Abstract
Objectives
The aims of the study were (1) to review the management strategy and clinical outcomes of all intraparotid facial nerve (FN) schwannomas (PFNSs) treated at a single tertiary academic center from 1975 to 2010 and (2) to summarize all previously reported cases of PFNS in the international literature.
Study design
A retrospective cohort study and literature review.
Methods
Fifteen patients were diagnosed and treated at the authors’ institution from 1975 to 2010. In addition, 124 published cases were systematically reviewed.
Results
The most common presentation of PFNS was a painless parotid mass with normal FN function. Eccentric, loosely attached intraparotid tumors underwent gross total resection with nerve preservation granting satisfactory postoperative FN function, whereas “inseparable” intraparotid tumors were observed in 8 cases with stable long-term size. Lesions that extended into the fallopian canal underwent complete resection with FN sacrifice and nerve grafting in 10 cases, whereas 1 patient received subtotal resection of the intraparotid portion with stereotactic radiotherapy targeting the intratemporal component.
Conclusions
Intraparotid FN schwannomas present similar to other primary salivary gland neoplasms, making an early diagnosis challenging. Intraoperative recognition of gross tumor characteristics and early histologic diagnosis with strategic biopsy are critical. Information including tumor location and extent, preoperative FN function, and the gross relationship between the tumor and the FN may guide the surgeon toward an optimal treatment plan emphasizing long-term neurologic preservation.
1
Introduction
Facial nerve (FN) schwannomas are benign, generally slow-growing tumors that arise from Schwann cells of the seventh cranial nerve, anywhere from the cerebellopontine angle to the terminal branches of the medial face. Intratemporal and intracranial lesions make up most FN tumors with only 9% involving a portion of the extratemporal segment .
Intraparotid FN schwannomas (PFNSs) most commonly present as a painless, slow growing parotid mass with normal FN function, making the preoperative diagnosis challenging . Imaging characteristics are generally nonspecific, and fine needle aspiration (FNA) is rarely yielding. Intraparotid FN schwannomas are frequently diagnosed intraoperatively when, during a parotidectomy, the surgeon is unable to locate the FN, and in an attempt to resect the tumor, the nerve is inadvertently injured or severed.
The goal of management remains long-term tumor control with an emphasis on preservation of FN function and facial cosmesis. Owing to the paucity of published reports and an unpredictable natural history, there is currently great controversy regarding management. Options include resection, either partial or complete , irradiation using stereotactic radiotherapy , or “watchful waiting” consisting of serial examination and imaging .
In the current study, we present 15 patients who were diagnosed with PFNS and treated at the authors’ institution from 1975 to 2010. In addition, we supplement these findings with a review of the world literature summarizing all previously published accounts. From these data, a management algorithm based on tumor morphology, location, size, and FN function is outlined.
2
Materials and methods
After institutional review board approval, a retrospective chart review was performed (1975–2010), and all patients with histologically confirmed PFNS were identified. Data including presentation, diagnostic testing, management strategy, intraoperative findings, clinical outcomes, and basic demographic data were collected. Facial nerve function was reported using the House-Brackmann (HBG) FN grading system . Patients with exclusively intracranial or intratemporal tumors were excluded. In addition, those patients with neurofibromatosis type 2 were excluded given the innate difference in tumor behavior and the potential for ipsilateral synchronous or metachronous FN tumors. These reports were then supplemented by a literature review summarizing all previously reported cases of PFNS in the international literature. To account for inconsistent reporting between publications, data were presented with fractions, where the denominator represents the total number of reports disclosing the details of a given variable.
2
Materials and methods
After institutional review board approval, a retrospective chart review was performed (1975–2010), and all patients with histologically confirmed PFNS were identified. Data including presentation, diagnostic testing, management strategy, intraoperative findings, clinical outcomes, and basic demographic data were collected. Facial nerve function was reported using the House-Brackmann (HBG) FN grading system . Patients with exclusively intracranial or intratemporal tumors were excluded. In addition, those patients with neurofibromatosis type 2 were excluded given the innate difference in tumor behavior and the potential for ipsilateral synchronous or metachronous FN tumors. These reports were then supplemented by a literature review summarizing all previously reported cases of PFNS in the international literature. To account for inconsistent reporting between publications, data were presented with fractions, where the denominator represents the total number of reports disclosing the details of a given variable.
3
Results
Over the last 35 years, 15 patients with PFNS were identified ( Tables 1 and 2 ). The mean age at diagnosis was 41 years (median, 37 years; range, 27–66 years; 8 women and 7 men). Of 15 patients, 13 presented with a painless parotid mass and normal FN function. One patient presented with a parotid mass, intermittent hemifacial spasm, and progressive facial pain, and a second patient presented with a tender parotid mass and normal FN function. None experienced preoperative hearing loss, vertigo, or tinnitus. The mean delay in diagnosis from initial symptom onset was 38.3 months (median, 12 months; range, 4 months–20 years).
| Case | Age/sex | Tumor-nerve relationship | Management | Preoperative HBG | HBG at last follow-up | Duration of follow-up | Tumor control outcome |
|---|---|---|---|---|---|---|---|
| 1 | 66/M | Inseparable | Biopsy, observation | 1 | 3 | 7 y | Growth of 7 mm at 3 y postoperative without change in symptoms |
| 2 | 36/F | Inseparable | Biopsy, observation | 1 | 1 | 1 y | No recurrence |
| 3 | 53/M | Loosely attached | GTR, FN preserved | 1 | 1 | 7 y | No recurrence |
| 4 | 27/F | Loosely attached | GTR, FN preserved | 1 | 1 | Lost to follow-up | — |
| 5 | 55/M | Loosely attached | GTR, FN preserved | 1 | 1 | 2 y | No recurrence |
| 6 | 44/M | Loosely attached | GTR, FN preserved | 1 | 1 | 2 y | No recurrence |
| 7 | 48/M | Loosely attached | GTR, FN preserved | 1 | 1 | 7 mo | No recurrence |
| 8 | 34/M | Inseparable | GTR, FN resected and grafted | 1 | 3 | 1 y | No recurrence |
| Case | Age/sex | Tumor location | Management ⁎ | Preoperative HBG | HBG at last follow-up † | Duration of follow-up | Tumor control outcome |
|---|---|---|---|---|---|---|---|
| 9 | 30/F | MS to PES | Intraparotid segment subtotal resection | 2 | 2 | 7 y | Residual progressive disease in mastoid segment Treated with stereotactic radiosurgery |
| 10 | 37/F | SMF to MT | GTR, FN resected and grafted | 1 | 4 | 2 y | No recurrence |
| 11 | 51/M | MS to PES | GTR, FN resected and grafted | 1 | 4 | 6 y | No recurrence |
| 12 | 34/F | MS to PES | GTR, FN resected and grafted | 6 | 6 | 17 y | No recurrence |
| 13 | 28/F | SMF to PES | GTR, FN resected and grafted | 1 | 3 | 2 y | No recurrence |
| 14 | 32/F | MS to MT | GTR, FN resected and grafted | 1 | 5 | 2 y | No recurrence |
| 15 | 40/F | MS to MT | Resected with facial-hypoglossal transposition | 1 | 6 | Lost to follow-up | — |
⁎ All patients with intratemporal tumor extension demonstrated inseparable tumor morphology.
† All patients with intratemporal tumor extension received gross total tumor-nerve resection and therefore had immediate postoperative HBG 6 function.
Preoperative computed tomography (CT) and or magnetic resonance imaging (MRI) were obtained in all the patients. All lesions demonstrated a hyperintense signal on T1-weighted gadolinium enhancement MRI with an iso- to hypointense T2-weighted signal. Computed tomography demonstrated smooth widening of the stylomastoid without bony erosion in 2 cases ( Figs. 1 and 2 ). There were no other consistent or distinguishing features seen on radiologic imaging; only in 1 instance was the diagnosis of PFNS entertained in the differential diagnosis of the interpreting radiologist. Four patients underwent preoperative FNA where 2 patients received the preliminary diagnosis of pleomorphic adenoma, 1 patient received the preliminary diagnosis of monomorphic adenoma, and the last yielding a nondiagnostic sample.
All 15 patients underwent some form of parotid surgery: 11 received superficial parotidectomy, 4 underwent total parotidectomy, and 6 of the 15 patients received concurrent mastoidectomy to access intratemporal extension. The intraoperative relationship of the FN to the tumor was found to be eccentric, loosely attached, and easily separable in 5 patients and “inseparable,” with either piercing or splayed nerve fibers, in 10 cases. All patients with loosely attached tumors did not have an intratemporal component, whereas 7 of the 10 patients with inseparable lesions involved the mastoid segment of the FN to varying degrees. All 5 patients with loosely attached tumors received gross total resection (GTR) with nerve preservation and demonstrated normal pre- and postoperative FN functions. Among the 10 patients with inseparable tumors, 2 patients were observed with serial clinical examinations after incisional biopsy; in 1 case, subtotal resection was used; and in the remaining 7 cases, GTR was performed with or without nerve grafting.
Both patients who underwent incisional biopsy had normal preoperative FN function; 1 patient worsened to an HBG 5 immediately after surgery and recovered to an HBG 3 over the ensuing 3 years, whereas the second maintained HBG 1 function ( Table 1 ). Of the 3 PFNSs, 1 was managed with tumor-nerve resection and was reconstructed with a greater auricular interposition nerve graft. Preoperative FN function was normal, and at 1-year follow-up, FN function had recovered to HBG 3. None of the patients with exclusive parotid involvement who were treated with surgical resection showed clinical or radiologic evidence of recurrence during follow-up (median, 24 months).
Seven patients with PFNS had intratemporal extension ( Table 2 ). One patient, with preoperative HBG 2 FN function, received subtotal resection of the intraparotid component without surgical treatment of the intratemporal segment; HBG 2 function was maintained immediately after surgery and remained stable during the course of follow-up. At 7-year follow-up, the residual mastoid component had increased in size, and the patient underwent single-session stereotactic radiosurgery (Leksell Gamma Knife [Elekta AB, Stockholm, Sweden]; marginal dose, 12 Gy; maximum dose, 24 Gy) without complication. No progression of remnant intraparotid tumor was seen during follow-up. The remaining 6 patients underwent mastoidectomy with en bloc resection of the tumor-nerve segment. Of 6 patients, 5 received either a sural or greater auricular nerve interposition graft, and 1 underwent an end-to-side facial-hypoglossal nerve transposition. Preoperative FN function was normal in 5 cases and HBG 6 in the remaining 1 case. Of patients with more than 1 year of postoperative follow-up, the median definitive postoperative FN function was HBG 4 (range, 3–6). The single patient with HBG 6 preoperative FN function never regained any function after reinnervation. Aside from duration of preoperative paresis/paralysis, there were no identifiable clinical factors that were associated with worse long-term FN outcomes, and none of 7 tumors recurred during follow-up.
3.1
Literature review
In 1927, Ibartz published the first report of a PFNS, and since this time, including the current series of 15 patients, a total of 124 cases have been reported in 53 case reports and small case series . Of the patients, 81.4% (83/102) had isolated parotid involvement, whereas 18.6% (19/102) of cases demonstrated an intratemporal component. The mean age at diagnosis was 44.7 years (median, 44 years; range, 6 months–91 years; 53% female and 47% male). The average maximum linear diameter tumor size at time of diagnosis was 2.6 cm (median, 3.0 cm; range, 1.0–6.5). Three cases of malignant nerve sheath have been reported .
The most common presentation of PFNS was a painless parotid mass (87.1%); less commonly, FN symptoms (18.5%) or pain (8.9%) manifested ( Table 3 ). Of the 23 patients presenting with FN symptoms, 5 had exclusively intraparotid tumors, whereas 18 had intratemporal extension. Preoperative FNA was performed in 39 cases, whereas only 2 cases (5.1%) were suggestive of a neurogenic source. Computed tomography and MRI were the most commonly ordered preoperative imaging studies, but no reliable features were identified that assisted in preoperative diagnosis.
| Signs and symptoms | Fraction | (%) | |
|---|---|---|---|
| Painless parotid mass | 108/124 | 87.1 | |
| FN symptoms (23/124, 18.5%) | Paresis | 18/23 | 78.2 |
| Paralysis | 2/23 | 8.7 | |
| Spasm or twitching | 3/23 | 13.0 | |
| Sensation (11/124, 8.9%) | Diminished or loss | 1/11 | 9.1 |
| Discomfort or pain | 10/11 | 90.9 | |
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