|Year : 2020 | Volume
| Issue : 4 | Page : 277-279
Facial palsy due to intraparotid schwannoma invading the stylomastoid foramen
Mehtab Alam, Sabeeh Beig, Kamlesh Chandra, Humra Shamim
Department of Otorhinolaryngology, Faculty of Medicine, AMU, Aligarh, Uttar Pradesh, India
|Date of Submission||10-Jun-2020|
|Date of Decision||13-Jul-2020|
|Date of Acceptance||21-Jul-2020|
|Date of Web Publication||23-Apr-2021|
Dr. Mehtab Alam
Department of Otorhinolaryngology, Faculty of Medicine, AMU, Aligarh, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Intraparotid facial nerve schwannomas are rare and facial palsy because of them is even rarer. They should be kept in the differential diagnosis of parotid swellings, though preoperatively they are difficult to diagnose. We herein report a case of 30-year-old female who presented with left-sided massive preauricular swelling with facial nerve palsy, on computed tomography, there was invasion and widening of the stylomastoid foramen. This mass was diagnosed as pleomorphic adenoma on fine-needle aspiration cytology and came out to be schwannoma on histopathological examination.
Keywords: Facial palsy, histopathological examination, intraparotid schwannoma, stylomastoid foramen invasion
|How to cite this article:|
Alam M, Beig S, Chandra K, Shamim H. Facial palsy due to intraparotid schwannoma invading the stylomastoid foramen. Indian J Otol 2020;26:277-9
| Introduction|| |
Schwannomas are benign encapsulated tumors arising from abnormally proliferative Schwann cells. Although facial nerve schwannomas are rare, majority of them involve a temporal portion of the nerve and only around 9% involve the extratemporal region.
Patients usually present with an asymptomatic slow-growing parotid mass, which is usually confused with the pleomorphic adenoma. Because the tumor develops in the nerve sheath, it compresses rather than invades the nerve, so involvement of the facial nerve, a feature associated with malignancies, is seen in only around 20% cases of facial nerve schwannomas. To make a preoperative diagnosis of intraparotid schwannoma is very difficult, though suspicion can arise intraoperatively, which is confirmed on histopathology. Surgery is a treatment modality of choice with a few postoperative morbidities and low recurrence rates.
| Case Report|| |
A 30-year-old female presented with a swelling in the left preauricular region for the past 2 years. She was also complaining of left-sided facial weakness, inability to close the left eye, and deviation of angle of the mouth toward the right for the past 3 months. The swelling gradually increased in size without any pain or fever; also there was no history of weight loss, restriction of jaw movement, ear discharge, and decreased hearing. She was on oral hypoglycemic for the past 8 months with a controlled blood sugar level. Clinical examination of the swelling revealed a single globular swelling approximately 7 cm × 7 cm, with a smooth surface and well-defined margins [Figure 1]. The swelling was firm to hard in consistency, a mobile without any signs of erythema and ecchymosis. The patient had left-sided House-Brackmann Grade IV lower motor neuron facial palsy [Figure 2]. The contrast-enhanced computed tomography (CECT) of the head and neck showed a heterogeneously enhancing soft-tissue lesion involving both lobes of the left parotid gland. Medially, the lesion was abutting carotid sheath with >180° of arc of contact with the carotid artery; also there was a loss of normal fat and abnormal enhancement in stylomastoid foramen suggestive of invasion and widening [Figure 3]. CECT gave the impression of three differentials, pleomorphic adenoma, malignant transformation within pleomorphic adenoma (carcinoma ex pleomorphic adenoma) and mucoepidermoid carcinoma. Fine-needle aspiration cytology (FNAC) was performed, which came out to be suggestive of pleomorphic adenoma. Keeping in view of clinical, radiological and cytological profiles, we planned for left-sided total parotidectomy with preauricular lazy-S incision extending up to upper neck skin crease.
|Figure 3: Computed tomogram (contrast-enhanced computed tomography) showing left-sided parotid mass with >180° of arc of contact with the carotid artery, and invasion and widening of the stylomastoid foramen|
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Surgically, this was a challenging case as the lesion was close to the major vessels. Intra-operatively surprisingly, the tumor was seen to be arising from the main trunk of the facial nerve and invading into the stylomastoid foramen. The mass was well encapsulated with normal adjoining parotid tissue and was removed in Toto and sent for histopathological examination [Figure 4]. Histopathology showed encapsulated hypercellular and hypocellular areas with palisading of spindle cells along with thick hyalinised vessels and myxoid changes, thus giving an impression of Schwannoma [Figure 5]. Postoperative recovery of the patient was good with no further deterioration in the facial nerve palsy.
Written and informed consent was taken from the patient for publishing the images related to the case report.
| Discussion|| |
Schwannomas are rare benign, slow-growing, encapsulated tumors that arise from Schwann cells. Till now, only around 100 cases of intraparotid facial nerve schwannomas had been reported in the literature, though its first description was given in 1927. Preoperative diagnosis of intraparotid facial nerve schwannoma is difficult due to its rarity and absence of typical clinical and radiological features. In a study of 3722 diagnosed cases of schwannomas, only 29 cases of facial schwannoma were found, and out of these, only eight arose from intraparotid portion of the facial nerve. In another study, there were only seven cases of facial schwannoma out of 113 patients of nerve sheath tumors of the head-and-neck region.
Although the tumor arises from the facial nerve, but in majority of the cases there is no involvement of the nerve, and the most common presenting feature is an asymptomatic mobile parotid swelling mimicking a pleomorphic adenoma. The clinical presentation can be variable, from an asymptomatic mass to a painful parotid mass with facial nerve dysfunction, so it is difficult to make a diagnosis of schwannoma preoperatively. On computed tomography scan a smooth, sharply circumscribed lesion is seen within the parotid substance. FNAC in majority of the cases, is nonspecific and may go in favor of pleomorphic adenoma, or a malignant mass. Histopathological examination is diagnostic revealing two histological patterns: Antoni A and Antoni B, Antoni A regions are compact and cellular, with elongated spindle cells and whorling or palisading nuclei aligned in rows (Verocay bodies). Antoni type B histology is loose and much less cellular, with a spongy appearance.
Treatment of intraparotid schwanomma is surgical excision. Intra-operatively if the tumor seems to be adherent to the facial nerve, frozen section examination should be done to rule out malignancy. The involvement of the main trunk of the facial nerve usually results in unsatisfactory outcomes; thus, the surgery should be aimed at the preservation of the facial nerve functions as much as possible.
In this case, preoperatively we were not thinking of facial nerve schwannoma as both CECT and FNAC were suggestive of pleomorphic adenoma, intra-operatively when the mass was seen to be arising from the main trunk of the facial nerve, then we thought of the neural origin of this tumor which was confirmed as schwannoma on histopathology.
| Conclusion|| |
Intraparotid facial nerve schwannomas are rare and only a few of them will cause facial palsy. It is extremely rare to have an invasion of the stylomastoid foramen by facial nerve schwannomas arising from the extra-temporal portion of the nerve. They should be kept in the differential diagnosis of parotid swellings, though it is very difficult to make a diagnosis of parotid schwannoma preoperatively.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]