Presentation on Ring Enhancing Lesions

1. Ring-Enhancing
Lesions
Brian Wells, MD, MS, MPH
Available online at http://www.slideshare.net/brianwells

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

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. 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. 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. 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. 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. 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

10. 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?

11. 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

13. 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

14. 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.

15. 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

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

18. 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

19. 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

20. 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”

21. 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

22. 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

23. 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.

24. 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

25. 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/

26. 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

27. 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/

28. 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.

29. 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

30. 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.

31. 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

32. 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

33. 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/

34. 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/