Ring Enhancing Lesions

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Ring Enhancing Lesions

  1. 1. Ring-Enhancing Lesions Brian Wells, MD, MS, MPH Available online at http://www.slideshare.net/brianwells
  2. 2. “Medicine as a computational science… as a probability science.”
  3. 3. 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?
  4. 4. Warm-up Question #2 What 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.
  5. 5. 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.
  6. 6. 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
  7. 7. 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.
  8. 8. 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
  9. 9. 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?
  10. 10. 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
  11. 11. 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
  12. 12. 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.
  13. 13. 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
  14. 14. Why are you showing me this? Why is this important? Can I leave now?
  15. 15. 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
  16. 16. 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
  17. 17. 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”
  18. 18. 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
  19. 19. 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
  20. 20. 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.
  21. 21. 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
  22. 22. 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/
  23. 23. Question from the NEJM • Which of the following organisms is most likely to cause a cerebral abscess in a solid-organ transplant recipient? A. Aspergillus B. Mycobacterium tuberculosis C. Staphylococcus aureus D. Toxoplasma gondii
  24. 24. 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 http://blogs.nejm.org/now/index.php/brain-abscess/2014/08/01/
  25. 25. 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.
  26. 26. 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
  27. 27. 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.
  28. 28. 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
  29. 29. 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
  30. 30. 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 http://blogs.nejm.org/now/index.php/brain-abscess/2014/08/01/
  31. 31. 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) http://blogs.nejm.org/now/index.php/brain-abscess/2014/08/01/

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