BRAIN MORPHOMETRIC ANALYSIS IN ACHONDROPLASIA

Rationale and objectives: We undertook an MRI brain morphometric analy sis to investigate the relationships between brain and skull base grow th and clinical function in patients with achondroplasia as compared t o normal controls. Methods: Patients selected for evaluation included pediatric patients who underwent T-1 and T-2 or dual-echo, proton-dens ity axial T-1- and T-2-weighted and T-1 sagittal brain MRI during 1988 to 1992. Study subjects (n = 11) were diagnosed with achondroplasia b y clinical and radiologic criteria and compared to an age- and gender- matched control group (n = 25). Twenty-four predetermined ventricular and brain parenchymal dimensions and area calculations were evaluated. Data were analyzed using two-tailed t tests, chi-squared analysis, AN OVA, and ANCOVA, adjusting for age and sex. Correlational analyses wit h respect to subject type and age were done separately. Results: There were 36 patients (11 subjects with 15 MRI examinations, mean age 2.3 years, and 25 controls with 26 MRI examinations, mean age 3.0 years). Significant differences existed for 11/17 measures. Achondroplasts had a significantly larger bifrontal width (p < 0.0001), bicaudate width (p < 0.0001), frontal horn diagonal length (p < 0.05), biatrial width (p < 0.0001), biparietal diameter (p < 0.05), and iter to incisural li ne distance (p < 0.0001). Achondroplasts had significantly smaller fro ntal lobe depths (p < 0.01), optic tract angles (p < 0.0001), foramen magnum diameters (p < 0.0001), and sinojugular transition zones (p < 0 .05). There were no differences in brainstem heights or fourth ventric ular widths between achondroplasts and controls. Furthermore, with res pect to age, frontal lobe depth was smaller when compared to controls and the descending sigmoid sinus area became increasingly larger. Conc lusions: Achondroplastic subjects experience dynamic changes in brain morphometry resulting in a rostral displacement of the brainstem with gradual compression of the frontal lobes due to enlargement of the sup ratentorial ventricular spaces commensurate with an increase in venous sinus distension.