The patient has loss of pain and temperature on the right side of his face. Sensation of the face is ipsilateral, so the issue must be on the patient's right side, which we can confirm by knowing that sensation of the body is contralateral, and he has lost left sided pain and temperature of the body.

Pain and temperature sensation of the body is part of the spinothalamic tract, which always runs laterally through the brainstem. This can be confirmed by remembering that sensation to the face also runs laterally through the brainstem. So, we can confirm this is a right sided lateral brainstem issue.

The loss of gag reflex and paralysis of the vocal cords imply impairment of cranial nerves IX and X, both of which localize to the medulla. Therefore, the answer is right dorsolateral medulla.

Lateral Medullary Syndrome (Wallenberg) - see FA for more details. Symptoms for this syndrome match up with what is being presented.

"Simple rules of the brainstem" (credit to our anatomy gods at UofL for organizing, also this image is fucking great for visual learners):

1. There are 4 structures always in the ‘midline‘ beginning with M
• Motor pathway (or corticospinal tract): damage results in contralateral weakness of the arm and leg
• Medial Lemniscus: damage results in contralateral loss of vibration and proprioception in the arm and leg
• Medial longitudinal fasciculus: damage results in ipsilateral inter-nuclear ophthalmoplegia (failure of adduction of the ipsilateral eye towards the nose and nystagmus in the opposite eye as it looks laterally)
• Motor nucleus and nerve: damage results in ipsilateral loss of the cranial nerve that is affected (III, IV, VI or XII)


2. There are 4 structures to the ‘side‘ (lateral) beginning with S
• Spinocerebellar pathway: damage results in ipsilateral ataxia of the arm and leg
• Spinothalamic pathway: damage results in contralateral alteration of pain and temperature affecting the arm, leg and rarely the trunk
• Sensory nucleus of CN V: damage results in ipsilateral alteration of pain and temperature on the face in the distribution of CN V (this nucleus is a long vertical structure that extends in the lateral aspect of the pons down into the medulla)
• Sympathetic pathway: damage results in ipsilateral Horner’s syndrome, that is partial ptosis and a small pupil (miosis)


3. The rule of CN 4’s (also found in FA2020 p504)
• 4 cranial nerves in the medulla (IX-XII)
• 4 in the pons (V-VIII)
• 4 above the pons (2 in the midbrain= III, IV, 2 in the cortex= I, II)
• The 4 motor nuclei that are in the midline are those that divide equally into 12 (except I and II), including III, IV, VI and XII (V, VII, IX and XII are in the lateral brainstem)

Posterior inferior cerebellar artery [PICA] supplies

1. Lateral medulla
2. Nucleus ambiguus (CN IX, X, XI)
3. Vestibular nuclei
4. Lateral spinothalamic tract, spinal trigeminal nucleus
5. Sympathetic fibers
6. Inferior cerebellar peduncle

Damage to PICA causes Lateral medullary (Wallenberg) syndrome.

Dysphagia, hoarseness, decreased gag reflex, hiccups. Vomiting, vertigo, nystagmus decreased pain and temperature sensation from contralateral body, ipsilateral face. Ipsilateral Horner syndrome. Ipsilateral ataxia, dysmetria.

Nucleus ambiguus effects are specific to PICA lesions.

“Don’t pick a (PICA) horse (hoarseness) that can’t eat (dysphagia).” Also supplies inferior cerebellar peduncle (part of cerebellum).

This was lateral medullar syndrome aka dorsolateral infarct of the PICA.