Ch. 2 Neurosurgical investigations Flashcards
Describe the flow of CSF from production to absorption
Choroid plexus of lateral ventricles, Foramen of Monro, Third ventricle, Cerebral acqueduct, Fourth ventricle, Foramen of Magendie and Luschka.
Next moves to spinal subarachnoid space, through basal cisterns, over tentorial hiatus, and then bathes the cerebral hemispheres until absorbed by arachnoid villi of dural sinuses
CSF is produced by the choroid plexus at a rate of _____ mL/min.
Approximately ____ mL of CSF is produced each day.
The total CSF volume is ____.
0.4 mL/min
500 mL produced each day
140 mL total CSF volume
What is the normal CSF opening pressure in the recumbent (lying down) position?
10-15 cm CSF
Define cistern
A collection of CSF at a site where the arachnoid layer out-pouches (i.e. is separate) from the underlying pia mater.
What are three spaces where CSF can be isolated from?
Lumbar spine (Lumbar puncture)
Cisterns (Cisternal puncture)
Ventricles (Ventricular cannulation)
What is the most important contraindication to a lumbar puncture?
Clinical evidence of raised intracranial pressure (e.g. papilloedema)
*May want to get CT or MRI to r/o space-occupying lesions
The iliac crests are a fairly reliable marker of what spinal level?
When performing a lumbar puncture which direction should the needle be pointing, cranially or caudally?
L3-L4
Cranially
What is the most common complication of lumbar puncture?
Why does it occur?
What should be done to reduce the risk or alleviate the pain?
Headache
Low CSF pressure from leak through the dural hole
Instruct the patient to remain lying down and stay adequately hydrated
Electrophoresis of CSF is useful if what type of disease is suspected?
Demyelinating
What are three structures on a head CT where calcification is a normal finding?
Pineal gland, choroid plexus, basal ganglia
What is the primary contrast agent used in CT scans?
Do the following enhance?
- High grade glioma
- Low grade glioma
- Most tumors
- AVMs
- Cerebral abscess
Radioactive iodine
High-grade glioma: Yes Low-grade glioma: No Most tumors: Yes AVMs: Yes Cerebral Abscess: Yes, but only peripheral enhancement
What is digital subtraction angiography?
A type of angiography where the pre-contrast image is subtracted from the post-contrast image to obtain an image of predominantly the vasculature
What is the difference between a CT of the spine and myelography?
In myelography a water-based contrast is injected into the dural sac
In MRI, what does “magnetic susceptibility” refer to?
What type of pathologies often display this feature?
The ease by which a tissue becomes magnetized when placed in a magnetic field.
Hematoma degradation products demonstrate susceptibility from deoxyhemoglobin and hemosiderin
On a T2 weighted MRI how does CSF appear?
How do blood vessels and sinuses appear?
CSF appears white and other fluid accumulations as well
Blood vessels and sinuses appear dark because the fast moving blood is not picked up
MR spectroscopy measures the peaks of various substances. When present at substantial amplitude, what do the following indicate on MR spectroscopy?
Lactate
Decreased N-acetyl aspartate
Choline
Increased lactate: indicates ischemia or anaerobic metabolism
Decreased NAA: Neuronal loss
Increased choline: increased cell turnover likely indicative of tumor
In regard to lesions near the skull, why is MRI superior to CT?
MRI does not have as much bone artifact compared to CT
Functional MRI utilizes BOLD sequences to look at metabolic activity in brain regions. How does this work (i.e. what is being measured)?
BOLD measures blood oxygen level dependent imaging and uses the ratio of oxy-Hb to deoxy-Hb to map metabolic activity during certain processes (e.g. repetitive hand movements)
How does restricted diffusion (e.g. infarct) appear on DWI and ADC images, respectively?
ADC: Dark
DWI: Bright
What two imaging modalities are very helpful in evaluating cerebral metabolism and blood flow in patients, especially in those with epilepsy?
Positron Emission Tomography (PET)
Single Photon Emission Computerized Tomography (SPECT)
When measuring muscle activity at rest, what type of potential is due to a single muscle fiber contracting and indicates active denervation?
What is a bundle of muscle fibers contracts?
Fibrillation: single muscle fiber contraction; active denervation
Fasiculation: bundle of muscle fibers contract
Positive sharp waves (i.e. sharp positive wave followed by a slow negative wave) during activity at rest during an EMG indicates what?
Chronic denervation
What will the amplitude and duration be for neuropathy on EMG?
Myopathy?
Neuropathy: Large amplitude, long duration
Myopathy: Small amplitude, short duration
What intraoperative monitoring options can a neurosurgeon use (e.g. evoked potential types)?
Visual evoked potential
Brainstem auditory evoked potential
Somatosensory evoked potential
Motor evoked potential
