Brain stem involvement in children with neurofibromatosis type 1: role of magnetic resonance imaging and spectroscopy in the distinction from diffuse pontine glioma.

OBJECTIVE: To evaluate the ability of magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) to distinguish neurofibromatosis Type 1 (NF-1) with brain stem enlargement from diffuse pontine glioma (PG) in pediatric patients.

METHODS: A chart review was used to identify all patients with NF-1 and diffuse brain stem enlargement who were seen at our institution and who had undergone MRI. Comparison groups were as follows: 1) eight patients who did not have NF-1 but who did have diffuse PG, and 2) seven healthy children. Midsagittal diameters of the pons, midbrain, and medulla were measured in all patients, and the results were statistically analyzed. Two MRS variables were also statistically compared: N-acetyl aspartate and the vector sum of the metabolites choline and creatine/phosphocreatine.

RESULTS: In MRI-based measurements, only the pontine midsagittal diameter differed significantly between the NF-1 and PG groups (P = 0.002). Altogether, 21 children underwent MRS, including 6 in the NF-1 group. Measures of both MRS variables were significantly lower in patients with PG than in the others (P < or = 0.007). The two MRS variables classified the 21 children into the three respective groups with 100% accuracy. Of the seven patients with NF-1, four presented with symptoms attributable to brain stem involvement. The brain stems of all seven patients with NF-1 were hyperintense on T2-weighted magnetic resonance images, and five were isointense on T1-weighted images; only one exophytic tumor was identified. Four of the patients with NF-1 were followed up clinically without treatment; all remained alive and neurologically stable for a median of 40 months. All eight patients in the PG group were symptomatic at presentation, and all except one died despite therapy.

CONCLUSION: Both MRI measurements and MRS seem to be useful for distinguishing patients with NF-1 and diffuse brain stem enlargement from patients without NF-1 but with diffuse PG. They should be most helpful in differentiating symptomatic patients with NF-1 from patients with PG, thereby minimizing aggressive treatment and its side effects in patients destined to have better outcomes.