Ring-enhancing brain lesions

Question 1

Differential diagnoses for ring-enhancing brain lesions “MAGIC DR”

Answer 1

Metastasis,
Abscess,
Glioma (also lymphoma),
Infarct,
Contusion,
Demyelination,
Radiation

Question 2

Imaging features of Metastases

Answer 2

1. MULTIPLICITY: frequently multiple lesions
2. LOCATION: predilection for the grey-white matter junction, and less frequently involve the deeper brain. They tend not to involve the periventricular white matter and rarely extend into the corpus callosum.
3. MORPHOLOGY: Typically spheres, well-circumscribed and easily separably from the adjacent brain parenchyma. Surrounded with vasogenic edema of varying amounts. Can be centrally necrotic/hemorrhagic.

Question 3

Imaging features of Glioma

Answer 3

1. MULTIPLICITY: Usually single lesion, sometimes multiple enhancing foci. BUT Cf with cerebral mets, the vast majority of cases of GBM with multiple areas of enhancement, will be embedded within the one area of FLAIR signal abnormality, or linked by abnormal FLAIR signal. This is termed multifocal glioblastoma.
2. LOCATION: Tends to be centred on the subcortical white matter, with frequent extension and spread along the subependymal tissues. Invasion and expansion of the corpus callosum is also frequently encountered.
3. MORPHOLOGY: Complex shape. Tends to have “peritumoral” components which demonstrate cortical expansion without enhancement.

Question 4

Imaging features of Lymphoma

Answer 4

1. CT hyperdense enhancing supratentorial mass,
2. MRI T1 hypointense, T2 iso- to hypointense, vivid homogeneous enhancement and restricted diffusion.
3. relatively little associated vasogenic oedema and no central necrosis, although it is important to note that in the setting of immunodeficiency, tumours are more likely to be:
   heterogeneous peripheral enhancement with central non-enhancement (due to necrosis). multifocal.
   surrounded by a greater degree vasogenic oedema.
4. MULTIPLICITY: solitary (60-70%) or multiple (30-40%). Solitary, large (> 4 cm) lesions are more suspicious
   for PCNSL, but solitary and multiple lesions
   occur with almost equal frequency.
5. LOCATION:
   * Lesions that involve the corpus callosum or the
   periventricular areas are more likely to be due
   to PCNSL (in comparison, toxoplasmosis commonly
   involves the basal ganglia).
   * Calcifi cation and haemorrhage are rare.
6. NM FACT: * A thallium scan will be positive (whereas a
   thallium scan is negative in toxoplasmosis).
   * Diff erentiation between PCNSL and toxoplasmosis
   is diffi cult, and interval scanning is often used
   in the absence of single photon emission CT.

Question 5

Imaging features of abscess

Answer 5

1. Abscesses result from hematogenous spread; direct spread from sinonasal or otomastoid infections, trauma, or surgery; or as a complication of meningitis.
2. MULTIPLICITY: can be solitary or multiple.
3. MRI: T2 hypointense capsule which is thinner toward the ventricles (prone to intraventricular rupture) with smooth rim enhancement and surrounding vasogenic edema. Pyogenic abscesses demonstrate central restricted diffusion. Toxoplasmosis, a parasitic infection in immunosuppressed
   patients, does not typically show restricted
   diffusion. Abscesses have decreased perfusion. MR spectroscopy
   shows an elevated lipid-lactate doublet.
4. Complications: look for dural venous sinus thrombosis, intraventricular rupture and ventriculitis.

Question 6

Imaging features of demyelinating disease

Answer 6

1. Multiple sclerosis is the most common primary demyelinating disease; ADEM is monophasic and more common in children.
2. Characteristic features include
   ovoid T2/FLAIR hyperintense lesions oriented perpendicular
   to the ventricles (Dawson fingers).
3. High specificity locations
   include the corpus callosum, optic pathways, and posterior fossa.
4. Enhancement suggests active demyelination. A solitary demyelinating lesion greater than
   2 cm in size can mimic a tumour, but is usually
   in a characteristic (periventricular) location in
   a young patient.
   * There may be “horseshoe-shaped” enhancement
   that is open towards cortex, that is,
   incomplete ring enhancement.

Question 7

Imaging features of Resolving Contusion

Answer 7

A history of trauma is important in differentiating
a contusion from other ring-enhancing lesions.

Blood products are present in varying stages, depending on the age of the hematoma.

Rim enhancement occurs within a few days in a vascularized capsule.

Acute blood products are
isointense on T1 and hypointense on T2.

Subacute blood products
(intra- or extracellular methemoglobin [MetHb]) are T1 hyperintense.

Intracellular MetHb is T2 hypointense; extracellular
MetHb is T2 hyperintense.

Question 8

Imaging features of Resolving Contusion

Answer 8

A history of trauma is important in differentiating
a contusion from other ring-enhancing lesions.

Blood products are present in varying stages, depending on the age of the hematoma.

Rim enhancement occurs within a few days in a vascularized capsule.

Acute blood products are
isointense on T1 and hypointense on T2.

Subacute blood products
(intra- or extracellular methemoglobin [MetHb]) are T1 hyperintense.

Intracellular MetHb is T2 hypointense; extracellular
MetHb is T2 hyperintense.