Oculomotor Synkinesis Secondary to Meningocele: Report of a Rare Case

Abstract

Oculomotor synkinesis or aberrant regeneration of cranial nerve III (CN III) typically results from trauma, aneurysm, or mass lesions. We present a rare case report with CN III palsy and synkinesis secondary to a meningocele in the left oculomotor cistern, causing mass effect on the oculomotor nerve. Imaging suggested underlying idiopathic intracranial hypertension (IIH) as a potential etiology. While mass lesions or trauma are common causes of oculomotor synkinesis, an association with meningocele has not been previously reported. This case highlights the importance of considering IIH-related meningoceles in unexplained CN III palsies.

 

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Keywords

oculomotor nerve - synkinesis - aberrant regeneration - meningocele - idiopathic intracranial hypertension

Introduction

The oculomotor nerve, or cranial nerve III (CN III), provides motor innervation to the inferior oblique muscle, the levator palpebrae superioris muscle, and superior, inferior, and medial rectus muscles.[1] It also allows for constriction of the pupil and accommodation of vision to near objects via parasympathetic nerve fibers to the constrictor pupillae and ciliary muscles.[1] A CN III palsy classically presents with a “down-and-out” appearance of the affected eye due to unopposed lateral rectus and superior oblique contraction, ptosis, and mydriasis.[1]

Oculomotor synkinesis, or aberrant regeneration of CN III, can occur following CN III palsy when some injured nerve fibers regenerate in a disordered fashion, innervating a different muscle than prior to injury.[2] This results in synkinetic eye movements, with voluntary muscle contraction accompanied by involuntary contraction of a different muscle due to stimulation by aberrant nerve fibers. This most often occurs due to trauma, aneurysm, or mass lesion, most commonly meningioma.[1] [3] In one small study of 20 patients, the incidence of oculomotor synkinesis after traumatic CN III palsy was 15%.[4]

We present a case of a patient who presented with a CN III palsy and oculomotor synkinesis caused by a meningocele involving the oculomotor cistern (OMC), possibly secondary to undiagnosed idiopathic intracranial hypertension (IIH).

 

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Case Report

Our patient was a 29-year-old male without relevant past medical or surgical history who initially presented in 2018 with 1 week of intermittent diplopia and left pupil mydriasis and underwent emergent workup, given concern for a CN III palsy. CT angiography of the head and MRI of the brain did not demonstrate evidence of aneurysm or other acute findings.

Subsequently, he was seen in our university neuro-ophthalmology clinic. Physical exam was notable for a left-sided CN III palsy with ptosis, mydriasis without afferent pupillary defect, restricted motion in all directions except abduction, and double vision on upward and downward gaze during adduction. He also had improvement in ptosis with adduction and downward gaze, known as the pseudo-von-Graefe's sign, suggestive of aberrant innervation of the levator palpebrae superioris by the fibers of CN III innervating the medial rectus and inferior rectus muscles, concerning for oculomotor synkinesis and prompting further workup.[3] He did not have papilledema on exam.

A month after the initial studies, the patient underwent repeat MRI of the brain with constructive interference in steady state (CISS) sequence, which showed a meningocele projecting into the left OMC, causing mass effect on the left oculomotor nerve with nerve atrophy. He was managed expectantly. On subsequent surveillance MRIs, there has been interval development of atrophy involving the cisternal segment of the left oculomotor nerve ([Fig. 1]). His symptoms mildly improved without intervention in the 5 months after symptom onset but have since plateaued, with persistent restricted motion, double vison, and intermittent blurry vision in his left eye. He was initially followed up with a yearly MRI of the brain for the first 2 years; thereafter, MRI of the brain every 2 years and findings had been stationary.

Fig. 1 (A, B, and D) Axial and coronal CISS sequences showing a cystic lesion projecting into and enlarging the posterior aspect of the left oculomotor cistern (arrowheads), causing mass effect and lateral displacement of CN III (red arrows). The normal right CN III can be seen in the R oculomotor cistern (yellow arrows). (C) Coronal T2-weighted sequence more anteriorly showing atrophy of the cisternal segment of the left oculomotor nerve (red arrow) and a normal oculomotor nerve in the right oculomotor cistern (yellow arrow).

Retrospectively, he had several imaging findings suggestive of IIH on initial presentation, including empty sella, prominent arachnoid granulations, stenosis of the bilateral sigmoid–transverse sinus junctions, and prominence of the perioptic subarachnoid space with tortuosity of the optic nerves ([Fig. 2]). Additionally, the patient has a high body mass index (over 40), known to be associated with IIH.

Fig. 2 (A) Sagittal T1-weighted post-contrast image demonstrating empty sella with osseous remodeling of the sella turcica (*). (B) Axial CISS sequence demonstrating distention of the perioptic subarachnoid space with tortuosity of the optic nerves (arrows). (C, D) Sagittal and coronal T1-weighted post-contrast images demonstrating stenosis of the bilateral and left sigmoid–transverse sinus junctions, respectively (arrowheads). A prominent arachnoid granulation is additionally noted.

 

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Discussion

The Monro-Kellie doctrine posits that the total volume within the rigid skull is constant, comprising brain tissue, cerebrospinal fluid (CSF), and blood. An increase in one component necessitates a compensatory decrease in another to maintain normal intracranial pressure.[5] In IIH, compensatory mechanisms try to redistribute or reduce CSF volume to maintain pressure homeostasis, leading to distention of optic nerve sheaths, flattening of the posterior globe/papilledema, empty sella, compression/stenosis of the distal transverse sinuses, and enlargement of any of the CSF-containing spaces or formation of meningocele, in places such as Meckel's cave, geniculate ganglion, and OMCs.

The OMC is a CSF-filled dural cuff that envelops the oculomotor nerve (cranial nerve III) as it traverses from the interpeduncular cistern into the lateral wall of the cavernous sinus.[6]

In addition to trauma and aneurysms, mass lesions are a common cause of oculomotor synkinesis; however, this is most commonly secondary to parasellar meningioma or pituitary adenoma,[1] [3] while oculomotor synkinesis secondary to a meningocele has not previously been reported.

The etiology of our patient's meningocele is unclear but most likely secondary to IIH, which is associated with meningoceles in up to 10% of patients.[7] He meets three out of four imaging criteria of IIH (empty sella, transverse venous sinus stenosis, distended and tortuous optic nerve sheath but not flattening of the posterior globe) and intermittently experienced associated symptoms of IIH, including intermittent blurred vision and diplopia.[7] While he did not present with papilledema, the absence of papilledema in IIH can occur after spontaneous CSF leak from the spine or skull base, reducing intracranial pressure and potentially resulting in a meningocele. Unfortunately, the patient was not asked about rhinorrhea at initial presentation, which would support a possible CSF leak, and he has not previously undergone lumbar puncture, which is necessary for a diagnosis of IIH.

 

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Conclusion

Our patient presented with a CN III palsy and oculomotor synkinesis caused by a meningocele involving the OMC and possibly secondary to underlying IIH.

 

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Conflict of Interest

None decalred.

Authors' Contributions

B.W.: writing the article, data collection, and image processing.

K.A.M.: revising the article, image processing.

L.F.F.: editing, reviewing, and supervision.

N.S.: conceptualization, writing, editing, and supervision.

Patient's Consent

Patient's consent has been taken for this study.

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• 4 Chua HC, Tan CB, Tjia H. Aberrant regeneration of the third nerve. Singapore Med J 2000; 41 (09) 458-459
• 5 Mangalore S, Rakshith S, Srinivasa R. Solving the riddle of “idiopathic” in idiopathic intracranial hypertension and normal pressure hydrocephalus: an imaging study of the possible mechanisms - Monro-Kellie 3.0. Asian J Neurosurg 2019; 14 (02) 440-452
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Publication History

Article published online:
10 July 2025