An Atypical Paediatric Optic Nerve Sheath Meningioma

ABSTRACT

A 16-year-old male presented with a three year history of right proptosis. All other ocular findings were normal. Imaging demonstrated a large, calcified, contrast-enhancing mass in the apical orbit. The tumour had high gallium-68-DOTATATE uptake and low 18F-2-fluoro-2-deoxy-D-glucose uptake. An incisional biopsy revealed a diagnosis of psammomatous optic nerve sheath meningioma (ONSM). One year later stereotactic radiotherapy was performed due to tumour growth. Tumour size and visual acuity remained stable in the six months after treatment. This case differs from previously reported paediatric ONSMs by its histo-clinical characteristics (exophytic-calcified mass, visual preservation, psammomatous histology).

Introduction

Optic nerve sheath meningiomas (ONSM) originate from arachnoidal (meningothelial) cells and occur frequently in women in the 3rd-5th decades of life.¹ Paediatric ONSMs are very rare and, unlike the adult type, have a high rate of association with neurofibromatosis type 2 (NF-2), rapid growth, and poor visual prognosis.² In both age groups, the diagnosis is often made by the combination of typical clinical and radiological findings. Herein, an unusual case of a paediatric primary ONSM diagnosed by biopsy is presented together with the relevant literature.

Case report

A 16-year-old male presented with a three year history of right proptosis (Figure 1). The patient’s medical history was unremarkable. He had an 8 mm proptosis in the right eye on exophthalmometry. Visual acuity was 1.0 in both eyes. There was no afferent pupillary defect. His colour vision, visual field tests and funduscopic findings were within normal limits. The extraocular eye movements were full in all directions with no complaints of diplopia. A paediatric consultation showed no findings of NF or any other extraocular abnormality.

Figure 1.

(a) and (b). A 16-year-old male presenting with right proptosis

Magnetic resonance imaging (MRI) showed a homogenous contrast-enhancing, oval mass of 18 × 18 mm diameter in the apical orbit (Figure 2). The lesion was located above and partially surrounding the optic nerve and did not extend intracranially. On non-enhanced computed tomography (CT) performed 19 months previously, the lesion was the same size and was densely calcified (Figure 3). There was a slight medial bowing of the adjacent medial orbital wall due to possible pressure erosion. Positron emission MRI demonstrated high gallium-68-DOTATATE uptake and low 18F-2-fluoro-2-deoxy-D-glucose (FDG) uptake in the tumour (Figure 4).

Figure 2.

Magnetic resonance imaging showing a large tumour arising from the right optic nerve and growing superiorly in an exophytic pattern. The lesion is prominently hypointense on the axial T2-weighted (a) and isointense to the muscles on the axial T1-weighted (b) images. On contrast-enhanced, fat suppressed T1-weighted axial (c) and coronal (d) images, there is avid enhancement of the lesion that is partially surrounding and overlying the right optic nerve (arrow)

Figure 3.

Non-enhanced axial (a) and coronal (b) computerised tomography scans showing a densely calcified intraconal mass in the right orbit

Figure 4.

Tumour demonstrates high gallium-68-DOTATATE uptake on radionuclide imaging

He had previously undergone a frontal cranio-orbitotomy elsewhere, but the lesion could not be reached. During an incisional biopsy via a lateral orbitotomy, the lesion was grey-pink coloured, densely vascularised, and firmly adherent to the surrounding tissues. An immuno-histological examination revealed a neoplasm consisting of uniform nuclei, spindle-shaped cells with dense psammomic bodies, typical parallel ‘whorl’ structures and perivascular alignment, showing anisocytosis and anisocaryosis. The appearances were consistent with a psammomatous-type meningioma (Figure 5).

Figure 5.

Tumour consisting of spindle cells (black arrow) and dense psammoma bodies (white arrows) (Haematoxylin-eosin x 40)

One year later, radiologically, the tumour diameter increased to 19.9 × 22 mm. His visual acuity was still 1.0. The patient received a total of 25 Gray fractionated stereotactic radiotherapy (RT). During the six-month follow-up period, visual findings and the radiological tumour size remained stable. The patient could not be followed up after six months because he returned to his home country.

Discussion

In a series of 250 consecutive paediatric orbital masses with biopsy, the rate of ONSM was 0.4%.³ Narayan et al. reviewed a total of 78 patients, together with their patients, who were reported in the English literature by 2017.⁴ According to the available data, the mean patient age was 9.5 years (range, 4–18 years), the female ratio was 61.5%, and 39.6% of cases (n = 23/58 patients) were associated with NF-2. The most common symptoms and signs were decreased vision (87%), optic disc oedema or atrophy (85%), proptosis (71%), ocular dysmotility (60%). The intracranial extension rate was 27% (n = 12/44 patients). In the current case, the only presenting symptom was proptosis.

Magnetic resonance and/or CT imaging is diagnostic in most cases of ONSM.¹ The tumour typically appears as iso-hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, although calcification can cause the tumours to be hypointense on T2-weighted inaging.

Tumour cells proliferate in the arachnoid space and the nerve sheath remains intact around the tumour. Accordingly, most ONSMs in all ages (74%) show a tubular or fusiform growth pattern, affecting pial vessel blood flow and axonal flow, leading to optic neuropathy.¹ In the current case, the ONSM was exophytic and globular. Tumour calcification was observed in 31% of ONSMs in one study and might be a sign of slow growth and indicate relatively good visual prognosis.⁵ In our patient, extraordinarily, the entire tumour had calcified. Histological type has not been specified in most previous paediatric ONSMs.⁴ In a study in which 13 paediatric ONSMs were classified according to the WHO criteria, 12 tumours (92%) were transitional or meningothelial type, and only 1 tumour (12%) was psammomatous.² Psammomatous meningiomas are characterised by being heavily calcified. To our knowledge, this is the first psammomatous paediatric primary ONSM reported with detailed clinical features.

The current case supports that ONSMs can demonstrate high gallium-68-DOTATATE uptake, which may help in diagnosis.⁶ FDG uptake of meningiomas may vary widely with respect to glucose metabolism and the proliferative activity of the tumour.⁷

Paediatric ONSMs may have a more aggressive course than adult ONSMs and may spread more frequently into the cranial cavity.^2,4 Visual status, tumour spread, and clinical behaviour are taken into consideration when deciding treatment. Treatment options include surgical excision and/or RT. For adult ONSMs, RT is the first treatment option in most cases, and although it does not reduce the tumuor size, it may preserve vision. Experience with RT in paediatric ONSMs is limited. It has been reported in a total of 12 patients including the present case, and most had no or short follow-up periods after RT.^2,4,8,9 The total radiation doses used were around 50 Gray, well above the ocular toxicity thresholds.^2,4,10 Radiation-related complications (e.g. secondary sarcomas, leukaemia, meningioma, hormonal insufficiency, and leukoencephalopathy) may occur more frequently in children. In aggressive tumours with vision loss, surgical excision may be a better choice for preventing tumour recurrence and for avoiding the possible complications of RT.

Declaration of interest statement

The authors have no conflict of interest.