrows).

Viral Meningitis and Meningoencephalitis

Viral Meningitis

• The diagnosis is made clinically and imaging has no contribution.

Viral Encephalitis

• Brain imaging is frequently normal in viral encephalitis. Occasionally, nonspecific changes consist of either sulcal effacement (H) (thin arrow), compared with normal sulcal spaces (thick arrow); or increased signal (I) (arrow), reflecting increased water content in the mildly swollen brain of the same patient

• These changes developed in a patient with probable enterovirus encephalitis but can be produced by many viruses, as well as after head injury and in various metabolic encephalopathies.

Herpes simplex virus encephalitis

. Abnormal signal and edema in the left temporal lobe (short bottom arrow), insula (long arrow) and cingulate gyrus (arrowhead), sparing deep nuclear structures with mass effect compressing the left lateral ventricle and uncal herniation; also not increased signal in the right inferomedial temporal lobe (short bottom arrow) and insular cortex (long arrow).

Cytomegalovirus encephalitis

Cytomegalovirus encephalitis. Characteristic enhancement in ependyma around lateral ventricles

Togavirus (Japanese Encephalitis)

Deep-seated structures characteristically involved: subcortical white matter (top arrow), thalami (middle arrow), and substantia nigra (bottom arrow)

HIV infection of CNS

• Characteristic abnormalities are brain atrophy and diffuse white matter attenuation

JCV infection- PMLE

• Progressive Multifocal Leuco Encephalopathy

• Typical multifocal and confluent subcortical nonenhancing white matter hyperintensities extending to the

cortical gray matter.

Acute disseminated or post infectious encephalomyelitis after virus infection

• Subcortical white matter lesions (short arrow) involving subcortical U fibers with tangential lesions (long arrow).

Varicella zoster virus vasculopathy.

• Ischemia/infarction more common in white matter (top arrow), particularly at gray-white matter junctions (short arrow), less frequently in gray matter (long arrow) and may enhance

Subdual And epidural Empyemas.• Empyema is a "closed space infection" occurring inside a body cavity

or space

Epidural Empyema CT Subdural Empyema CT

Subdural Empyema

Axial T1WI shows hypointense subdural fluid collection along the right fronto-parietal convexity (small arrows) with minimal air-fluid level (arrowhead).

The right subdural fluid collection is hyperintense in axial T2WI (arrows).

Axial post-contrast T1WI shows ring enhancement of the right subdural fluid collection (arrow) with associated meningeal enhancement

Axial diffusion weighted images shows increased signal of the right subdural fluid collection (arrow) with low apparent diffusion coefficient.

Brain AbscessA brain abscess is a focal, suppurative infection within the brain parenchyma, typically surrounded by a vascularized capsule.

MRI is better than CT for demonstrating abscesses in the early (cerebritis) stages and is superior to CT for identifying abscesses in the posterior fossa.On contrast-enhanced T1-weighted MRI, a mature brain abscess has a capsule that enhances surrounding a hypo dense center and surrounded by a hypo dense area of edema.On T2-weighted MRI, there is a hyper intense central area of pus surrounded by a well-defined hypo intense capsule and a hyper intense surrounding area of edema.The distinction between a brain abscess and other focal CNS lesions such as primary or metastatic tumors may be facilitated by the use of diffusion-weighted imaging sequences on which brain abscesses typically show increased signal and low apparent diffusion coefficient.

Brain Abscess CT and MRI Intra-axial mass, located in the posterior left frontal lobe, in the superior frontal gyrus just anterior to the precentral gyrus. There is surrounding vasogenic edema, which expands the left precentral gyrus. Mass shows a well-defined rim on MR, somewhat irregular, consistent with a capsule. Central portion shows pronounced diffusion restriction.

Cerebritis

On T2-weighted MRI image (TR/TE2500/90) the lesion is hyperintense.

Contrast-enhanced T1-weighted image (TR/TE/flip° 20/2.1/35°) shows no enhancement.

CECT Brain : poorly defined hypodense and non-enhancing area of cerebritis in the right parietal lobe.

Multiple areas of dilated perivascular spaces with restricted diffusion (arrows), suggesting development of multiple parenchymal foci of cerebritis.

TB Meningitis

Contrast-enhanced computed tomography (CT) scan in a patient with tuberculous meningitis demonstrating marked enhancement in the basal cistern and meninges, with dilatation of the ventricles.

Contrast-enhanced computed tomography (CT) scan of a child with tuberculous meningitis demonstrating acute hydrocephalus and meningeal enhancement.

MRI is more sensitive than CT scanning in determining the extent of meningeal and parenchymal involvement

T2-weighted magnetic resonance image of a biopsy-proven, right parietal tuberculoma. Note the low–signal-intensity rim of the lesion and the surrounding hyperintense vasogenic edema.

T1-weighted gadolinium-enhanced magnetic resonance image in a patient with multiple enhancing tuberculomas in both cerebellar hemispheres.

T1-weighted gadolinium-enhanced magnetic resonance image in a child with a tuberculous abscess in the left parietal region. Note the enhancing thick-walled abscess.

T1-weighted gadolinium-enhanced magnetic resonance image of the thoracic spinal cord in a patient with acquired immunodeficiency syndrome (AIDS) and leptomeningeal tuberculosis. Note the numerous granulomas on the dorsal surface of the cord and the dural enhancement.

T2-weighted magnetic resonance image of the thoracic spinal cord of a patient with 2 hyperintense intramedullary tuberculomas.

CNS Toxoplasmosis

• CT- The typical lesion is an hypodense focal area with ring contrast-enhancement and edema

Nonenhanced T1-weighted images in a patient infected with human immunodeficiency virus and cerebral toxoplasmosis. These images show hypointense, asymmetrical, bilateral periventricular/basal ganglial lesions.

T1-weighted axial gadolinium-enhanced magnetic resonance images. These images show 2 complex, ring-enhancing lesions in the basal ganglia on the right, with surrounding notable white matter edema. This appearance is typical of central nervous system toxoplasmosis, which has the propensity for involvement of the basal ganglia.

Axial fluid-attenuated, inversion recovery brain magnetic resonance image in a patient infected with human immunodeficiency virus and cerebral toxoplasmosis. These images show intense signal at the sites of the infection.

Neurocysticercosis

Four types

• Meningeal• Parenchymal (Single or Multiple)• Intraventricular• Mixed

Nonenhanced CT scan of the brain demonstrates the multiple calcified lesions of inactive parenchymal neurocysticercosis

Enhanced CT scan of the brain in a patient with neurocysticercosis demonstrates a live cyst with a minimally enhancing wall and an eccentric hyperattenuating scolex.

In the colloid stage(when the larva begins to die), the cyst is encapsulated; it contains a high-protein fluid, and it demonstrates ring enhancement. Often, associated edema or enhancement is noted in the brain parenchyma

CT images of the brain in a patient with neurocysticercosis show numerous parenchymal lesions.

Left, CT scan of the brain shows marked dilatation of the right lateral ventricle in a patient intraventricular neurocysticercosis. Right, Contrast-enhanced ventriculogram shows a fourth ventricular cyst as a filling defect in the contrast-enhanced spinal column.

MRI

T1-weighted (T1), T2-weighted (T2), and fluid-attenuated inversion recovery (FLAIR) MRIs show a typical cyst with a scolex (arrow) in a patient with neurocysticercosis (NCC).

T1-weighted (T1) and T2-weighted (T2) MRIs show a degenerating colloid cyst with a hypointense wall and hyperintense surrounding edema, which is best depicted on T2-weighted images. The patient has neurocysticercosis (NCC).

Fungal Infections

Cerebral aspergillosis in an immunocompromised patient., Axial T2W MRI shows multiple hyperintense lesions with central hypointensity in the left cerebral white matter, right parietal cortex, and occipital cortex

Cryptococcus neoformans infection of the CNS in an HIV-positive individual., Axial FLAIR-FSE MRI shows high signal lesions in the basal ganglia bilaterally with swelling and hyperintensity of the cerebral cortex bilaterally.

On MR images, widened perivascular spaces appear as multiple, bilateral, small round-to-oval lesions in the basal ganglia and midbrain. These show slightly higher signal than cerebrospinal fluid on T1W images and high signal on T2W images.

Hydatid Cyst Brain