Advanced adenoid cystic carcinoma of the skull base - The role of surgery.

Background: Adenoid cystic carcinoma (ACC) is a salivary gland malignancy with a propensity for perineural spread and diffuse soft tissue infiltration. In the head and neck this unique biological behaviour can result in skull base involvement. A lack of consensus regarding management of ACC involving the skull base in conjunction with the technical and reconstructive challenges of oncological resection in this region has led to variation in practice between institutions.

Method: Retrospective multicentre review of patients with advanced ACC infiltrating the skull base, treated surgically by the Queensland Skull Base Unit between 2005 and 2017, with a minimum follow up time of 24  months.

Results: 32 patients were treated for ACC with skull base involvement with oncological resection and post-operative radiation in the study period with a median follow up of 82.18  months (33.11-159.53 months). 5 and 10  year locoregional control were both 88.2% (95% CI 67.5-96.1) despite a high rate of microscopically positive margins (81.3%). Metastatic disease rates were high, resulting in low rates of disease free survival (DFS) (53.0% at 5 years (95% CI 33.7-69.0) and 23.0% at 10 years (9.5-39.8)). Overall survival (OS) was high (5 year 91.8% (95% CI 71.1-97.9), 10 year 63.7% (95% 37.5-81.2)), despite the advanced nature of disease.

Conclusion: High rates of locoregional control can be achieved in skull base ACC with oncological resection of disease and post-operative radiation. Whilst disease recurrence rates are high, a majority of recurrence is metastatic and does not confer poor intermediate term overall survival.