CNS Infections 2003

8/3/2019 CNS Infections 2003

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CNS INFECTIONS


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MENINGITIS

The meninges consist of three layers: thedura mater; the arachnoid mater; and thepia mater.

However, for a better understanding ofmeningeal inflammation in neuroimaging, itis helpful to use the anatomicfunctionalclassification of lepto- and pachymeninges

The leptomeninges (skinny meninges)comprise the membranes of the arachnoidand the pia mater

The pachymeninges (thick meninges) consistof the dura mater and the outer layer of the


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INFECTIOUS MENINGITIS

Can be divided into acute pyogenic (bacterial), lymphocytic(viral), and chronic (TB) meningitis

Bacterial meningitis is the purulent infection of the cerebraland spinal leptomeninges

Infection may arise from hematogenous spread during

systemic infection, from a chronic suppurative focus, or percontinuitatem during acute or chronic infections of theparanasal sinus, the middle or inner ear, or the mastoid.

Another path of infection is brain injury with open orcovered disruption of the dura mater, especially when theparanasal sinus or the air-filled cavities of the temporal

bone are involved in the fracture In neonates, the most common pathogens are group-BStreptococcus and Escherichia coli, in infants, it isHaemophilus influenzae, Streptococcus pneumoniae, andNeisseria meningitidis. In adolescents and adults,Streptococcus pneumoniae and Neisseria meningitidis arefound most often.


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COMPLICATIONS

Extraventricular obstructivehydrocephalus (EVOH)

Ventriculitis, choroid plexitis

Abscess, empyema, effusion

Cerebrovascular (arteritis, infarct,venous

thrombosis) Cerebral edema, infarction

DWI useful in depicting perfusion

alterations


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CT FINDINGS

NECT o Normal study is most common o Mild ventricular enlargement, Subarachnoid space

enlargement, Basal cisterns effaced. Low density areasrelated to perfusion alterations

CECT o Enhancing exudate in sulci, cisterns may be seen CTA: Arterial narrowing, occlusion CT exam should be performed in all patients with

suspected bacterial meningitis prior to lumbarpuncture to rule out brain edema and potential

herniation. Parenchymal lesions are often difficult to distinguish;

however, CT is a simple and fast tool to rule out severecomplications of bacterial meningitis, such as resorptivehydrocephalus, swelling, venous thrombosis, or infarction.

CT also provides important information about probable

pathologies of the skull base, the temporal bone, and thenasal sinus, such as fractures, purulent sinusitis, otitis


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MR FINDINGS

FLAIR: Hyperintense signal in sulci,cisterns

DWI o Variable, may show restriction o Most useful for vascular complications Tl C+: Exudate typically enhances.

Abnormal enhancement of the leptomeninges is

usually asymmetrical and extends into thebasal cisterns

MRA: Arterial narrowing, occlusion When patients with bacterial meningitis

develop focal neurological symptoms orseizures, MRI is the tool of choice to


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Pneumococcal meningitis in a 5-year-old child. a AxialT1-weighted image after contrast administration. bSagittalT1-weighted image after contrast administration


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c Axial T2-weighted image. d Axial FLAIR image.Bifrontal subdural exudates (c,d) with relativelyhigh signal compared with the CSF (d), indicatingan elevated content of proteins


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Pyogenic meningitis. T2-weighted axial image (a) at the level of midbrainshows evidenceof dilated lateral and third ventricles. T1-weighted axial image (b) showsno other abnormality. MT T1-weighted axial image (c) shows hyperintense

thick meninges in the basal cisterns and along the Sylvian fissures andanterior interhemispheric fissure which show enhancement in postcontrastMT TI-weighted image (d).


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Breast, lung mostcommon distantprimary tumors Primary CNStumors include:GBM,medulloblastoma,pineal tumors,

choroid plexustumors Primary tumoroften known

Lacy leptomeningeal

enhancement typical May haveventricular, duralbased enhancingmasses


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BRAIN ABSCESS

Focal pyogenic infection of the brainparenchyma, typically bacterial; fungal orparasitic less common

Four pathologic stages: Early cerebritis, late

cerebritis, early capsule, late capsule Early cerebritis: +/- Mild patchy enhancement o Late cerebritis: Irregular peripheral rim

enhancement o Early capsule: Low density center with thin,

distinct enhancing capsule. Deep part ofcapsule is thinnest; thickest near cortex

o Late capsule: Cavity shrinks, capsulethickens. May be multiloculated and have"daughter abscesses

Hemorrhage common in fungal cerebritis


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(Left) Axial T2WI MR shows an ill-defined hyperintense mass in the rightfrontal and parietal lobes of this 40year old male with severe headachesand elevated ESR Early cerebritis.(Right) Coronal T1 C+ MR shows

patchy enhancement, edema andmass effect.


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(Left) Axial T2WI MR shows the typical hypointenserim with surrounding hyperintense edema in this 38 yearold male with early capsule formation. (Right)Axial OWlMR shows characteristic restricted diffusion of the earlycapsule stage. The ADC map showed markedly decreased

signal centrally within the abscess.


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Thick, nodularenhancing walltypical Low signal on DWI(occasionally high,can mimic abscess)

History of traumaor vascular lesion Blood productspresent

Enhancementoften incompletering Characteristiclesions elsewherein brain

Small amount ofmass effect forsize of lesion

Usually no diffusion restrictiH/o primary tumor


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VENTRICULITIS

Ventricular ependyma infection relatedto meningitis, ruptured brain abscess, orventricular catheter

Ventriculomegaly with debris level,enhancing ependyma, periventricular T2hyperintensity


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Ventriculitis as a complication of meningoencephalitis. A 79-year-old man,severe meningoencephalitis (streptococci). a Axial T2-weighted image. bAxial DWI. Pathological substrate with intermediate to hypointense signal on

T2-weighted images (a) and strongly hyperintense signal on DWI due torestricted diffusion (b) in the lateral ventricles, suspicious for pus.


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Ependymalenhancement,typically nodular Parenchymaldisease usually

present

Primary brain tumors:GBM,medulloblastoma,pinealtumors,

ependymoma, choroidplexus tumors Metastatic tumorfrom extracranialprimary (Le.,breast)

History of trauma;other sequelae seen Ventricles typicallynot enlarged

Prominentependymal veins Vascularmalformations: AVM,DVA, cav malf

Abnormal venousdrainage (Le., Sturge-Weber)


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EMPYEMA

Loculated collection of pus in subdural orepidural space, or both

Extra-axial collection with rim

enhancement Location: Supratentorial typical SDE: Convexity in > 50%, parafalcine in

20% EDE: Often adjacent to frontal sinus SDE: Crescentic typical; may be

lentiform on coronal images

EDE: Biconvex, lens-shaped (lentiform)


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(Left) Axial T1 C+ MR shows a left frontal subdural empyemawith extension along the falx (arrow), typical of SDE. Noteenhancement along the deep margin. Adult patient with frontalsinusitis. (Right) AxialT1 C+ MR shows a right frontal subduralempyema with loculation and enhancement (arrow). Note the left

frontal subdural effusion with no Enhancement


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MR shows bloodproducts, may beloculated Often enhancesalong edge, typicallythinner than SDE May beindistinguishable;

history may help

Sterile, CSF-likecollection associatedwith meningitis Follows CSF on allMR sequences Usuallynonenhancing; mayenhance mildly

Frontal andtemporal regionscommon, oftenbilateral

Nonenhancing CSFcollection, oftentrauma history

Primary tumor oftenknown, typicallybreast, prostate Often diffuse,nodularenhancement May have

associated bonemetastases


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TUBERCULOSIS

Most TB CNS infections are secondary result of hematogenous spread (oftenpulmonary)

Meningitis is most common manifestation. Meningitis + parenchymal lesionshighly suggestive

TBM: Basal meningitis o Tuberculomas: Typically parenchymal, supratentorial (often parietal lobes)

Infratentorial lesions are less common, can involve brainstem (up to 8%) Dural tuberculomas may occur NECT o TBM: May be normal early (10-15%) Isodense to hyperdense exudate effaces CSF spaces, fills basal cisterns,

sulci

o Tuberculoma: Hypodense to hyperdense round or lobulated nodule/masswith moderate to marked edema

Ca++ uncommon (approximately 20%) CECT o TBM: Intense basilar meningeal enhancement o Tuberculoma: Solid or ring-enhancing "Target sign": Central Ca++ or

enhancement surrounded by enhancing rim (not pathognomonic for TB)


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MRI

Increased signal in sulcal spaces, predominantly in basalcisterns on FLAIR due to exudates

The MR features of the individual tuberculoma depend onwhether the granuloma is noncaseating or caseating with asolid center, or caseating with a liquid center. Thenoncaseating granuloma is usually iso/hypointense on T1-and hyperintense on T2-weighted images. Thesegranulomas show homogeneous enhancement afterinjection of paramagnetic contrast agent.

The caseating solid granulomas appear relativelyiso/hypointense on T1-weighted images withiso/hyperintense rim and isointense to hypointense on T2-

weighted images. The rim may be inseparable from edemawhen present on T2-weighted images or appearshyperintense in the absence of edema

The granulomas with central liquefaction of the caseousmaterial appear centrally hypointense on T1- andhyperintense on T2-weighted images with a variable

peripheral hypointense rim on T2-weighted imagesdepending on the amount of liquefaction of the solid


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COMPLICATIONS

Hydrocephalus: It is usually of the communicating type, secondaryto the blockage of the basal cisterns by the inflammatory exudatebut occasionally may be the obstructive type secondary to a focalparenchymal lesion with mass effect or due to entrapment of theventricle by granulomatous ependymitis

Choroid plexitis: It is usually associated with intense enhancement

of the ventricular lining (ventriculitis) and meningitis Vasculitis: Because of the predominant basal distribution ofexudate, a majority of the infarcts are in the basal ganglia andinternal capsule region owing to the involvement of thelenticulostriate arteries. Brainstem and major territory infarcts areuncommon

Cranial neuropathies: On contrast-enhanced MRI, the proximal

portion of the root at the nerve entry/exit zone is mostly affectedand may be associated with enhancement. Cranial nerveinvolvement has also been shown by the mass effect on the nervein the subarachnoid space as well as by nuclear and supranuclearinvolvement of the cranial nerve nuclei in the brainstem due toinfarct, focal cerebritis, or tuberculoma


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(Left) Axial CECT shows an irregular, peripherally enhancing mass in the leftfrontal lobe with central necrosis and surrounding edema. Solitary tuberculomamimics tumor (Courtesy R.Ramakantan, MO). (Right)Axial CECT shows an intracranial empyema(arrows) and a subgaleal

abscess in this young adult with a history of IV drug use, TB. Bone windowsshowed osteomyelitis


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(Left) Axial T2WI MR shows a hypointense cerebellarmass (arrow), typical of caseating tuberculoma. Note thesurrounding edema,mass effect and hydrocephalus. T2 hypointensity can helpindiagnosis of TB. (Right) AxialT1 C+ MR in same case

shows peripheral


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Tuberculous ependymitis (ventriculitis) in a 53-yearoldpatient with tuberculous meningitis. Coronal T1-weightedimage after contrast administration. Ependymal

enhancement(arrow).


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Fig 5.1ah. A 24-year-old man who suffered fromfever, headacheand weight loss for several weeks and came to admissionafter a seizure. a Non-enhanced CT. b Axial DWI. c

SagittalT1-weighted image after contrast administration. dCoronalT1-weighted image after contrast administration. e,f AxialT1-weighted image after contrast administration. g AxialT2-

weighted image. h Axial DWI (follow-up). (a) Enlargedventricles.On DWI (b) focal hyperintensities are seen at thelevel ofthe right thalamus and the basal ganglia (arrow) withreduced

ADC values, reflecting acute infarcts. Key to the diagnosisisthe severe basal meningeal enhancement as seen on thesagittaland coronal reconstruction of 3D T1-weighted images(c,d).

Marked contrast enhancement of the right seventh and


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TUBERCULOSIS - MRS

Reveal lipid resonances at 0.9, 1.3, 2.0and 2.8 ppm and phosphoserine at 3.7ppm.

Reflects the high lipid content of thecasseous material

Normal or decreased choline, Cr, NAA.


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TUBERCULAR ABSCESS

FOCAL OR DIFFUSE


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FOCAL OR DIFFUSEPACHYMENINGITIS

Isolated involvement of the dura mater isconsidered as an unusual presentation ofCNS tuberculosis. Pachymeningeal

tuberculosis is an entity distinct from theinflammation of the dura mater adjacent toan intraparenchymal tuberculoma that hasbeen shown on histopathology to be present

in almost 50% of all tuberculomas. Pachymeningeal tuberculosis consists of

either isolated dural involvement or apredominantly dural-based lesion with

secondary pial or parenchymal involvement


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Diffuse pachymeningitis.T2-weighted axial image (a)at the level of fourth ventricle shows a focalhypointense lesion in the fourth ventricle.Postcontrast T1-weighted axial (b) and coronal (c)images show enhancement of the intraventricularlesion and diffuse enhancement of the dura mater.


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NCC

Intracranial parasitic infection caused by the pork tapeworm, Taenia solium Four pathologic stages: Vesicular, colloidal vesicular, granular nodular,

nodular calcified Best diagnostic clue: Cyst with "dot" inside

Location Convexity subarachnoid spaces most common

May involve cisterns> parenchyma> ventricles Parenchymal cysts often hemispheric, at gray-white junction Intraventricular cysts are often isolated: Fourth ventricle is most common Basal cistern cysts may be racemose (grape-like) NECT Vesicular stage (viable larva): Smooth, thin-walled cyst, isodense to CSF, no

edema. Hyperdense "dot" within cyst = proto scolex Colloidal vesicular stage (degenerating larva): Hyperdense cyst fluid with

surrounding edema Granular nodular (healing) stage: Mild edema Nodular calcified (healed) stage: Small, Ca++ nodule


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NCC

CECT Vesicular stage: No (or mild) wall enhancement Colloidal vesicular stage: Thicker ring-enhancing fibrous capsule Granular nodular stage: Involuting enhancing nodule Nodular calcified stage: Shrunken, calcified nodule Subarachnoid lesions: Multiple isodense cysts without scolex, may cause

meningitis Intraventricular cysts not well seen on CT, may see hydrocephalus

MRI:

Vesicular stage: cytic lesion with eccentric scolex

Colloid vesicular: Cyst mildly hyperintense to CSF on T1/T2W images. Mild tomarked perilesional edema appears

Granular nodular stage: Cyst wall retracted and thickened. Edema decreases

Nodular calcified: Calcified nodule. Edema disappears

MRS:

Few reports show increased lactate, alanine, succinate, choline and decreasedNAA and Cr


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Vesicular neurocysticercosisMR images obtained in a 45-year-old woman with

headaches show vesicular neurocysticercosis in the

subarach-noid space of the temporal lobe (large arrows

in ac, arrow in d). The cyst contents appear similar to

CSF on the T1- and T2-weighted images


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DW AND FLAIR

and do not demonstrate fluid restriction on the diffusion-weighted image.

There is no surrounding edema on the fluid-attenuated inversion recovery

image or enhancement after the intravenous administration of contrast

material. The round structure within the cyst represents the scolex (small

arrows in ac). (e) Follow-up nonenhanced CT scan obtained after

antihelminthic therapy shows calcification of the nodule (arrowhead).


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Multiple neurocysticercosis cysts in a 25-year-old man

with headache, nausea, and vomiting. a Axial T2-weighted


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(Left) Axial CECT shows right external capsule cyst withcentral "dot" representing a scolex. No edema orenhancement is seen, NCC vesicular stage. Calcified leftputamen nodule, granular nodular stage. (Right) Axial T2WIMR shows cysts in subarachnoid spaces (arrows), filling the

Sylvian fissure and causing mild mass effect on the cerebralpeduncle. Note the lack of a scolex, typical of cisternal NCC.


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(Left) Axial CECT shows a ring-enhancing mass with surrounding edema in thefrontal lobe. Patient with headaches and seizures. Ventricular lesion is not wellseen (arrow). NCe, colloidal vesicular stage. (Right) Axial TlWI MR shows thefrontal lesion and the intraventricular cyst. Note cyst wall (open arrow) and thehyperintense scolex (arrow). TlWI and FLAIR MR are helpful to identify

ventricular lesions


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OTHER PARASITIC

INFECTIONS


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AMEBIC ENCHEPHALITIS

Meningoencephalitis; single ormultiple focal,

nodular or ring-enhancingmasses


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ECHINOCOCCOSIS

Large uni- ormultilocular cyst+/- detached

germinalmembrane,daughter cysts,no edema


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Large, well-defined rounded hyperintense area with hypointense rim on T2-weighted image (a). The lesion appears hypointense on non-enhanced T1-weighted image (b). Particulate wall-adherent substrate within the cyst thatprobably represents daughter scolices and hydatid sand


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SCHISTOSOMIASIS

Causes non specificgranulomatousinfmammation.

On MRI the lesions

are T2hyperintense andshow acharacteristicpattern of contrast

enhancement onT1-weightedsequences, which isa centrally linearenhancement

surrounded by

(Left) Axial T7 C+ MRshowsposterior fossa masses withpunctate enhancement

(arrows


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The left parietal lesion shows punctate contrast enhancement

(b) surrounded by edema as vizualized best on FLAIRimaging (a).


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CRYPTOCOCCOSIS

Cryptococcus is the third most commoncause ofCNS infection in AIDS patients,ranking behind HIV and Toxoplasma

The imaging findings may consist of

meningoencephalitis, intraventricular orintraparenchymal cryptococcomas,gelatinous pseudocysts, or hydrocephalus

Dilated perivascularlar spaces resulting fromthe presence of gelatinous pseudocysts are a

frequent finding Meningoencephalitis results in T2

hyperintensity within the region ofinvolvement, and meningeal enhancementmay be seen


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Axial T2-weighted image showsmultiple foci of high signal intensitywithin thebilateral basal ganglia, findingsconsistent with gelatinouspseudocysts in dilated perivascularspaces(arrows). Enlargement of the


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ASPERGILLOSIS

A fumigatus is the mostcommon causativeagent

Three imaging patterns: (a) multiple corticaland subcortical regions of low attenuation on

CT images, with T2 hyperintensity seen incorresponding areas on MR images; (b)multiple ring-enhancing lesions; and (c)dural enhancementadjacent to enhancing

lesions of the paranasal sinuses or calvaria. The presence of hemorrhage associated

with the lesions and intraparenchymalhemorrhage in an immunocompromised

patient should cause one to consider


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Disseminated aspergillosis in a 39-year-old AIDSpatient. (a) Axial T2-weighted FLAIR image showstwo well-circumscribed foci of hyperintensity within thecentrum semiovale. There is nosignificant surrounding edema. (b) Axial postcontrastT1-weighted image demonstrates low-


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Aspergillosis in a 36-year-old woman with HIV infection whoexperienced a rapid decline in consciousness. (a) Axial unenhancedCT image reveals a large parenchymal hemorrhage involving

the left hemisphere that caused mass effect and midline shift. (b)hoto ra h o the ross s ecimen demonstrates the lar e area


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[

(a) Sagittal unenhanced T1-weighted MR image shows a 3-cm mass (*) withheterogeneous signal intensity in the right frontal lobe. The mass has a thin,

hyperintense rim (arrowheads), a finding that is consistent with methemoglobin. Arrows

indicate a large surrounding area of hypointensity, a finding that is consistent with

vasogenic edema. (b) On a sagittal contrast materialenhanced T1-weighted MR

image, the mass shows only slight rim enhancement (arrows). (c) Coronal

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CNS Infections 2003