Posterior Fossa Decompression for Chiari Malformations

Operative Planning

Review imaging (sagittal magnetic resonance imaging is the study of choice)
Assess level of descent of posterior fossa structures; this determines the level of spinal exposure that will be necessary
Note level of transverse sinus, which will be low in Chiari II

Special Equipment

Dural substitute if performing dural opening procedure (the authors use bovine pericardium in children, but pericranium, autologous fascia, cadaveric dura, Gore-Tex [W. L. Gore & Associates, Inc., Elkton, MD], etc., are acceptable)
Ultrasound for nondural opening technique

Operating Room Set-up

Room should be warm to ensure normothermia (heat lamps for infants)
Intravenous antibiotics with skin flora coverage (cefazolin 2 g for adults, 30 mg/kg in pediatrics) should be given 30 minutes prior to incision
Single preoperative dose of dexamethasone

Intraoperative Neurophysiologic Monitoring

Somatosensory evoked potential (SSEP) and brain stem auditory evoked response (BAER) monitoring (institutional evidence to support its use)
Obtain baseline prior to positioning
Repeat potentials after positioning to ensure that the neck is not excessively flexed
Continuous monitoring during case

Patient prone
Head supported in neutral position on padded horseshoe in children up to age 2 to 3 years, and in either padded horseshoe or three-pin Mayfield fixation in older children and adults
Neck flexed until two fingers can just fit between chin and upper sternum
Eyes are checked to prevent compression by horseshoe
All pressure points are padded (adhesive foam rubber may be placed on bony prominences prior to turning; this is particularly important in thin children)

Planning of Minimal Shave

Drape

3M drapes placed along sides of neck to prevent prep solutions from threatening the security of the endotracheal/nasotracheal tube in young children with uncuffed tubes or causing corneal damage
Four towels and Steri-Drape
Split or fenestrated sheet

Planning of Sterile Scrub