Semester 2 Neuro, Week 2 - Brainstem

At the level of the medulla, the pathologist would expect to see the Inferior Olivary Nucleus. The Inferior Olivary Nucleus is located in the medulla and is involved in motor coordination and learning. It receives input from the cerebral cortex and sends output to the cerebellum. This nucleus plays a crucial role in the coordination of movements and is involved in the control of balance and coordination.

Based on the symptoms described, it is likely that the patient has damage to the right caudal medulla. The deviation of the tongue towards the right indicates a weakness or paralysis of the left side of the tongue, which is controlled by the hypoglossal nerve (CN XII). The deviation of the uvula towards the left suggests a weakness or paralysis of the right side of the soft palate, which is controlled by the vagus nerve (CN X). These findings are consistent with damage to the right caudal medulla, where the nuclei for CN XII and CN X are located.

At the level of the midbrain, the Edinger-Westphal nucleus is expected to be seen. This nucleus is responsible for controlling the pupillary reflex and accommodation reflex, which are important for regulating the size of the pupil and adjusting the shape of the lens for near vision. It is located in the midbrain, specifically in the oculomotor nuclear complex, and receives input from the pretectal area. The other options listed, such as the rostral nucleus solitaries, accessory nucleus, spinal nucleus of V, and inferior olivary nucleus, are not typically found at the level of the midbrain.

The correct answer is the Principal (main) sensory nucleus of V. This nucleus is responsible for relaying touch and proprioceptive information from the face to the somatosensory cortex. It is a second-order neuron, meaning it receives input from first-order neurons and sends that information to higher processing centers in the brain. The other options listed are not specifically involved in relaying touch and proprioceptive information from the face to the somatosensory cortex.

The patient's symptoms suggest a lesion in the right lateral medulla. The difficulty swallowing indicates involvement of the glossopharyngeal and vagus cranial nerves, which are located in the medulla. The loss of pain and temperature sensations on the left side of the body below the neck suggests involvement of the spinothalamic tract, which also passes through the medulla. Additionally, the loss of pain and temperature sensations on the right side of the face indicates involvement of the trigeminal nerve, which has a nucleus in the medulla. Therefore, the most likely location of the lesion is the right lateral medulla.

A lesion at the level of the cerebral peduncle would affect the descending fibers of the corticospinal tract. The corticospinal tract is responsible for voluntary movement and carries signals from the motor cortex to the spinal cord. When this tract is disrupted, it can lead to an abnormal response known as the Babinski sign. Normally, when the sole of the foot is stroked, the toes curl downwards. However, in the presence of a lesion affecting the corticospinal tract, the toes instead extend upwards, indicating an abnormal response. This abnormal response is known as a positive Babinski sign. Therefore, a lesion at the level of the cerebral peduncle would result in a positive Babinski sign.

The left spinal tract of V and the left spinal nucleus of V are responsible for transmitting pain and temperature sensation from the face to the brain. Therefore, if these structures are affected by an arterial infarct, it would result in a loss of pain and temperature sense on the left side of the face.

The medial lemniscus carries sensory information related to touch and pressure from the opposite side of the body. In this case, the infarct affects the right medial lemniscus, resulting in a loss of touch and pressure sense on the left side of the body below the neck.

The left pons is involved in this case because it controls the movement of the left eye. The symptoms described, including right-sided hemiplegia and right-sided cerebellar ataxia, indicate a lesion on the opposite side of the brain. Since the left eye is unable to abduct, it suggests that the left abducens nerve, which controls eye abduction, is affected. The abducens nerve originates in the pons, therefore, a lesion in the left pons would explain the patient's inability to abduct the left eye.

A paralysis of upward gaze and loss of the consensual pupillary light reflex suggests dysfunction in the midbrain. The pineal gland is located in the midbrain and is responsible for regulating sleep-wake cycles. Tumors in the pineal gland can compress nearby structures, leading to neurological symptoms such as those described in the patient. Therefore, a tumor in the pineal gland is a likely explanation for the constellation of symptoms observed in the 52-year old male.

The bone fragment lodged into the lateral aspect of the dorsal columns in the cervical spinal cord on the left side suggests damage to the sensory pathways responsible for touch, pressure, and vibration. Since the fragment is on the left side, it is likely to affect the sensory input from the left side of the body. Therefore, touch, pressure, and vibration of the left arm will most likely be affected in this patient's presentation.