Infections of the Brain and

Meninges

Mohamed SamirAssist. LecturerEpisode 2 “The Good, The Bad and The Infectious”

Infections

Congenital / Neonatal Acquired

• Cytomegalovirus.• Toxoplasmosis.

• Rubella.

• Herpes Simplex.

• HIV Infection.• Enteroviruses.

• Meningitis.• Pyogenic

Parenchymal Infections.

• Encephalitis.

• TB & Fungal Infections.

• Parasitic Infections.

Acquired:♣ Non-Specific:

1- Meningitis.

2- Pyogenic Parenchymal Infections.

3- Encephalitis.

♣ Specific:

1- TB & Fungal Infections.

2- Parasitic Infections.

MeningitisMeningitis

• The most common form of CNS

infections.

• 3 General Categories.

1- Acute Pyogenic Meningitis.

2- Lymphocytic Meningitis.

3- Chronic Meningitis.

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Bacteria:

Acute Pyogenic Meningitis

• Neonates…. – Group B Streptococcus species (49%) – Escherichia coli (18%)

• Children and infants ….– Haemophilus influenzae (40-60%) – Neisseria meningitidis (25-40%)

• Adults ….– S. pneumoniae (30-50%) – N. meningitidis (10-35%) – Staphylococcus species (5-15%)

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Acute Pyogenic Meningitis

Routes of Infection:

1. Hematogenous spread.

2. Local extension from contiguous extracerebral

infection

3. Direct implantation of bacteria into the

meninges.

Clinical:

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Acute Pyogenic Meningitis

Classic triad (85% of patients with bacterial

meningitis)

• Fever

• Headache

• Stiff neck

Complications:

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Acute Pyogenic Meningitis

1. Hydrocephalus.

2. Ventriculitis.

3. Subdural Effusion.

4. Empyema.

5. Infarction.

6. Parenchymal abscess.

• Viral (Enteroviruses 50-80%).

• Mostly benign and self-limited.

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Acute Lymphocytic Meningitis

Imaging of Acute Meningitis

The most important role of CT in imaging patients with meningitis is to evaluate for:

1.Contraindications to a lumbar puncture.

2.Complications of meningitis.

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CT:

Acute Meningitis

• NECT:

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CT:

Normal (>50% of patients).

Mild ventricular dilatation.

Cerebral edema.

Focal low-attenuating lesions.

Effacement of sulci.

Obliteration of the basal cisterns.

Acute Meningitis

• CECT:

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CT:

Acute Meningitis

• Diffuse meningeal enhancement.

• Cerebritis.

• Abscess.

• Subdural fluid collection.

• Subdural empyema

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CT:

Acute Meningitis

CT scans may reveal the cause of

meningeal infection

Negative results on CT imaging

do not exclude the presence of

acute meningitis.

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MRI:

Acute Meningitis

The most sensitive modality due to increased

contrast resolution, and the absence of artifact

caused by bone.

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MRI:

Acute Meningitis

Obliterated cisterns and the distention of the

subarachnoid space with widening of the

interhemispheric fissure

T1WI:

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MRI:

Acute Meningitis

Cortical hyperintensities that

are believed to represent

edema

T2WI:

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MRI:

Acute Meningitis

•Diffuse enhancement of the

subarachnoid space.

T1WI+GAD:

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MRI:

Acute Meningitis

Empyema

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MRI:

Acute Meningitis

Cerebritis

Find 3

Differences

Parenchymal InfectionsParenchymal Infections

1. Bacterial (Pyogenic).

2. Viral.

Pyogenic Parenchymal InfectionsPyogenic Parenchymal Infections

Cerebritis.

Abscess.

Pyogenic Parenchymal Infections

Pathology:

Four stages have been described in abscess evolution:

1. Early cerebritis.

2. Late cerebritis.

3. Early capsule formation.

4. Late capsule formation.

Pyogenic Parenchymal Infections

CT:

• CT manifestations of an intracranial

abscess depend on the stage of the

abscess formation

Pyogenic Parenchymal Infections

CT:

• During early cerebritis, nonenhanced CT scans may demonstrate normal findings or may show only poorly marginated subcortical hypodense areas.

Pyogenic Parenchymal Infections

CT:

• Contrast-enhanced CT studies demonstrate

an ill-defined contrast-enhancing area

within the edematous region

Pyogenic Parenchymal Infections

CT:

• During the early stage of a formed

abscess, the lesion coalesces, with an

irregular enhancing rim that

surrounds a central low-attenuating

area.

Pyogenic Parenchymal Infections

CT:

• Scans obtained with a time delay

following contrast enhancement in

cerebritis may show contrast "filling

in" the central low-attenuating

region. A formed abscess will not "fill

in" the central portion of the abscess.

Pyogenic Parenchymal Infections

CT:

• A relatively thin well-delineated capsule

marks the final stage of a fully formed

abscess.

• Peripheral edema results in considerable

mass effect with sulcal obliteration

Pyogenic Parenchymal Infections

MRI:

1. Early cerebritis stage

The early cerebritis stage presents as an ill-defined hyperintense

zone that can be noted on T2-weighted imaging.

Pyogenic Parenchymal Infections

MRI:

1. Early cerebritis stage

• Contrast-enhanced T1-weighted studies

demonstrate poorly delineated enhancing

areas within the isointense-to-mildly

hypointense edematous region

Pyogenic Parenchymal Infections

MRI:

2. Late cerebritis stage • During the late cerebritis stage, the central

necrotic area is hyperintense to brain tissue on

FLAIR and T2-weighted sequences.

• The thick somewhat irregularly marginated rim

appears isointense to mildly hyperintense on T1-

weighted images and isointense to relatively

hypointense on FLAIR and T2-weighted scans.

• The rim enhances intensely.

Pyogenic Parenchymal Infections

MRI:

3 & 4- Early and late capsule stages

• The collagenous abscess capsule is visible prior to contrast

as a comparatively thin-walled isointense-to-slightly

hyperintense ring that becomes hypointense on T2-

weighted MRIs.

Pyogenic Parenchymal Infections

MRI:

Diffusion-weighted MR may be useful in

differentiating abscess from necrotic tumor.

Diffusion-weighted echo planar images

demonstrate an abscess as a high signal

intensity with a corresponding reduction

in the apparent diffusion coefficient. The

brightness on DWI is related to the

cellularity and viscosity of the contents

within the abscess cavity.

Pyogenic Parenchymal Infections

MRI:

MR spectroscopy is useful in differentiating ringlike

enhanced lesions that cannot be diagnosed correctly

using enhanced MRI alone. MR spectroscopy can help to

specifically differentiate tumor, radiation necrosis, or

abscess by identifying their different spectral profiles.

Pyogenic Parenchymal Infections

MRI:

• 99mTC HMPAO labeled leukocytes.

• Radiolabeled polyclonal immunoglobulins

Pyogenic Parenchymal Infections

Nuclear Medicine:

Find 2 Differences

EncephalitisEncephalitis

•Diffuse non-focal brain parenchymal

inflammatory disease

• HSV TYPE 1 & 2

• Others; equine viruses. CMV, Parvoviruses, …..

Encephalitis

Agents:

Encephalitis

Encephalitis

Agents:

Encephalitis

• In adults, herpes simplex virus type 1 (HSV-1) accounts

for 95% of all fatal cases of sporadic encephalitis and

usually results from reactivation of the latent virus.

• In children and neonates, herpes simplex virus type 2

(HSV-2) accounts for 80-90% of neonatal and almost all

congenital infections.

Encephalitis

Agents:

Encephalitis

• In the typical adult infected with HSV-1, the neuronal

spread of the latent virus occurs from the peripheral

neuron in retrograde fashion to the brain, usually

through the trigeminal or olfactory tract.

Encephalitis

Pathology:

Encephalitis

• Fulminant hemorrhagic and necrotizing

meningoencephalitis. Typical gross findings include

severe edema and massive tissue necrosis, with

petechial hemorrhages and hemorrhagic necrosis.

Encephalitis

Pathology:

Encephalitis

• The virus has a predilection for the limbic system,

involving one or both temporal lobes, and often

involving the hippocampus, parahippocampus, and

amygdala. Frontal and parietal spread also can occur.

Encephalitis

CT:

Encephalitis

• CT classically reveals hypodensity in the temporal lobes either unilaterally or

bilaterally, with or without frontal lobe involvement.

• Hemorrhage is usually not observed.

• A gyral or patchy parenchymal pattern of enhancement is observed. Contrast

enhancement generally occurs later in the disease process.

Encephalitis

CT:

Encephalitis

Encephalitis

MRI:

Encephalitis

• T2-weighted MRI reveals hyperintensity corresponding to

edematous changes in the temporal lobes, inferior frontal

lobes, and insula, with a predilection for the medial

temporal lobes.

Encephalitis

MRI:

Encephalitis

• Foci of hemorrhage occasionally can be observed

Encephalitis

MRI:

Encephalitis

• Restricted diffusion in herpes encephalitis exist with

corresponding T2 hyperintensity reflecting edema

Encephalitis

MRI:

Encephalitis

• MR spectroscopy using proton

spectroscopic MRI has demonstrated a

reduction of the N-acetylaspartate (NAA)-

to-choline ratio.

Find ANY Difference !!!!!

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