[Differential diagnosis of tailgut cyst in the case of a rectal carcinoma with presacral mass].

Cystic masses of various different origins and degrees of malignancy occur in the presacral space. Apart from benign, malignant and acute inflammatory masses, the benign lesions include a group of cystic structures to which the dysgenetic cysts belong. The tailgut cyst is a relatively rare type of gastrointestinal origin from this group. We present the case of a stenosing rectal carcinoma in which a presacral mass was additionally found, which did not get smaller compared to the rectal tumour during combined preoperative radiochemotherapy, with a lymphoma being suspected. After extirpation of the tumour, histopathological processing revealed a stenosing rectal carcinoma with an adjacent dysgenetic lesion--a tailgut cyst. Although dysgenetic lesions are rare as presacral masses, this must also be taken into account as a differential diagnosis in the various imaging procedures such as endosonography, CT and MRT when a rectal carcinoma is present.