Investigations in Neurosurgery

Dr. Ari SamiNeurosurgeonCollege of MedicineUniversity of Sulaimani

Skull X-rays• Standard views:– Lateral– Postero-anterior– Towne`s (fronto-occipital)

• Look for:– Fractures– Bone erosion: focal( pituitary fossa)– generalized (Multiple myeloma)– Bone hyperostosis: focal (Meningioma),

generalized (Paget`s disease)– Abnormal calcification: tumors

(meningioma), aneurysmal wall– Midline shift of pineal body– Signs of increased intracranial pressure– Configuration: platybasia, basilar impression

Computed tomography (CT) scanning

• A pencil beam of X-ray traverses the patient's head and a diametrically opposed detector measures the extent of its absorption.

• Determination of absorption values for multiple small blocks (voxels)

• Reconstruction of these areas on a two-dimensional display (pixels) provides the characteristic CT scan appearance

Interpretation of the cranial CT• Ventricular system: size, position, compression

• Width of cortical sulci and sylvian fissure:• Skull base and vault: hyperostosis, osteolytic lesion,

remodelling, depressed fracture• Multiple lesions: tumor, abscesses, granuloma,

infarction, trauma• Abnormal tissue density:

– Midline shift– Ventricular compression– Obliteration of the basal cisterns, sulci– High density( blood, calcification in tumor or AVM or

hamertoma)– Low (infarction, tumor, abscess, oedema, encephalitis,

resolving hematoma)– Mixed (tumor, abscess, AVM, contusion, hemorrahgic

infarct)

Magnetic Resonance Imaging

(MRI)

MRIMagnetic resonance imaging (MRI) is an imaging technique

used primarily in medical settings to produce high quality images of the soft tissues of the human body.

It is based on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique to obtain microscopic chemical and physical information about molecules

MRI has advanced beyond a tomographic imaging technique to a volume imaging technique

• The composition of the human body is primarily fat and water

• Fat and water have many hydrogen atoms • 63% of human body is hydrogen atoms• Hydrogen nuclei have an NMR signal• MRI uses hydrogen because it has only one proton

and it aligns easily with the MRI magnet.• The hydrogen atom’s proton, possesses a property

called spin 1.A small magnetic field2.Will cause the nucleus to produce an NMR signal

• The spinning hydrogen protons act like small , weak magnets.

• They align with an external magnetic field (Bø).• There is a slight excess of protons aligned with

the field. (for 2 million , 9 excess) ~6 million billion/voxel at 1.5T• The # of protons that align with the field is so very

large that we can pretty much ignore quantum mechanics and focus on classical mechanics.

• Now if an electromagnetic radio frequency (RF) pulse is applied at the resonance (Larmor, precession, wobble) frequency, then the protons can absorb that energy, and (at the quantum level) jump to a higher energy state.

• At the macro level, the magnetization vector, Mø, (6 million billion protons) spirals down towards the XY plane.

• Once the RF transmitter is turned off three things happen simultaneously. 1. The absorbed RF energy is retransmitted (at the resonance frequency). 2. The excited spins begin to return to the original Mz orientation. (T1 recovery to thermal equilibrium).3. Initially in phase, the excited protons begin to dephase (T2 and T2* relaxation)

FLAIR (T2 with water suppression)T2 with fat suppressionT1 with contrastEchoplanarProton densityMR spectroscopy (MRS)Functional MRI (fMRI)Perfusion MRMR angiography/venography (see image below)Diffusion and diffusion tensor MRDiffusion-weighted imaging (good for small strokes)Gradient echo (GRE)Fast imaging employing steady-state acquisition (FIESTA)

Advantages• Can select any plane, e.g. coronal,

sagittal, oblique.• No ionizing radiation.• More sensitive to tissue changes, e.g.

demyelination plaques.• No bone artifacts, e.g. intracanalicular

acoustic neuroma

Disadvantages

• Limited slice thickness-3mm.• Bone imaging limited to display of

marrow.• Claustrophobia.• Cannot use with pacemaker or

ferromagnetic implant.

MR angiography• Rapidly flowing

protons can create different intensities and by a special sequence can demonstrate vessels, aneurysms, and AVM

MRI• Diffusion-weighted MRI• Perfusion-weighted MRI• Functional MRI• MR spectroscopy (N-acetylaspartate,

lactate,ATP, and inorganic phosphate)

Ultrasound• Extracranial: Doppler, colour

doppler• Intracranial-transcranial doppler

ultrasound:– Assessment of intracranial

hemodynamics– Detection of vasospasm in SAH

Angiography • DSA: subtraction of a

pre-injection film from the angiogram eliminates bone densities and improves vessel definition– Phases:

• Arterial• Capillary• Venous

Carotidvertebral

Interventional angiography• Embolization

– Particles (ivalon sponge)– Glue (isobutyl-2-cyanocrylate)– Balloon (detachable) for CC fistula– Platinum coils– Stents – Angioplasty

Radionuclide imagingRadionuclide imaging• Single photon emission Single photon emission

computed tomography computed tomography (SPECT):(SPECT):– Uses compounds labelled with

gamma-emitting tracers (ligands) and a rotating gamma camera is often used for detection

– Detection of early ischemia– Evaluation of patients with

intractable epilepsy of temporal lobe origin

– Thallium SPECT: differentiate low from high grade tumors.

Radionuclide imagingRadionuclide imaging• Positron emission tomography (PET):Positron emission tomography (PET):

– Utilises positron-emitting isotopes bound to compounds of biological interest

Lumbar punctureLumbar puncture• CSF analysis• CSF drainage and pressure reduction• Avoid LP:

– If raised intracranial pressure is suspected– If platelet count is less than 40 000 and

prothrombin time is less than 50% of control

Myelography

OthersOthers

• EEG• Evoked potentials:

– Visual– Auditory– Somatosensory

• EMG and NCS• Neuro-otological tests

– auditory system– vestibular system

BAER - brainstem auditory evoked response

• Brainstem auditory evoked response (BAER) is a test to measure the brain wave activity that occurs in response to clicks or certain tones.

• The test is done to:– Help diagnose nervous system problems and hearing loss

(especially in newborns and children)• Find out how well the nervous system works

– Check hearing ability in people who cannot do other hearing tests.

– This test may also be performed during surgery to decrease the risk of injury to the hearing nerve and brain.

• Abnormal test results may be a sign of hearing loss, multiple sclerosis, acoustic neuroma, or stroke.

• Abnormal results may also be due to:• Brain injury• Brain malformation• Brain tumor• Central pontine myelinolysis• Speech disorders•

• The waveform represents specific anatomical points along the auditory neural pathway: the cochlear nerve and nuclei (waves I and II), superior olivary nucleus (wave III), lateral lemniscus (wave IV), and inferior colliculi (wave V). Delays of one side relative to the other suggests a lesion in the 8th cranial nerve between the ear and brainstem or the brainstem itself.