Work out where the problem is in the brainstem using 'the rule of 4'.

The brainstem is incredibly complex. It contains nuclei, pathways and structures, many with unusual names such as the olives, medial longitudinal fasciculus and the superior and inferior colliculi. The neurological examination can only assess some of them. This article is designed to help make sense of the signs in the more common brainstem syndromes using 'the rule of 4'.