PMC9663478_01
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].
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F1
MRI findings indicative of the retroperitoneal mass were as follows (Figure 1).
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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F2
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.
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.
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F3
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 +).
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.
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F4
On 6-month follow-up, abdominal enhanced CT revealed retroperitoneal lesion recurrence (Figure 4); however, there remained no obvious abnormality in either kidney.