Quadrigeminal cistern arachnoid cyst as a probable cause of hemifacial spasm

Abstract

Arachnoid cysts arising in the quadrigeminal cistern (ACQCs) are uncommon. A 68-year-old woman presented with an unsteady gait, facial spasm, and cerebellar ataxia. Non-contrast head computed tomography showed a cystic mass centered in the quadrigeminal cistern accompanying ventriculomegaly. On MRI, the cyst appeared hypointense on T1- and hyperintense on T2-weighted sequence. There was no restricted diffusion on diffusion-weighted imaging. The cerebral aqueduct was obstructed and the prepontine cistern was narrowed. The left vertebral artery (VA) coursed adjacent to the facial nerve at its origin. The patient underwent neuroendoscopic fenestration of the posterior wall of the third ventricle and ventral wall of the ACQC. Postoperatively, the patient's symptoms resolved. MRI showed a considerable reduction in the ACQC and expansion of the prepontine cistern, whereas the relationship between the left VA and the proximal segment of the facial nerve did not change. We assumed that the pre-existing close relationship between the VA and facial nerve might have been aggravated by the anterior displacement of the brainstem, thus causing the facial spasm.

Keywords: Arachnoid cyst; Endoscopic fenestration; Hemifacial spasm; Quadrigeminal cistern.

Fig. 1

(A–C) Non-contrast axial CTs at presentation showing a well-demarcated, hypodense cystic mass (Cy) centered in the quadrigeminal cistern with lateral extension into the ambient cisterns (A, arrows), superior extension to the level of the pineal gland, and inferior extension into the posterior cranial fossa (C, arrow) with accompanying ventriculomegaly

Fig. 2

Axial T1-(A), axial (B), and sagittal (D) T2-, and axial diffusion-weighted (C) MRI showing the cyst (Cy) appearing hypointense on T1- and diffusion-weighted imaging and hyperintense on T2-weighted sequence. Compressed by the cyst, the aqueduct is obstructed (D, orange arrows) and the prepontine cistern narrowed (D, blue arrow) by the displaced brainstem.

Fig. 3

(A–C) Serial constructive interference in steady-state images showing the left vertebral artery adjacent to the facial nerve (VII) at the original site of the brainstem. (D) Cerebral MRA, anteroposterior view, showing the elongated left vertebral artery (arrows). Cy, cyst; P, pons; VIII, vestibulocochlear nerve.

Fig. 4

Intraoperative photos showing endoscopic perforation of the posterior wall of the third ventricle (A) and after perforation of the ventral cyst wall (B). Note that the bilateral trochlear nerves (IV) are observed through the arachnoid membrane-like cyst wall. Aq, obstructed aqueduct; ChP, choroid plexus; I, inferior; L, left; R, right; S, superior; V, vein.

Fig. 5

Axial (A) and sagittal (B) T2-weighted MRI showing reduction of the cyst (Cy), ambient cisterns, and ventriculomegaly (yellow arrow) and expansion of the prepontine cistern (orange arrows) with the patent aqueduct (blue arrow). (C–E) Serial constructive interference in steady-state images showing no significant changes in the relationship between the left vertebral artery and the proximal segment of the facial nerve (VII). P, pons; VIII, vestibulocochlear nerve; 4thV, fourth ventricle.