case_images: PMC6489054_01
case_images: Computed tomography (CT) and magnetic resonance imaging (MRI). a CT shows a 50 x 22 x 30 mm, right, retroperitoneal, well-circumscribed, unilocular, cystic mass with calcification (arrow). b The intensity of the content of the cystic lesion was low on T1-weighted image and high on T2-weighted image (arrowhead).
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case_images: PMC6489054_01_crg-0013-0159-g01.jpg
case_images: F1
case_images: Enhanced abdominal computed tomography scan revealed a right retroperitoneal well-circumscribed unilocular cystic mass of 50 x 22 x 30 mm in size with no signs of invasion to the surrounding tissue (Fig. 1a). Magnetic resonance imaging showed homogeneous low intensity on T1-weighted imaging and high intensity on T2-weighted imaging (Fig. 1b).
case_images: Intraoperative finding. a The tumor was a grayish mass with slight protrusion to the peritoneum. b The retroperitoneal fat tissue surrounding the tumor was attached as the surgical margin. c On the dorsal side, the iliopsoas muscle (indicated by a *) was exposed.
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case_images: PMC6489054_01_crg-0013-0159-g02.jpg
case_images: F2
case_images: Furthermore, a lateral approach was performed to mobilize the right-sided colon, thereby leading to a visualization of the tumor contour (Fig. 2a). Using laparoscopic coagulation shears, we resected the retroperitoneum following the surgical margin at approximately 2 cm from the cystic wall, which was surrounded with retroperitoneal fat tissue (Fig. 2b). Since the tumor had direct contact with the iliopsoas muscle without invasion, the dissecting layer was set along the iliopsoas muscle on the dorsal side (Fig. 2c).
case_images: Macroscopic findings of the resected specimen. a The resected specimen was monolocular and mostly a fibrous cystic lesion with calcification of the cystic wall but without mural nodules. b Dorsal view of the specimen. c The content inside the lesion was a slightly mucinous yellowish fluid.
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case_images: F3
case_images: The size was 55 mm in maximum with surrounding fat tissue (Fig. 3a, b), and the cystic lesion contained relatively clear serous fluid with elevated tumor marker levels (CEA, 4,665 ng/mL and cancer antigen 125 [CA125], 21,040 U/mL); however, the CA19-9 level was normal (Fig. 3c).
case_images: Histopathology of the resected specimen. a, b The cystic wall consisted of thin fibrous tissues with a partial single-layered cuboidal-to-flat glandular epithelium without cellular atypia (a: HE. x20. b: x100). Immunohistochemical staining was positive for keratin AE1/AE3 (c) and negative for CDX2 (d).
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case_images: F4
case_images: Histopathological findings showed that the cystic wall consisted of thin fibrous tissues with partial single-layered cuboidal-to-flat glandular epithelium without cellular atypia (Fig. 4a, b). Immunohistochemistry revealed keratin AE1/AE3 positivity and CDX2 negativity (Fig. 4c, d).