Unilateral midbrain infarct presenting as dorsal midbrain syndrome
- Correspondence to Meheroz H Rabadi, Department of Neurology, Veterans Affairs Medical Center at Oklahoma University, 921 NE 13th Street, Oklahoma City, OK 73104, USA;
- Received 14 January 2013
- Revised 22 February 2013
- Accepted 13 March 2013
- Published Online First 5 April 2013
Brainstem and cerebellar lesions are commonly associated with disorders of extraocular movements and these have localising value. The dorsal midbrain syndrome is characterised by (1) impaired voluntary vertical eye movements, (2) light-near dissociation of the pupillary response (pseudo-Argyll Robertson pupils), (3) convergence nystagmus on attempted upward gaze, (4) lid retraction (Collier sign) and (5) skew deviation.1 ,2 This syndrome is usually produced by pressure on the midbrain tectum.2 In this syndrome, the mesencephalic reticular formation that includes the rostral interstitial nucleus of medial longitudinal (riMLF) fasciculus and its connection with the interstitial N of Cajal and Darkschewitsch and the posterior commisure are involved. The riMLF is located dorsomedial to the rostral end of the red nucleus, rostral to the oculomotor nucleus and ventral to the periaqueductal grey matter (figure 1).3
A 63-year-old man presented with a sudden onset of dizziness and binocular diplopia. He was a known hypertensive, current heavy smoker, obese with obstructive sleep apnoea and paroxysmal atrial fibrillation. His neurological examination on admission showed retraction of the left eyelid, downward skew deviation of the left eye, impaired vertical voluntary gaze (upward gaze was more affected than downward gaze), absent vertical smooth pursuit and convergence paralysis with normal reactive pupils (figure 2). MRI scan of the brain showed an acute infarction dorsally in the left rostral midbrain on diffusion and T2-weighted images (figure 3). Patient received alternate day eye patching for his complaint of double vision, which resolved within 3 months of his being discharged home.
This is an unusual case of dorsal midbrain syndrome because, first, it usually results from extrinsic compressive lesions such as thalamic and pineal gland tumours or untreated hydrocephalus, resulting in dilation of the aqueduct Sylvia.2 ,4 Much less common are intrinsic midbrain lesions such as strokes and demyelination5 responsible for dorsal midbrain syndrome. When this occurs, strokes have mainly been due to hypertensive thalamic bleeds dissecting into the tectal area.1 ,6 Unilateral infarction of the dorsal midbrain is very uncommon,7 and is usually cardioembolic in nature as was most likely the case in this patient with atrial fibrillation. The blood supply to the riMLF is from the paramedian branches, which arise from the P1 segment of the posterior cerebral artery.8 Second, is the absence of pupillary abnormalities such as anisocoria and light-near dissociation, which are universal in this syndrome. This patient had a normal pupillary response, suggesting a circumscribed and not a mass lesion impinging on the tectal plate with sparing of the III cranial nerve (Edinger–Westphal) nucleus. Third, the upward gaze limitation noted here has usually been due to bilateral involvement of the riMLF with disruption of its crossing fibres at or near the posterior commissure. This vertical gaze limitation is supranuclear in origin as reflex vertical eye movements from vestibular and oculocephalic stimulations are preserved. This case suggests that a very circumscribed lesion can affect upward gaze mechanism without affecting pupillary function. There have been only four cases of unilateral dorsal midbrain infarctions presenting as dorsal midbrain syndrome reported in the literature.1 ,6 ,9 ,10 Similar eye movement disorders are also seen in ‘Top of the Basilar Syndrome’ and infarction involving the paramedian (or thalamoperforating) artery (a variant called the artery of Percheron). However, in both latter cases, altered level of consciousness is the overriding clinical presentation, and the radiological findings on axial fluid attenuated inversion recovery and/or diffusion-weighted imaging are distinctly different.11–13
Competing interests None.
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