Arachnoid Cyst in Middle Cranial Fossa With Intraorbital Cyst (Orbital Meningocele)

Abstract

Intracranial arachnoid cysts are extra-axial non-enhancing cerebrospinal fluid (CSF) density lesions. These are usually incidental findings on radiological investigations. Usually, the patients with arachnoid cysts are asymptomatic until the cyst grows large while symptomatic patients present with headaches, seizures, and focal neurological deficits. The adjacent calvarial bone may show remodeling and scalloping. Magnetic resonance imaging (MRI) stands superior in soft-tissue contrast and multiplanar imaging in excluding other lesions from the arachnoid cyst. Arachnoid cysts follow CSF signals in all pulse sequences with no gadolinium enhancement. Intraorbital extension of the intracranial arachnoid cyst (intraorbital meningocele) is rarely reported in the literature and occurs through the small bony defect. We report a case of a 20-year-old male presenting with proptosis who was detected to have an arachnoid cyst in the middle cranial fossa with intraorbital extension through a small bony defect in the lateral wall of orbit with the resultant orbital cyst.

Keywords: arachnoid cyst; intra-orbital cyst; intra-orbital meningocele; orbital cyst; orbital meningocele.

Figure 1. (a) Frontal view showing normal left eye six months back. (b) Frontal view during present hospital admission with proptosis of the left eye.

Figure 2. (a) Ultrasound examination of the left orbit showing well-defined anechoic cystic lesion without solid component, septations, or calcification and intracranial cyst behind the left sphenoid wing without solid component, septations, or calcification. (b) Ultrasound examination cranially to the previous image showing intraorbital cyst and intracranial cyst in the left middle cranial fossa.

Figure 3. (a) Axial T1WI. (b) Axial T2WI. (c) FLAIR axial. (d) Sagittal T1 images showing CSF signal intensity extra-axial cystic lesion in the left middle cranial fossa and intraorbital cystic lesion.

Figure 4. (a) Coronal T2WI through orbit. (b) Coronal T2WI through middle cranial fossa showing intraorbital cystic lesion and extra-axial cystic lesion in the left middle cranial fossa, respectively.

Figure 5. (a) Diffusion-weighted imaging (DWI) and (b) apparent diffusion coefficient (ADC) map showing no diffusion restriction in the intracranial or intraorbital lesion. (c) The magnitude and (d) phase images of SWI showing no “blooming” artifact in the intracranial or intraorbital lesion.

Figure 6. (a) T1 VIBE axial and (b) T1 VIBE sagittal oblique images showing the bony defect (black arrow) along posterior-lateral bony orbital wall communicating intraorbital and intracranial cysts.

VIBE - volumetric interpolated breath-hold examination

Figure 7. (a) T1 fat-saturation pre-contrast and (b) T1 fat-saturation post-contrast images showing no abnormal contrast enhancement.

Figure 8. (a) CT axial section and (b) reformatted sagittal oblique view showing scalloping of left sphenoid wing with a small bony defect (black arrow) communicating intraorbital and intracranial cystic lesions.