Intraparotid Facial Nerve Schwannoma: An Enigma for Surgeons

ABSTRACT

Intraparotid schwannoma is a peripheral nerve sheath tumor arising from the facial nerve. Because of their rarity, surgeons always confront with diagnostic dilemmas. Since it is frequently diagnosed in the younger age group, surgical management is quite challenging. Meticulous dissection of the facial nerve during the surgery is of utmost importance. We report a case of 10-year-old boy with parotid swelling, who underwent superficial parotidectomy in our center. The final histology showed intraparotid schwannomma.

INTRODUCTION

Schwannomas are commonly diagnosed peripheral nerve sheath tumors, generally benign and well-circumscribed.[1] Facial nerve schwannomas are typically painless and slow-growing, with 9% located intraparotid. They account for 0.5%–1.2% of all parotid gland tumors.[2] Due to their rarity and similarity to other benign parotid tumors, diagnosing intraparotid schwannomas is challenging. Accurate diagnosis is crucial to prevent mismanagement. Recent reviews have analyzed 87 studies, documenting 275 cases.[3]

CASE REPORT

A 9-year-old patient presented with a 1-year history of a painless, slowly growing mass in the right preauricular region, without associated symptoms such as pain or facial nerve paresis. [Figure 1]. Examination revealed a firm 4 cm × 4 cm mass in the right parotid region, with no facial nerve weakness. Fine-needle aspiration cytology (FNAC) was inconclusive. Magnetic resonance imaging (MRI) showed a benign parotid tumor, 3.1 cm × 2.6 cm × 2.2 cm, with a lobulated hyperintense lesion and cystic areas, confined to the superficial lobe.

Figure 1.

Parotid swelling

The patient underwent superficial parotidectomy through a lazy S incision. A sub-superficial musculoaponeurotic system flap was used, and the tumor was dissected from all five branches of the facial nerve [Figure 2]. Postoperatively, the patient developed mild facial nerve weakness (HB Grade III). Histopathology confirmed schwannoma, characterized by a hypocellular tumor with spindle cells and Verocay bodies [Figures 3 and 4]. The tumor was benign, and no adjuvant therapy was needed.[4]

Figure 2.

Intraoperative image after excision of the tumors, with intact facial nerve branches

Figure 3.

Salivary gland (left) with adjacent circumscribed tumor. H and E, ×100

Figure 4.

Spindle cells with nuclear palisading (Verocay bodies) characteristic of schwannoma. H and E, ×100

DISCUSSION

Intraparotid schwannomas mimic other benign parotid tumors, making diagnosis difficult. Radiologically schwannomas lack any pathognomonic features although the study by Shimizu et al. states that 3 out of 5 lesions exhibit a target-like appearance with a peripheral increased signal intensity and central decreased signal intensity on T2-weighted MR images.[5] The findings in MRI in various included studies showed the tumor mass located below stylomastoid foramen produce characteristic “string sign” which is formed due to vertical orientation of soft tissue on either side of the mass. The string is actually a representation of the entering and exiting nerve that is in continuity with the nerve sheath tumor.

Ultrasonography-guided FNAC although one of the first diagnostic tools to be used in case of parotid swelling is of limited accuracy when it comes to diagnosing schwannomas with only 17.6% of the cases with an accurate diagnosis.[6]

Intraoperative presentation of schwannomas is also varied, with some being easily separated from the nerve while most being coherent to the nerve. The gross appearance of the tumor does not differ significantly from other parotid tumors; however, a characteristic feature is difficulty in identifying the main trunk.[7]

Marchioni et al. proposed a classification of intraparotid schwannomas based on anatomical and pathological evaluation. Type A included those which could be safely dissected from the tumor, Type B includes those which lead to the partial sacrifice of the facial nerve involving one of the peripheral branches, Type C includes the sacrifice of the main trunk, whereas Type D required sacrifice of the facial nerve involving the main trunk and at least one of the temporofacial or cervicofacial branches.[8]

The management of intraparotid schwannoma is a topic of debate for the last two decades. Some authors advocate surgical management, whereas others support “wait-and-watch” approach for cases with minimal or no facial nerve dysfunction and no intratemporal extension.[4]

CONCLUSION

There are no established guidelines for the management of pediatric intraparotid schwanomma. However, to prevent misdiagnosis and inappropriate treatment, we advise meticulous parotidectomy with excision of the tumor.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal patient identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.