lymphangiomas are rare benign tumors that are preferentially located in the head and neck in children ( 1 ) . lymphangiomas in the peritoneal cavity are extremely rare occurring most commonly in the mesentery , followed by the omentum , mesocolon , and retroperitoneum . the etiology is unclear , but they are considered primarily to congenital in origin ( 2 ) . we report the case of a young woman with appendicular pain caused by a cystic lymphangioma of the right iliac fossa : a rare but possible differential diagnosis . a 17-year - old female patient presented with a dull abdominal pain in the right iliac fossa and flank of a 1-month duration . an abdominal examination revealed hyperactive bowel sounds and tenderness during palpation in the central abdominal quadrant and right iliac fossa in mc burney point . neoplastic markers ( afp , cea , ca 19 - 9 , ca 15 - 3 , ca125 , tps ) were negative . axial and coronal t2-weighted tse images showed the presence of a fluid - filled cystic lesion in the retrocaecl adipose tissue . an ultrasonographic and ct scan of the abdomen revealed the presence of a cystic mass ( max diameter 60 mm ) in the retrocaecal adipose tissue that was in proximity of the caecum , appendix and ileum . in addition , the ct scan revealed the presence of multiple hypodense formations in the body and tail of pancreas . during the hospital the exam revealed in the retrocaecl adipose tissue the presence of a fluid - filled formation with a diameter of 60 mm that appeared indissociable from the caecum for the presence of a tissue connection ( fig 1 ) . other cystic lesions ( communicating with pancreatic duct ) were present in the whole pancreas and in the right kidney . fluid - filled cystic lymphangioma with polycyclic edge and internal septa ( intraoperative specimen ) the patient underwent exploratory surgery : at laparotomy a yellowish oval formation with a diameter of 6 cm was found arising from the mesentery of terminal ileum with partial adhesion of the appendix . the lesion had a cystic aspect and was fluid - filled ( fig 2 ) . the patient has been followed - up for two years with semestral clinical examination and abdominal eco scan and no recurrence occurred . intra - abdominal mesenteric lymphangioma is an uncommon tumor that usually manifestes in early adulthood . this tumor has an incidence of approximately 1/20,000 and 1/250,000 hospital admissions , and it is more frequent in men than women with a m / f ratio of 3:1 ( 3 ) . in intraperitoneal sites , the small bowel mesentery ( 70% ) is the commonest localization , with 5060% of all cysts located in the ileal mesentery . ( 4 ) the etiology of mesenteric lymphangioma is considered to be congenital , with abnormal embryonic development of the lymphatic system causing sequestration of lymphatic tissue ( 1 ) : infact in our patient also other cystic lesions ( kidney and pancreas ) were found at abdomen ct / mri . radiological investigations are a useful diagnostic tool , but definitive diagnosis is confirmed by histopathology after a complete surgical resection . ( 5 ) at immunochemistry : the lining mesothelial cells are immunoreactive for cytokeratin and negative for factor viiiis . double staining with prox1 and cd31 is the most reliable method for characterizing lymphangioma endothelial cells.(6 )