Int. Med J Vol. 5 No 2 December 2006
Intraparotid Facial Nerve Schwannoma: A Case Report.
A A Khadri*, M N Azmi*, R Ahmad§
*Department of Surgery, Faculty of Medicine, International Islamic University Malaysia
§ Department of Otorhinolarygology, Faculty of Medicine, International Islamic University Malaysia
ABSTRACT
Neoplasms of the facial nerve presenting as a parotid mass are uncommon. In the absence of a facial palsy, preoperative diagnosis of parotid tumour as schwannoma is very difficult1. A rare case of solitary schwannoma involving the branches of the facial nerve is described.
Key Words: Parotid gland, facial nerve, Schwannoma
INTRODUCTION
Schwannomas (neurilemmomas) are ectodermal benign encapsulated tumors, which arise from the sheath of peripheral and cranial nerves. Facial nerve schwannoma can arise from any segment of the nerve, from the glial-Schwann cell junction at the cerebellopontine angle to the peripheral branches in the face2. Rarely do they arise from the intraparotid portion of the facial nerve. The following case is illustrated because it appeared as an asymptomatic parotid tumour with normal facial nerve function and intraoperatively found to be a cystic tumour involving the bifurcation and lower branches of the left facial nerve.
Case Report
A 50-year-old man presented with a two years history of a gradually enlarging left parotid mass. He denied of any facial pain, weakness or twitching. Examination revealed a 3 x 4 cm firm non-tender mobile mass anterior to the left tragus and facial nerve function was normal. No other abnormality noted on head and neck examination. Fine needle aspiration cytology was carried out and was reported as a neural or fibrohistocytic lesion.
Intraoperatively, a cystic swelling measuring 3 x 2 cm was seen located between the superficial and deep lobe of the parotid gland. The lesion originated from the bifurcation of facial nerve with the lower and peripheral branches embedded in the mass. However the mass was dissected free from these branches with apparent anatomical preservation of the nerve. Post-operatively the patient developed lower motor neuron weakness of the left side of face, which improved with physiotherapy. Histological examination revealed a benign schwannoma.
DISCUSSION
Since Schmidt first described a facial schwannoma in 1930, it has been well documented in the medical literature4. Benign schwannoma is a slow growing encapsulated tumour arising from the neuroectodermal sheath of Schwann. Approximately 25-30% of all reported schwannomas occurs in the head and neck and most of these arise in relation to the eighth nerve2. The main symptoms are usually of facial weakness or paralysis. Preoperative facial nerve paresis or paralysis was found in 20% of all cases2. This is remarkable because facial nerve involvement is characteristic of malignant parotid tumours. In our case, the tumour originated from the bifurcation of nerve involving the lower branch of the facial nerve with normal facial nerve function.
Neurogenic intraparotid facial nerve neoplasms always present as a preauricular or facial mass3. Nearly half of these extratemporal tumours involve the main trunk of the nerve. Hemifacial spasm or twitching suggest the presence of a compressive or infiltrative lesion and may precede facial paralysis by weeks or months. Neurogenic neoplasms are rarely suspected and as such pre-operative electrodiagnostic test are often not considered.
Benign neoplasms are of two types: schwannoma and neurofibroma. Schwannomas are different from neurofibromas with regards to its histological appearance and biological behavior. Schwannoma is a solitary, encapsulated tumour, usually attached to a nerve that appears to push axons aside as it grows and therefore surgical removal with preservation of the nerve is usually possible as noted in this patient. Neurofibromas on the other hand, are nonencapsulated, and composed of an admixture of all elements of a peripheral nerve. Microscopically Shwannomas show two patterns, Antoni Type A in which the cells are spindle shaped, compactly arranged with long oval nuclei oriented with their long axis parallel to each other and Antoni Type B in which with less cellular areas, reticular, with cells showing vacuolation and xanthomatous changes.
The histological difference between schwannomas and neurofibromas of the facial nerve may dictate the type of surgical resection. Theoretically, schwannomas can be stripped free of the nerve without sacrificing it, as in this case. In contrast, fibres from the facial nerve pass directly through a neurofibroma and separation of the nerve fibres from the tumour is rarely possible. Neurofibromas generally require nerve sectioning and cable grafting, using the sural nerve for a long defect and the greater auricular nerve for a short defect.
In conclusion, while neurogenic tumours of the facial nerve in the parotid gland are rarely anticipated and electroneuronography is yet inconclusive, they should be suspected intraoperatively if the tumour is inseparable from the nerve. With pathologic confirmation, the patient should undergo staging radiography to define the extent of the lesion. Furthermore, intraoperative confirmation of the tumour by frozen section biopsy is imperative because nerve preservation can be attempted in benign tumours whereas the nerve may have to be sacrificed in malignant tumours.
REFERENCES
1. B N Kumar, R M Walsh, N M Walter, A Tse, J T Little. Intraparotid facial nerve schwannoma in a child. The Journal of Laryngology and Otology. 1996; 110: 1169-1170
2. Shah HK, Kantharia C, Shenoy AS. Intraparotid Facial nerve schwannoma. J Postgrad Med. 1997; 43: 14-5
3. Chong K W, Chung Y F A, Khoo M L C, Lim D T H. Management of intraparotid facial nerve schwannoma. ANZ Journal of Surgery. 2000; 70: 732-734
4. Robert J C, Mark May, Barry M, S. Intraparotid facial nerve schwannoma: Diagnostis and management. Otolaryngol Head Neck Surg. 2004; 130: 586-92.
Correspondence to:
Assoc. Prof. Dr Azmi Md Nor,
Department of Surgery,
Faculty of Medicine,
International Islamic University Malaysia,
25710 Kuantan, Pahang,
Malaysia