This occurs as the mass effect truncates the anterior aspect of the frontal horn and widens the contralateral frontal horn. There is asymmetry at the anterior falx with a widened CSF space on the contralateral anterior falx . This image also demonstrates ipsilateral lateral ventricle compression with contralateral lateral ventricle and atria dilation. Probably the easiest method of evaluating for subfalcine shift is a straight line drawn in the expected location of the septum pellucidum from the posterior most aspects to the falx on axial images. Shift of the septum pellucidum from this midline can be measured in millimeters and compared over time to determine any change.
Gross photo demonstrates shift to the cingulate sulcus under the falx .
This corresponds well to the coronal CT examination again showing the ipsilateral frontal horn narrowing, contralateral cistern widening, and shift of the cingulate gyrus under the falx. The falx itself has an arch like configuration with the anterior aspect of the falx higher than the more posterior aspect. This allows a space for the cingulate sulcus to extend through. This can cause a crease on the ipsilateral cingulate gyrus as on this gross photo . Complications of subfalcine herniations include ipsilateral anterior cerebral infarction.