Unusual imaging characteristics of cystic meningioma in cerebellopontine angle

Abstract

We report a case of cystic meningioma at the left cerebellopontine angle (CPA). Magnetic resonance imaging demonstrated both solid and cystic components in the tumor. The cystic component appeared slightly hyperintense compared to cerebrospinal fluid on fluid-attenuated inversion recovery (FLAIR) imaging. A hypointense tubular structure was identified in the cystic component on 3D driven equilibrium sequencing. These imaging findings are unusual for cystic meningioma. However, awareness of these unusual imaging features is important to determine appropriate treatment strategies although cystic meningioma at the CPA is extremely rare.

Introduction

Intracranial meningioma is the second most common extra-axial tumor of the cerebellopontine angle (CPA) after vestibular schwannoma.^1–4 Meningioma with macroscopic cystic components is occasionally observed in clinical practice. However, cystic meningioma arising at the CPA is exceedingly rare. ⁵ On magnetic resonance imaging (MRI), the previous literature suggests that cyst wall enhancement is usually observed and cystic components show similar intensity to cerebrospinal fluid (CSF) on all sequences including fluid-attenuated inversion recovery (FLAIR) imaging and diffusion-weighted imaging (DWI).^5,6 This case report describes a case of cystic meningioma at the left CPA with unusual imaging characteristics.

Case report

A 72-year-old woman presented with a 2-week history of left facial sensory disturbance. Imaging showed a left CPA mass and she was therefore referred to our hospital for further examination and treatment. Neurological examination revealed mild sensory impairment in the distribution of the left trigeminal nerve. No quadriplegia or facial nerve palsy was evident. On computed tomography (CT), a hypodense tumor with calcification was apparent at the left CPA, attached to the left petrous bone (Figure 1(a)). MRI was performed using a 3.0-T scanner (Ingenia, Philips Medical Systems, Best, the Netherlands). MRI demonstrated both solid (9 × 8 mm in size) and cystic components (24 × 10 mm in size) in the tumor. The solid component showed homogeneous enhancement around the calcification (Figure 1(b)). The cystic component appeared hypointense on T1WI and DWI (Figure 1(c)), and slightly hyperintense compared to CSF on FLAIR imaging (Figure 1(d)). Solid and cystic components were clearly depicted on 3D driven equilibrium sequence (DRIVE), which permits high-resolution MR cisternography to examine the CPA, ⁷ with the following scan parameters: repetition time, 1500 ms; echo time, 232 ms; flip angle, 90°; matrix, 300 × 300; and slice thickness, 1 mm) (Figure 1(e)). A hypointense tubular structure was identified in the cystic component on DRIVE (Figure 1(f)). Cystic meningioma was highly suspected based on these imaging characteristics.

Figure 1.

(a) Axial computed tomography (CT). (b) Contrast-enhanced T1-weighted imaging. (c) Diffusion-weighted imaging (DWI). (d) Fluid-attenuated inversion recovery (FLAIR) imaging. (e and f) Axial (e) and coronal (f) reconstructions of 3D-driven equilibrium sequence (DRIVE) on magnetic resonance imaging (MRI). (g and h) Hematoxylin and eosin (HE) staining of solid (g) and cystic components (h) in the CPA tumor. On CT, the left CPA tumor appears as a hypodense mass with calcification attached to the left petrous bone (a; arrow). The solid component shows homogeneous enhancement around the calcification (b; arrow). The cystic component reveals hypointensity on DWI (c; arrow), and slight hyperintensity compared to cerebrospinal fluid on FLAIR imaging (d; arrow). MRI demonstrates that the tumor contains both solid (e; arrow) and cystic components (e; arrowhead). A hypointense tubular structure is identified in the cystic component on DRIVE (f; arrowhead). Histologically, meningothelial cells are observed within both the solid component (g; arrow) and the cyst wall (h; arrow).

Total resection (Simpson grade 1) of the tumor was performed. At surgery, the cystic component was found to contain viscous fluid. Histologically, meningothelial cells were observed within both solid and cystic components (Figure 1(g) and (h)). The solid component comprised clusters of meningothelial cells with abundant psammoma bodies. These features confirmed the diagnosis of meningothelial meningioma (World Health Organization grade I). No neurological symptoms were identified after resection of the tumor, and follow-up CT performed 4 months later revealed no evidence of recurrence.

Discussion

Cystic meningioma accounts for 3.5 % of intracranial meningiomas. ⁶ CPA meningioma comprises approximately 2% of all intracranial meningiomas. ¹ Only 12 cases of cystic meningioma at the CPA have been reported in the literature. ⁵ Most of these have involved the clear cell tumor subtype occurring in children or young adults. Nauta et al. ⁸ classified cystic meningioma into four types based on relationships between the tumor, cyst, and surrounding brain. According to that classification, type 1, 2, or 3 cystic meningiomas contain brain parenchyma. In contrast, cystic components in type 4 appear at the interface between the tumor and brain, and the cysts are present in neither the tumor nor the brain.

The vast majority of cystic components have been reported as hypointense on FLAIR imaging. ⁶ The contents within cystic components have been reported as xanthochromatic, highly proteinaceous, ischemic necrosis, intratumoral hemorrhage, or active secretion from tumor cells.^9,10 Most cyst walls have shown contrast enhancement on MRI, ⁶ unlike our case. Interestingly, neoplastic cells were identified within the cyst wall irrespective of the presence of cyst wall enhancement. ⁶ Therefore, gross total resection of the tumor including cystic component is recommended as long as technically possible. ⁶ The identification of vascular entrapment might be useful to diagnose cystic meningioma at the CPA. Mechanical trapping of CSF has been assumed to result in the formation of the cystic component.^6,10 A hypointense tubular structure in the cystic component on the heavily T2-weighted 3D DRIVE sequence could be one of the key imaging features.

Differential diagnoses include vestibular/facial nerve schwannoma, epidermoid/dermoid cyst, arachnoid cyst, neurenteric cyst, or collision tumor. The presence of calcification close to petrous bone in combination with the patient’s age and gender indicates a greater likelihood of meningioma. Collision tumor comprising meningioma and neurenteric cyst would be considered a differential diagnosis given the signal intensities of the cystic component in this case. However, neurenteric cysts are typically midline and anterior to the brainstem. ¹¹

In conclusion, we have here reported a case of cystic meningioma at the left CPA. MRI demonstrated unusual, potentially characteristic findings such as signal intensities in cystic components differing from CSF, cyst wall enhancement, and vascular entrapment.

ORCID iD

Koji Yamashita https://orcid.org/0000-0002-7417-739X