Chiari Malformation

Read the imaging and the exam - MRI of the head and cervical spine gives tonsillar descent below the McRae line, posterior fossa size, and syrinx extent; CSF flow (cine) sequences show obstruction at the foramen magnum. Document baseline cranial nerve, motor, and sensory findings so a new postoperative deficit is recognizable as new.

Bulbar function drives aspiration risk - Lower cranial nerve (IX, X, XI, XII) compression produces dysphagia, hoarseness, and vocal cord paralysis. Ask directly about swallowing difficulty and voice change and listen for stridor — those findings, not the tonsillar measurement, tell you whether the airway is protected.

Sleep apnea - Pharyngeal muscle weakness from brainstem, upper cord, or lower cranial nerve compression causes sleep apnea, and apnea is a recognized presentation in Chiari II infants. Ask about snoring and sleep disturbance, and plan a fully awake extubation with demonstrated airway reflexes.

Avoid Valsalva - Coughing, straining, and sudden jolting of the head can precipitate symptoms by increasing tonsillar descent — the same reason the classic headache is exacerbated by Valsalva. Blunt the airway reflexes and aim for a smooth induction and emergence rather than accepting bucking on the tube.

Treat the neck as abnormal - Chiari commonly coexists with basilar invagination, atlanto-occipital assimilation, Klippel-Feil, and Sprengel deformity, and limited neck motion is a common presenting complaint. Get cervical imaging and range of motion preoperatively, keep the head neutral, and plan video laryngoscopy instead of forceful extension at an already crowded foramen magnum.

Syringomyelia - Present in 20-85% of Chiari I. It gives dissociated sensory loss (pain and temperature gone, fine touch and proprioception preserved), classically in a cape distribution, with hand and arm weakness and atrophy, lower limb spasticity, and progressive scoliosis. Position and pad insensate limbs deliberately and document the deficit before you start.

Hydrocephalus and shunts - Ask about a VP shunt and how many revisions. New headache, vomiting, papilledema, developmental change, or any change in baseline function points to shunt failure and rising ICP — that is a preoperative CT, not a proceed.

Posterior fossa decompression - Suboccipital craniectomy with or without duraplasty is the usual operation. Complications to watch for postoperatively are CSF leak, meningitis, pseudomeningocele, and acute hydrocephalus, all of which show up as a deteriorating exam.

Chiari II and myelomeningocele - Latex precautions from birth and throughout. Support the uninvolved back with towels and donut rings during induction, or induce in the lateral decubitus position, to keep pressure off the lesion. Repair is done prone, blood loss can be considerable with large lesions, and postoperative prone ventilation for 1-3 days is common.

Technique for neonatal repair - Most centers use general endotracheal anesthesia. A case series of 14 neonates describes spinal anesthesia with hyperbaric 0.5% tetracaine with epinephrine injected into the caudal end of a lumbar myelomeningocele.

Preoperative workup in myelomeningocele - CBC with type and crossmatch, a basic metabolic panel for electrolyte derangement or dehydration from a large lesion, cranial ultrasound for ventriculomegaly, and renal ultrasound for genitourinary abnormalities. Nearly all of these patients have a neurogenic bladder with recurrent UTIs and intermittent catheterization.

Chiari malformations — historically Arnold-Chiari malformations — are a spectrum of hindbrain deformities at the craniocervical junction. Type I, the common adult form at roughly 0.5-3.5% of the population, is caudal descent of the cerebellar tonsils more than 5 mm below the foramen magnum, usually because an underdeveloped skull base leaves the posterior fossa too small for the cerebellum. Type II adds brainstem and vermian herniation and is paired with myelomeningocele in nearly every case.

In both, crowding at the foramen magnum obstructs CSF flow, producing hydrocephalus (about 10% in type I, 70-90% in myelomeningocele patients) and syringomyelia (20-85% of type I). The anesthetic problem is a fixed, crowded outlet plus a compressed brainstem: anything that raises intracranial or CSF pressure drives further tonsillar descent, and lower cranial nerve compression takes out the airway reflexes that normally protect the patient.