case_images: PMC9663478_01
case_images: Magnetic resonance imaging (MRI) findings. Low signal on T1WI and heterogeneously high signal on T2WI [(A,B), arrows], and high signal on axial diffusion-weighted imaging [DWI, B600; (C), arrow] indicate the presence of a retroperitoneal mass. Axial early arterial and portal venous post-contrast T1-weighted fat-suppressed imaging findings indicating a heterogeneously enhanced mass are shown [(D,E), arrows]; Retroperitoneal mass enhancement is more obvious in the delayed post-contrast T1-weighted fat-suppressed image [(F), arrow].
case_images: fmed-09-1024008-g001.jpg
case_images: PMC9663478_01_fmed-09-1024008-g001.jpg
case_images: F1
case_images: MRI findings indicative of the retroperitoneal mass were as follows (Figure 1).
case_images: Whole body 18F-fludeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) as a screen for primary malignancy. An axial computed tomography (CT) image demonstrating a retroperitoneal soft tissue density mass at the level of the left hilum is shown in (A) (arrow). PET (B), fused PET/CT images (C), and a maximum intensity projection (MIP) image (G) revealing significantly increased FDG activity in the left retroperitoneal mass (arrow) are shown. An axial CT image (D) reveals the presence of a lymph node adjacent to the mass (arrow), while PET (E) and fused (F) images show significant uptake of FDG by the retroperitoneal lymph node.
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case_images: PMC9663478_01_fmed-09-1024008-g002.jpg
case_images: F2
case_images: A whole body 18F-fludeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) (Figure 2) was performed to identify primary malignancy, PET/CT images demonstrated a retroperitoneal soft tissue density mass with Significantly increased FDG activity (SUVmax: 19.6), and revealed a lymph node adjacent to the mass with elevated FDG uptake (SUVmax: 7.9).18F-FDG PET/CT did not detect potential tumors in other parts of the body.
case_images: Pathological and immunohistochemical (IHC) findings. Post-operative pathological findings (A) reveal clear cell carcinoma (left retroperitoneal),the large polygonal tumor cells with transparent cytoplasm are arranged in a nest like manner, and the stroma is rich in small blood vessels. IHC findings (B):Pax8 immunohistochemical staining of tumor cells is positive, indicating its renal origin.
case_images: fmed-09-1024008-g003.jpg
case_images: PMC9663478_01_fmed-09-1024008-g003.jpg
case_images: F3
case_images: A post-operative pathological examination (Figure 3A) indicated clear cell carcinoma (left retroperitoneal) and metastatic lymph nodes. The following immunohistochemical findings (Figure 3B) suggested the carcinoma was renal in origin: Ki-67 (approximately 30% +), PAX8 (+), CK8 (+), vimentin (+), and PLAP (weak +).
case_images: Abdominal enhanced computed tomography (CT) findings at 6-month follow-up. Axial images from non-enhanced CT (A) to CT enhanced in arterial phase (B) and venous phase (C). Non-enhanced CT (A) reveals the presence of a soft tissue density nodule in the surgical area (left para-abdominal aorta), CT enhanced in arterial phase (B) moderately enhanced nodules in the operative area, and decreased enhancement in venous phase (C). No obvious abnormalities in either kidney are shown.
case_images: fmed-09-1024008-g004.jpg
case_images: PMC9663478_01_fmed-09-1024008-g004.jpg
case_images: F4
case_images: On 6-month follow-up, abdominal enhanced CT revealed retroperitoneal lesion recurrence (Figure 4); however, there remained no obvious abnormality in either kidney.