Complete Reversibility of the Chiari Type II Malformation After Postnatal Repair of Myelomeningocele.

OBJECTIVE: It was believed that Chiari type II malformation (CM-II) was always present in a myelomeningocele (MMC). In fact, it is associated in about 80% of cases. Improvement of the hindbrain herniation after prenatal closure of MMC has challenged the idea that this condition was irreversible. Only 2 studies report ascent of the cerebellar tonsil after postnatal closure. This work aimed to study a large group of patients with MMC who benefited from a postnatal repair to evaluate the rate of long-term total reversibility of CM-II.

METHODS: Sixty-one patients were included. Mean time of follow-up was 8.1 years. The presence of CM-II after closure of the MMC was assessed on the most recent brain scan available for each patient.

RESULTS: Forty-seven patients (77%) had a CM-II at birth (confirmed before the MMC repair). There was a significant correlation between the level of the malformation and the presence of a CM-II at birth (P = 0.003). After MMC closure, only 28 (45.9%) patients had a remaining CM-II. The reversibility rate was 40.4%. The reversibility was higher in lower level malformations (P = 0.004). The number of patients treated for hydrocephalus was significantly higher in the group of patients with remaining CM-II (P = 0.004). Only 11.5% of the children needed surgery for a symptomatic CM-II.

CONCLUSIONS: MMC is not always associated with CM-II. The outcome of CM-II has improved. Postnatal closure can reverse the CM-II. This must be kept in mind when analyzing the result of prenatal series.