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Ring Enhancing Lesions
 

Ring Enhancing Lesions

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Presentation on Ring Enhancing Lesions

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    Ring Enhancing Lesions Ring Enhancing Lesions Presentation Transcript

    • Ring Enhancing Lesions Brian A. Wells, MD, MS, MPH September 16th, 2013
    • “Medicine as a computational science… as a probability science.”
    • 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 MRI Pre-gadolinium Axial T1WI MRI Post-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.
    • Axial T1 MRI + Gad Hypo/isointense lesion with ring enhancement Axial DWI MRI Hyperintense on DWI = restricted diffusion Axial FLAIR MRI + Gad Enhancing lesion surrounded by hyperintense edema Axial ADC Map Hypointense on ADC = Restricted diffusion
    • 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
    • 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 show restricted diffusion even in the 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
    • Thank you for your attention!