Renal cell oncocytoma tumor evolutions: a case report

This report delineates the clinical progression of a renal oncocytoma in a 38-year-old female, initially asymptomatic, over a three-year follow-up period following her treatment for papillary thyroid cancer. The timeline of this case is as follows: In 2016, the patient was treated with total thyroidectomy and I131 for thyroid cancer. During an annual follow-up, an incidental renal mass was detected via FDG PET/CT, initially characterized as a benign, non-FDG-avid renal oncocytoma. Over two years, this lesion demonstrated a remarkable increase in FDG uptake and a slight growth in size, coupled with new I131 uptake in subsequent scans. These findings led to a reassessment of the diagnosis, initially suggesting a potential small renal cell carcinoma (RCC). Histopathological analysis eventually confirmed the diagnosis of oncocytoma. This case is notable for the tumor’s unusual metabolic evolution and the challenges it posed in differential diagnosis.

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Discussion
Renal oncocytoma is usually asymptomatic and is observed incidentally during routine examination for non-urological abnormalities (1).It usually appears as a solitary tumor measuring between 4-8 cm, which may infiltrate peripheral renal   Enhanced MRI for the abdomen revealed solid enhancing left lower pole lesion with diffusion restriction.
tissues (2,3).CT can reveal the presence a solid homogeneous lesion with a centrally located scar, and arteriography may reveal a spoke-wheel vascular pattern (1,4).However, these markers do not definitively distinguish oncocytoma from other renal tumors.As a result, numerous patients with oncocytoma are treated aggressively, due to the possibility of renal malignancy.
In the present case, the tumor was observed during routine examinations.Over a three-year of follow-up, there was interval increase in metabolic activity, although no evidence of local invasion or distant metastasis was demonstrated.
To our knowledge, there has been no published cases demonstrating a metabolic evolution of renal oncocytoma over three-year period, or renal oncocytoma of high I-131 accumulation on post-therapy scan.
Given the significant differences in management approaches of oncocytomas compared to RCC and other renal tumors, it is important to recognize that oncocytomas can yield false positive results on 18F-FDG PET, and absolute radiologic differentiation of oncocytoma from RCC remains challenging.

Conclusion
This case study presents a rare evolution of renal oncocytoma in a patient with a history of papillary thyroid cancer.The tumor developed GLUT I transporter for FDG and sodium-iodide symporter expression, with accumulating I-131 over three years, highlighting the complexity and diagnostic challenges in such cases.

FIGURE 1 FDG
FIGURE 1 FDG PET/CT axial (A-C) and coronal (D-F) PET, CT and fused PET/CT images of the left lower pole renal mass (arrow) demonstrating no FDG uptake.Whole body I 131 post therapy scan (G, H) performed within 6 weeks of the FDG-PET/CT scan, shows no appreciable I 131 accumulation within the renal mass.

FIGURE 2 FDG
FIGURE 2 FDG PET/CT axial (A-C) and coronal (D-F) PET, CT and fused PET/CT images of the left lower pole renal mass (arrow) demonstrating intense FDG uptake with SUV max 11.5.Whole body I 131 post therapy anterior and posterior scan (G, H) performed within 6 weeks of the PET image, shows I 131 accumulation within the renal mass (yellow arrow).