A mucinous tumour of the urachus: adenoma or low grade mucinous cystic tumour of uncertain malignant potential?

We report a case of urachal glandular neoplasia in a male aged 72 years. The lesion had a papillary and villiform structure, and exhibited serrated features as seen in some colorectal neoplasms. The tumour cells expressed carcinoembryonic antigen, whereas the normal urachal epithelium did not. There was a striking resemblance to low grade mucinous cystic tumours of uncertain malignant potential as described in the appendix and elsewhere. Although such lesions in the urachus have been called adenomas, we argue that their potential to cause pseudomyxoma peritonei deserves a different terminology, and that 'mucinous tumour of uncertain malignant potential' is appropriate.