Retroperitoneal cystic masses arising outside from the major retroperitoneal organs within that compartment are rare. The treatment strategy for cystic retroperitoneal masses varies depending on the cause and its nature, so differentiation between the cystic masses is essential. Cystic retroperitoneal masses can be divided into neoplastic (cystic lymphangioma, teratoma, mucinous cystadenoma, cystic changes in solid neoplasm, metastatic nodes, pseudomyxoma retrpopertonei), and nonneoplastic (pseudocyst, lymphangioma, lymphocele, urinoma) masses. Sometimes it is not easy to diagnose a cystic retroperitoneal mass as many overlapping features exist among the various retroperitoneal cystic masses.
The cystic nature of the nodes has been attributed to the tumor cells obstructing the flow of the lymph resulting in cystic enlargement of the nodes. Retroperitoneal metastatic nodes in a primary testicular seminoma are common, usually solid or solid cystic due to necrosis; however, nodes with an utterly cystic nature are rare.
Retroperitoneal lymphangioma is a benign tumor of congenital lymphatic origin. It occurs due to the failure of the developing lymphatic tissue to establish normal communication with the remainder of the lymphatic system . Therefore lymphangiomas are considered congenital rather than an acquired tumors. The other explanations for the origin of lymphangioma include obstruction of lymph channels secondary to fibrosis, inflammation, trauma, node degeneration, or failure of endothelial secretory function . Usually, they occur in the head and neck region; however, they can involve the retroperitoneum, a rare location [4, 6, 7]. Cystic lymphangiomas can occur anywhere in the pararenal, perirenal, or pelvic extraperitoneal spaces and may cross more than one compartment of the retroperitoneum . Cystic lymphangioma or hygroma consists of multiple dilated, poorly developed lymphatic channels. The cystic spaces are lined with endothelium and contain multiple thin septa and chylous fluid. On ultrasound, a lymphangioma is seen as a cystic mass with multiple, fluid-containing cystic regions, separated by thin septae. In CT, they typically appear as thin-walled, multiseptated cystic masses [4, 6]. The attenuation values are usually that of fluid and may cross one retroperitoneal compartment to an adjacent one is characteristic of the mass . Sometimes, the walls and septae are imperceptible. Rarely, they may have wall calcification . In our case, the lesions had all the above-mentioned cystic lymphangioma features on ultrasonography, CT, and MRI.
The other close differential in our case was pseudomyxoma retroperitonei. These usually occur in the peritoneal cavity; however, these may occur in the retroperitoneum [8, 9]. On CT, they appear as multicystic masses with thick walls and septa that displace and distort adjacent structures [8, 9]. Curvilinear or punctate mural calcifications may also occur.
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