Uncommon perineal tumours: caution with aggressive surgical management.

An asymptomatic 66-year-old woman showed a large perineal mass extending close to pelvic organs on MRI. CT-guided needle biopsies revealed a desmoid tumour (DT). The patient refused radical surgery. Four years later, the tumour had marginally increased in size and was still asymptomatic. The revision of earlier biopsies then revealed typical aspects of aggressive angiomyxoma (AA). AA and DT are rare mesenchymal tumours of low-grade malignancy, usually of large size, that occurs in female pelvi-perineal region. Radical resection with wide margins is classically advocated in such tumours in order to prevent the high risk of recurrences. However, due to a slow growth, rare infiltration of adjacent organs and a very low metastatic potential, a watchful waiting policy can be proposed when high postoperative morbidity is expected. In order to propose the accurate treatment, frontline biopsies of the tumour are essential.