[Music] okay welcome back now that we've learned about both cortical and subcortical strokes let's move down to the brain stem with brain stem strokes localization starts to become much more complicated but before we get into these specifics first things first how do we even know that we're dealing with the brain stem stroke in the first place the pattern that should immediately make you think it's in the brain stem is the presence of crossed findings where deficits in the face are on the opposite side as deficits in the body take a few moments to repeat this to yourself cross findings equals brain stem stroke crossed findings equals brain stem stroke cross findings equals brain stem stroke once you have a sense that a lesion is in the brain stem your job then becomes to figure out exactly where there are three questions to answer here number one what part of the brain stem is the lesion in the midbrain the pons or the medulla two is it more medial or lateral in this region and three is the lesion on the right or left side to answer the first question we'll need to use what we know about the cranial nerves in each region recall the rule of force which states that the first four cranial nerves exit from the brain and midbrain with three and four specifically exiting from the midbrain while the middle four exit from the pawns and the last four exit from the medulla the presence or absence of dysfunction in these nerves serves as a helpful map of sorts to tell you what part of the brainstem has been affected on an up down axis for example if someone presents with an oculomotor nerve palsy the lesion is likely to be at the level of the midbrain in contrast someone presenting with facial nerve paralysis is likely to have a lesion at the level of the pons while a patient presenting with hypoglossal nerve paralysis is more likely to have a stroke in the medulla to answer the second question whether the lesion is more medial or more lateral it can be helpful to think about which structures are found medially in the brainstem and which are found laterally there are four main medial structures to think of and luckily they all begin with the letter m the motor pathway going to the body the medial lemniscus carrying fine touch vibration and proprioception the medial longitudinal fasciculus that controls movements of the eyes and the motor component of some cranial nerves including the three nerves controlling eye movements and the hypoglossal nerve controlling the tongue in contrast there are four main structures that are found to the side that each begin with the letter s the spinocerebellar pathway connecting to the cerebellum the spinothalamic tract carrying crude touch temperature and pain the sympathetic pathway traveling to the face and the nuclei for several sensory neurons coming from the face via the trigeminal nerve the presence or absence of any of these functions can help you figure out the coordinates of the lesion on a medial lateral axis finally to answer the third question which side the lesion is on in general you can expect that deficits in the face will be ipsilateral to the side of the lesion while deficits in the body will be contralateral to the side of the lesion this is because the cranial nerves exit from the brain stem and innervate structures on the same side while motor and sensory pathways traveling to the body all cross further down and with these basics reviewed you are now equipped to localize lesions in the brain stem let's walk through a few cases together starting with the medulla at the bottom and working our way up as its name suggests medial medullary syndrome involves a lesion in the medial medulla this manifests through contralateral hemopresis of the body but not the face contralateral loss of epicritic sensation and ipsilateral tongue weakness notably protopathic sensation is intact let's see how we could have predicted the location of this lesion based on the clinical findings first we know we're in the brainstem because of the presence of crossed findings with contralateral hemiparesis in the body but not the face next we can figure out the level of the lesion by determining what cranial nerves are involved given that tongue movement maps to the 12th cranial nerve we can feel confident saying that this lesion is localized to the medulla the tongue weakness will be ipsilateral since you lick your wounds to determine whether the lesion is medial or lateral consider that the motor pathway motor function of the hypoglossal nerve and epicritic nerves traveling in the medial lemniscus are all involved while side structures such as the spinothalamic tract are not based on this information we can determine that the lesion is in the medial medulla on test questions you may sometimes get asked not only to identify where the stroke is but also what artery is likely involved medial medullary syndrome is typically caused by a stroke in the anterior spinal artery there are some key words you want to associate here you need to link medial medullary syndrome the anterior spinal artery in the clinical findings of tongue weakness and other motor findings the best way to do that is by focusing on all the m's in the word medial medullary and thinking of the mcdonald's arches you use your tongue to eat hamburgers and fries that mcdonald's sells the golden arches also resemble the anterior spinal artery itself so when you hear medial medullary think of the mcdonald's arches to bring all these concepts together in contrast to medial medullary syndrome lateral medullary syndrome involves loss of protopathic sensation contralaterally in the extremities and ipsilaterally in the face ipsilateral horner syndrome problems with balance including ataxia vertigo and nystagmus and difficulties with both speaking and swallowing our first clue that this is in the brainstem is the crossed findings our next clue comes from looking at the cranial nerves involved to determine the level the presence of swallowing and speech difficulties strongly suggests involvement of the glossopharyngeal in vagus nerves which are the 9th and 10th cranial nerves and therefore exit from the medulla to determine medial versus lateral let's look at whether the structures involved are found medially or to the side given that there appears to be involvement of the sensory pathways such as the spinothalamic tract the sympathetic nervous system with ipsilateral horners and the spinocerebellar pathway with ataxia vertigo and nystagmus we can conclude that this indeed involves the side of the medulla rather than the middle lateral medullary syndrome is associated with a stroke in the posterior inferior cerebellar artery so a stroke in the pica leads to problems with chewing you can remember this by thinking of the pokemon pikachu this should help you associate a stroke in the pica with some of its most specific findings which in this case involve difficulty with chewing and speaking moving on from the medulla to the pons lateral pontine syndrome is in many ways quite similar to lateral medullary syndrome which we just talked about this is because the medial lateral axis of the lesion is the same so many of the same findings including loss of protopathic sensation contralaterally in the extremities and ipsilaterally in the face ipsilateral horner syndrome and ipsilateral cerebellar deficits will still be present instead only the level of the lesion has changed meaning that different cranial nerves are going to be involved with cranial nerves 5 through eight now being at play with the seventh cranial nerve affected facial sensation and loss of taste from the anterior two-thirds of the tongue can appear in addition involvement of the eighth nerve can result in partial or complete deafness lateral pontine syndrome is associated with a stroke in the anterior inferior cerebellar artery just as we can use pikachu to remember some of the more specific findings of lateral medullary syndrome we can think of the aica as causing problems in the f-a-i-c-a-i-l sensation just as lateral pontine syndrome is very similar to lateral medullary syndrome so too is medial pontine syndrome similar to medial medullary syndrome with crossed findings and motor involvement as before the main distinction has to do with the cranial nerves involved the motor component of cranial nerves five through eight involve facial muscles and extraocular eye movements so medial pontine syndrome can also lead to facial asymmetry and horizontal gaze palsy however there's also another medial structure that we need to account for in the pons that wasn't in the medulla the medial longitudinal fasciculus this means that medial pontine syndrome can produce internuclear ophthalmoplegia which we covered in an earlier video on the visual pathway medial pontine syndrome is associated with occlusion of branches off of the basilar artery so blockages in these branches can present as facial asymmetry and internuclear ophthalmoplegia you can remember this association by thinking of the phrase branches off the base lead to problems in the face upward we will now talk about a medial midbrain stroke like all brainstem strokes we have talked about so far mid-brain strokes will produce crossed findings however because only two cranial nerves exit from the midbrain the ocular motor and trochlear nerves the cross findings will tend to be more subtle involving only eye movements rather than a more dramatic presentation like facial asymmetry however the rule of cross finding still exists it just involves less nerves than before instead your primary clue to a mid-brain stroke will be an ocular motor nerve palsy manifesting in ptosis madriasis in a down and out position of the pupil in addition to some form of motor findings depending on the exact areas involved the motor findings can present in a variety of different ways the condition most classically associated with the medial midbrain stroke is called weber syndrome weber syndrome involves the combination of an ipsilateral oculomotor nerve palsy and contralateral hemiplegia those are the cross findings so that you know what's in the brainstem so how can we remember weber syndrome think about what happens when you're walking and suddenly get a spider web in your eye you immediately try to close the eye on that side and you will likely try to use your ipsilateral arm to swipe the spider web away meaning that the contralateral side stays still almost as if it's paralyzed go ahead and do these motions a few times close your eye and use your ipsilateral arm to swap the spider web away while keeping your contralateral arm paralyzed that's weber syndrome and it's what you see with a medial midbrain stroke the last stroke we'll talk about is a stroke in the basilar artery itself as seen in this image the basilar artery runs alongside the pawns medulla and sends off branches to the midbrain because it supplies all three parts of the brain stem a stroke in the basal or artery can have wide reaching and severe consequences one possible manifestation of a basilar artery stroke is known as locked in syndrome a tragic condition in which someone is completely paralyzed due to damage of the corticospinal tract as well as most of the cranial nerves however because cortical functions remain intact the person is usually completely aware of their situation depending on the extent of the damage higher cranial nerves may be spared so someone with this condition may be taught to communicate using eye movements and blanks overall locked in syndrome is a devastating reminder not only of the differences between cortical and subcortical functions but also of just how important the brain stem is for our ability to function and on that depressing note let's take a moment to celebrate getting through this video this is dense stuff but there's a logic here that makes us that any time you spend learning will be greatly rewarded on boards and on wards if you want to test your knowledge with some practice questions which i highly recommend that you do there are some in my book memorable neurology which is available on amazon using the link in the description until next time good luck