Ring Enhancing Lesions

Ring-EnhancingLesions

Brian Wells, MD, MS, MPHAvailable online at http://www.slideshare.net/brianwells

“Medicine as a computational science… as a probability science.”

Warm-up Question #1

Asymptomatic 24 year old.

Is there an abnormality?

Is it pathologic?

What is it likely to be?

How common is it?

Warm-up Question #2What classic sign is seen in this CT?

Of what disease is it a sign?

Is the disease active?I love the alphabet.

You forgot to thank Berg and

Lesniowski.

HIV/AIDS and the CNS• 10% of patients have neurological signs and

symptoms when they first present with AIDS.• 30-60% of patients with AIDS will develop

neurological complications during the course of their illness.

• 70-90% of patients with AIDS show CNS involvement at autopsy.

• Understanding and recognizing the appearance of CNS complications in patients with AIDS is important in promptly recognizing, diagnosing and initiating proper treatment.

DDx of CNS complications in AIDS• HIV encephalitis• Opportunistic Infections:

– Toxoplasmosis– Cryptococcosis– CMV– TB– PML (JC virus)– Bacterial– Fungal

• Neoplasm– Primary CNS lymphoma– Kaposis Sarcoma

Menu of Radiologic Tests• Primary Modalities:

– CT (w/wo contrast)• MRI (w/wo contrast)• T1, T2, FLAIR• DWI/ADC Maps

• Adjunctive Modalities:– FDG-PET– Thallium 201 SPECT– Special MRI protocols

• MR Spectroscopy• Perfusion MR

Adjunctive modalities are not used in the routine imaging or evaluation of CNS lesions in patients with AIDS. They are primarily used when the identity of a lesion is in question and additional non-invasive imaging would potentially alter treatment. PET and SPECT scanning are used most frequently. MR spectroscopy and perfusion MR are not routinely used and will not be discussed.

Computed Tomography

Pros

1. Fast

2. Readily available

3. Can scan people with contraindications to MRI

Cons• Less sensitive• Limited evaluation of the

posterior fossa• Can miss some white

matter brain disease• Radiation

Questions!

• From what events do we draw much of our understanding of radiation?

• How do we determine risk with regards to radiation exposure?

• Can a pregnant woman receive a CT?

Magnetic Resonance Imaging

Pros

1. Better than CT at determining if lesion is truly solitary

2. Increased sensitivity to subtle white matter disease and posterior fossa lesions

3. May be able to identify small peripheral lesions missed by CT that are more accessible for biopsy

4. No radiation

5. Multiple imaging sequences can aid diagnosis (DWI/ADC/FLAIR)

Cons• More costly• Less readily available

Additional sequences available via MRI allow us to better characterize the center of the lesion and surrounding tissue.

Axial T1WI MRIPre-gadolinium

Axial T1WI MRIPost-gadolinium

Diffusion Weighted Imaging (DWI)

• DWI makes use of Brownian motion to image local water diffusion. Macromolecules and cells in the brain restrict the diffusion of water.

• Apparent Diffusion Coefficient (ADC): The signal intensity of DWI depends on factors other than diffusion information (spin density, TR, TE). By combining multiple DWIs, these other factors can be eliminated. ADC also eliminates “T2-Shine through” on DWI caused by intense T2 signals.

AxialT1 MRI + Gad

Hypo/isointenselesion with ringenhancement

AxialDWI MRI

Hyperintense onDWI = restricted

diffusion

AxialFLAIR MRI

+ Gad

Enhancinglesion surroundedby hyperintense

edema

Axial ADCMap

Hypointense on ADC =

Restricteddiffusion

Why are you showing me this? Why is this important? Can I leave now?

Differential Diagnosis of Ring Enhancing Lesions• Infection

– Toxoplasma– Cystercercosis– Brain abscess (bacterial, fungal)

• Neoplasms– Brain tumors/metastases– Primary CNS lymphoma

• Demyelinating Disease– MS– ADEM

• Vascular lesions– Resolving infarction– Hematoma– Thrombosed aneurysm

• Radiation necrosis• Postoperative change

When we consider what is most likely in a patient with HIV/AIDS, our

differential is narrowed to:• Toxoplasmosis• Brain abscess

• CNS lymphoma

Toxoplasmosis• Protozoal infection, typically reactivation of infection causing

CNS disease in deficient cell-mediated immune status of advanced AIDS

• Signs/Symptoms: headache, fever, seizures, encephalopathy, AMS, neurological deficits

• Important to quickly diagnose because very treatable with antibiotics

• Typically multiple ring-enhancing lesions typically in basal ganglia and corticomedullary junction (80-90%) + anti-Toxoplasma IgG (95%) + CD4 < 100 (>90%)

• Main differential is CNS lymphoma• Multiple treatment regimens, including pyrimethamine,

sulfadiazine, and leucovorin to name a few

Source: Johns Hopkins Antibiotics Guide

Toxoplasmosis Imaging

• CT– Non-contrast – isodense to gray matter, but can be

detected secondary to edema and mass effect• Hyperdense if hemorrhagic

– Contrast – Ring-enhancing in ~90% of cases

• MRI– T1 – hypointense/isointense to gray matter– T2 – isointense/hyperintense to gray matter– Ring-enhancing, sometimes with central focus of

enhancement – “target sign”

Primary CNS Lymphoma

• Most common AIDS related neoplasm• Second most common cerebral mass lesion in

AIDS patients• Almost always of B-cell, Non-Hodgkins type• Likely related to EBV• Symptoms: Similar to toxoplasmosis – neurological

deficits, encephalopathy, seizure• Medial survival < 1 year• Treatment: Radiation and corticosteroids

Primary CNS Lymphoma

• CT– Isodense to hypodense

• MR– T1 – hypointense– T2 – isointense to hyperintense– Usually irregular enhancement or ring enhancement– Can have a wide range of appearances– Usually periventricular/periependymal

Primary CNS Lymphoma – Varying Appearances

T1 + Gad – hypointense with ring enhancement

T1 + Gad – Homogeneously enhancing lesion

Provenzale JM. Radiol Clin North Am 1997;35(5):1127-66.

Bacterial abscess• Cerebral abscess is most often the result of hematogenous

dissemination from a primary infectious site• Often present with headache, AMS, nausea, vomiting,

seizures, neurological deficits due to expanding mass• Less common in AIDS

patients than toxoplasma or primary CNS lymphoma

David Yousem and Robert Grossman. Neuroradiology. Third Edition

What are the most appropriate diagnostic tools in cases of suspected brain abscess?

• CT with contrast provides a rapid means of detecting size, number, and localization of abscesses.

• MRI combined with DWI and ADC is valuable to differentiate abscess from primary, cystic, or necrotic tymors.

• Sensitivity/Specificity 96% (PPV 98%; NPV 92%) in differentiating abscess from primary or metastatic cancer.

• Cultures identify the pathogen 25% of the time

http://blogs.nejm.org/now/index.php/brain-abscess/2014/08/01/

Question from the NEJM

• Which of the following organisms is most likely to cause a cerebral abscess in a solid-organ transplant recipient?A. AspergillusB. Mycobacterium tuberculosisC. Staphylococcus aureusD. Toxoplasma gondii

Answer

• Patients who have received solid-organ transplants are at risk not only for nocardial brain abscess but also for fungal abscess (aspergillus or candida)

• Abscess formation after neurosurgical procedures or head tram is likely Staph aureus, S. epidermidis, or gram-negative bacilli.

• Abscess due to spread from parameningeal foci of infection is frequently streptococcus, but staph and polymicrobial also occur

• HIV is associated with Toxoplasma


Abscess Imaging Characteristics• The characteristics of cerebral abscess depend on the

pathologic phase during which the abscess is being examined.

• T1 – Hypointense• T2 – Hyperintense with a typical epicenter at the

corticomedullary junction and patchy enhancement.• Capsule is hypointense on T2

– A thin rim of low signal on T2WI and possibly high signal on T1WI characterize the wall of an abscess and would be more unusual for necrotic tumors.

• The vast majority of pyogenic abscesses evoke considerable edema.

DWI/ADC

• One specific application of MRI that has attempted to distinguish ring-enhancing lesions

• Currently cannot accurately distinguish toxoplasmosis from CNS lymphoma due to broad overlapping range of diffusion values– Toxo tends to have restricted diffusion– CNS lymphoma tends to have increased diffusion

• DWI/ADC is useful for identifying pyogenic abscesses which are consistently hyperintense on DWI and hypointense on ADC

DWI/ADC

• Remember that the vasogenic edema surrounding the pyogenic abscess will be bright on ADC maps, indicating NO restricted diffusion unlike the abscess itself, which is dark on ADC with restriction of diffusion. The low ADC is probably related to high protein, high viscosity, and cellularity (pus) within the abscess cavity.

DWI/ADC Examples

Bacterial Abscess Toxoplasmosis - DWI

DWI ADC Does not consistently showrestricted diffusion even inthe same patient.

Zimmerman. Clinical MR Neuroimaging pg 355, 366

Advanced Imaging Techniques

• Nuclear medicine offers ways to differentiate between infectious and neoplastic lesions.

• Due to time constraints, we will not discuss these.

Lymphoma showing hypermetabolic activity on FDG-PET

What is the typical presentation?

• Headache is the most frequent manifestation• Fever and AMS are frequently absent• Neurologic signs depend on the site of the abscess

and can be suble for days to weeks.• Behavioral changes can occur with abscesses in

the frontal or right temporal lobes• Abscesses in the brain stem or cerebellum may

present with cranial-nerve palsy, gait disorder, headache, or AMS due to hydrocephalus

• 25% will have seizures


How should a brain abscess be managed?

• 27% are polymicrobial, so broad spectrum therapy is used until results of cultures are known

• Diameter >2.5 cm is an indication for neurosurgical intervention (though data from comparative studies is lacking, and size cannot be regarded as a definitive indication for aspiration)

• Glucocorticoid therapy is useful to reduce cerebral edema (though data from randomized studies is lacking and glucocorticoids may reduce passage of antimicrobial agents into the CNS)


Ring Enhancing Lesions

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