Internal Medicine Journal 2005; 35: 263–266

PERSONAL VIEWPOINT – CLINICAL TIPS

The rule of 4 of the brainstem: a simplified method for understanding brainstem anatomy and brainstem vascular syndromes for the non-neurologist
P. GATES
The Geelong Hospital, Barwon Health, Geelong, Victoria, Australia

The rule of 4 is a simple method developed to help
‘students of neurology’ to remember the anatomy of the brainstem and thus the features of the various brainstem vascular syndromes. As medical students, we are taught detailed anatomy of the brainstem containing a bewildering number of structures with curious names such as superior colliculi, inferior olives, various cranial nerve nuclei and the median longitudinal fasciculus. …ver más…

4 The Sympathetic pathway: ipsilateral Horner’s syndrome, that is partial ptosis and a small pupil (miosis).

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Gates

Figure 1 Cross-section of the brainstem (in this case the medulla, but the same rule of 4 applies to the pons) showing the
4 Midline structures and the 4 Lateral (Side) structures aspect of the brainstem. The size of the coloured areas does not represent the actual anatomical size, but are made large enough to see and label. 1 MN, motor nucleus (3, 4, 6 or 12); 2 MLF, median longitudinal fasciculus; 3 ML, medial lemniscus; 4 MP, motor pathway (corticospinal tract); 5 SC, spinocerebellar;
6 SP, spinothalamic; 7 SY, sympathetic; 8 SV, sensory nucleus of 5th cranial nerve. (Adapted from figure 7.90, page 955,
Gray’s Anatomy, 37th edn; PL Williams, R Warwick, M
Dyson, LH Bannister, eds. Churchill Livingstone 1989)1

These pathways pass through the entire length of the brainstem and can be likened to ‘meridians of longitude’ whereas the various cranial nerves can be regarded as
‘parallels of latitude’. If you establish where the meridians of longitude and parallels of latitude intersect then you have established the site of the lesion.
Figure 2 shows the ventral aspect of the brainstem.
The 4 cranial nerves in the medulla are:
9 Glossopharyngeal: ipsilateral loss of pharyngeal sensation.
10 Vagus: ipsilateral palatal weakness.
11 Spinal accessory: