Expanding the spectrum of congenital anomalies of the diencephalic-mesencephalic junction.

INTRODUCTION: We aimed to describe the clinico-radiological findings of patients with disorders of diencephalic-mesencephalic junction (DMJ) formation and midbrain anteroposterior patterning. METHODS: We reviewed the DMJ anatomy of 445 patients with brain malformations. Associated supra/infratentorial abnormalities and clinical findings were noted. Craniocaudal and anteroposterior diameters of midbrain, pons, medulla, vermis, and transverse cerebellar diameter were compared with age-matched controls. Post hoc tests were corrected according to Bonferroni (p(B)). RESULTS: Two patterns of DMJ anomaly were identified in 12 patients (7 females, mean age 41 months). Type A was characterized by hypothalamic-mesencephalic fusion on axial plane, with possible midbrain ventral cleft (7 patients). Anteroposterior (p(B) = .006) and craniocaudal (p(B) = .027) diameters of the pons, craniocaudal diameter of the vermis (p(B) = .015), and transverse cerebellar diameter (p(B) = .011) were smaller than the controls. Corticospinal tract, basal ganglia, and commissural anomalies were also associated. Clinical findings included spastic-dystonic tetraparesis, hypothalamic dysfunction, epilepsy, and severe developmental delay. Type B was characterized by incomplete thalamic-mesencephalic cleavage on sagittal plane, with parenchymal bands connecting the interthalamic adhesion with the midbrain (five patients). Anteroposterior diameters of midbrain (p(B) = .002), pons (p(B) = .0004), and medulla (p(B) = .002) as well as the vermian anteroposterior (p(B) = .040) and craniocaudal diameters (p(B) = .014) were smaller than the controls. These patients were less neurologically impaired, most presenting mild developmental delay. CONCLUSIONS: The spectrum of DMJ patterning defects is wide and may be associated with several brain malformations. Infratentorial brain structures should be carefully evaluated to better define the type of associated midbrain-hindbrain anomalies.