Abstract

Background: Orbital schwannomas arising from the frontal nerve are a rare but distinct entity.

Case Description: A 16-year-old girl presented to our hospital with gradually progressive proptosis. Computed tomography (CT) performed 2 years ago incidentally detected a retrobulbar mass in the left orbit measuring 13 mm × 14 mm × 10 mm, which was not identified on CT performed at the age of 4 years. CT taken at presentation revealed marked tumor growth over 2 years, measuring 24 mm × 20 mm × 17 mm. On magnetic resonance imaging (MRI), the tumor appeared homogeneously isointense both on the T1- and T2-weighted sequences. The patient underwent transcranial tumor resection. Following unilateral frontal craniotomy, an osteotomy was made to the left anterior fossa floor. On reflecting, the periorbita revealed the frontal nerve with the proximal segment intermingled with the tumor. The levator and superior rectus muscles were flattened and located immediately beneath the tumor. A gross total resection was performed. Microscopic findings of the resected tumor were consistent with schwannoma.

Conclusion: Frontal nerve schwannomas may grow rapidly under certain conditions. Periodic follow-up using MRI and timely resection is recommended when an asymptomatic orbital tumor, possibly a frontal nerve schwannoma, is detected in young patients.

Keywords: Frontal nerve, Orbital tumor, Schwannoma, Transcranial approach

INTRODUCTION

Peripheral nerve sheath tumors of the orbit and ocular adnexa are a distinct group of neoplasms characterized by nonspecific clinical presentations, variable tumor locations, challenging therapeutic efforts, and occasional diagnostic dilemmas.[ 12 ] Among these tumors, 50% are estimated to originate from the frontal nerve.[ 16 ] However, schwannomas arising from the nerve and its orbital tributaries have been rarely reported.[ 2 , 3 , 6 , 7 , 13 , 14 , 17 ]

The frontal nerve is an orbital branch of the first trigeminal division.[ 4 , 11 ] It commonly courses in the posteroanterior direction in the orbital cavity, maintaining a superficial location on the upper surface of the levator palpebral superioris muscle just beneath the periorbita [ Figure 1 ]. The nerve divides more or less rapidly into the supraorbital and supratrochlear nerves. Due to its characteristic location and course, the nerve can be a useful landmark for transcranial orbital surgeries.[ 10 ] Transcranial approaches are thought to be a safe and reliable means for the resection of many orbital tumors, especially when they are located in the anterior, posterolateral, and superior compartments of the orbit.[ 1 , 5 , 8 ]

Figure 1:

Superolateral and posterior view of a dissected left orbit, after removing the (a) superior and lateral walls and (b) fat tisue, show the frontal nerve consistently coursing on the upper surface of the levator muscle, just beneath the periorbita (arrows). LG: Lacrimal gland, LM: Levator palpebral superioris muscle, LN: Lacrimal nerve, SObM: Superior oblique muscle, SRM: Superior rectus muscle. The dissection was performed by one of the authors (S.T.).

Herein, we report a case of frontal nerve schwannoma in an adolescent girl that rapidly grew over 2 years and was resected through the transcranial route.

CASE PRESENTATION

A 16-year-old previously healthy girl presented to the hospital with gradually progressing, painless proptosis for 1 year. Her medical history was unremarkable, and she had not undergone any prior orbital surgery. Computed tomography (CT) performed at the age of 4 years for an accidental simple head injury did not reveal any abnormal findings in the left orbit [ Figures 2a and b ]. However, CT performed at the age of 14 years for an accidental facial injury incidentally detected a retrobulbar mass in the left superior orbit measuring 13 mm × 14 mm × 10 mm [ Figures 2c - e ]. At that time, the patient did not present with any symptoms associated with the lesion and was observed without periodic radiological evaluation. At the current presentation, she exhibited considerable left proptosis and moderate restriction in upward gaze. An ophthalmological examination did not show any visual impairment. CT performed at this time revealed an oval-shaped tumor in the left superior orbit measuring 24 mm × 20 mm × 17 mm, indicating marked tumor growth for the last 2 years. No intralesional calcifications or hemorrhagic changes were observed. Post-contrast images showed a slight enhancement of the tumor. The ophthalmic artery and its branches were found to course along the lower surface of the tumor [ Figure 3 ]. On magnetic resonance imaging (MRI), the tumor was well-circumscribed, appearing homogeneously isointense on both T1- and T2-weighted images. Intralesional cysts were not found. The T2-weighted sequence showed a hypointense, linear structure surrounding the inferior and medial surfaces of the orbital tumor. Due to the mass effect of the tumor, the left optic nerve (ON) was considerably displaced downward [ Figure 4 ]. The patient rejected a contrast-enhanced MRI examination, and it was not performed. The patient underwent transcranial tumor resection. Following a left frontal craniotomy, the frontal lobe was epidurally elevated [ Figure 5a ]. Next, an osteotomy was made to the left anterior fossa floor, which exposed the offending tumor located immediately beneath the periorbita [ Figure 5b ]. Reflection of the periorbita exposed the proximal segment of the frontal nerve intermingled with the tumor [ Figure 5c ]. The tumor encapsulated and consistently elastically hard, was circumferentially dissected from the surrounding tissues [ Figure 5d ]. The levator palpebral superioris and superior rectus muscles (SRMs) were flattened and located immediately beneath the tumor. A gross total resection was achieved using an intracapsular debulking maneuver. The microscopic findings of the resected specimens were consistent with Antoni type A schwannoma, comprising oval- or fusiform-shaped tumor cells arranged in palisading patterns [ Figure 6 ]. Postoperatively, hypoesthesia was present in the left forehead that showed a remarkable amelioration over the next 6 weeks. Upward gaze restriction showed gradual improvement over the next 3 weeks. Non-contrast MRI performed on postoperative day 18 demonstrated restoration of the ocular position and distinguishable extraocular muscles in the left orbit [ Figure 7 ].

Figure 2:

(a and b) Non-contrast axial computed tomography scans taken at the age of 4 years do not show any lesion in the left superior orbit. (c-e) Non-contrast (c) axial, (d) coronal, and (e) sagittal computed tomography scans taken at the age of 14 years show a small retrobulbar mass in the left superior orbit, measuring 13 mm × 14 mm × 10 mm (asterisk) ON: Optic nerve.

Figure 3:

Non-contrast (a) axial, (b) coronal, and (c) sagittal computed tomography scans taken at the presentation show an oval-shaped tumor in the left superior orbit, measuring 24 mm × 20 mm × 17 mm, indicating a marked tumor growth for recent 2 years. Intralesional calcifications or hemorrhagic changes are not found. (d-f) Post-contrast coronal computed tomography performed at the presentation, at the levels of the (d) orbital apex, (e) maximal dimension of the tumor, and (f) anterior ethmoidal foramen, show the ophthalmic artery and its branches (arrows) coursing along the lower surface of the tumor (asterisk), in addition to slight enhancement of the lesion, ON: Optic nerve, Dashed arrow: Anterior ethmoidal artery.

Figure 4:

Coronal (a) T1- and (b) T2-weighted magnetic resonance imaging show a well circumscribed tumor in the left orbit appearing homogeneously isointensity on both sequences (asterisk). On T2-weighted imaging, a hypointense, linear structure surrounding the inferior and medial surfaces of the tumor is noted (b, arrows). The left optic nerve shows a considerable downward displacement ON: Optic nerve.

Figure 5:

Intraoperative photos showing the procedures in a step-by-step manner. (a) Epidural elevation of the frontal lobe exposed the left anterior fossa floor (asterisk). (b) Making a microsurgical osteotomy to the left floor revealed the offending tumor located immediately beneath the periorbita. (c) Reflection of the periorbita exposed the frontal nerve with the proximal segment intermingled with the tumor (arrows). (d) The tumor was circumferentially dissected from the surrounding tissues with the frontal nerve (arrows). T: Tumor.

Figure 6:

Photomicrographs of the resected specimens showing oval- or fusiform-shaped tumor cells arranged in palisading patterns (arrows) with fibrous interstitial tissues. The inset shows a magnified view. Cell atypia or mitotic figures are not found. Hematoxylin and eosin staining, ×40; inset, ×200.

Figure 7:

(a) Axial and (b) coronal T2-weighted magnetic resonance imaging performed on postoperative day 18 demonstrates restoration of the ocular position and distinguishable extraocular muscles on the left orbit. LM: Levator palpebral superioris muscle, SObM: Superior oblique muscle, SRM: Superior rectus muscle.

DISCUSSION

Orbital schwannomas most frequently affect middle-aged individuals and arise from the frontal nerves.[ 16 ] Such schwannomas can exhibit variable neuroimaging appearances, necessitating to assume of schwannoma for any masses found in the superior orbit.[ 17 ] The present tumor showed homogeneous intensity on MRI, a less common appearance for schwannomas.[ 17 ] In contrast, T2-weighted imaging found a hypointense structure along the inferior and medial surfaces of the tumor, suggesting tumor compression to the extraocular muscles. Then, the tumor was thought to be located superior to the levator palpebral superioris and SRMs, with a possible diagnosis of frontal nerve schwannoma. Intraoperative findings were consistent with a schwannoma arising from the frontal nerve.

Frontal nerve schwannomas can be approached through a superior orbitotomy, lateral orbitotomy, craniotomy, or their combinations.[ 4 , 6 , 14 , 17 ] In the present case, unilateral frontal craniotomy combined with a superior orbitotomy provided a satisfactory view for microsurgical tumor resection. Hassler and Schick reported that the supraorbital approach, a combination of superior orbitotomy and frontal craniotomy, is useful for resecting lesions located superior to the ON.[ 5 ] Furthermore, Mourier et al. proposed that conventional lateral orbitotomy does not allow a satisfactory view of the superior part of the orbit, in addition to a rather narrow surgical field.[ 9 ] In most cases, the transcranial route can provide an adequate window for the resection of frontal nerve schwannomas. In cases where tumors are located in the anterosuperior orbit, a minimally invasive transorbital (transpalpebral) endoscopic approach can be a useful means.[ 2 ]

Schwannomas are benign peripheral nerve sheath tumors with common indolent growth. However, the present tumor showed unusually rapid growth over 2 years. Vahdani et al. reported an atypical orbital schwannoma in a 12-year-old patient without neurofibromatosis who presented with unusually rapid growth for 5 months. The tumor did not show any evidence of cystic degeneration, hemorrhage, or sarcomatous features.[ 15 ] The authors speculated that a prior biopsy might have accelerated tumor growth. Our patient had not undergone any prior orbital surgery. Under certain circumstances, benign schwannomas may grow rapidly. Hence, periodic follow-ups with MRI and timely surgical resection are recommended when an asymptomatic orbital tumor, possibly a frontal nerve schwannoma, is detected in young patients.

CONCLUSION

Frontal nerve schwannomas may grow rapidly under certain conditions. Periodic follow-up using MRI and timely resection is recommended when an asymptomatic orbital tumor, possibly a frontal nerve schwannoma, is detected in young patients.

Ethical approval

The Institutional Review Board approval is not required.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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