Fusiform appearance of optic nerve sheath meningioma: Correlating clinical and imaging findings.

Introduction

Orbital optic nerve meningiomas (ONSMs) arise from the cap cells of the arachnoid round the intraorbital portion of the optic nerve.[1]

Diagnosis of ONSM is primarily based on imaging findings. Magnetic resonance imaging has become the gold standard for visualization of ONSMs.[2]

A number of radiographic growth patterns have been described: Tubular, globular, fusiform, and focal.

Case Report

A 72-year-old woman presented to the consulting room with the complaint of proptosis in the left eye. The patient referred that proptosis was initially observed several years ago [Figure 1].

Figure 1

(a) Clinical photograph of the patient showing noticeable proptosis of the left eyeball (black arrows) (b) Clinical photograph of the same patient (superior view)

Visual acuity examination was performed on both eyes (Snellen optotype at 6 m distance) and yielded 20/25 with correction of +0.50 D sphere in the right eye and 20/25 with correction of +1.75 D sphere in the left eye. Color perception found to be normal.

Anterior segment examination for both eyes did not show any severe pathology. Fundoscopic examination did not reveal edema or atrophy of the optic disc.

Standard visual field examination was performed in the patient twice and showed peripheral scotoma in the left eye [Figure 2].

Figure 2

Visual fields examination of the left eye demonstrating an extended area of reduced sensitivity. Note that the lesion affects mostly the inferior and temporal part of the visual field

Magnetic resonance imaging (MRI) study of the orbital cavities was ordered. In the MRI protocol T2, T2 with fat saturation, T1, T1 with fat saturation sequences, pre- and post-gadolinium injection on three different planes (axial, sagittal, and coronal) were performed. A fusiform mass of 3.4 cm was demonstrated in the left orbit. The mass appeared as hypointense to brain and optic nerve tissue on T1-weighted images and slightly hyperintense on T2-weighted images. There was no intracranial extension of the lesion or any sign of neighboring structure invasion [Figure 3].

Figure 3

(a) Axial MRI image (T1 with fat saturation). Note the spindle-like tumor of the left optic nerve that caused the proptosis (yellow arrows) (b) Axial MRI image (T2 with fat saturation) demonstrating a well defined retro bulbar mass in the left orbital cavity. Note that there is no sign of intracranial extension and that the optic nerve is masked by the lesion (red arrows) (c) Coronal MRI image showing a slightly difference of signal intension between orbital cavities (green arrows)

The benign noninvading growth pattern and the relatively steady clinical appearance corroborated the possibility of meningioma, and as a consequence diagnosis of optic nerve sheath meningioma was suggested.

After completing the examinations, the therapeutic strategy suggested to the patient by ophthalmologists and neurosurgeons included a systematic follow-up every 6 months in view of the fact that visual performance remained stable for a certain number of years.

Discussion

These tumors are not related with any mortality or major neurological morbidity. The most vital manifestation of ONSMs, when untreated, is nearly at all times monocular visual deterioration. Therefore, treatment of ONSM has, in general, been considered apart from cases in which the progression of visual loss is insignificant.

Management of ONSMs has involved observation without treatment, mostly in cases of high functional vision or negligible visual decline. In such cases, a clinical examination, including assessment of visual acuity, color vision, and visual fields, should be conducted twice a year for 2 to 3 years, then once a year if the patient's visual function has remained stable.[3]

Due to technical complexities and tendency in the direction of postoperative blindness, surgery for ONSM has been replaced by radiation therapy which is now recognized as the most appropriate vision-preserving therapy for the management of ONSM in nondiabetic patients with progressive visual loss.[4] In specific, the short- and long-term efficacy of stereotactic fractionated radio therapy in preserving or improving vision came out to be exceptional.[5]

In the case presented, procedures such as biopsy or surgery were considered pointless, while patient's age was reasonably advanced and the danger of potential injure to the optic nerve considered elevated.