CSF sampling Flashcards
Indications for CSF sampling?
To rule in/out neuroloogical diseases
PUO if meningitis suspected
To facilitate myelogram (remove similar amount of CSF as the volume of contrast that is instilled)
Where to take CSF sample?
If suspect pathology is cranial to foramen magnum (so mostly central lesions cranial to C2: Atlantooccipital approach or standing C1-C2 approach
If suspect pathology is caudal to C2: Lumbosacral approach
If not sure, then may do both (or start with one and if no abnormalities do the other)
Neurolocalisation flowchart?
Contraindications for CSF sampling?
History of trauma (if potential fractures, haemorrhage in CSF etc - more likely to have increased ICP)
Increased intracranial pressure - more likely to result in pressure on the brainstem during sampling (can be indicated on CT/MRI, trauma)
Danger to humans and horse should be considered
GA/sedation effects on condition (and recovery of neurological horse)
Generally reserve it for when other diagnostics have not reached a diagnosis (e.g. CT, neuro exam)
Where are the 3 main sites for CSF sampling in horses?
Under GA:
- Atlantooccipital method (at the back of the head) - under GA
Standing:
- C1-C2 (come laterally under US guidance)
- Lumbosacral (between wings of sacrum)
What is the method for atlantooccipital sampling of CSF fluid? How much to take?
GA only
Clip and prep poll of horse - tell O will clip mane!
Flex head (maximises AO space)
Use 18G 3.5 inch/9cm spinal needle
Palpate the wings of the atlas (often can see them clearly, but if not in fat horse place tippex dot once palpated)
- These will be the lateral landmarks
- Aim at the midline between these two dots
Aim for the lower jaw and slowly advance 5cm (in 500kg adult horse) until feel ‘pop’
Can be useful to have second person in front of the horse looking back at the needle and checking it stays parallel to the ground without moving dorsal or ventral
Once feel pop remove stylet - wait a moment and then should see CSF should flow without aspiration
Replace stylet for adjustment if not in (want to avoid trauma to spinal cord and best to have stylet in place when moving needle to avoid creating core lesion)
Collect sample freely (if needed can very gently aspirate but must be slow to reduce increasing pressure on back of the brain)
Collect multiple 1ml volumes (as may get some blood in first one but then as flows more freely get better quality samples)
Replace stylet to remove needle if possible
NSAID afterwards and feed from a height for 24-48hrs as may have sore neck
Should be normothermic afterwards so concern if pyrexia
Can get large volumes e.g. 50ml+, but for diagnostics only need about 5ml
Which is preferred CSF sample area in a post mortem e.g. if suspected EHV?
Atlanto-occipital
What is the method for C1-C2 CSF sampling in horses?
Well tolerated
Standing sedation - well sedated, ideally in stocks
Palpate the wings of the atlas (C1)
Often have to move headcollar in front of ear
Scan area behind atlas and mark with tipex where to go (curvilinear probe)
- Usually if place top of probe where hair is eminating from crest then need to put needle in just below probe)
- Should see muscle overlying spinal cord between C1 and C2, spinal cord is within dura mater
- Aiming for subarachnoid space, between dura mater and pia mater
- Crucial to not hit the spinal cord (can aim needle so that if go too far will hit bone, rather than cord)
Prep site and inject sc local anaesthetic
Make sure still well sedated and standing well on head stand
Use 18G 3.5inch/9cm spinal needle
Place needle dorsomedially below the probe
Keep probe still on optimal image throughout and ensure needle perfectly lined up with probe, move needle not probe
Advance slowly and watch on US
If heading more towards C2/spinal cord then withdraw and re-approach
Once feel puncture, withdraw stylet slowly and CSF should flow freely (less so than AO but usually still does, just slow)
Sometimes need gentle aspiration
Collect in 1ml lots
Can use second person to aspirate/take over holding probe, or put probe down once it’s flowing
Replace stylet for adjustments
Method for lumbosacral approach to CSF sampling in horses?
Well sedated and stocks highly advisable as can kick out violently
Midline point between tuber sacrale
Palpate cranial border of tuber sacrale and mark these, then go to midline between the two
Can often feel a space between the spinal processes in front of the midline pointing forwards and behind the midline pointing backwards (if not too fat)
Can scan if required
Injected sc local anaesthetic +/- stab incision through the skin
Use 18G 6-8inch spinal needle
Slow steady introduction straight down - care not to deviate laterally or cranially/caudally (have someone stood at back of horse)
Remove stylet as you puncture dura (‘pop’) - usually 6 inches deep in average sized horse
Gentle aspiration required
Care as violent reaction possible when puncture dura - may kick out or go down
Which tubes to collect CSF in? What should normal sample be like?
‘Plain’ red top tubes do actually have a chemical in them to help shelf life, which interferes with cytology
So ideally need specific CSF tubes (are actually plain)
Or universal container (urine pot), esp if don’t need it sterile
Or in syringe with screwed on top
Rapid analysis is beneficial if can have quick look before sending
Note higher blood and protein values in LS vs AO collected sample - so include approach on lab form
Samples should be largely acellular, so if seeing lots of cells then is abnormal
