Posterior cranial fossa box expansion leads to resolution of symptomatic cerebellar ptosis following Chiari I malformation repair.

Chiari I malformation occurs when the cerebellar tonsils herniate downward through the foramen magnum into the upper cervical spinal canal. If the posterior fossa craniectomy during corrective surgery leads to excessive enlargement of the foramen magnum, the complication of cerebellar ptosis may result. To treat this difficult problem a posterior cranial fossa box expansion was devised and studied. Patients who developed symptomatic cerebellar ptosis (confirmed by MRI) following cranial vault decompression for Chiari I malformations underwent a posterior fossa box expansion (n=7). This procedure involved coverage of posterior aspect of the enlarged foramen magnum with a split-thickness calvarial bone graft box. The box reconstruction provided separation between the neck musculature, soft tissues from the neural tissue; prevention of cerebellar prolapse; and expansion of the posterior cranial vault. Patients had a mean of 12+/-1 months between initial suboccipital craniectomy and confirmation of symptomatic cerebellar ptosis. Mean age at the time of posterior fossa box reconstruction was 31+/-9 years (range of 14 to 44 years). Preoperative symptoms of headache (7/7, 100%), upper extremity numbness (5/7, 71%) or paresthesias (3/7, 43%), respiratory disturbance (2/7, 29%) and inability to walk (2/7, 29%) improved in all patients postoperatively. At more than 12 month follow-up 6/7 patients (86%) were both disease-free (MRI confirmation) and symptom-free. One out of seven patients had return of headache in a more mild form. Thus, in our patient group the posterior fossa box reconstruction led to resolution of symptomatic cerebellar ptosis following Chiari I malformation repair.