Etiopathology of Arnold-Chiari malformation: a fetal rat model of dysraphism.

OBJECTIVES: We report an experimental fetal rat model with the aim of comparing two surgical methods used to check Arnold-Chiari Malformation (ACM) by dysraphism. We also wanted to (1) determine which type(s) of ACM akin to human anatomical findings were generated with the model and (2) study whether a cerebrospinal fluid pressure gradient could be responsible for ACM's etiopathology. MATERIALS AND METHODS: At E20, a mean of two fetuses per pregnant rat underwent an incision at the 2-3 lumbar level, deep into the medulla oblongata central canal, by two different surgical methods. Cesarian section was performed at E22. Dysraphic fetuses were examined clinically. Those born alive and controls without lesions were anatomically and histologically studied. RESULTS: Method 2 was better than method 1 at reproducing the model. 100% of operated fetuses showed no spontaneous motility or sensibility to pressure on the posterior limbs in addition to anatomopathological evidence of type II ACM. CONCLUSIONS: A high rate of ACM could be checked by dysraphism with both methods. The opening of the central canal was demonstrated to generate a cerebrospinal fluid pressure gradient responsible for the herniation of encephalic structures comparable with human ACM. We believe this model may be useful for evaluating further strategies for prenatal treatment.