Three possibilities to account for an ipsilateral horizontal gaze palsy: may be due to unilateral lesion affecting
The ipsilateral PPRF only
The ipsilateral abducens nucleus alone
Both the ipsilateral PPRF and abducens nucleus
All the cells necessary for ipsilateral horizontal gaze:
Motoneurons whose axons form the sixth nerve (VIN) to innervate the ipsilateral lateral rectus muscle
Internuclear neurons which send axons across the midline to opposite MLF and ultimately to the medial rectus motoneurons in the contralateral oculomotor nucleus (III N).
Pathogenesis of Certain Signs Ocular Motor Possible Pathophysiologic Deficit Substrate Ipsilateral adduction weakness Ipsilateral slowed abducting saccades Contralateral abduction nystagmus Interruption of axons of abducens internuclear motoneurons Inadequate inhibition of medial rectus motoneurons Impaired inhibition of contralateral medial rectus or Interruption of descending fibers to contralateral abducens nucleus or Involvement of adjacent PPRF
Neurology 1983; 33:971-980
Reported Boston Total cases series
Brainstem Infarct 12 4 16
Multiple Sclerosis 2 14 16
Pontine Glioma 2 1 3
Arteriovenous Malformation 1 0 1
Pontine Hemorrhage 8 0 8
Basilar Artery Aneurysm 0 1 1
Cerebellar Astrocytoma 2 0 2
Metastatic Melanoma 1 0 1
Ependymoma Fourth Ventricle 1 0 1
29 20 49
Table 1. The one-and-a-half syndrome: Etiology
Diplopia 12 Blurred Vision 8 Oscillopsia 4 Difficulty looking to one side 2 “ Quivering” of the eye 1 No visual complaint 3 Table 2. One-and-a-half syndrome (N = 20): Visual Symptoms
Cranial Nerve Involvement I 0 II 1 III 0 V 3 VII 4 VIII 2 IX 3 XI 0 XII 2 Horner’s Syndrome 1 Weakness or spasticity 6 Sensory deficits 7 Abnormally brisk or asymmetric reflexes 5 Extensor plantar responses 9 Incoordination 10 Table 4. One-and-a-half syndrome (N = 20): Associated neurologic signs
Esotropia of the ipsilateral eye
Patient 1. The one-and-a-half syndrome (A) Mild left INO looking right. (B) Esotropia OS (ipsilateral) in the primary position of gaze. (C) Horizontal conjugate gaze palsy attempting to look left. (D) Normal convergence.
Paralytic Pontine Exotropia
Patient 2. Paralytic pontine exotropia. (A) Horizontal conjugate gaze paresis looking right. (B) Exotropia OS (contralateral) in the primary position of gaze. (C) Right INO looking left. (D) Right “peripheral-type” ipsilateral facial palsy. (E) Impaired convergence.
Patient 2. Paralytic Pontine Exotropia
Horizontal conjugate palsy looking right.
Exotropia OS contralateral in the primary position of gaze.
Right INO looking left
Right “peripheral-type” ipsilateral facial palsy
In paralytic pontine exotropia the exotropic eye shows:
Abduction nystagmus during attempts to move it laterally
Extreme slowness of adduction saccades when eye fixing to move it to the midline
Paralytic Pontine Exotropia attributed to:
Tonic contralateral deviation of the eyes
Implies acute ipsilateral PPRF lesion
Failure of ipsilateral eye to deviate medially explained by the INO
Paralytic pontine exotropia OS
Paralytic pontine exotropia right horizontal gaze palsy