Chiari decompression

Chiari Decompression

 

  1. Introduction- “there are Chiaris and then there ARE Chiaris”. The key to a successful Chiari operation is to properly define the patients that will benefit the most from a suboccipital craniectomy, C1 laminectomy, and duraplasty. Patients with a Chiari 1 malformation present with a multitude of symptoms and for the large part all have headaches. The characteristic “Chiari” headache is occipital and worse with valsalva. Patients will often have an absent gag reflex but will otherwise have a normal neurological exam.
  2. Radiographic/MRI- ALWAYS look for hydrocephalus or a mass lesion that is causing tonsillar descent. YOU MUST IMAGE the BRAIN. A posterior fossa decompression in the setting of hydrocephalus could be very dangerous
    1. Syringomyelia- is more common in the pediatric population
  3. Positioning
    1. Prone, Chest rolls, reverse trendelenburg to make the operative site flat, legs up or a foot board. You want to make sure that the patient is not hanging in pins. The patient needs to be taped so that they do not slide down the table
    2. Mayfield pins- below the equator and in most children you do not want to tighten above 40 pounds. This is of course further dependent on the age of the child.
    3. Chin tucked with bed in reverse Trendelenburg
    4. Arms padded and at the side
    5. Legs- Foot rest in larger children
    6. Tape across shoulders and above/below elbow
  4. Prep and Landmarks
    1. Shave- midline from below C2 to just below the vertex
    2. Mark the incision from the inion to C2
    3. There is a separate jump incision that is 3cm in length (to harvest a 1 x 4cm graft)
    4. Drape- blue towels, ioban, drapes
  5. Incision and approach
    1. Extend the incision from the inion to C2. There is an ongoing mantra during this operation: “This is a midline operation”. Nothing good is going to happen if you wander far off midline. This is most true on the approach.
    2. Incise the skin with a scalpel down through the dermis into the subcutaneous fat. Stop and bovie any bleeding but becareful not to burn the skin edges (I like an insulated, flat tip bovie). The sharp Colorado tip is often used in children but I believe is a dangerous instrument form dorsal cervical operations in children
    3. You and your assistant use adson forceps with teeth to hold up the skin edges and bovie down to the fascia. Either place an Anderson Cerebellar retractor or switch to Penfield (Oakesian), Debakeys, or Gerald pickups. The retractor tends to distort the anatomy so you must be careful that you stay in the midline raphe.
    4. Bovie through the raphe, stay in the midline, and intermittently feel for the large, bifid spinous process of C2.
    5. Don’t work yourself in to a hole. Expose the skull from the inion to foramen magnum, 20-25mm of C1, and the superior part of C2 lamina
    6. Use the aforementioned pickups (I like penfield’s) and open the “space of Pang” between the occiput and C1. Some like to use the bipolar to open this plane.
  6. Bone removal
    1. Occipital bone removal- 25mm medial-lateral and 20mm Vertical from foramen magnum
    2. C1 laminectomy- 25mm. The question is where is the vertebral artery? The vert is typically at least 17mm from the midline (Children and adults).
  7. Dural opening-
    1. Open the dura. There is a lot of personal preference on how to open the dura. It doesn’t really matter though everyone makes a big deal that it does. Y, T, t, H. Just open the dura across the craniocervical junction

i.     Several argue to leave the arachnoid intact and some argue to perform a bone only decompression

ii.     I like opening the arachnoid in children because 12% will have a veil occluding the fourth ventricular outlet. It probably does not matter in adults

iii.     Bone only decompressions should only be considered in certain circumstances and potentially in Chiari 2 decompressions (will address in a separate article).

  1. Sew in a pericranial graft or use a dural substitute (Durerepair-Medtronic or Duragen- Integra)
  2. Test the patch with a valsalva. Meticulous closure will guard against a pseudomeningocele
  3. Blue glue? Not a huge fan of fibrin glue but it may give you additional piece of mind
  1. Closure
    1. Muscle dead space 0-Vicryl
    2. Interrupted 0-Vicryl fascial closure- WATERTIGHT
    3. Buried interrupted 2-0 Vicryl subcuticular
    4. Running Nylon (adults), Monocryl (children)
  2. Post-op Orders
    1. Narcotics
    2. Steroids- only if a lot of blood of subarachnoid space/excessive post-op nausea
    3. Antiinflammatory
    4. Robaxin (adults)
Joseph MillerChiari decompression

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