MR imaging of abnormally rotated medulla oblongata, and a criterion for assessment of its normal orientation.

In the MR imaging study of a 4-yr-old patient the medulla oblongata was detected to be rotated 25 degrees counter-clockwise with respect to the remainder of the brain and skull. A similar condition was not visually detected in the evaluation of consecutive 1100 CT and 500 MR imaging studies. The orientation of the medulla oblongata was then geometrically assessed on selected, axial inversion recovery MR images in a series of 50 normal pediatric patients. It was detected that in 70% of cases (n = 35) a line connecting the anterior median fissure and the posterior median sulcus of the medulla oblongata (interfissural line) was parallel to or blended with a vertical reference line passing through the third ventricle (midplane axis). In 30% of cases (n = 15) the interfissural line deviated from the midplane axis up to 10 degrees. It appears that deviation of the medulla oblongata to this extent should be considered to be within normal limits.