cystic tumour of the atrioventricular nodal region cystic tumour of the atrioventricular nodal region cystic tumour of the atrioventricular nodal region is a very rare tumour of the heart in the region of the atrioventricular node. it is also known as mesothelioma of the atrioventricular node. cystic tumour of the atrioventricular nodal regionmicrograph of a cystic tumour of the atrioventricular nodal region. h&e stain.specialtycardiology, oncology presentation it may present as a cardiac arrhythmia or as sudden cardiac death. pathology cystic tumours of the atrioventricular nodal region, true to their name, have cystic spaces, which are lined by a single layer of histomorphologically benign epithelial cells. the appearance is similar to that of lymphangioma and this is a name that has been used for this tumour. treatment the treatment of cystic tumours of the atrioventricular nodal region is surgical excision.