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INTRODUCTION
CNS is made up of millions of neurons and supporting cells
Impulses transmitted through ion exchanges.
Why? Where? When? ?How- still largely unknown.
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INTRODUCTION
Peculiarities of the CNS:
Regeneration is minimal or absent.
Almost completely enclosed by bone.
Standard surgical principles do not apply.
Incomplete understanding of pathology and recovery processes.
Functions of various CNS areas is yet to be defined.
Clinical examination is often inadequate to plan specific
approaches like surgery.
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INTRODUCTION
Neurological disorders can be structural or functional or both.
Diagnosis and treatment often requires multi-specialty inputs.
Clinical history and examination guide the investigation.
Investigative findings should always be correlated with the
patient’s clinical features.
Investigations only supplement and do not substitute a thorough
patient interview and examination.
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UNCOMFORTABLE PARADOX
Neuroimaging is least useful in the most common neurological disorders.
It is of limited use in the following disorders:
Headaches- especially migraine
Seizures and epilepsy.
Trigeminal neuralgia
Bells palsy.
Neuropathies.
Myopathies.
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CT CONTRAST
• Improves detection and
characterization of intra cranial
lesions.
• Opacifies blood vessels and
detects areas of abnormal BBB
break down.
• Normal renal function is a pre-
requisite.
• Ionic vs non-ionic contrast.
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NEUROTRAUMA
Gold standard
Can be done rapidly.
Easily available.
Minimum patient preparation.
Repeatability.
Can be done in uncoooperative
patients and ICU patients.
Highly sensitive for blood.
Bony details are well visualized and
hence useful for detecting fractures.
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DIFFUSE AXONAL INJURY
MRI brain showing acute axonal injury.
CT brain showing multiple small areas of
hemorrhage consistent with diffuse
axonal injury.
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TUMORS
Calcified tumor with
perilesional edema, probably a
meningioma.
Solitary lesion with contrast enhancement
with significan tperilesionaledema and mass
effect: glioblastoma/ brain abscess.
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TUMORS
• CT is excellent in imaging
calcified tumors and for
detecting intra-tumor
bleeds.
• However, in all other
aspects CT is far inferior to
MRI which is the preferred
imaging modality for
tumors.
• MRI is often diagnostic and
obviates the need for biopsy
in many cases.
MRI brain allows accurate estimation of the
size, relation to surrounding structures and
also nature of the lesion using MRS.
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HYDROCEPHALUS
• MRI is the investigation of
choice for hydrocephalus.
• It can identify the type,
severity, cause and quantify
the obstruction far more
accurately than CT scan.
• In NPH, MRI can determine
the CSF flow velocity across
the obstruction and
prognosticate surgical
outcome.
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STROKE
Evolved left MCA territory infarct
more than 24 hours old.
Evolving left MCA territory infarct
of 16 hours duration.
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CT VS MRI IN STROKE
CT brain on the left shows very subtle loss of grey-white differentiation
in the left frontal region. This is easily made out on MRI diffusion. CT
angiogram and CT perfusion can together provide excellent imaging of
brain circulation but is more expensive, requires longer scan time and
higher radiation exposure.
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DIFFICULT SITUATIONS IN THROMBOLYSIS
“Maximum benefit with minimum complications”
“Correct patient selection”
Denial of treatment or inappropriate use= malpractice/negligence.
• Time of onset not clear.
• Deceptive time of onset.
• Stroke with fall.
• Cause of paralysis in the past is not clear- Stroke Vs Hemorrhage.
• Estimation of size of infarct.
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CTA and CTP STUDIES in STROKE
• CTA and CTP can be performed immediately after conventional CT
scan, requiring only 5-10 minutes of additional time. It can be done in
the same examination, with separate contrast boluses.
• Allows detection of occlusion of large vessels and assessment of
perfusion status of brain parenchyma.
• Can help in deciding between intravenous and intra-arterial
thrombolysis.
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CTA in CAROTID DISEASE
• Provides an anatomic depiction of the carotid lumen and allows
imaging of adjacent soft tissue and bony structures.
• 3D reconstruction provides accurate measurements of the lumen
diameter unlike MRA which tends to overestimate stenosis.
• Especially useful in difficult situations like short neck, severe kinking,
severe calcification or high bifurcation.
• Sensitivity for carotid occlusion is between 97-99 % compared to DSA.
• Sensitivity for severe carotid disease is 77% and specificity is 95%.
• Preferred modality of imaging to plan for intervention.
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CTA in SUBARACHNOID HEMORRHAGE
CTA brain showing a small
right ACA aneurysm.
3D Reconstruction using CTA showing large
aneurysm in right MCA.
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CTA IN SUBARACHNOID HEMORRHAGE
• Investigation of choice in the initial evaluation of SAH.
• Can identify aneurysms as small as 3-5 mm.
• Sensitivity compared to DSA is 83-98% and improving constantly.
• Sensitivity is 97% with multidetector machines.
• Preferred over MRA and even conventional angiography because of
speed and reliability.
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INFECTIONS
CT brain with contrast showing a right
cerebellar ring- enhancing lesion.
CT brain plain showing numerous
calcified lesions of neurocysticercosis.
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INFECTIONS
CT brain with contrast showing
tuberculoma of the left frontal region
with perilesional edema and mass effect
with midline shift.
CT brain with contrast showing
enhancing meninges with basal
exudates with hydrocephalus.
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LIMITATIONS OF CT
• CT is practically useless in
identifying demyelinating
disorders like Multiple sclerosis.
• It has poor sensitivity for
chronic ischemic and toxic,
metabolic disorders.
• It is very poor at identifying
degenerative diseases like
Alzheimer's disease, progressive
supranuclear palsy.
Comparison of CT (left) and MRI (right)
brain scans in multiple sclerosis. CT looks
almost normal whereas MRI shows
marked abnormalities.
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ADVANTAGES
• Best preliminary neuroimaging test, especially in emergencies.
• Cheap, easily available, with readily available expertise.
• Adequate for routine decision making.
• Repeatability.
• 3D reconstruction provides valuable additional information.
• Can be performed in patients who are uncooperative, critically ill, with
prosthesis and those with pacemaker and other electronic devices.
• Has reduced need for invasive imaging techniques.
• Excellent for bone and blood imaging.
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DISADVANTAGES
•Involves radiation
•Inferior to MRI in resolution, contrast and in diagnostic yield.
•Inferior to MRI in acute stroke, demyelinating disease, epilepsy,
neuroinfection, degenerative diseases among others.
•Affected by bony artifacts.
•Posterior fossa structures are poorly visualised.
•Not useful in spinal cord imaging.
•Cannot be used in pregnant women.
•CT Contrast is more toxic than MRI contrast.
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TECHNIQUE
• PET relies on the detection of positrons emitted during the decay of a
radionuclide that has been injected into a patient.
• Most commonly used moiety is fluoro-deoxy glucose.
• Multiple images of glucose uptake activity are obtained after 45-60 min.
• Images reveal differences in regional glucose metabolism among
normal and pathological brain structures.
• PET-CT or PET-MRI refers to functional imaging superimposed on
high resolution of CT or MRI scans and provide more precise
anatomical and functional diagnosis.
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DEMENTIAS
Centre images show
bilateral parieto-
temporal areas of
hypometabolism in
patients with AD,
corresponding to the
atrophy seen on MRI.
Right sided images
show bilateral fronto-
temporal areas of
hypometabolism in
patients with FTD
corresponding to the
atrophy seen on MRI.
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PARKINSON’S DISEASE
DaTscan
(phenyltropane):
Top panel: a normal
scan.
Middle panel:
abnormalities in the
putamen (reduced
uptake) in a patient
with Parkinson’s
disease.
Lower panel: a return to
an almost normal scan
following the
introduction of
levodopa.
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SCHIZOPHRENIA
FDG PET comparing patients with schizophrenia (left) with normal
subjects (right) shows increased metabolism in the stratum and medial
prefrontal cortex in schizophrenia patients.
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CEREBRAL METASTASIS
Treated case of melanoma of the toe. Focus of intense FDG uptake is seen in the
midline anterior to the third ventricle on axial PET (a) and fused PET/CT
images (b) suggesting the diagnosis of cerebral metastasis.
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Operable case of lung cancer
for preoperative staging for
brain metastases.
Contrast enhanced T1 W axial
MRI (a) shows a well-defined
enhancing metastatic lesion
in the pons (arrow).
Lesion is not appreciated on
axial PET and fused PET/CT
images (b and c)
