Investigations for CNS
1- neuroimaging:Now days the most useful imaging modalities are harmless to patients.
In most situations the only modalities to be consider is ( MRI ) and in patients whom MRI cannot be performed ( CT ) is usually satisfactory.
CT scan is the first choice to exclude surgical emergencies.
Plain x-rays of the skull is obsolete, but a limited role for plain x-rays of the spine.
Plain x-rays:
skull fractures either pathological or non-pathological.
spine:
trauma.
instability in non-traumatic conditions. e.g RA, down syndrome.
spondylotic spinal stenosis.
spinal metastasis and other tumors which destroy or erode bone need to remove 50-70 % of bone mass before it become apparent on plain x-rays.
osteomylitis with root or spinal cord compression.
chest x-rays used to excluding many systemic diseases which may present neurologically.
CT scanning:
CT scan account for 13% of the radiological examinations and 30% of the overall radiation exposure attributable to examinations.
Although (MRI) has better sensitivity than (CT) for detecting intra-axail and extra-axial brain and spine lesions.
CT still remains the quickest and most efficient means of screening the patient with certain condition such as head trauma, calcification, SAH, fracture of orbit, temporal bone, and skull.
Indications:
acute head trauma.
SAH.
fractures of orbit, temporal bones, face and skull.
detection of calcification.
subtle bony irregularities.
bony spinal lesions.
disease of the temporal bone.
sinusitis.
9- when MRI is contraindicated.
Intracranial calcifications:
physiological.
pineal gland ( 20%).
choroid plexus ( usually bilateral )
dura matter and falx cerebri.
B. non-physiological.
neoplasm.
inflammatory.
infections like TB.
vascular malformation and chronic subdural hematoma.
MRI scanning:
T1 weighted images ( T1W) are most useful for analyzing anatomical details and are employed in conjunction with gadolinium contrast because enhancing lesions appear bright on it.
T2 W are very sensitive to the presence of increase water and can visualize edema.
Indications:
subacute/chronic hemorrhage.
acute infraction diffusion weighted images.
carotid or venous dissection.
neoplasm.
immunosuppressed with focal findings .
vascular malformation.
infection and abscess.
white matter disorders.
dementia.
partial complex seizure.
cranial neuropathy.
meningeal disease.
spinal stenosis.
cervical spondylosis.
myelopathy .
Contraindications:
cardiac pacemaker.
cochlear prostheses.
intracranial aneurysm clips.
ocular implants.
magnetic dental implants.
magnetic sphincters.
deep brain stimulators.
foreign bodies in the eyes.
severe claustrophobia.
swan- ganz catheter.
Angiography:
it is invasive test.
The indication for diagnostic angiography have greatly diminished since the advent of CT.
Four vessels technique performed, two carotid and two vertebral arteries.
Indications:
aneurysms greater than 4mm in diameter are reliably shown.
AVM.
arteritis.
carotid stenosis is controversial
dural sinus thrombosis.
preliminary to endovascular treatment.
Complications:
hematoma or infection in 5% at the arterial puncture.
arterial vasospasm.
stroke in 1-2%.
death in 1-2%. CSF : samples of CSf may be obtained with relative ease at the bedside by lumbar puncture. The best positioned on the side, flexed and with the spine horizontal.The needle is usually introduced at the L3/L4 interspace which is indicated by a line drawn joining the tips of the iliac crests.
Indications for brain imaging prior to LP:
S & S of raised ICP ( headache, vomiting, papelledemia).
Focal neurological deficit.
Fixed dilated or poorly reactive pupil.
Coma or a rapidly deteriorating concious level.
Signs of posterior fossa lesion ( dysarthria, ataxia ).
Immunocompromized patients ( malignancy, transplants )
Normal CSF:
Clear colourless fluid.
Pressure 40-180 mm H2o.
Cells 0-5 lymphocytes.
Sugar 2.5-4.4 mmol/l ( 2/3 of blood glucose )
Protien o.2 o.5 g/L
Abnormal CSf findings:
Bacterial meningitis.
Viral meningoencephalitis.
T.B. meningitis.
Subarachnoid hemorrhage.
Low CSF protien:
CSF leaks.
removal of a large csf volume.
3-pseudotumor cerebri in 1/3 of patient.
4-acute water intoxication.
aged between 6 months – 2 years.
hyperthyroidism.
leukemias.
Elevated CSF protein with a cellular response:
G.B.S ( AIDP)
chronic inflammatory demylinating polyneuropathy.
schwannoma.
spinal cord compression.
Elevate CSF glucose:
premature infant and newborns.
hyperglycemic states.
Special CSF tests:
-A- oligoclonal bands:
use of variety of supporting media including agarose gels and polyacrylamide gels, for the electrophoretic separation provides a visual separation of homogeneous immunoglobulins as bands when stain appropriately.
Three patterns of bands can be observed in the gamma region monoclonal, polyclonal, and oligoclonal ( 2-5 bands).
A single oligoclonal band is commonly seen in otherwise normal CSF of normal subjects.
Two or more is abnormal.
Causes of oligoclonal bands:
multiple sclerosis 83-94% of definite ms.
subacute scleroting panencephaliktis ( SSPE). In 100% of patients .
CNS infection in 50% of bacterial, viral and fungal infections.
CNS inflammatory disorders.
vasculitis
neurosarcoidosis.
CNS lupus
G.B.S
behcet disease.
-B- myelin basic protein:
it is a product of oligodendroglia, it is antigen represent when there is damage to CNS appear in the CSF, blood and urine.
its concentration in normal CSF is very low less than 0.4mg/dl.
Common causes of elevated MBP:
multiple sclerosis.
sroke.
trauma.
tumors.
CNS infections
polyneuropathy.
dementia.
leukodystrophy.
Contraindications:
intracranial space-occupying lesions.
infection at the site of LP.
suspicion of abscess at the site of LP.
coagulation disorders like, thrombocytopenia, hemophilia and vit. K deficiency.
Complications of LP:
low pressure headache occurs in 20%.
backache.
introduced infection.
precipitation of pressure cone with a cranail or spinal mass lesion.
subarachnoid or epidural haemorrhage ( anticoagulants, bleeding disorders)
cranial nerve palsies. Diplopia from 6th CN.
dermoid formation.