brain stem Anatomy simplifying cranial nerves and Vascular Supply a 55-year-old man comes into the emergency room with sudden onset dizziness slurred speech and difficulty swallowing he has a past medical history of hypertension and a 20 pack year smoking history his physical exam demonstrates diminished gag reflex difficulty with finger to noose testing on the left side reduced pain and temperature sensation on the left side of the face and right side of his body and finally left tosis and meiosis given the rapid onset of symptoms and crossed face and body signs a brain stem stroke is high on the differential brain stem Anatomy can be complex with numerous cranial nerve nuclei and a unique vascular Supply the rule of four technique created by Australian neurologist Dr Peter Gates simplifies brain stem anatomy and helps in lesion localization based on clinical findings enabling rapid diagnosis and appropriate management the brain stem consists of the midbrain pawns and medulla the various Pathways that Traverse the brain stem and the cranial nerve nuclei contained within it can be simplified by the rules of four the rules are number one four midline structures that start with M the structures and Associated deficits are motor pathway contralateral arm and leg weakness medial liscus contralateral arm and leg vibration and proprioception loss medial longitudinal fasiculus iol lateral internuclear abdal plegia motor nuclei and nerve ipsilateral weakness of motor cranial nerve involved number two four side structures that start with s spinal cerebellar Pathways ipsilateral Axia of arm and leg spinothalamic pathway controlateral loss of pain and temperature sensation of arm and leg sensory nucleus of cranial nerve 5 ipsilateral loss of pain and temperature sensation of face sympathetic pathway ipsilateral Horner syndrome number three four cranial nerves in the medulla 9 10 11 12 four in the ponds 5 6 7 8 and four in and above the midbrain 1 2 3 4 number four four motor cranial nerve nuclei that are near the midline are the factors of 12 except 1 and 2 5 7 9 10 and 11 are in the lateral brain stem any medial brain stem syndrome affects the four M and the respective motor cranial nerve any lateral brain stem syndrome affects the four S's and epil lateral loss of the respective lateral cranial nerves or the cranial nerves on the side associating a leion location with a vascular territory can be done by following a simplified vascular Supply pattern for medial structures the midbrain and pawns are supplied by paramedian branches of the vasular artery while the medulla receives blood from the anterior spinal branches of the vertebral arteries the lateral structures have a different pattern in the midbrain blood comes from branches of the posterior cerebral arteries in the pawns from circumferential branches of the basill artery and in the medulla from branches of the posterior inferior cerebr arteries keeping the rules of four in mind we can localize the region of the brain stem that has been affected the case provided earlier had slurred speech and difficult difficulty swallowing which can be attributed to cranial nerves nine the glop feral nerve and 10 the vagus nerve respectively these cranial nerves are part of the lowermost four cranial nerves and can thus be localized to the medulla as they cannot divide into 12 they localize the lateral medulla next the Tois and meiosis point to sympathetic pathway dysfunction along with the loss of ation to the face and body suggests damage to the Sentry nucleus of cranial ner 5 and the spinothalamic tract these are the S structures that point to the side or lateral medulla using the rules of four one can use the findings on physical exam to localize areas of dysfunction within the brain stem matching the area dysfunction with the vascular distribution can help with localizing and diagnosing a specific brain stem stroke syndrome other brain stem pathologies such as infections space occupying lesions or inflammatory disorders can also be localized based on the rule of four depending on clinical context and symptoms Tempo timing and frequency but the rule of fall was created specifically for vascular injury as highlighted in this case the acute tempo of symptoms and Vascular risk factors of hypertension and smoking suggest that the patient experienced a stroke specifically to the lateral medula supplied by the posterior inferior cerebr artery for more information on the rule of four and diagnosing brain stem syndromes please see the cause resources for more information on this and other neurologic conditions please visit a.com neobites