Brain morphometric analysis in achondroplasia

We undertook an MRI brain morphometric analysis to investigate the relationships between brain and skull base growth and clinical function in patients with achondroplasia as compared to normal controls.

Patients selected for evaluation included pediatric patients who underwent T1 and T2 or dual-echo, proton-density axial T1- and T2-weighted and T1 sagittal brain MRI during 1988 to 1992. Study subjects (n = 11) were diagnosed with achondroplasia by 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, ANOVA, and ANCOVA, adjusting for age and sex. Correlational analyses with respect to subject type and age were done separately.

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 line distance (p < 0.0001). Achondroplasts had significantly smaller frontal 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 ventricular widths between achondroplasts and controls. Furthermore, with respect to age, frontal lobe depth was smaller when compared to controls and the descending sigmoid sinus area became increasingly larger.

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 supratentorial ventricular spaces commensurate with an increase in venous sinus distension.