A child with unilateral abducens nerve palsy and neurovascular compression in Chiari malformation type 1 resolved with posterior fossa decompression: illustrative case

Abstract

Background: Unilateral cranial nerve (CN) VI, or abducens nerve, palsy is rare in children and has not been reported in association with Chiari malformation type 1 (CM1) in the absence of other classic CM1 symptoms.

Observations: A 3-year-old male presented with acute incomitant esotropia consistent with a unilateral, left CN VI palsy and no additional neurological symptoms. Imaging demonstrated CM1 without hydrocephalus or papilledema, as well as an anterior inferior cerebellar artery (AICA) vessel loop in the immediate vicinity of the left abducens nerve. Given the high risk of a skull base approach for direct microvascular decompression of the abducens nerve and the absence of other classic Chiari symptoms, the patient was initially observed. However, as his palsy progressed, he underwent posterior fossa decompression with duraplasty (PFDD), with the aim of restoring global cerebrospinal fluid dynamics and decreasing possible AICA compression of the left abducens nerve. Postoperatively, his symptoms completely resolved.

Lessons: In this first reported case of CM1 presenting as a unilateral abducens palsy in a young child, possibly caused by neurovascular compression, the patient's symptoms resolved after indirect surgical decompression via PFDD.

Keywords: Chiari malformation type 1; abducens nerve; cranial nerve VI palsy; pediatric neurosurgery.

FIG. 1

Preoperative views (A and B) of the patient’s left sixth nerve palsy when attempting forward primary gaze.

FIG. 2

In the RetCam photographs of both of the patient’s optic nerves, there was a scalloped border to the left optic nerve but no significant elevation of overlying tissue. Ultimately, however, no significant clinical swelling of either optic nerve was determined from this study.

FIG. 3

A: Preoperative midsagittal noncontrast CT scan demonstrating 13 mm of downward herniation of the cerebellar tonsils. B: Preoperative midsagittal T1-weighted MRI with a similar degree of downward tonsillar herniation. C: Axial T2 CISS MRI demonstrating an aberrant vessel loop thought to be arising from the left AICA and contacting the left CN VI.

FIG. 4

A: Postoperative midsagittal T1-weighted MRI with significant posterior fossa decompression and improvement in tonsillar herniation through the foramen magnum. B: Axial T2 CISS MRI demonstrating decompression of the left CN VI with an increase in the space between the nerve and aberrant vessel loop.

FIG. 5

A: Postoperative photograph of the patient attempting forward gaze with resolved sixth nerve palsy. B: The patient demonstrating full abduction of the left eye postoperatively. The photograph was taken a few weeks after discharge.