Background
The retroperitoneum (RP) may be affected by variety of infectious, inflammations, rare benign tumors or malignant neoplasms that can be either primary or metastatic. Malignant tumors of the retroperitoneum happen four times more often than benign lesions.(1, 2)
Benign retroperitoneal tumors (RPT) are usually detected clinically and the most common one is neurogenic tumors (30%), followed by teratomas (15%).
Malignant RPTs are very rare tumor, count 0.1-0.2 % of all malignant tumors. Most of them are primary tumors, in them the most common type is retroperitoneal but metastatic tumors may involve retroperitoneum. (3, 4). Metastatic RPTs may originate from kidney , bladder or genitalia.(5)
Invasion of malignant tumors to the retroperitoneal is very rare and usually has been reported as an unusual presentation of gastrointestinal stromal tumors (GISTs).(6, 7)
On the other hand, appendiceal tumors are rare and usually manifest as appendicitis. Most are harmless and can be handled with appendectomy.(8) The WHO classifies three subtypes of
mucinous appendiceal neoplasms; mucinous adenoma, low-grade appendiceal mucinous neoplasm (LAMN), and mucinous adenocarcinoma (9)
In this case report we present a novel case of an appendix tumor which manifested with retroperitoneal mass by invasion from peritoneal cavity.