A 12-year-old boy is being evaluated for worsening headaches for the past several months. He also has had paresthesia, weakness, and stiffness of the extremities. MRI of the brain reveals an expansile mass in the lower pons, as shown in the image below: Which of the following is most likely to be observed in this patient due to direct involvement of nerve nuclei by the brain lesion?

Question

A 12-year-old boy is being evaluated for worsening headaches for the past several months.  He also has had paresthesia, weakness, and stiffness of the extremities.  MRI of the brain reveals an expansile mass in the lower pons, as shown in the image below:  Which of the following is most likely to be observed in this patient due to direct involvement of nerve nuclei by the brain lesion?

Quizplus · Accepted Answer

11ec160b_359f_33f8_9249_776e2fad6195_MD0001_00 This patient has a mass compressing the inferior pons (eg, pontine glioma). Major nuclei in the pons include the following: CN V: trigeminal motor nucleus (innervation to the muscles of mastication) and the main trigeminal nucleus (sensory innervation to the face and jaw) CN VI: abducens nucleus (motor innervation to the lateral rectus muscle) CN VII: facial nucleus (motor innervation to the muscles of facial expression) CN VIII: dorsal and ventral cochlear nuclei (hearing) and the vestibular nucleus (head position and movement) The vestibular portion of CN VIII conveys information about head position and movement and is involved in the vestibuloocular reflex (VOR), which stabilizes the gaze during head movement. Therefore, damage to the vestibular nuclei of CN VIII can lead to nystagmus due to impairment of the VOR. (Choice A) Asymmetric pupils can occur with damage to nuclei of the oculomotor nerve (CN III). The oculomotor nucleus provides motor innervation to the extraocular muscles, and the accessory nucleus (ie, Edinger-Westphal) provides parasympathetic input to the iris and lens (eg, pupillary constriction, iris accommodation). Both nuclei are located in the midbrain rather than the pons. (Choice C) Tongue atrophy can occur with damage to the nucleus of the hypoglossal nerve (CN XII). The hypoglossal nucleus is located in the medulla. (Choice D) The trapezius muscle is innervated by the accessory nerve (CN XI), which has fibers coming from the spinal accessory nucleus (located in the spinal cord) and the nucleus ambiguus (located in the medulla). (Choice E) Vertical diplopia can occur with damage to the nucleus of the trochlear nerve (CN IV), which innervates the superior oblique, or the oculomotor nucleus (CN III). Both nuclei are located in the midbrain. Educational objective: The nuclei of the vestibulocochlear nerve (CN VIII) are located in the pons. The vestibular portion of CN VIII conveys information about head position and movement and helps to stabilize the gaze during head movement; damage can lead to nystagmus.

A 12-Year-Old Boy Is Being Evaluated for Worsening Headaches for the Past