Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 51, Num. 3, 2003, pp. 388-389

Neurology India, Vol. 51, No. 3, July, 2003, pp. 388-389

A patient with reversible pupil-sparing Weber's syndrome

Umasankar U, Huwez FU
Stroke Unit (Lister Ward), Basildon University Hospital, Basildon, Essex SS16 5NL

Correspondence Address:
Stroke Unit (Lister Ward), Basildon University Hospital, Basildon, Essex SS16 5NL
usankar68@hotmail.com

Code Number: ni03126

ABSTRACT

This is a case report of a lady who presented with pupil-sparing Weber's syndrome. She had left oculomotor nerve palsy with normal pupil and right hemiparesis. The patient subsequently made a good recovery. An ischemic lesion of the lower mid-brain was demonstrated on the MRI scan of the brain, which corresponds to the motor nucleus of the oculomotor nerve. The article also describes the neuroanatomy of the oculomotor nerve and how its partial lesions lead to sparing of the pupil. In addition, this case report documents that a pupil-sparing Weber's syndrome could be reversible.

INTRODUCTION

A complete oculomotor (3rd) nerve lesion results in ipsilateral ptosis, pupillary dilatation, loss of pupillary and accommodation reflexes and lateral deviation of the eye.[1] If the 3rd nerve palsy is associated with contralateral hemiplegia, the condition is described as Weber's syndrome.[2] However, this syndrome may be reversible as described in this report.

CASE REPORT

A 68-year-old lady noticed weakness of the right arm and leg and diplopia on waking in the morning. She had been a diabetic and hypertensive for the past 20 years. She underwent pituitary surgery (hypophysectomy) in 1977. This operation was not complicated by any cranial nerve palsy. Her medications included gliclazide, metformin, insulin, thyroxine, genotropin, desmopressin and aspirin. On presentation, she had a right hemiparesis and a left 3rd nerve palsy (drooping of eyelid/ lateral deviation of the eye/ diplopia on looking to the right) without involvement of the pupils. A Computerized Tomograph (CT) scan of the brain showed possible lacunar infarcts in the basal ganglia. Over the next week her hemiparesis resolved completely and her diplopia was getting better. Two weeks later, she had no more diplopia and was discharged with no neurological sequel. She subsequently had a Magnetic Resonance Imaging (MRI) of the brain which established the diagnosis. The MRI showed numerous small T2W signal hyperintensities within the cerebral white matter [Figure-1] and the lower mid-brain [Figure-2], consistent with infarcts. The diagnosis of Weber's syndrome without pupillary involvement was made on the basis of a crossed hemiplegia: left 3rd nerve palsy and right hemiparesis.2

DISCUSSION

Weber's syndrome was described in 1863 by the German physician Hermann Weber.[2] He described a 52-year-old man who presented with right limb weakness and left oculomotor palsy (involving the pupils) caused by a hemorrhage in the left cerebral peduncle. The clinical findings of Weber's syndrome include an ipsilateral 3rd nerve palsy and a contralateral limb weakness due to a lesion in the mid-brain (crus cerebri). Subsequently, cases have been reported wherein mid-brain lesions can produce a 3rd nerve lesion sparing the pupils, be it due to infarct, tumor or bleed.[3],[4],[5],[6]

The 3rd nerve nuclei are located in the mid-brain and are approximately 10 mm in length from the rostral to caudal extent.[3] It consists of: (a) the Edinger-Westphal nucleus located in the upper mid-brain supplying fibers to the pupils and (b) the motor nucleus located in the lower mid-brain supplying the extra-ocular muscles, except the lateral rectus and the superior oblique.[7] Fascicles from the nuclei run forward and laterally through the red nuclei and converge at the inter-peduncular fossa before emerging from the mid-brain. As the nuclei and fascicles are spread across a relatively wide area, mid-brain lesions can lead to partial 3rd nerve lesions. Hence a lesion of the lower mid-brain affects the extraocular muscles but spares the pupils, whereas lesions involving both the upper and lower parts of the mid-brain are associated with pupillary dilatation. This explains the pupillary sparing in Weber's syndrome in this patient. Earlier, we reported another patient who had pupil-sparing Weber's syndrome but her neurological deficits persisted and the patient required long-term nursing care.[8] However, the patient described here had all the features of a pupil-sparing Weber's syndrome with a definite MRI-documented ischemic lesion in the lower mid-brain, and she showed neurological and functional recovery.

In this case, the sudden onset of pupil-sparing left 3rd nerve palsy and contralateral hemiplegia indicates a mid-brain vascular lesion. There was a difference between the CT scan and the MRI scan findings which reflects the better sensitivity of the MRI scans to detect lesions of the brainstem. The pathological lesion in this patient indicating Weber's syndrome was shown on the MRI scan as an ischemic lesion in the lower part of the mid-brain where the motor part of the 3rd nerve nucleus is located, whereas there was no pathological lesion in the upper mid-brain where the Edinger-Westphal nucleus is found. Although the MRI scan showed multiple infarcts in the cerebral white matter, they were probably due to her long-standing diabetes and hypertension and these were not associated with functional or neurological deficits.

Pupil-sparing 3rd nerve palsy can also occur with extra-axial lesions i.e. due to lesions affecting the nerve trunk as in ischemic damage to the nerve and in patients with diabetes mellitus.[3] After emerging from the mid-brain, the 3rd nerve lies between the posterior cerebral artery and the superior cerebellar artery. It runs forward parallel to the posterior communicating artery and enters the orbit through the superior orbital fissure, dividing into an upper and a lower branch. The upper branch supplies the levator palpebrae superioris and superior rectus muscles. The lower branch supplies three muscles: the medial rectus, the inferior rectus, and the inferior oblique muscle.[1] The nerve to the inferior oblique muscle conveys the preganglionic parasympathetic fibers to the ciliary ganglion from which the post-ganglionic parasympathetic fibers arise to supply the ciliary muscle and the muscles of the iris (pupilloconstrictor fibers). The pupilloconstrictor fibers and those innervating the levator palpebrae lie in a superficial and dorsal position on the nerve relaying in the ciliary ganglion which is in the posterior orbit. Because of this anatomical characteristic, a fixed dilated pupil is often the first sign of 3rd nerve (oculomotor) compression, and ptosis the second, before external ophthalmoplegia develops.[9]

Finally, this report demonstrates a crossed hemiplegia with 3rd nerve palsy (pupil-sparing) due to an infarct in the lower part of the mid-brain as documented by the MRI scan. The other interesting feature to note in our report is that the patient recovered completely and was discharged with no neurological sequel. This indicates that some of these patients may have a good prognosis.

REFERENCES

Copyright 2003 - Neurology India. Also available online at http://www.neurologyindia.com

The following images related to this document are available:

Photo images