Posterior cranial fossa maldevelopment in infants with repaired open myelomeningoceles. Double trouble or a dynamic process of posterior cranial fossa abnormalities

OBJECTIVE Two degrees of posterior cranial fossa (PCF) maldevelopment can be hypothesized in children with myelomeningocele (MMC). This paper investigate the PCF deformation by quantitative MRI analysis in MMC subjects with and without Chiari 2 malformation (CM2). METHODS Posterior cranial fossa volume (PCFV), posterior cranial fossa brain volume (PCFBV), lengths of PCF, ventriculomegaly, level and extension of the dysraphism were analyzed in magnetic resonance imaging (MRI) of 51 newborns with MMC surgically repaired at birth (and 41 controls). The possible correlation among PCF hypoplasia, level/extension of the spinal dysraphism and ventriculomegaly was assessed. RESULTS In MMC and CM2, the dysraphism level was above L4 in 30 and below L4 in 10 subjects. PCFV/PCFBV ratio, supraocciput and exocciput lengths were significantly reduced; foramen magnum diameters, mammillo-pontine distance and pons length were significantly increased (p < 0.05). In isolated MMC, the dysraphism level was below L4 in all cases. PCFV/PCFBV ratio and supraocciput length were significantly reduced; pons length was significantly increased (p < 0.05). The lower the MMC level, the lower the incidence of CM2. A positive correlation was found between PCF hypoplasia and MMC level above L4 (p < 0.001), while a negative correlation was found between PCF hypoplasia and MMC extension (p = 0.006), PCF hypoplasia and ventriculomegaly (p = 0.02). CONCLUSIONS PCF hypoplasia has to be considered a dynamic maldevelopment process in the two cohorts rather than two separated entities. The level of MMC is the main but not the unique cause influencing the severity of PCF maldevelopment.