Neuroradiology lecture aug2007

Diagnostic Imaging Methods
in Central Nervous System
Disorders
P. Danilo J. Lagamayo, MD


Headache:
Primary:
Migraine
Cluster
Tension
Secondary:
Increased Intracranial Pressure:
Neoplasms
Abscess
Granulomas
Meningeal Irritations:
Meningitis
Subarachnoid Hemorrhage
Vascular Disorders:
Stroke
Malformations
Arteritis
Head Trauma:
Concussion
Hematoma
Other Cranio-Facial Pains:
Trigeminal Neuralgia


Incidence of Primary Brain

Tumors:
- 6 persons / 100,000
population / year
- about 1 in 12 primary brain
tumors
occur in children
under 15 years old.


Clinical Presentation of Brain
Tumors:
Focal neurologic deficit
Increase intracranial
pressure:
Headache that is more severe in AM
- Nausea / Vomiting
- Diplopia
- Papilledema
- Ontundation &
Lethargy (ominous)
Focal
neurologic signs and symptoms:
- seizure, seen in about ½ of


Clinical Presentation of Brain
Tumors: (II)
Non-localizing
findings:

- fatigue
- malaise
- impotense
-

glactorrhea
growth failure
- macrocephaly in young children


Pathological Classification of
Intracranial Tumors:
Neuroepithelial:
Astrocytes Astrocytoma
Oligodendrocytes - Oligodendroglioma
Ependymal cells
& Choroid PlexusEpendymoma
Choroid Plexus Papilloma
Neurons Gangliomas,
Gangliocytomas,
Neuroblastomas
Pineal cells Pineocytomas
Pineoblastomas
Poorly differentiated


Pathological Classification of
Intracranial Tumors: (cont.)
Meninges
- Meningioma

Nerve sheet cells Neuroma
- Neurofibroma
Blood vessels
- Hemangioblastomas Germ cells
- Germinoma
- Teratoma
Tumors
of maldevelopmental origin
Craniopharyngioma
- Epidermoid/Dermoid
cyst


Pathological Classification of
Intracranial Tumors:
Anterior pituitary gland
- Pituitary adenoma
- Adenocarcinoma
Local extension
- Chordoma from adjacent
- Glomus jugulare tumors
- Chondroma
- Chondrosarcoma
- Cylindroma


Incidence of Tumors:
Glioblastoma - - - - - - - - 55% Astrocytoma - - - - - - - - 20.5%
Ependymoma - - - - - - - 6% Medulloblastoma - - - - - 6% Oligodendroglioma _ - - 5% Choroid Plexus
Papilloma

2%
Other less common entities:
Neuronal tumors –
Gangliocytomas,
ganglioglioma
Embryonal
– PNET
Pineal
Region – germ cell


Primary Imaging
Methods for Diagnosis of
CNS tumors:
- MRI
- CT scan
- Angiography


Advantages of CT Scan
-

Wide availability;

-

Can accommodate life support systems;

-

Fast imaging methods

-

Can show bone structures and their pathologic changes like fractures;

-

Cheap.


Disadvantages of CT Scan
•

Cannot demonstrate soft tissue detail of the sella turcica, the brain stem and the cerebellum;

•

Not very sensitive to white matter lesions;

•

Cannot differentiate encephalomacic lesions of hemorrhage from infarcts;

•

Uses ionizing radiation and cannot be used on pregnant patients.


Advantages of MRI

• Unaffected by the thick bone encasement of
the calvarium in the posterior fossa and the
sellar turcica;
• Accurate determination of the age and
evidence of hemorrhage;
• More sensitive for detection of white matter
lesion;
• Ability to perform multiplanar imaging;
• Does not use radiation and can be safely
used on pregnant patients.


Disadvantages of MRI
•

Longer time needed to complete an examination;

•

Needs patient cooperation, e.g. patient must not move during an imaging sequence that can take anywhere from 1 minute to as
long as 7 minute;

•

Any metal implement is not allowed into the MR room.


Disavantages of MRI
•

Cannot image patients with:

– Pacemakers
– Neurostimulators
– Newly applied vascular clips
– Vacular clips with ferromagnetic materials
(steel or iron)
– Metal foreign bodies in the orbit
– Claustrophobic patients
– Patients who need extensive life support


Causes of Low Signal
Intensity in Tumors in T2WI:
Paramagnetic effects
- Iron with dystrophic Ca or
necrosis
Ferritin/hemosiderin from prior bleed
- Deoxy hgb in acute bleed
- Intracellular met hgb in early
subacute bleed
- Melanin (or other
free radicals)


Causes of Low Signal
Intensity in Tumors in T2WI
(cont.):
Low spin density
- Calcifications

- Scant cytoplasm
(high
nucleus:cytoplasm ratio)
Dense Cellularity
Fibrocollagenous stroma
Macromolecule content
Very high (nonparamagnetic) protein content

-


Causes of High Signal Intensity
in Tumors in T1WI:
Paramagnetic effects from hemorrhage
- Subacute – chronic
blood (met hgb)
Paramagnetic
materials w/out hemorrhage
- Melanin
- Naturally occuring ions associated with
necrosis of calcification:
Manganese, Iron, Copper
Non-paramagnetic effects
- Very high
(non-paramagnetic) proteins
- Fat
-


Requirements for contrast

enhancement:
absence of blood-brain barrier
- adequate delivery of contrast
material
- extracapillary interstitial
space to
accommodate contrast
- appropriate contrast dosage
- spatial resolution
- imaging parameters to
allow contrast
detection
- time for
-


Mechanism for contrast
enhancement in CNS tumors:
Formation of capillaries with
deficient blood-brain barrier rather
than the destruction of blood-barrier is
presumed as the mechanism for tumor
enahcement.
The capillaries of metastatic
tumors to the brain has no blood-brain
barrier since these tumors come from
elsewhere and not from the brain.


Type of enhancement:

immediate or delayed
- evanescent or
persistent
- dense
and homogenous
minimal or irregular
-

Note: Lack of tumor enhancement do
not signify lack of tumor.


Effects of Tumor Necrosis on
Signal Intensity:
Short relaxation times Hemorrhage
Liberation of
cellular iron
Release
of free radicals
Proteinaceous debris
Prolong relaxation
increased
times
water

Cystic change with


Frequently Cystic Tumors
Colloid cyst

Craniopharyngioma
Desmoplastic infantile ganglioma
Dermoid
Ependymoma (supratentorial and spinal)
Epidermoid
Ganglion cell tumors
Glioblastoma (cystic necrosis)
Hemangioblastoma
Pilocytic astrocytoma
Pleomorphic xanthoastrocytoma
Rathke cleft cyst


Magnetic Resonance Criteria for Cystic Lesions

Morphology

Sharply demarcated, round
smooth

Signal Intensity

Isointense to cerebrospinal fluid
on all spin echo images (tumor
cysts can be hyperintense due to
↓ T1)

Fluid-debris levels
(bleed into necrotic
or cystic regions)

Intracellular blood-cyst fluid
Intracellular blood-extracellular
blood

Motion of intralesional fluid

Lesion emanates ghost images
along phase-encoding axis
Intralesional signal loss
(especially on steady-state
sequences)


Hemorrhagic Tumors
Primary brain tumors
Glioblastoma/anaplastic asctrocytoma
Anaplastic
oligodendroglioma/oligodendroglioma
Ependymoma
Teratoma
Metastatic disease
Melanoma
Renal cell carcinoma
Choriocarcinoma
Lung carcinoma
Breast carcinoma
Thyroid carcinoma