Shunts


NB: this is adult shunting. peds has its own entire worldview about this topic that is very different.


primary placement


- set up your shunt. if valve is programmable, program it to your setting of choice before you take it out of sterile packaging. Once you're scrubbed, put it into sterile saline, pump until it fills up. Also inject your tubing full of sterile saline, clamp the distal end and attach proximal end to valve, tie to secure with silk ties. Also soak your proximal catheter in sterile saline.
- start with abdomen. measure using your tunneler from belly to retroauricular releasing incision that you plan to make. Make sure you will reach. Allow at least 3-5 cm of redundancy on both sides otherwise you will drive the strugglebus with the sheath getting sucked in on either end. incision lateral to rectus abdominus over rectus sheath, dealer's choice, go through subcutaneous tissue until you hit fascia, tunnel upwards until you hit somewhere behind the ear, then make an incision over your tunneler, pull it out, leave sheath there.
- then make your head incision per instructions below:
- for a virgin head, use the left diagram as your guide - red is kocher's point, blue is the shunt, green is the ideal incision. It allow you to enough exposure to drill the burr hole. If you have to come back for revision, you can extend the incision along the dotted green lines - discussion below.
- if you are doing a shunt after an EVD (i.e. post SAH hydro) and you are in the unfortunate situation of having to deal with a large vertical incision (dark red), most people will extend it anterior (purple line). But this may take you into the forehead if the incision is too anterior. Another alternative that I would do is extend it back, the grey line, and use generous retraction.

- this is why if you place a ventric, use a stab incision or a horizontal incision - it makes tunneling harder, but you save yourself a lot of grief if you have to do a shunt, or even a worse, a crani.
-Then you use some forceps to dissect a pocket for the valve (and you must dissect generously, make a big pocket).
- Then tunnel from head to retroauricular incision. Leave the sheath in place. .
- put distal tubing into the proximal sheath, pull it through, then through distal, pull it through. ideally you get it all the way through the sheath but I've noticed that if you just get it in at least 15-20 cm,  it'll stay in the sheath as you pull and won't pull out. you can try irrigation to help it along, sometimes it works. protip: when you are pulling the sheath+catheter out of abdomen, hold your hand at the belly to catch the catheter to prevent it from being sucked back in.
- If needed, drill burr hole, place ventricular catheter. If its an EVD, pull it out and either hard pass or soft pass the new catheter. Put the little plastic stopper at the depth you want it to be at. Screw in the anchor. NB: when you are draping for EVD to VPS, drape the exit site of ventric out
- trim ventricular catheter to desired length, then attach to valve and secure with silk tie. pull on distal end until it's well seated in the pocket. make sure CSF drips out of distal end. you can try pumping the shunt a few times to prime it
- put distal tubing into abdomen - can be done with either a trocar or old school (aka general surgery style) with picking up layers of fascia individually and cutting through them. some people pursestring the fascia around the tubing to keep it in. you don't have to, but in people who you think are at high risk of their catheter backing out (i.e. extremely overweight people), its probably a good idea.
- close. do not hit the catheter or the valve.


Revisions
- NB: you will need a white connector tubing, get it before the case
- when you come back, open the frontal incision just enough to access the point where the proximal catheter connects into the valve. Disconnect, and check for proximal flow (can use metal tip + manometer to check ICPs), and check for distal flow through both the valve and the distal catheter together simultaneously (syringe + manometer + metal tip + white connector tubing into valve. If the valve+distal tubing are patent, then you just do a proximal revision and you don't have to open the incision bigger.
- if either the valve or the distal catheter are failing, you have to open the incision big enough to access the entire valve so that you can pull it out and check the distal tubing independently from valve. If the valve is failing, replace it. If the distal tubing is failing, try to pull it out, if you can't, leave it in as an orphan catheter, tunnel a new one.
- the key concept is that once you pull peritoneal tubing out of belly, you cannot push it back in. It's physics - you are trying to push a long, soft, floppy tube down a scarred down (or even not-scarred down) path, it won't go. And if you try to shove the valve into the pocket and close over it, the tubing will kink. Therefore, you have to open the pocket bigger until the point where you see the distal tubing connect to the valve. Either anchor the distal tubing there and don't pull it out any more, and then put a new valve on, or if you do have to pull it out, then trim it down again such that the valve will be seated all the way back in the pocket.


more later, too tired to write more now.



Extradural Chiari


Before the case, look at the MRI to evaluate where the vertebral arteries course to make sure they are out of your intended bony decompression.


Pins - two on left, one on right. Pin bilat 1cm above pinna, and then the 3rd anterior on forehead behind hairline. Bias pins anterior as the patient is prone, also helps with being able to swing Mayfield forward.


Position prone, arms tucked. Translate and flex head (ie while prone and in pins, pull entire head upwards until neck and head are in line with superior aspect of back). Flex head as much as possible -- make sure there are still 2 fingerbreaths between chin and chest/table. Most people with chiari have a steeply sloped occiput so the more flexion you can get the easier the procedure.


Midline incision from inion to arch of C2. Knife through skin and dermis, bovie through midline. When dissecting, remember that some people have an incomplete ring of C1. Don't dig with the bovie, paint across and let things fall apart gently. Start at the occiput and go down, and when you get close to foramen magnum, use a penfield 1 or a curette to dissect the tissue off the bone and feel for the edge of the bone.


Nuchal fascia ends at superior nuchal line; Some people like to open fascia in a Y or T fashion, leaving cuff at superior nuchal line to sew to for closure. Some don't. If there is any chance of doing intradural decompression, harvest a pericranial graft.


feel for the posterior ring of C1, use curette/pen 1 to dissect tissues off bone. Generally speaking, you are safe approximately 10-12 mm on either side of midline. Go slowly, feel for the lip of vertebral sulcus. The vert classically runs up the transverse foramina, then curves medial at the posterior ring of C1, and enters dura. There should be a (thinner vs thicker) lip of bone between vert and posterior aspect of C1. Some people will thus bovie with abandon across posterior ring of C1, however this lip may be very thin vs absent, and you risk ending up in the vert.


Between C1 and foramen magnum there is some soft tissue that frequently contains an epidural venous plexus that can bleed a lot. carefully bipolar it, pull it apart, and cut. If it bleeds, don't panic, just put gelfoam and surgiflo


Different ways to do craniectomy
- can use fluted ball drill on occipital bone, starting at thumbprints (which are thinnest parts) and eggshell out the bone and figure out depth, then drill across through the keel, then use kerrison to remove the remainder of bone - lateral, inferior, and medial.
- can use perforator on thumbprints, and then use the B1 with a footplate to cut across to connect them, and then down to foramen magnum, then remove the bone en bloc.
- craniectomy goal is to decompress to lateral aspect of ring of C1. The most medial aspect will also be the most shallow; as you get more lateral, the bone will get thicker and will pinch the dural sac more; this is the scariest bone to take but also frequently missed and important to decompress


C1 laminectomy
- once you identify the safest lateral aspect of the C1 ring, you can drill troughs into it, stopping every so often to push down against the remaining bone to feel for its give, and then pull out the ring en bloc.


then use pickups, woodson, knife to remove the thick outer leaflet of dura at the craniocervical junction, leaving behind the soft inner dural layer


at this point, some people will ultrasound the craniocervical junction to ascertain the extent of compression, and if there is still compression, will open the dura and patch graft.

Asleep DBS

Walk into room
Anesthesia does their thing
Retape eyes with tegaderm
Turn bed 90 degrees so head is facing ceretom
Pin with doro frame (radiolucent head holder) - shoulders may get in the way - pad shoulders with foam
Fix Mayfield on inner side of head holder
Bottom of Mayfield has to be angled back towards patient's feet - if its angled forward, it will hit CT scanner and you won't be able to get entire head in scan
Shave head
Prep with chloraprep then chlorhexidine then alcohol
Put in 5 fidicuial screws - 2 frontal, 1 left posterior (above/behind L ear), 2 right posterior (one by bregma, one above/behind R ear), roughly in a circle - bias screw 3 (posterior L screw) medial to allow for tunneling
CT scan
Put suction-cup registration device on head, non-sterile registration of fiducial screws with blue thing
Use stealth to determine optimal entry points
Mark entry holes with pen. Draw upside down U-shaped incision lines approx 1 cm radius around point
Prep again
Hand drill to mark entry points
Drape - body drape, 4 drapes in square on head - include fiducial screws in field. Ioban.
Incision
dissection between galea and periostium around incision and in flap. Or subperiosteal. depends on who you ask.
Hemostasis
On L side, dissect posteriorly to form pocket
Burr holes
Hemostasis
Screw in stimlock - do not strip screws - screws on both side, slit pointing down
Screw in base - two screws that are closer together approx 10 o'clock and 2 o'clock, the one pointing down at 6 o'clock. do not strip screws. Base has to be tight, all things are registered off base.
Make sure clip fits
Attach dome
Attach other registration device to left dome.
put steatlh probe into dome, find optimal trajectory and depth. tell scrub tech so they can set the cannula.
Attach nexdrive micropositioner
Then put in cannula
Figure out where it will enter dura. Bipolar dura at that point. a lot. Cruciate incision with 11-blade
Attempt to pass cannula - if any resistance, bipolar + 11 blade again. you need to get through Pia.
push in cannula to pre-determined depth into center hole
remove stylet
Place extender
Pass electrodes
remove cannula
apply clip to base of electrode
mark electrode where its coming out of the clip
Tisseal into burr hole
CT scan - merge with preop MRI with plan. deviation of <2mm is acceptable. More requires electrode replacement
Remove everything
close - do not hit the electrode with your needle. electrode is very sensitive and fragile.

DBS generator

pocket - incision 1 finger breath below clavicle approx 5-6 cm long. Cut down until you get deep to fascia into fat layer but above muscle, make a pocket deep enough to fit finger to knuckle.

ear incision - far down enough to be over the curve of skull (sucks to tunnel over the curve), but high up enough to access leads. bovie to bone. Look up to find leads, flip them out. use heavy scissors to start tunneling process to get through neck fascia, open them, then pull them back out. LEFT lead has tie on it. Use tunneler to get to pocket. go above the clavicle. anesthesia gets upset if you tunnel into subclavian artery. screw extension leads onto tunneler and pull back to incision (L and R extension leads are the same).

connect extension leads to head leads-- white = right, blue = left. Starting with left, remove plastic coverings off head lead, wipe lead with blood, put raytech below for clean field, put new clear plastic covering thingy on (skinny side first) connect extension lead on; when you screw the leads on, you must hold the lead by contact 1 tightly  (i.e. provide counter-torque) otherwise you risk breaking the electrode. if you break the electrode, you're fired. screw to 1 click of tightness. Repeat with right electrode - only use white covering instead of clear.

connect leads to generator (for medtronic, left is contacts 1-7, right is 8-15, left goes in front, right in back, front is the brand name side). screw to 3 clicks of tightness. tuck generator into pocket, rep checks impedance. very high impedance = suboptimal contact between electrode contacts. very low = concern for short circuit i.e. electrode breakage. If all goes well, pull the electrodes straight. close pocket and head.


DBS generator replacement

Knife through skin, then continue with knife while feeling with your fingers. the only way you screw this up is by cutting the leads. cut towards the generator. Cut through capsule with knife, make sure to turn the corners around both edges. Pull out generator with kocher. unscrew/remove leads one at a time! front/left lead first. correction, the other way you screw this up is by mixing up L and R leads. Connect leads to new generator first left, then right - put the leads all the way in, make sure good contact, screw to 3 clicks of tightness. put generator back into pocket, brand name side up. Test generator to check impedances. If good, anchor with non-absorable suture if needed, close.

ACDF 

Head towards anesthesia. towel roll under shoulders horizontally. head taped down - straight (important bc you don't want to fuse them turned, also helps identify midlines structures during surgery). arms tucked. 

Mark midline cartilagenous structures, SCM, sternal notch. Use fluoro to localize your levels 

- FYi - hyoid is approx C3, thyroid cartilage is approx C4-5, cricoid cartilage is approx C6

Small horizontal incision for 1-2 levels, big horizontal incision for 3 level, at 4+ levels you probably need CEA style vertical incision. 

Dissect through skin to fat - once you approach platysma, put scissors underneath to elevate it and cut through it horizontally with bovie. Then dissect rostral and caudal in a sub-platysmal plane. 

Find plane medial to SCM - and go straight through to to vertebrae. if you need to cut omohyoid, you can. SCM and carotid should be lateral, esophagus and trachea should be medial. If it doesn't dissect easily, you are in the wrong plane. Put in retractors (we often use clowards). 

Use kittners to get all the fascia off the spine. Mountains are disks, valleys are vertebrae. Localize your operative level -  recommend caspar pin into one of the vertebrae you are fusing; some people do needle into disc but this can theoretically poke a hole in the wrong annulus (does this increase risk of future disk hernation?) and then you have to pull it out and mark that level somehow and your mark could come off or it could slip out etc. To avoid adjacent segment disease, expose only the operative levels (ie. if you are doing 4-6 ACDF, expose only the bottom of 4 and the top of 6, only enough to get your plate in. 

Once your level is confirmed, use bovie to elevate longus coli off just to the uncovertebral joints - don't go more lateral than that - you risk injury to sympathetic chain under longus coli, you also risk injury to verts. Your cloward (or whatever) retractors should be flush all the way to the vertebrae while doing this - otherwise if your bovie slips and there is no retractor stopping it, you will run into the carotid/IJ laterally or the esophagus medially. That is bad. 

Measure depth and put in your color-coded retractor system of choice - Trimline, phantom, etc. Put in the remaining caspar pins, make sure they are all midline and lined up neatly. Use knife to cut square into your disk. Don't cut too aggressively lateral, thats where the vert lives. 

Use a combination of curette (straight and curved), pituitary, kerrison and drill to remove the disk. Use the straight curette against the endplates to prepare them to receive fusion graft. you know you are at PLL when you feel the posterior edge of the disks. if there are osteophytes at the posterior aspect, drill them down. 

Taking of PLL is controversial - some people always do it, some people rarely do it, some people say do it only if there is significant central stenosis/myelopathy (i.e. may not be needed if you are only doing foraminotomy). If you take PLL, then use nerve hook to get under PLL and flick towards center to get it away; you are done only when the shiny pretty dura is visible the entire length of the disk. 

Make sure to run nerve hook at either edge to ensure the foramina are open and free. if they are not, take a kerrison and bite stuff off until they are open. 

Make sure your endplates are prepared! Free of cartilage. That will prevent fusion. However do not be too aggressive, otherwise if you have no endplate then your graft will subsist (i.e. sink into cancellous bone) 

Put in your sizing tool - it should fit very snug. determine appropriate size of graft. Then put in graft. it is our humble opinion that PEEK cages with tiny-ass bone insert fail more often than all-bone allografts. Whatever. something to ensure fusion. certainly do not leave in an all-metal/all-PEEK construct with no bone/fusion material. That is just silly. Hammer it in; ideal graft placement is relatively anterior, but fully flush at the anterior edge. 

Plate over the system - screws should angle towards the center of each vertebrae (i.e. at bottom edge of bone screws will be angled inferior and medial. 

Two view XR at the end. 

Thoughts: 

- A fast surgeon can complete a 1 level ACDF in 45 mins and a 2 level in 90. This is the goal to shoot for. 

- if you ever do skip-level ACDFs (i.e you fuse 4-5 and 6-7), the intervening levels will fail and they will fail soon. additionally - if you fuse 5-6, because there is limited movement at 7-1 -- 6-7 may fail. 

- when to do ACDF rather than PIF - when compression is mostly anterior rather than from ligamentum/uncovertebral hypertrophy, or when there is a kyphotic deformity you are trying to correct by jamming in a wedged graft 

- if the disk is herniated such that it's in the middle of the vertebrae - consider corpectomy instead

- if there are many (i.e. entire subaxial cervical spine) levels of significant disk herniation causing bad cervical stenosis, and you don't want to do a 5 level ACDF, can consider big posterior lami and fusion instead. can also consider multi-level laminoplasty, either swing-door or french door. Risk for worsening of kyphosis, but typically not a problem unless >5 degrees of kyphosis already. Laminoplasty at C2 and C7 tend to cause a lot of pain but not so much in between (consider laminoplasty for C3-C6 + laminectomy C7 if needed). Can still do foraminotomy. 

- if there are many (i.e. entire subaxial cervical spine) levels of significant disk hernation causing bad cervical stenosis, and the person is 90 years old or a medical train wreck and you want to get them off the table as fast as possible, then consider big posterior lami without fusion - although the risk of subsequent kyphotic deformity will be high 

- if there is mostly uncovertebral disease and/or the patient is mostly having radiculopathy symptoms - consider posterior foraminotomy only. 

original scan on bottom, new scan 1 year later on the top 

- on original scan - L4-5 foraminal stenosis- you would expect an L4 radiculopathy since foraminal stenosis affects the exiting nerve root, and the L4 nerve root exist at L4-5. 

- on new scan - now stenosis is at the lateral recess, you an see from the different slices that the traversing nerve roots get crushed by the disk. You would expect an L5 radic since the L5 nerve roots are passing by at this level. 

Trauma Crani:

- after intubation, turn bed 90 degrees with the operative side facing away and the ET tube facing anesthesia. 

- position supine, head turned as much as you can - if patient is in c-collar or old, may need to bump shoulder in order to get enough posterolateral exposure of head

- shave generously, at least half head, sometimes whole head is easier.

- incision 1 cm off midline (plan incision 1 cm off midline, and then plan burr holes 1 cm from incision, that way you are 2 cm from sinus). Start anterior at the edge of hairline then travel back along the vertex - posterior limit is transverse sinus (and realistically, how far back you can reach on the head, which is a function of positioning). Travel laterally above the root of zygoma, then curve in front of ear -  stay 1 cm away. Any closer to tragus and you risk violating EAM, any further and you risk facial nerve.

- use the knife to cut down to bone; over temporalis muscle, knife through skin to temporalis and then bovie through temporalis. If you hit STA, bipolar it until it stops bleeding.
- raney clips on scalp. not everyone likes these. some people like them edge to edge on scalp, some only like them where scalp is bleeding, some never use them at all. if you use them, make sure to include galea in clips. 

- if not super emergent, consider stopping at pericranium and harvesting pericranial flap in case you get into frontal sinus. Also consider trying to save STA.... In a true crash crani, all you care about is speed; aim to get from skin incision to open dura in 15 mins, and to get out of the OR and into the ICU in less than hour. 

- position periosteal at the root of the zygoma, scrape upwards to get temporalis muscle off in one piece quickly. 

- retract flap using whatever system suits you; many like the towel clamps on flap and then some system to attach the towel clamps to

- Burr holes : keyhole, right above root of zygoma (as far down as you can get basically), posterior at least 1-2 cm above transverse sinus if not more, and then 1-2 up top - at least 2 cm off midline.

- remove remaining bone left by perforator drill bit, with straight curette, dissect off dura with woodson; some people will use other devices like penfield 1 or 3 to get additional dura off bone.
- turn the crani - start at the temporal bone. When turning on forehead, if you start at lateral edge of head and turn flap up towards forehead (rather than stating at the vertex and turning down) less risk of getting into frontal sinus.

- if blood starts coming out at copious volume when you are near the vertex, it may just be a venous lake in bone; apply bone wax to bone edges; if it stops, its not the sinus. If it is the sinus, do not panic, put a big gelfoam over it and wait for it to stop. Do not use small gelfoam for this, there's a chance it'll get sucked into the sinus and cause an obstruction.

- dissect dura off bone, remove bone flap

- if you caused a durotomy with the footplate or with the burr holes, reasonable to make a c-shaped dural opening. Alternatively, if you think there is a good chance you'll be able to do dural re-closure/bone replacement immediately, also reasonable to make c-shaped incision as it is easier to close.

- if brain is very swollen and you are aiming for maximum decompression, open dura in stellate manner.
- if brain is swollen, make sure to extend the craniotomy flush to the floor of the middle fossa - if this is not done, the temporal lobe will not be decompressed and the patient can still have temporal lobe swelling and uncal herniation even after decompression. use rongeur in biting, not tearing or twisting motions. 

- evacuate hematoma.
- if you are doing a loculated/membraney subdural, do not strip the membrane. Peeling off membrane takes off a layer or two of cortical cells and predisposes people to seizures/status.
- inspect dural edge and bone edge for bleeding, acquire hemostasis.
- replace bone flap if you think appropriate.
- always leave a drain. always leave a drain. always leave a drain. curl it around so the entire flap is included within the area that is being drained. the point is you can't get perfect hemostasis because you don't want to apply so much electrocautery to the flap so that it won't heal, but if you leave without a drain or place it suboptimally people can get really bad subgaleal hematomas. and a subgaleal hematoma in a person with no bone = epidural hematoma.
- close the galea. remember the words of harvey cushing.
- staples to skin for speed