Important Neurological Investigations

There are a large number of neurological disorders and so a number of different investigations are available to help reach the proper diagnosis and then accordingly a proper management.

Here we can discuss a few important ones:

X- Ray Skull
It may show

• Fracture of skull valut or base.
• Enlargement or destruction of pituitary fossa due to tumor or raised intracranial pressure.
• Intracranial calcification due to tuberculoma.

X- Ray Spinal cord
It may show fractures, spondylosis ( degenerative bone disease ) or any destructive bone lesion due to infection or metastasis.

Computed Tomography ( CT Scan )It is an x-ray slice of 5-10 mm thickness in which different tissues have different densities.

Hypodense tissues ( looking blackish )

• Infarction, tumor, abscess(having white rim and black center), cerebral edema, encephalitis and resolving hematoma.
• CSF and air looks blacker.

Hyperdense tissues ( looking Whitish )

• Bone, blood(hemorrhage) and calcifications.

Advantages of CT scan

• CT scan easily demonstrates
• Cerebral tumors
• Intracerebral hemorrhage and Infarction
• Subdural and Extradural hematoma
• Subarachnoid hemorrhage
• Lateral shift of midline structures
• Cerebral atrophy
• Pituitary mass lesion

Limitations of CT scan

• Lesions less than 1cm may be missed.
• Lesions with attenuation similar to that of bone may be missed if near the skull.
• Lesions with attenuation similar to that of brain are poorly imaged such as plaque of multiple sclerosis and subdural hematoma.
• CT scan sometimes misses lesions within the posterior fossa.
• The spinal cord is not directly imaged without contrast.
• The procedure requires a cooperative patient.

Magnetic Resonance Imaging ( MRI )MRI can detect brain tumors, infarction, hemorrhage and lesion of posterior fossa. In the spinal cord MRI shows tumors, syringomyelia, cord compression and vascular malformations.

Advantages of MRI compared to CT

• MRI can select any plane e.g coronal, sagittal and oblique.
• No ionizing radiations.
• More sensitive to tissue changes e.g plaques of demylination ( multiple sclerosis ) are seen.
• No bone artifacts.
• Spinal cord and nerve rots are imaged directly with no need of contrast.
• Lesions less than 0.5 cm are seen.
• Magnetic resonance angiography images blood vessels without need of contrast.

Limitations of MRI

• It takes time
• Expensive
• Needs patient’s cooperation.

Electroencephalography ( EEG )
EEG is the recording of the electrical activity of the cerebral cortex obtained with 16 electrodes applies to the skull at various points simultaneously for 10 to 30 minutes. The main value of EEG is in diagnosing epilepsy and diffuse brain diseases. However patients with epilepsy often have a normal EEG in between seizures.

Epilepsy: Spikes or spike and wave abnormalities are the hall mark.

Diffuse brain disorders: generalized slow wave EEG pattern appears in encephalitis, dementia and metabolic encephalopathies.

Brain death; EEG is isoelectric in deep coma and brain death.

Electromyography ( EMG )
A concentric needle electrode is inserted into voluntary muscle. The amplified recording is viewed on oscilloscope. Three main features can be demonstrated:

• A normal pattern
• Denervation and re innervation
• Myopathic, myotonic or myasthenic changes.

Nerve Conduction Studies ( NVC )Nerve conduction studies help in diagnosing neuropathies and nerve entrapment.

Cerebral Evoked PotentialsVisual evoked potential record the time for a visual stimulus to reach the occipital cortex. Their value is chiefly in demonstrating previous retrobulbar neuritis which leaves a permanent delay in latency despite recovery of vision.

CSF AnalysisUsually done for CNS infections like meningitis.

Biopsy
Brain : CT guided biopsy of intracranial mass is now a standard procedure.

Peripheral Nerve: Biopsy usually of sural nerve at ankle aids in diagnosis in certain neuropathies.