Midline shift is one of the most important signs of elevated intracranial pressure. Midline shift occurs when a mass compresses the ventricles, resulting in asymmetry. Midline shift is quantified by measuring the septum pellucidum (thin wall between L/R lateral ventricles) and the anterior/posterior insertions of the falx cerebri. > 5mm is a neurosurgical emergency. In this figure, the right lateral ventricle is compressed with bowing of the septum to the left.