4.1 Synopsis of key findings and comparison with other studies
The natural history of RPA is not well understood. Recurrences usually develop at 7 years and occasionally 20 years after the operation1. The annual growth rate of identified recurrences, as measured on repeat MRI, is variable: 21% of tumours are stable, 10.2% increase and 14% reduce in volume4. It is not known if clinical recurrences following conservative parotid resections become evident after a long subclinical course. Our study is the first to search radiologically for occult recurrent foci after capsular dissection of PA with a mean postoperative follow up of 6 years (median 5.6 years). We were not able to find any occult recurrence. Schapher et al performed clinical and ultrasound examinations in 98 patients after PA resection (31 patients underwent ECD) at the 1st and >10th postoperative year2. They found no recurrence in the ECD group. One patient (after partial parotidectomy) developed a subclinical recurrence, detected by routine ultrasound. Moonis et al also performed follow up MRI or CT scans in patients who underwent PA resection (ranging from enucleation to formal parotidectomy) but do not provide details on the frequency of the imaging protocol5. They have detected 2/24 recurrences with MRI: one as an incidental finding after a neck MRI for a different indication and another one on regular scanning.
Our 3.2% recurrence rate lies within the range of reported figures from large CD series with adequate followup (2%)6. The overall recurrence rate in two large cohort studies including 9003 PA resections, irrespective of surgical approach, is 3.1%1. Thirteen patients (21.3%) in our study had an incomplete capsule and two of them recurred. Dulguerov et al have summarised the histological evidence that supports the association of an incomplete capsule and recurrence7. However, other histological characteristics such as pseudopodia and satellite nodules are also common in specimens with an incomplete capsule and may be more relevant to the risk of subsequent recurrence8.