Redo Posterior Fossa Decompression with Duraplasty for the Treatment of Chiari Type I Malformation

Redo posterior fossa decompression with shrinkage of cerebellar tonsils and duraplasty

Redo decompression of a Chiari I malformation that presents with symptom reoccurrence after previous posterior fossa decompression with or without duraplasty.  In this patient, duraplasty was not performed at the time of the initial operation due to presence of a venous lake.  Pre-operative MRI confirms low-lying tonsils to the C2 vertebral level with significant crowding at the foramen magnum.  In general, Chiari decompression should only be performed in patients who have symptoms such as Valsalva-induced headache, brainstem compression (sleep apnea, dysphagia), or spinal cord dysfunction or in patients with radiographic findings of syrinx.

Absence of symptoms referable to Chiari malformation, tonsillar ectopia due to other etiologies such as increased intracranial pressure, intracranial mass lesion, or lumboperitoneal shunt.  Dura should not be opened if a venous lake is identified during surgery.  Venous lakes usually spontaneously resolve by the age of 2 years.  Patients with Chiari II malformation associated with myelomeningocele should under hydrocephalus/shunt evaluation prior to Chiari decompression.

Bipolar Cautery
microscope

After induction of general anesthesia, the patient was positioned prone on laminectomy rolls with the head flexed and secured in a Sugita headrest using 6 pins.  Other pin headrests such as the Mayfield are also available if the surgeon does not use the Sugita.  Prone positioning in a horseshoe is an option for patients who are too young for pins.  Neuromonitoring with somatosensory evoked potentials, motor evoked potentials, brainstem auditory evoked responses, and lower cranial nerve electromyography was used.​

History and physical examination, brain MRI confirming presence of Chiari malformation and excluding intracranial mass lesion, entire spine MRI to evaluate for syringomyelia.  Head and upper cervical spine CT scan to evaluate prior craniectomy and laminectomy is optional but preferred at this institution.
 

Incision extending from just below external occipital protuberance to C2 spinous process.  Prior craniectomy noted and exposed.  Dura opened in Y-shaped fashion from top of craniectomy defect down into spine.  Cerebellar tonsils lying below the foramen magnum, extending down to the C2 vertebral level.  Foramen of Magendie explored for presence of fourth ventricular outlet obstruction

Intraoperative: Bleeding can occur, especially from a venous lake or from the occipital and/or circular sinuses.  If a venous lake is seen, the dura should not be opened.  If the dura is opened, care needs to be taken when crossing midline and when crossing the craniovertebral junction in order to maintain hemostasis from the venous sinuses.  Cerebellar, brainstem, or spinal cord injury is also a rare complication that is best avoided with careful identification of the anatomy and preservation of arterial supply.

Early Postoperative: CSF leak is best avoided with meticulous duraplasty and soft tissue closure.  Duraplasty should be as watertight as possible.  The paraspinous muscles should be reapproximated in layers and at the cervical fascia closed in a watertight fashion.  Chemical meningitis and hydrocephalus can occur if too much blood is allowed to entire the ventricular system.  Hemostasis should be achieved prior to opening the dura and and blood that does enter should be irrigated out prior to dural closure.  As with all surgeries, infection is also a risk which is best avoided with meticulous sterile technique and preoperative antibiotics.

Late Posteroperative: Symptoms recurrence can occur.  This is best avoided by performing adequate decompression at the time of surgery.  Cerebellar slump occurs when too much of the occipital bone is removed.  This can become symptomatic and require posterior fossa cranioplasty.​

Dr. Albert is the site principle investigator at Arkansas Children's Hospital for the Park-Reeves Syringomyelia Research Consortium. He receives no honoraria for this work.

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