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Central nervous system lesions
Published in Ibrahim Natalwala, Ammar Natalwala, E Glucksman, MCQs in Neurology and Neurosurgery for Medical Students, 2022
Ibrahim Natalwala, Ammar Natalwala, E Glucksman
TRUE – Internuclear opthalmoplegia is a clinical sign of extraocular muscle weakness related to the dysfunction of the medial longitudinal fasciculus tract. The medial longitudinal fasciculus pathways connect the paramedian pontine reticular formation (PPRF) and the abducens nucleus complex to the oculomotor nucleus, which allows conjugate eye movements to take place. The following image shows internuclear opthalmoplegia on clinical examination.
Cranial Neuropathies I, V, and VII–XII
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Lesions in the pons affecting the facial motor nucleus or facial nerve fascicles result in an ipsilateral peripheral (or lower motor neuron) facial nerve palsy with upper and lower facial weakness. This manifests with weakness of frowning, eye closure, and elevation of the eyebrow in addition to involvement of muscles of the lower face. Pontine lesions involving the facial nucleus/fascicles generally affect neighboring structures including CN VI nucleus and fascicles (reduced abduction in ipsilateral eye), paramedian pontine reticular formation (impaired conjugate horizontal gaze to ipsilateral side), corticospinal tract (contralateral arm and leg weakness), CN V spinal tract and nucleus (ipsilateral facial numbness), and spinothalamic tract (contralateral hemibody numbness).20
Neuro-ophthalmology
Published in Mostafa Khalil, Omar Kouli, The Duke Elder Exam of Ophthalmology, 2019
The abducens nucleus is located in the pontine tegmentum ventral to the fourth ventricle. The nucleus is located near the paramedian pontine reticular formation (PPRF) and surrounded by looping fibres of CNVII. CNVI exits the brainstem at the pontomedullary junction and crosses over the petrous apex of the temporal bone through an osteofibrous channel, called Dorello's canal. It is at the Dorello's canal where CNVI is susceptible to stretching in cases of increased intracranial pressure. CNVI then travels through the cavernous sinus, lateral to the internal carotid. It then enters the orbit via the SOF, through the tendinous ring, to innervate the LR muscle.
Eight-and-a-Half Syndrome Secondary to Neurotoxoplasmosis: A Rare Case Report
Published in Neuro-Ophthalmology, 2022
Joaquim Francisco Cavalcante-Neto, Gabriel Costa dos Reis, Mateus Aragão Esmeraldo, Bianca Ratts Freitas dos Santos, Paulo Roberto Lacerda Leal, Keven Ferreira da Ponte, Gerardo Cristino-Filho, Espártaco Moraes Lima Ribeiro
EHS is a combination of one-and-a-half-syndrome and an ipsilateral peripheral facial palsy (collicular/fascicular facial palsy) (1½ + 7). Its pathophysiology is explained by a lesion incorporating the facial nucleus/fasciculus, the medial longitudinal fasciculus, and the paramedian pontine reticular formation/abducens nucleus, which is the centre of horizontal gaze control, synchronising horizontal gaze during movements of the eyes and head.1,5,6 Therefore, the caudal paramedian tegmentum of the pons is the main lesion site which causes EHS. This spectrum may be classified into classic EHS (without accompanied symptoms), EHS variants (with vertical or bilateral gaze palsies), and eight-and-a-half plus syndrome (nine, thirteen-and-a-half, and fifteen-and-a-half syndromes).6
Sixteen‐and‐a‐half syndrome: a variant in the spectrum of Fisher's one‐and‐a‐half syndrome
Published in Clinical and Experimental Optometry, 2019
Christopher J Borgman, Alex M Jackson
Additionally, involvement of the ipsilateral medial longitudinal fasciculus (originating in the contralateral abducens nucleus) will result in an ipsilateral internuclear ophthalmoplegia, giving the ocular motility a pattern consistent with OAAH.2003 Isolated paramedian pontine reticular formation lesions are associated with the presence of intact vestibular‐ocular reflexes.1998 If the vestibular‐ocular reflex is absent then the lesion involves the abducens nucleus.1998 However, retained vestibular‐ocular reflex is rarely encountered in clinical practice due to the proximity of the paramedian pontine reticular formation with the other structures usually implicated in this same area.1998 In this patient, the vestibular‐ocular reflex was abolished, suggesting her left abducens nucleus was implicated within the ischemic lesion.
Disorders of vision in multiple sclerosis
Published in Clinical and Experimental Optometry, 2022
Roshan Dhanapalaratnam, Maria Markoulli, Arun V Krishnan
Saccades are initiated at the paramedian pontine reticular formation and the speed of saccades is regulated at the dorsal cerebellar vermis. The basal ganglia are responsible for descending gaze control pathways and lesions in this area may result in saccadic intrusions (multiple episodic rapid eye movements), in addition to hypometric saccades and impaired pursuit. The cerebellum provides coordination input for eye movements, and the flocculus and paraflocculus are responsible for smooth pursuit.79 Feedback from the vestibular system provides information for this coordination of movement in context of head movement, and the flocculus and paraflocculus therefore play an important role in the VOR.