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Schwannomas are relatively rare and are typically slow growing. They constitute approximately 1% of all intraorbital tumours. They typically originate from the intraorbital divisions of trigeminal V1, although other sensory nerves can be involved.
We present a case of a fast-growing schwannoma in a 6-year-old male who presented with a progressive unilateral proptosis and rapidly compressive optic neuropathy secondary to a tumour of the inferior oblique branch of the inferior division of the oculomotor nerve.
An otherwise healthy 6-year-old male of Asian descent presented to the ER with a 1- to 2-month history of unilateral right-sided proptosis. There was no report of visual changes, diplopia, or an ocular deviation noticed by the mother. Visual acuity was measured at 20/25 OD and 20/20 OS with intraocular pressure of 18 and 19, respectively. Extra ocular movements (EOMs) were full bilaterally. Exophthalmometry demonstrated unilateral proptosis, with a measurement of 16 mm OD and 14 mm OS. There was a right relative afferent pupillary defect measuring 0.9 log units; the pupils were otherwise normal. Fundoscopy demonstrated circumferential disc swelling on the right and a healthy and normal optic nerve head on the left with a cup-to-disc ratio of 0.1. Magnetic resonance imaging (MRI) and follow-up were organized.
Two weeks later, he presented again with what his mother indicated was a severe drop in visual acuity and worsening proptosis. Visual acuity was reduced to 20/60 OD, and proptosis was increased by 2 mm OD. Fundoscopy on the right demonstrated the previously seen disc edema and new retinal vessel tortuosity. MRI showed a homogenously T1 intermediate hypointense and heterogeneously T2 hyperintense lesion with postcontrast enhancement of a 28 × 22 × 16 mm intraconal mass with posterior globe indentation (Figs. 1A, 1B, and 1C). The mass did not appear to extend intracranially and did not appear to involve the optic nerve.
Fig. 1(A) Coronal T2 hyperintense enhancing mass. (B) Axial T1 hypointense enhancing mass. (C) Axial T1 image demonstrating ocular axial displacement of the right globe.
Computed tomography (CT) imaging was done to aid in surgical planning and to evaluate for bony changes to aid diagnosis. CT imaging demonstrated an intraconal well-circumscribed ovoid homogenous-appearing lesion of approximately 2.4 × 2.1 × 2.4 cm with displacement of the optic nerve superiorly over the mass. There was evidence of medial wall remodeling, which radiologically suggested chronicity. Despite the CT findings suggesting a chronic lesion, an urgent lateral orbitotomy was performed to remove the lesion.
The diagnosis of schwannoma was made with compact areas of Antoni A pattern and small areas of loosely arranged foci of Antoni B; the tumour was S-100 positive and neurofilament protein negative. Ki67 staining was positive in <10% of cells (Figs. 2A and 2B). Neither the radiology reports nor the pathology reports indicated that the lesion had cystic components. On 1-month follow-up the patient was 20/100 OD and unable to fully elevate or depress the eye with an Exotropia (XT) of 20Δ and a fully mydriatic pupil showing no direct or consensual response. Three-month follow-up demonstrated improved visual acuity of 20/60 with pinhole to 20/40, with slightly limited elevation and full depression with less XT of 16Δ. Six-month follow-up demonstrated improved visual acuity to 20/40 without pinhole, and no horizontal deviations were noted. EOMs were full except for an inability to fully elevate the right eye in adduction with a left hypertropia of 10Δ. The patient's binocularity was measured at 63 arcsec, and his right pupil remained mydriatic. Patching was prescribed. On 12-month follow-up his best corrected visual acuity was 20/30 OD. He remains mydriatic and demonstrates an inability to fully elevate the right eye in adduction (Fig. 3). Glasses were prescribed with 4 base in prism bilaterally, and patching for his amblyopia was continued.
Fig. 2(A) Histopathologic slide of an hematoxylin and eosin stain demonstrating compact areas of Antoni A and loose areas of Antoni B cellular organization. (B) S100-positive stain.
Schwannoma is a benign abnormal proliferation of Schwann cells with a capsule and has a predilection for sensory nerves in the orbit, most commonly involving the supratrochlear or supraorbital nerves.
although there were no signs of neurofibromatosis in our patient. When considering schwannoma as a diagnosis, compatible CT features include a well-demarcated hypo- or isodense homogenous lesion with no bony invasion or muscle infiltration and the presence of bony remodeling. MRI characteristics include T1 hypointensity and T2 hyperintensity, and most will enhance with contrast, although there have been reports of cystic nonenhancing masses. Rapidly expanding atypical presentations of schwannomas have been documented in adults, and it is thought that the expansion may be due to cystic changes.
MRI T2 signal is bright, and in later disease there may be regional lymph node involvement. Histopathology in schwannoma demonstrates clear areas of Antoni A or B organization and small Ki67 aggregation, and it is S100+. All these findings were consistent with our case, except for the speed with which proptosis and optic neuropathy progressed.
On the most recent follow-up, our patient was unable to fully elevate in adduction and has persistent mydriasis. This localizes the affected nerve to the inferior oblique, which is responsible for elevation in adduction and for providing branches of the parasympathetic efferent innervation of the pupil to the ciliary ganglion. Oculomotor schwannoma is uncommon, and to our knowledge there are only 40 case reports, with 13 documented pediatric cases not associated with neurofibromatosis type 2 and only 1 case report of an inferior oblique origin in a pediatric population reported before our current case.
Proptosis is not an uncommon presentation in pediatric populations. We present a rare pediatric case of rapid clinical presentation of proptosis and compressive optic neuropathy secondary to an intraconal schwannoma originating from the inferior oblique branch of the inferior division of the oculomotor nerve with a good surgical outcome and preservation of visual acuity.
Footnotes and Disclosure
The authors have no proprietary or commercial interest in any materials discussed in this article.
References
Khan S.N.
Sepahdari A.R.
Orbital masses: CT and MRI of common vascular lesions, benign tumors, and malignancies.
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