Morphometric analysis of posterior fossa after in utero myelomeningocele repair.

OBJECT

Myelomeningocele (MMC) is characterized by a defect in caudal neurulation and appears at birth with a constellation of neuroanatomical abnormalities, including Chiari malformation Type II. The authors investigated the effects of antenatal versus postnatal repair of MMC through a quantitative analysis of morphometric changes in the posterior fossa (PF).

METHODS

The authors retrospectively reviewed the records of 29 patients who underwent in utero MMC repair, 24 patients who underwent postnatal repair, and 114 fetal and pediatric controls. Tonsillar displacement, cerebellum length, pons length, clivus-supraocciput (CSO) angle, and PF area were compared in antenatal and postnatal MMC repair groups as well as in controls without neural tube defects by using t-tests and correlation coefficients.

RESULTS

Initially, the in utero CSO angle was significantly more acute in all patients with MMC--prenatally and postnatally repaired--as compared with controls (57.8° vs 75.4°, p < 0.001); however, the angle rapidly changed and became similar to that in controls between 30 and 31 weeks' gestation to approximately 80°, with antenatal repair having little effect. Postnatally, the CSO angle decreased in controls (R = -0.58) and in the antenatal repair group (R = -0.17). The cerebellum and pons length demonstrated no significant differences in any group. Overall, tonsil descent was corrected in the antenatal repair group as compared with postnatal repair (p < 0.001), and the PF area increased in all 3 groups in utero. Growth was less rapid in patients with MMC compared with controls, but this was corrected by antenatal repair (p = 0.015).

CONCLUSIONS

Myelomeningocele was associated with tonsillar herniation and a smaller PF than in control fetuses. Antenatal surgical repair corrected both abnormalities. The CSO angle began significantly more acutely in patients with MMC, but normalized with development regardless of when surgery was performed. Determining the clinical effects of antenatal repair requires further follow-up.