Extracapsular dissection for clinically benign parotid lumps: reduced morbidity without oncological compromise

1Parotid tumours are uncommon, with the majority presenting as discrete lumps arising within the superficial portion of the gland. Conventional teaching prescribes removal of these tumours by superficial parotidectomy (SP), which encompasses facial nerve identification and en bloc removal of the superficial portion of the gland. Extracapsular dissection (ECD) is an alternative approach to the removal of such lumps involving meticulous dissection immediately outside the tumour capsule while still preserving the facial nerve, and is distinct from enucleation. Based on the traditional view that many parotid tumours (notably pleomorphic adenomas) breach their capsule and so are theoretically at risk of recurrence from surgery close to the capsule (the ‘tumour bud’ concept), ECD has been received with caution. However, we have previously demonstrated in 475 patients with pleomorphic adenomas that ECD is associated with long-term low recurrence rates (< 2%) comparable with SP, but fewer complications. Thus, in the practice of treating parotid pleomorphic adenomas, ECD reduces morbidity without oncological compromise. However, this procedure may not be appropriate for malignant tumours. The potential risk in ECD is encountering a malignant tumour masquerading as a benign lump – if this occurrence is common and the subsequent course of the cancer is adversely affected, it would prohibit the use of ECD as an alternative to SP for a simple parotid lump. This study addressed this question by analysing the outcome of 821 consecutive patients with parotid tumours treated at one centre over 40 years, and in particular, focuses on outcome when the histology was a carcinoma.

2Between 1952 and 1992, 821 patients with previously untreated epithelial parotid neoplasia were treated at the Christie Hospital, Manchester. The preoperative diagnosis was made on clinical grounds; fine needle aspiration cytology was not used. Tumours were classified by clinical criteria into (i) ‘simple’, which are discrete, mobile, and less than 4 cm in diameter (for the purpose of this paper, this is synonymous with ‘clinically benign’); and (ii) ‘complex’, which are greater than 4 cm and/or demonstrate fixity, facial nerve involvement, palpable cervical nodes, or deep lobe involvement. For tumours with a malignant histology, simple tumours equated to AJCC Stage I disease. Complex tumours were not treated by ECD, and excluded from the analysis. The histological diagnoses were updated in the mid-1970s in line with the WHO classifications. Median follow-up was 12 (range 5–32) years.

3Among the ‘simple’ tumours, 503 patients underwent ECD, 159 patients underwent SP. The choice of technique was made on clinical criteria, namely mobility at surgery after raising the skin flap. This procedure has been described in detail elsewhere. In this technique, the plane of dissection is within a compartment of loose areolar tissue approximately 2–3 mm from the tumour. This contrasts sharply with enucleation, which breaches the capsule and removes the tumour within. Postoperative adjuvant radiotherapy (RT) was used selectively, either for spillage of benign tumour or for those malignant tumours with a positive margin, spillage, adenoid cystic or high-grade carcinomas.

4Comparisons of means were by Student's t-test; proportions were compared by χ2-tests or Fisher's exact test, where expected frequencies were less than five. Cancer-specific survival and recurrence rates were calculated by the Kaplan–Meier method and differences tested by log-rank (STATA version 7.0, College Station, CA, USA).

5The baseline characteristics for the 821 tumours are outlined in Table 1. The majority (662 or 81%) presented as ‘simple’ lumps, of which only 32 or 5% proved to carcinomas. By contrast, two-thirds of ‘complex’ tumours had a malignant histology. The pattern of malignant histological types differed between ‘simple’ and ‘complex’ tumours: notably, two-thirds of ‘simple’ lumps with subsequent malignant histology were either acinic cell or low-grade mucoepidermoid carcinoma.

6In the 32 patients with ‘simple’ lumps, which proved to be carcinomas, 12 underwent ECD and 20 underwent SP. Following surgery, over half of these patients received radiotherapy (ECD, 7/12: SP, 12/20)–the indications are shown in Table 2. While these surgical groups were not randomly determined, the clinicopathological characteristics were broadly comparable (Table 3 ). The 5- and 10-year cancer-specific survival rates were 100 and 98%, respectively for ECD and SP (Figure 1A). Local recurrences developed in six cases (ECD, 1: SP, 5), with no statistical difference by log-rank testing between the two groups (Figure 1B). Only one of the six cancer recurrences occurred in a patient who had received both surgery and radiotherapy (Table 4 ); thus, radiotherapy per se may have been a confounding factor in determining recidivism.

7Of the 630 patients with ‘simple’ lumps and benign histologies, there were 10 recurrences at 15 years. Eight recurrences occurred after 491 ECDs (1.7% at 15 years by life-table analysis); two recurrences occurred after 139 SPs (1.8% at 15 years by life-table analysis).

8The complications by surgical groups and histological categories are shown in Table 5. Among the 630 patients with a ‘simple’ tumour and benign pathology, ECD was associated with significantly reduced morbidity compared with SP, including transient facial palsy (P < 0.001), Frey's syndrome (P < 0.001), and amputation neuroma (P < 0.001) (Table 5). Salivary fistulae developed without obvious causes in three patients treated by ECD but resolved spontaneously within 3 months. For the patients with ‘simple’ tumours and malignant histologies, complication rates were generally higher, but this was based on small patient numbers. There were no apparent differences between ECD and SP.

9This study has demonstrated that the majority of parotid tumours present as a clinically benign lump, and of these, only 5% subsequently prove to be carcinomas. This study establishes ECD as a viable alternative surgical approach to superficial parotidectomy in such tumours, for it has the advantage of reduced morbidity without untoward effects on oncological outcome.

10The advantages of this study were large numbers of patients treated with a similar surgical philosophy, and followed for a long period. Thus, we were able to show that out of 662 clinically benign parotid lumps, SP was avoided in 503 patients, and replaced with a more conservative procedure carrying significantly less morbidity. In adopting this conservative approach, there was a diagnostic error rate of 32/662, with 12 patients treated ‘inappropriately’ by ECD. The question was whether these ‘errors’ resulted in a poor outcome, but this was not the case. The authors accept that the 12 patients should ideally have been treated by some form of parotidectomy, and in such circumstances, seven patients may have avoided RT–these represent the penalty paid for saving 503 patients the need to undergo parotidectomy.

11The merit of classifying discrete parotid lumps into ‘simple’ or ‘complex’ is confirmed in this study. Using clinical judgement alone, the assessment of 662 simple lumps (‘benign tumours’) was correct in 95% of the cases. Following a final step of clinical assessment at surgery, 12 of the 32 malignant tumours were removed by ECD rather than SP (a clinical diagnostic error rate of 1.8%). This equates to a test sensitivity of 93% and a positive predictive value of 95%. In theory, if clinical assessment is supplemented with fine needle aspiration cytology, these predictive values may increase.

12Only 5% of clinically benign parotid tumours were carcinomas and notably two-thirds of these were low-grade cancers (acinic cell and low-grade mucoepidermoid carcinomas). Half required postoperative radiotherapy but this did not represent overtreatment of Stage I disease. Irrespective of the surgical approach, the long-term prognosis in this group was good. A similar experience was reported by, who encountered 20 (4%) carcinomas unexpectedly in a series of 539 otherwise unremarkable parotid tumours. These tumours were treated surgically as nonmalignant lumps, yet subsequently followed a benign course.

13As long-term low recurrence rates are now the norm for parotid pleomorphic adenomas, there is an emerging trend towards low morbidity surgery. Series employing either total parotidectomy or formal superficial parotidectomy report high rates of transient facial nerve palsy (15–70%) and Frey's syndrome (13–66%) (reviewed in ). Recent studies have advocated a more conservative parotidectomy, partial superficial parotidectomy, and report lower transient facial nerve rates (20–33%) and Frey's syndrome rates (7–20%). Still lower rates of morbidity have been reported, following ECD with 3–11% transient facial nerve palsy and 0–5% Frey's syndrome. The very low rates of gustatory sweating after ECD are presumably due to less disruption of the parotid tissue. ECD also avoids the unsightly complication of retromandibular depression frequently observed after superficial parotidectomy.

14As the needs for reducing morbidity and maintaining facial aesthetics increase, ECD represents the current limit of conservative parotid surgery. A common feature of all minimally invasive therapies is that the technique leaves little room for error. With acceptance of these limitations, the findings of this study demonstrate that ECD is a scientifically valid and oncologically safe approach to the management of the clinically benign parotid lump.