Expected headings
"Rules"
"Rule 1"
"Rule 2"
"Rule 3"
"Rule 4"
"Examples"
"Example 1"
"Example 2"
"There are 4 cranial nerves from above the pons (including 2 from the midbrain), 4 from the pons, and 4 from the medulla oblongata:"
"There are 4 ‘midline’ (i.e. medial, but actually paramedian) structures beginning with ‘m’:"
"There are 4 ‘side’ (i.e. lateral) structures beginning with ‘s’:"
"CN III (oculomotor nerve): from the midbrain, involvement leads to a classic 'down and out’ appearance with the eye resting in abduction, slight depression and intorsion due to paralysis of adduction, elevation and extorsion, the pupil is often not involved (see oculomotor nerve palsy)"
"importantly, the vestibular nuclei are located in the lateral medulla, involvement of which leads to vertigo, vomiting and nystagmus 4, although intractable vomiting can also occur due to damage to the area postrema in the dorsomedial aspect of the medulla 5"
"Working to make a diagnosis as in real-life, if a patient is considered, using Gates' rule of 4 of the brainstem, presenting with right-sided deafness, ataxia, Horner syndrome, paralysis of the face, loss of pain and temperature from the face, and left-sided loss of pain and temperature in the limbs."
"given that the nuclei of CN VII and CN VIII (accounting for right-sided deafness) are involved, this must be a right-sided pontine lesion; it is uncertain if the lesion is medial or lateral at this stage"
"given that the motor nucleus of CN VII (accounting for the right-sided facial paralysis) is involved, and this number does not divide equally into 12, this must then also be a lateral lesion; although the use of further rules may not be necessary at this stage it is a good exercise in understanding"
"involvement of the 's' structures, namely the spinothalamic pathway (accounting for the left-sided loss of pain and temperature in the limbs), spinocerebellar pathway (accounting for right-sided ataxia), descending sympathetic pathway (accounting for right-sided Horner syndrome), and the sensory nucleus of CN V (accounting for the right-sided loss of pain and temperature from the face), provide further confirmation of localisation to the right lateral pons"