How does a small area cause big syndromes? A case report of a patient with one-and-a-half syndrome and MRI review of the anatomical pathways involved in causing different pontine neuro-ophthalmological syndromes

Purpose

To describe the clinical symptoms, anatomical location of the injury and different etiologies of one-and-a-half syndrome and its variants.

Observations

A small lesion to the brainstem can cause complex syndromes that involve the disfunction of different nuclei and pathways. A 52-year-old man presented with sudden onset of diplopia characterized by horizontal gaze palsy and internuclear ophthalmoplegia (INO). With these clinical characteristics, the patient was diagnosed with the one-and-a-half syndrome. Neuroimaging revealed an acute/subacute ischemic lacunar event in the pontine tegmentum. The one-and-a-half syndrome is described as a horizontal gaze palsy in one direction (damage to the paramedian pontine reticular formation [PPRF] or the VI nerve nucleus) and an internuclear ophthalmoplegia in the other direction (damage to the medial longitudinal fasciculus). Along with the traditional description, the closed anatomical proximity with other nuclei and pathways makes possible the appearance of other more complex syndromes that have been grouped as the one-and-a-half syndrome and its variants.

Conclusions and importance

A detailed clinical neuro-ophthalmologic examination, along with a clear understanding of the neuroanatomical pathways, gives clinicians a good diagnostic opportunity to determine the precise location of injuries to the brainstem.

An Anatomic, Imaging, and Clinical Review of the Medial Longitudinal Fasciculus

The medial longitudinal fasciculus (MLF) is a paired, highly specialized, and heavily myelinated nerve bundle responsible for extraocular muscle movements, including the oculomotor reflex, saccadic eye movements an smooth pursuit, and the vestibular ocular reflex. Clinically, lesions of the MLF are classically associated with internuclear ophthalmoplegia. However, clinical manifestations of a lesion in the MLF may be more complex and variable. We provide an overview of the neuroanatomy, neurologic manifestations, and correlative examples of the imaging findings on brain MRI of MLF lesions to provide the clinician and radiologist with a more comprehensive understanding of the MLF and potential clinical manifestations for an MLF lesion.

One-and-a-half syndrome with its spectrum disorders

One-and-a-half syndrome is a syndrome characterized by horizontal movement disorders of the eyeballs, which was first reported and named by Fisher in 1967. It presents a combination of ipsilateral conjugate horizontal gaze palsy (one) and ipsilateral internuclear ophthalmoplegia (INO) (a half). On the basis of the one-and-a-half syndrome, there are a series of related rare syndromes called the one-and-a-half syndrome spectrum disorders. This article reviews rare cases of one-and-a-half syndrome spectrum disorder, describes the clinical and pathological features of different syndromes, and summarizes their nomenclature.

Gaze palsy and exotropia in internuclear ophthalmoplegia

BACKGROUND AND PURPOSE

Unilateral gaze palsy associated with internuclear ophthalmoplegia (INO), i.e., one-and-a-half syndrome, is well known. Exotropia can also be associated with INO, but it has been reported only rarely. We sought to determine the frequencies and courses of gaze palsy and exotropia in INO.

METHODS

Patients hospitalized with acute-onset INO during the period January 2009 through December 2013 were identified from our clinical registry. Associated gaze palsy and exotropia were evaluated in the identified patients.

RESULTS

Twenty-five patients with unilateral INO and 7 patients with bilateral INO were included in this study. Of the 25 patients with unilateral INO, 4 (16.0.0%) had ipsilateral gaze palsy (one-and-a-half syndrome), 8 (32.0%) had exotropia (non-paralytic pontine exotropia), and 6 (24.0%) had both ipsilateral gaze palsy and exotropia (paralytic pontine exotropia). Six (85.7%) of the 7 patients with bilateral INO had exotropia. The gaze palsy persisted more than 1 week in 40.0% of patients, whereas the exotropia disappeared within 1 week in 92.9% of patients when the INO was unilateral.

CONCLUSION

Exotropia is not uncommon in the acute stage of INO. However, it is often overlooked because of its short duration.