A Retroperitoneal Isolated Enteric Duplication Cyst Mimicking a Teratoma: A Case Report and Literature Review

Enteric duplication cysts lacking anatomic association with the gastrointestinal tract are called isolated enteric duplication cysts (IEDCs). We present an atypical case of a retroperitoneal IEDC with a tortuous tubular complex shape that enfolded the surrounding retroperitoneal fat and mimicked a retroperitoneal teratoma. Multiplanar reconstruction images should be used to evaluate such a lesion correctly. A tortuous tubular complex shape could be a key finding to differentiate from other retroperitoneal cysts.

Herein, we report a case of a retroperitoneal IEDC that formed a curious shape. This mass was misdiagnosed to include a fat component and was difficult to discriminate from a teratoma. We also discuss the radiological findings useful to a correct diagnosis of retroperitoneal IEDC.

Case Presentation
A 35-year-old woman visited our institution with an abdominal mass detected on abdominal ultrasound. The patient had no history of parity, drug use, or surgical intervention. On contrast-enhanced computed tomography (CT), a mass with a distorted shape and a diameter of 7.5 cm occupied the region between the right lobe of the liver and the right adrenal gland. The mass, which consisted of nodular fatty components, was well-circumscribed without contrast enhancement. A high-density fluid-fluid level was also seen ( Figure 1). On magnetic resonance imaging (MRI), the cystic component showed heterogeneous high intensity on fatsuppressed T2-weighted images (Figure 2(a)) and relatively homogeneous isointensity compared to the muscle on T1weighted images (Figure 2(b)). On chemical shift images, microscopic fat was not observed in the cystic component. On DWI, the cystic component showed slightly high intensity and its ADC value was 2.0 × 10 −3 mm 2 /sec, suggesting slightly restricted diffusion compared with the cerebrospinal fluid ( Figure 2(c)). A nodular fatty component was again identified on MRI (Figures 2(a) and 2(b)). Based on the presence of a fatty component and possibly calcification or iodine inside the mass, our preoperative diagnosis was retroperitoneal teratoma. The patient underwent laparoscopic surgical intervention. Macroscopically, the mass was a tortuous tubular cyst. The nodular fatty component indicated on preoperative images was not a part of the mass but rather a part of the normal retroperitoneal fat that the complex cyst enfolded. The mass was separated from the colon and the right adrenal gland. Microscopically, the wall of the cyst consisted of welldeveloped smooth muscle and an epithelial lining representing the large-intestine mucosa. Its content was viscous mucus ( Figure 3). The final diagnosis was retroperitoneal IEDC. Retrospective multiplanar reconstruction (MPR) oblique images revealed the appearance of a tortuous tubular cyst clearly and showed that the nodular fat-density component of the mass was continuous with the normal retroperitoneal fat (Figure 4).

Discussion
EDCs are congenital enteric malformations with a cystic appearance, a well-developed coat of smooth muscle, and an epithelial lining representing some portion of the intestinal tract mucosa [28]. On CT and MRI, EDCs are wellcircumscribed fluid-filled cysts with a slightly enhanced thin wall, which is located in or adjacent to the normal gastrointestinal wall. The density and intensity of the intracystic fluid can vary depending upon mucous concentration, viscosity, and the existence of intermixed hemorrhage [29,30]. In our case, the CT and MRI findings on the internal characteristics of the cystic component are consistent with those of the previous reports on EDCs.
Another point to discuss is that the mass enfolded surrounding retroperitoneal fat and mimicked a fat-containing tumor. A misdiagnosis resulting from that resemblance may derive from the tortuous tubular complex shape described above. Retrospectively, however, MPR images were useful for differentiating the IEDC from retroperitoneal teratoma because the nodular fat-density component of the mass was continuous with the normal retroperitoneal fat. In addition, MPR images also clearly revealed a tortuous tubular cyst. This image reconstruction technique is of great value for grasping the three-dimensional anatomy of a lesion [33]. For retroperitoneal masses, surgery is basically performed, although ultrasound-guided aspiration and ethanol sclerotherapy can be sometimes performed instead [34]. MPR images can enable surgeons to choose more appropriate operative methods.
In conclusion, a retroperitoneal IEDC can show a tortuous tubular shape and enfold surrounding retroperitoneal fat due to its complex shape. MPR images should be used to evaluate such a lesion correctly. A tortuous tubular complex shape could be a key finding to differentiate from other retroperitoneal cysts.