Infections of the Brain and

Meninges

Mohamed SamirAssist. Lecturer

Acquired:♣ Non-Specific:

1- Meningitis.

2- Pyogenic Parenchymal Infections.

3- Encephalitis.

♣ Specific:

1- TB & Fungal Infections.

2- Parasitic Infections.

1. Acquired:♣ Specific:

Fungal Infections.

Parasitic Infestations.

TB.

Fungal Infections

Fungal Infect ions

Immunicompetent:• Histoplasmosis.

• Blastomycosis.

• Coccidioidomycosis.

• Aspegillosis (Rare).

Immunocompromized:• Aspergillosis.

• Candidiasis.

• Cryptococcosis.

Fungal Infections

• Direct extension (Fungal Sinusitis).

• Hematogenous.

Fungal Infections

• Granulomatous Reaction.• Aspergillosis → invades blood vessels-Hgic infarcts.

• Cryptococcosis → gelatinous perivascular space

pseudocysts.

• Coccidioidomycosis → meningitis – caseating

granulomas

Fungal Infections

Fungal Infections

Fungal Infections

Parasitic Infestations

Parasitic Infestations

• Toxoplasmosis.

• Cysticercosis.

Toxoplasmosis

• Toxoplasma gondii

• Intracellular protozoal parasite

• Human infection usually occurs via the oral or

transplacental route.

• Most T gondii infections are subclinical, but

severe infection can occur in patients who are

immunocompromised

Toxoplasmosis

• In immunocompetent hosts, cysts containing live T

gondii organisms cause no harm; most patients remain

asymptomatic but seropositive.

• However, if the immune system of the host declines, the

cysts may reactivate, causing disseminated infection that

manifests as encephalitis, myocarditis, or chorioretinitis.

• In immunocompromised patients, T gondii infection is

potentially fatal. If seronegative, these patients can be

infected via the usual oral route or via transplantation of

an organ. More commonly, infection results from

reactivation of latent tissue cysts.

Toxoplasmosis

• CT scans of the brain may show

single (30%) or multiple

nodular/Ring enhancing lesions.

• Edema of the surrounding white

matter is often depicted.

CT

Parasitic Infestations

CT

Toxoplasmosis

•Approximately 75% of the nodules are

located in the basal ganglia, but others are

scattered throughout the brain at the gray

matter–white matter junction.

Toxoplasmosis

Calcification may occur following

medical treatment.

Toxoplasmosis

MRI

•T1-weighted precontrast

images, the lesions are

hypointense to brain tissue.

Toxoplasmosis

MRI

• T2-weighted MRI, the foci of

infection are usually

hyperintense, but they can

occasionally be isointense to

hypointense.

Toxoplasmosis

MRI

• Focal nodular or ring

enhancement occurs in

approximately 70% of

patients after gadolinium

enhancement.

Toxoplasmosis

MRI

• Active lesions often are

surrounded by edema.

Toxoplasmosis

• The characteristic sign of CNS toxoplasmosis is the

asymmetric target sign, which is detectable on both CT

scans and MRI, though MRI is more sensitive. The

asymmetric target sign represents a ring-enhancing

abscess, which contains similar ring-enhancing abscesses,

which contain similarly enhancing, eccentric nodules in the

abscess cavity.

Toxoplasmosis

Toxoplasmosis

• Lesions of CNS lymphoma often are solitary, whereas

nodules of CNS toxoplasmosis are more often multiple.

• A diagnosis of toxoplasmosis is favored over a diagnosis of

lymphoma when more than 3 lesions or slender, ring-

enhancing foci are seen or when marked edema is present.

In addition, toxoplasmosis is more common subcortically

than lymphoma and seldom affects the corpus callosum

Toxoplasmosis

MRI

Disease CT T1-weighted T2-weighted ContrastEnhancement

MRSpectroscopy

Toxoplasmosis Hypodense masses with

ring enhancement

Hypointense lesions.

Discrete hyperintense foci

– moderate edema

Ring enhancement

Markedly elevated lactate and lipids with

depleted metabolites.

Lymphoma Hyperdense masses with solid or ring

enhancement

Hypointense. Iso to Hyperintense

masses – moderate edema

Homogeneous or ring

enhancement

Elevated choline with

mildly to moderately

elevated lactate and lipids.

Cysticercosis

Cysticercosis

• Cysticercosis is the most common

parasitic infestation affecting the central

nervous system.

• Taenia solium.

Cysticercosis

CNS cysts are encountered in 4 types in NCC:

(1) Meningeal (racemose variety).

(2) Parenchymal (solitary or multiple cysts).

(3) Ventricular (usually solitary).

(4) Mixed.

Stages of NCC:

• The host can tolerate the worm as long as the

embryo is alive. Viable cysticerci are associated

with minimal inflammation (vesicular stage).

Cysticercosis

Stages of NCC:

• The worm usually dies 2-6 years after infection, and

the disintegration of the parasite triggers a vigorous

tissue reaction, the cyst wall is infiltrated and

surrounded by predominantly mononuclear cells.

Inflammatory cells enter the cyst fluid (colloid stage).

Cysticercosis

Stages of NCC:

• As the host's immune response progresses,

fibrosis encompasses the cysticercus, with

collapse of the cyst cavity (granular-nodular

stage). The dead parasite decays into an

eosinophilic desiccated material.

Cysticercosis

Stages of NCC:

• The final stage is a calcified nodule, presumably

the result of dystrophic calcification of the

necrotic larva (calcific stage).

Cysticercosis

Cysticercosis

The various pathologic states that may be seen in NCC include the following:

(1) Meningoencephalitis

(2) Granulomatous meningitis.

(3) Focal granuloma.

(4) Focal or diffuse multiple cysts.

(5) Hydrocephalus.

(6) Intraventricular cysts.

(7) Ependymitis.

(8) Arteritis.

Cysticercosis

The viable cyst appears as a thin-walled fluid-filled

cyst with a mural nodule (live scolex).

The cyst causes no inflammatory reaction or edema,

and it does not enhance

CT

Cysticercosis

In the colloid stage, 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

Cysticercosis

CT

Cysticercosis

As the cysticercus becomes fibrotic or

collapses, a focal area of enhancement

suggestive of granuloma is seen

(granular-nodular stage)

CT

Cysticercosis

CT

Cysticercosis

An inactive lesion is densely

calcified with no enhancement

typically 2-10 mm in diameter

CT

Cysticercosis

• Intraventricular cysts result in obstructive hydrocephalus.

• Cysticerci can be seen in any of the ventricles.

• CT scans may reveal evidence of obstructive hydrocephalus or

dilatation or distortion of the involved ventricle.

CT

Cysticercosis

CT

CT scans obtained after the

intraventricular administration of

contrast material delineate the cyst

and the site of the obstruction

Cysticercosis

CTSubarachnoid NCC is described in 3 subtypes as follows:

(1) If it is located in the gyri of the cerebral convexities.

(2) When cysticerci are found in the fissures (eg, Sylvian fissure).

(3) Cysticercosis of the basal cisterns is characterized by arachnoiditis and

seen as focal or diffuse meningeal enhancement or vasculitis with stroke.

Patients often develop communicating hydrocephalus.

Cysticercosis

CT

Cysticercosis

MRI

T1WIs clearly show an eccentric,

hyperintense, 2- to 5-mm scolex

The demonstration of a scolex is

pathognomonic for NCC.

Cysticercosis

MRI

When the larva begins to die (colloid stage), the fluid in the

cyst becomes more turbid, and it is mildly hyperintense to

CSF on both T1WIs and T2WIs. The surrounding edema

is hypointense on T1WIs and hyperintense on T2WI.

Cysticercosis

MRI

The hypointense cyst wall stands out

between the hyperintense cyst fluid

and edema on T2WI.

The cyst wall may be enhancing in the

granular-nodular stage.

Cysticercosis

MRI

Cysticercosis

MRI

Tuberculosis

Tuberculosis

• Mycobacterium Tuberculosis.

• Hematogenous.

Tuberculosis

• CNS TB affects the brain and meninges.

• Infection starts in a subpial or subependymal cortical

focus (ie, Rich focus), resulting in a granuloma that

erodes into the subarachnoid space causing basal

leptomeningitis.

Pathophysiology:

Tuberculosis

• The meningitis usually causes communicating

hydrocephalus, but it may also cause obstruction of

the foramina of Luschka and Magendie, resulting in

obstructive hydrocephalus.

• Vasculitis involving the lenticulostriate and

thalamoperforatoring arteries may occur and cause

small infarcts in the deep gray nuclei and deep white

matter.

Pathophysiology:

Tuberculosis

• Tuberculous meningitis.

• Focal parenchymal granulomas (e.g. tuberculomas).

• Tuberculous abscesses.

• Tuberculous cerebritis.

Tuberculosis

• CECT of the brain depicts prominent

leptomeningeal and basal cistern

enhancement.

• Ventricular dilatation (eg, dilatation of the

third and fourth ventricles) due to

hydrocephalus is usually seen.

CT

Tuberculosis

• With ependymitis, linear

periventricular

enhancement or

calcifications are present.

CT

Tuberculosis

• Often, low-attenuating

focal infarcts are seen in

the deep gray matter nuclei,

deep white matter, and

pons; these infarcts result

from associated vasculitis.

CT

Tuberculosis

Parenchymal tuberculomas demonstrate various patterns:

• Noncaseating granulomas are homogeneously enhancing lesions.

• Caseating granulomas are rim enhancing; if these have a central

calcific focus, they may form a target-like lesion.

• Granulomas may also form a miliary pattern with multiple tiny

nodules scattered throughout the brain.

CT

Tuberculosis

CT

Tuberculosis

CT

Tuberculosis

• Gadolinium-enhanced T1-

weighted images demonstrate

prominent leptomeningeal and

basal cistern enhancement.

MRI

Tuberculosis

• With ependymitis, linear

periventricular enhancement is

present. Ventricular dilatation due to

hydrocephalus is usually seen.

• Deep gray matter nuclei, deep white

matter, and pontine infarctions.

MRI

Tuberculosis

Parenchymal tuberculomas demonstrate various patterns:

• They are typically hypointense on T2-weighted images, but they

may be hyperintense as well.

• Noncaseating granulomas are homogeneously enhancing lesions.

• Caseating granulomas are rim enhancing.

• Granulomas may also form a miliary pattern

• Lesions are typically surrounded by hyperintense edema.

MRI

Tuberculosis

MRI

Tuberculosis

MRI

Tuberculosis

• MR spectroscopy can be used to characterize

tuberculomas and differentiate them from neoplasms.

• Tuberculomas show elevated fatty-acid spectra.

MRI

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