brain and meningeal infections in hiv - radiologist's perspective

BRAIN AND MENINGEAL INFECTIONS IN HIV

Under the guidance ofDr.M.V.Ramanappa,

HOD,Dept of Radiodiagnosis,

Santhiram Hospital,Nandyal.

Presented by,Dr.P.Sreekanth,

2nd year PG,Dept of Radiodiagnosis,

Santhiram Hospital,Nandyal.


HIV ENCEPHALOPATHY

BRAIN AND MENINGEAL INFECTIONS IN HIV : HIV Encephalopathy

• HIV-associated cognitive-motor complex (also termed HIV encephalopathy, HIV-associated dementia or AIDS dementia complex) presents with cognitive impairment, behavioural change and motor symptoms.

• The clinical picture is of a subcortical dementia with slowness, forgetfulness and apathy.

• The prevalence of HIV encephalopathy is 10–20 per cent of AIDS cases and is rising as patients live longer. The incidence has halved since the introduction of HAART.

• Multinucleate giant cells and microglial nodules characterize HIV encephalitis, the pathological correlate of HIV encephalopathy. Myelin loss, macrophage infiltration and gliosis are also seen. HIV encephalitis occurs because of cerebral infection with HIV.


• The commonest imaging finding in HIV encephalopathy is cerebral atrophy, the extent of volume loss correlates with cognitive impairment.

• White matter lesions in the centrum semiovale and periventricular regions are the next most frequent abnormality.

• These appear as areas of low attenuation on CT, and T2-prolongation on MRI, which lack mass effect and do not enhance.

• The white matter changes tend to progress with time, becoming diffuse and confluent.

• Atrophy and white matter lesions can coexist or occur independently of one another ( Fig. 58.9 ).


HIV Encephalopathy

PML


• MR spectroscopy (MRS) shows decreased N-acetyl aspartate (NAA), reflecting neuronal loss, increased choline, a marker of membrane turnover, and increased myoinositol, a glial cell marker. These abnormalities can be detected in patients with normal MRI. Cognitively normal HIV-infected patients may also show increased choline and myoinositol, but little or no change in NAA. The spectroscopic abnormalities can reverse with HAART.

• PET and SPECT may show hypermetabolism in the basal ganglia and thalami in patients with a normal MRI; these abnormalities correlate with neuropsychiatric measures of dementia. In advanced disease cortical hypometabolism is seen. Although the sensitivity of these techniques is high, the specificity is undetermined and the role in clinical practice is not established.

• Diffusion tensor MR imaging (DTI) shows reduced whole-brain fractional anisotropy (FA) in cognitively impaired HIV-infected patients. The reduction in FA correlates with the severity of cognitive impairment.

• Patients receiving HAART may show stabilization or even regression of MRI abnormalities. Early follow-up imaging may show lesion progression but this is not indicative of treatment failure.


CEREBRAL TOXOPLASMOSIS


• Toxoplasmosis is the commonest cause of a cerebral mass lesion in AIDS and also the most treatable.

• It results from reactivation of latent infection by Toxoplasma gondii, for which the definitive host is the cat.

• Patients present subacutely with headache, fever, confusion, personality change and focal neurological deficits.

• Histopathology shows a multifocal haemorrhagic necrotizing encephalitis with the development of organizing abscesses.

• Imaging typically shows multiple lesions, 1–4 cm across, at the corticomedullary junction and in the basal ganglia ( Fig. 58.10 ).

Figure 58.10 Typical toxoplasma abscesses and response to treatment. Transverse T2W images (A, C, D) and coronal T1W image (B). Multiple masses of varying sizes with a propensity to involve the basal ganglia and corticomedullary junction and associated with perilesional oedema may occur (A). High signal seen on the T1W images is due to haemorrhage (B). In response to therapy for toxoplasma (C, D), the size of the lesions and the surrounding oedema are reduced. Responding lesions may show increased intensity on T2W images and some show a surrounding low signal rim due to haemosiderin (arrow).


• Single lesions and lesions in the brainstem or cerebellum are uncommon. The lesions show ring or nodular enhancement with associated oedema and mass effect( Fig. 58.11 ).

• Enhancement may be diminished or absent in severely immunocompromised patients.

• MRI is more sensitive than CT to foci of haemorrhage within the lesions. • The principal differential diagnosis is from primary CNS lymphoma,

which can appear identical and can coexist in the same patient ( Fig. 58.12 ).


• In comparison to pyogenic abscesses cerebral toxoplasmosis is hypointense to white matter on DWI, indicating no restriction of diffusion.

• A diffuse form of toxoplasmosis is not infrequent at postmortem examination. It appears as ill-defined foci of T2 prolongation at the corticomedullary junction, with mild and patchy enhancement.

• Lifelong treatment is necessary, usually with pyrimethamine and sulfadiazine. Most lesions show reduced enhancement, oedema and mass effect within 2–4 weeks.

• Small lesions may heal completely whilst larger lesions can show persistent enhancement for more than 2 years on maintenance therapy.


PRIMARY CEREBRAL LYMPHOMA


• Primary cerebral lymphoma is the AIDS-defining diagnosis in 5 per cent of patients.

• The incidence has reduced in the era of HAART. Most patients present with rapid progression of confusion, lethargy, memory loss and focal neurology.

• Cerebral lymphoma is often multifocal in AIDS; lesions are commonest in the cerebral white matter but also occur in the basal ganglia, corpus callosum and ventricular margins (Figs 58.13, 58.14). Lesions abut the ependyma, leptomeninges or both in 75 per cent.


• Imaging shows well-defined round or oval lesions of high attenuation on unenhanced CT, and lower signal intensity than grey matter on T2W MRI.

• This reflects the dense cellularity of lymphoma. • Lesions have relatively little mass effect and oedema for their size. • Haemorrhage is unusual and calcification seen only after treatment.• Enhancement is typical, often in a smooth or nodular ring

surrounding a zone of central necrosis, in contrast to the solid enhancement seen in immune-competent patients.

BRAIN AND MENINGEAL INFECTIONS IN HIV• Whilst they can be indistinguishable, there are some features that favour a diagnosis

of lymphoma over toxoplasmosis. • A single enhancing mass lesion in AIDS is more likely to be lymphoma, as are larger

lesions and those with central low intensity on T2W images. • Subependymal spread is a feature of lymphoma but is not seen in toxoplasmosis.• Thallium-201 SPECT and FDG-PET show greater uptake in lymphoma than

toxoplasmosis though this is unreliable in lesions smaller than 2 cm. Although lymphoma sometimes shows restricted diffusion, ADC values often overlap with those of toxoplasmosis, limiting the value of DWI in distinguishing between the two.

• Metastases from systemic lymphoma typically involve the meninges ( Fig. 58.15 ); parenchymal disease without leptomeningeal involvement is rare.

• Lymphoma may respond dramatically to radiotherapy and/or corticosteroids but usually the prognosis is poor, HAART has prolonged median survival from 2–8 months.


CRYPTOCOCCOSIS

BRAIN AND MENINGEAL INFECTIONS IN HIV• This is the second commonest opportunistic CNS infection in AIDS. • Patients most often present with headache, fever and altered mental state.• The earliest imaging manifestation is dilatation of perivascular spaces, most often in

the basal ganglia but also in the brainstem and cerebral white matter ( Fig. 58.16 ). • These spaces are distended by mucoid material, organisms and inflammatory cells,

and appear as multiple small foci of high signal on T2W images. • With disease progression cryptococcomas develop at these sites, forming lesions 3

mm to several cm in size. • Cryptococcomas are of low to intermediate signal on T1W and high signal on T2W

images, lack surrounding oedema and do not show restricted diffusion.• Enhancement of cryptococcomas or the leptomeninges is rare because these patients

are profoundly immunocompromised.


PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY

BRAIN AND MENINGEAL INFECTIONS IN HIV• Progressive multifocal leukoencephalopathy (PML) is a central demyelinating

disease resulting from the reactivation of a latent infection of oligodendrocytes by JC polyomavirus.

• Eighty per cent of adults show serological evidence of prior exposure to the JC virus.

• The incidence of PML is about 4–5 per cent of AIDS cases; it is the AIDS-defining illness in about 1 per cent.

• Clinically, limb weakness is the commonest presentation, with an insidious onset and a progressive course involving visual field defects, speech abnormalities, ataxia and dementia.

• Pathologically, there is demyelination, astrocytosis and oligodendrocytes with intranuclear inclusions.

BRAIN AND MENINGEAL INFECTIONS IN HIV• Lesions can occur in any part of the brain but are commonest in the parieto-

occipital regions. • MRI shows multifocal, asymmetric bilateral white matter lesions that are of

high signal on T2W and low signal on T1W images ( Fig. 58.17 ). • Extension to the subcortical U-fibres gives the lesions a characteristic

‘scalloped’ appearance. • Apparent involvement of the basal ganglia can occur when lesions affect the

white matter tracts that course through this site. • Rarely, lesions may show mild mass effect and peripheral enhancement;

restricted diffusion can be observed in areas of active disease progression.

HISTOPLASMOSIS

HISTOPLASMOSIS

• Histoplasmosis occurs in up to 5 per cent of AIDS patients in areas where Histoplasma capsulatum is endemic.

• CNS manifestations include meningitis with involvement of adjacent vessels, and single or multiple abscesses.

• Imaging may show meningeal enhancement, cerebral infarcts, or focal enhancing lesions with mass effect and oedema.

NEUROSYPHILIS

NEUROSYPHILIS

• CNS involvement can occur at any stage of syphilis, in HIV-infection its course may be more aggressive.

• Meningovascular syphilis causes a small-vessel endarteritis that appears as arterial segmental ‘beading’ on angiography, with associated infarcts in the basal ganglia.

• Cerebral gummas are rare, typically arise from the meninges, and appear as mass lesions with variable MR signal characteristics and enhancement.

CEREBROVASCULAR DISEASE

CEREBROVASCULAR DISEASE

• Cerebral infarcts occur in fewer than 5 per cent of AIDS patients.• Causes include infective vasculitis (CMV, varicella zoster or

tuberculosis) and embolism from HIV cardiomyopathy. • HIV also causes a dilating vasculopathy that results in fusiform

aneurysms of the intracranial vessels.

HERPES VIRUSES

HERPES VIRUSES

• Cytomegalovirus, herpes simplex and varicella zoster viruses can cause encephalitis, necrotizing ventriculitis ( Fig. 58.18 ), and myelitis in AIDS.

• In encephalitis imaging may be normal, show nonspecific white matter lesions or focal enhancing lesions.

• Ependymal enhancement occurs with ventriculitis; myelitis manifests as nonspecific swelling and signal change in the spinal cord.

HERPES VIRUSES

CANDIDIASIS

CANDIDIASIS

• Although mucocutaneous candidiasis is common in HIV-infected patients, CNS involvement is rare.

• Haematogenous dissemination results in meningitis and/or cerebral abscesses.

• Imaging appearances are nonspecific; clinical confirmation is dependent on CSF analysis or brain biopsy.

TUBERCULOSIS

TUBERCULOSIS

• Intracranial tuberculosis is mostly seen amongst IV drug misusers.

• The radiological manifestations are similar to those in immunocompetent patients, hydrocephalus and meningeal enhancement being the commonest.

• Parenchymal lesions, in the form of tuberculomas and abscesses, are more frequent in HIV infection

INCIDENTAL WHITE-MATTER HYPERINTENSITIES

INCIDENTAL WHITE-MATTER HYPERINTENSITIES

• Focal white-matter hyperintensities, often multiple, are seen in up to 26 per cent of HIV-positive patients and up to 24 per cent of seronegative men of matched ages.

• No associations with neurological abnormalities, CD4 count, or vascular risk factors have been identified.

• These lesions are probably incidental and of no clinical significance

THANK YOU

brain and meningeal infections in hiv - radiologist's perspective

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