Longitudinal evaluation of apparent diffusion coefficient in children with neurofibromatosis type 1

Foci of T2-prolongation in both supra- and infratentorial brain in neurofibromatosis type-1 (NF1) patients have been called hamartoma-like NF1 lesions (HLL); however, their behavior is not consistent with this definition. Diffusion-weighted imaging has been used to study structure and cellularity of intracranial lesions. We applied this technique to characterize HLL as they change with time in pediatric patients.

We retrospectively studied 12 children (ages 2-20 years) with proven NF1. Forty lesions were studied longitudinally on multiple exams for a total of 166 measurements. Apparent diffusion coefficients (ADCs) were also obtained from a comparison group comprising 14 normal children (ages 2-16 years).

The ADC for the lesions was generally greater than normal brain. Both supra- and infratentorial lesions had increasing ADC with patient age. This is contrasted to our comparison group of normal subjects who showed decreasing ADC with age. Linear regression analysis of infratentorial lesions yielded a slope of 2.70 x 10(-6) mm2 x s(-1) x year(-1) versus a slope of 17.57 x 10(-6) mm2 x s(-1) x year(-1) for supratentorial lesions.

Our observed increase in ADC of lesions in pediatric patients with NF1 suggests increasing water in the extracellular space and/or decreasing cellularity with patient age. This change may be due to increased number or size of myelin vacuoles in NF1 lesions. Supratentorial lesions had a statistically significant increase in the rate of change of ADC compared with infratentorial lesions which may reflect an intrinsic difference in the lesion or similar lesions expressed in different environments.