Isolated abducens nucleus syndrome due to pontine tegmentum infarction

Introduction: Abnormalities of horizontal gaze could be caused by damage of the abducens nucleus due to ischemic lesion. We report a patient with isolated horizontal gaze palsy as a result of a small ischemic lesion of the pontine tegmentum. Observation: A 61-year-old man, with medical history of diabetes mellitus, dyslipidemia and high blood pressure, was hospitalized after 12 hours of transient dizziness and diplopia. On examination, he had conjugate eye deviation to the right side with horizontal gaze paralysis toward controlateral side. Vertical eye movements, convergence and pupillary reflex were preserved with no peripheral facial palsy. Brain MRI revealed a small lesion in the left pontine tegmentum. Patient received aspirin with atorvastatin and the gaze palsy has been disappeared three weeks later. Discussion: Conjugate lateral eye movement paralysis is commonly attributed to lesions of the caudal pons involving the abducens nucleus. horizontal gaze palsy is often associated to an ipsilateral peripheral facial palsy. In our case, the left lateral gaze palsy was isolated. The pontine lesion should be strictly confined the abducens nucleus which is extremely rare. the outcome of eye movement deviation in brainstem lesions is favorable within few weeks. Conclusion: Our case provides evidence that small pontine lesions can damage the abducens nerve nucleus without causing ipsilateral peripheral facial palsy.

“Nine Syndrome”: A Rare Neuroophthalmological Syndrome Associated with HIV Vasculopathy

There are many named brainstem syndromic variants of medullary infarcts among which “eight-and-a-half” syndrome is a rare condition that involves ipsilateral abducens nucleus or paramedian pontine reticular formation, ipsilateral medial longitudinal fasciculus, and adjacent facial colliculus/facial nerve. Here, we describe a new variant of brainstem syndrome, which includes the clinical features of “eight-and-a-half syndrome” with associated hemiparesis. This patient is a known case of HIV illness since 6 years on antiretroviral therapy, presented with features of “Nine” syndrome.

Brainstem and Cerebellar Involvement in Ramsay Hunt Syndrome

We present a case of a 62-year-old Caucasian male with laryngeal cancer and Ramsay Hunt Syndrome otherwise known as herpes zoster oticus due to reactivation of the varicella zoster virus. Classic findings include the triad of ipsilateral facial paralysis, otic pain, and herpetic lesions in the sensory supply of the facial nerve. The common pathogenesis is associated with anterograde axonal reactivation of the varicella zoster virus in the geniculate ganglion. Unique features of our case include retrograde transaxonal spread of the varicella-zoster virus from the geniculate ganglion into the brainstem and cerebellum including involvement of the abducens nucleus, facial nucleus, middle cerebral peduncle, and inferior cerebellar peduncle. This presented as left facial paralysis, left sixth nerve palsy, horizontal diplopia to the left lateral gaze, profound truncal ataxia, and left-sided dysmetria. Clinical awareness that Ramsay Hunt syndrome may also involve the brainstem and cerebellum is critical in evaluating the clinical neurologic findings and expanding the diagnostic workup to include brain magnetic resonance imaging and cerebrospinal fluid analysis, including varicella zoster polymerase chain reaction. Encephalitis requires longer duration administration of high-dose intravenous acyclovir in conjunction with steroids. Delays in treatment are often associated with unsatisfactory outcomes with extensive residual deficits.

Discharge properties of morphologically identified vestibular neurons recorded during horizontal eye movements in the goldfish

Computational capability and connectivity are key elements for understanding how central vestibular neurons contribute to gaze-stabilizing eye movements during self-motion. In the well-characterized and segmentally distributed hindbrain oculomotor network of goldfish, we determined afferent and efferent connections along with discharge patterns of descending octaval nucleus (DO) neurons during different eye motions. Based on activity correlated with horizontal eye and head movements, DO neurons were categorized into two complementary groups that either increased discharge during both contraversive (type II) eye (e) and ipsiversive (type I) head (h) movements (eIIhI) or vice versa (eIhII). Matching time courses of slow-phase eye velocity and corresponding firing rates during prolonged visual and head rotation suggested direct causality in generating extraocular motor commands. The axons of the dominant eIIhI subgroup projected either ipsi- or contralaterally and terminated in the abducens nucleus, Area II, and Area I with additional recurrent collaterals of ipsilaterally projecting neurons within the parent nucleus. Distinct feedforward commissural pathways between bilateral DO neurons likely contribute to the generation of eye velocity signals in eIhII cells. The shared contribution of DO and Area II neurons to eye velocity storage likely represents an ancestral condition in goldfish that is clearly at variance with the task separation between mammalian medial vestibular and prepositus hypoglossi neurons. This difference in signal processing between fish and mammals might correlate with a larger repertoire of visuo-vestibular-driven eye movements in the latter species that potentially required a shift in sensitivity and connectivity within the hindbrain-cerebello-oculomotor network. NEW & NOTEWORTHY We describe the structure and function of neurons within the goldfish descending octaval nucleus. Our findings indicate that eye and head velocity signals are processed by vestibular and Area II velocity storage integrator circuitries whereas the velocity-to-position Area I neural integrator generates eye position solely. This ancestral condition differs from that of mammals, in which vestibular neurons generally lack eye position signals that are processed and stored within the nucleus prepositus hypoglossi.

"Eight and a half" and "nine syndrome" rare presentation of pontine lesions; case reports and review of literature

Background: Eight-and-a-half syndrome (EHS) is one-and-a-half syndrome [(conjugated horizontal gaze palsy and internuclear ophthalmoplegia (INO)] plus ipsilateral fascicular seventh cranial nerve palsy. Involvement of lower pontine tegmentum including the abducens nucleus, the ipsilateral medial longitudinal fasciculus (MLF), and the adjacent facial colliculus contribute to the clinical findings of EHS. Recently, nine syndrome with addition of hemiparesis or hemianesthesia to EHS (due to involvement of adjacent corticospinal tract or medial lemniscus) is suggested. Methods: Consecutive patients with presentation of EHS or nine syndrome were reviewed from referral neuro-ophthalmology and strabismus clinics. Results: Three cases of EHS were identified with different etiologies of intracerebral hemorrhage (ICH), demyelination, and neuromyelitis optica spectrum disorder. Moreover, one case of "nine syndrome" due to ICH was described. Brain magnetic resonance imaging (MRI) in all of them revealed lesion in lower tegmentum of pons. Conclusion: Apart from different etiologies, recognition of EHS or nine syndrome allows precise localization of the lesion to lower pontine tegmentum ipsilaterally.

Functional diversity of motoneurons in the oculomotor system

Extraocular muscles contain two types of muscle fibers according to their innervation pattern: singly innervated muscle fibers (SIFs), similar to most skeletal muscle fibers, and multiply innervated muscle fibers (MIFs). Morphological studies have revealed that SIF and MIF motoneurons are segregated anatomically and receive different proportions of certain afferents, suggesting that while SIF motoneurons would participate in the whole repertoire of eye movements, MIF motoneurons would contribute only to slow eye movements and fixations. We have tested that proposal by performing single-unit recordings, in alert behaving cats, of electrophysiologically identified MIF and SIF motoneurons in the abducens nucleus. Our results show that both types of motoneuron discharge in relation to eye position and velocity, displaying a tonic–phasic firing pattern for different types of eye movement (saccades, vestibulo-ocular reflex, vergence) and gaze-holding. However, MIF motoneurons presented an overall reduced firing rate compared with SIF motoneurons, and had significantly lower recruitment threshold and also lower eye position and velocity sensitivities. Accordingly, MIF motoneurons could control mainly gaze in the off-direction, when less force is needed, whereas SIF motoneurons would contribute to increase muscle tension progressively toward the on-direction as more force is required. Anatomically, MIF and SIF motoneurons distributed intermingled within the abducens nucleus, with MIF motoneurons being smaller and having a lesser somatic synaptic coverage. Our data demonstrate the functional participation of both MIF and SIF motoneurons in fixations and slow and phasic eye movements, although their discharge properties indicate a functional segregation.