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

Abstract

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.

Keywords: Brainstem; Diplopia; Neuro-ophthalmology; Ocular motility; One-and-a-half syndrome; Stroke.

Fig. 1

Nine gaze positions and Diffusion-Weighted Imagining (DWI) sequence gadolinium-enhanced magnetic resonance imaging (MRI). Primary position with exotropia of the left eye (E), limited adduction (F), and abduction (D) of the right eye, and limited adduction of the left eye (D). The DWI sequence shows an acute/subacute ischemic lacunar event in the right pontine tegmentum (arrow) (J).

Fig. 2

Horizontal eye movements pathway. Schematic diagram of horizontal eye movements pathway in a gadolinium-enhanced brain magnetic resonance imaging (MRI) showed in T2 weighted, coronal reconstruction. MR, Medial Rectus; LR, lateral rectus, III; third cranial nerve nucleus, IV; fourth cranial nerve nucleus, VI; sixth cranial nerve nucleus, VN; vestibular nuclei.

Fig. 3

Brainstem lacunar stroke. Specific location of the lacunar stroke in the right pontine tegmentum (A). Schematic diagram of the lesion in the pathway (B). III; third cranial nerve nucleus, IV; fourth cranial nerve nucleus, VI; sixth cranial nerve nucleus, VN; vestibular nuclei.

Fig. 4

One-and-a-half syndrome spectrum disorders. Schematic diagram of the lesion of one-and-a-half syndrome spectrum disorders. Cross-section at the level of lower pons. (A) and (B) One-and-a-half syndrome; (C) Eight-and-a-half syndrome; (D) Nine syndrome; (E) thirteen-and-a-half syndrome; (F) fifteen-and-a-half syndrome (G) sixteen-and-a-half syndrome. The yellow area represents the injury. ML, medial lemniscus; MLF, medial longitudinal fascicle; CST, corticospinal tract; PPRF, parapontine reticular formation. . (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)