Solitary Renal Metastasis in Esophageal Squamous Cell Cancer Detected on F-18 FDG PET/CT - A Rare Presentation

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A 62-year-old male presented with progressive dysphagia for the past 1 month with significant weight loss. The esophagogastroscopy revealed an ulceroproliferative growth in the lower thoracic esophagus, which was confirmed as esophageal squamous cell cancer (E-SCC) on biopsy. On baseline staging fluorine-18 fluoro-D-glucose positron emission tomography-computed tomography (F-18 FDG PET/CT) scan [Figure 1], the maximum intensity projection [Figure 1a] image showed focal radiotracer uptake in the lower thorax and left lumbar region which localized metabolically active thickening in the lower thoracic esophagus [Figure 1b] and an irregular hypodense lesion in the left kidney on fused PET/CT images [Figure 1c and d]. The possible differentials of the renal lesion were either synchronous renal malignancy or metastatic from the esophageal primary. A PET-guided core needle biopsy from the left kidney lesion [Figure 1e and f] showed an invasive tumor, with individual cell keratinization and keratin pearls suggestive of metastatic SCC. The patient was thus referred for palliative systemic chemotherapy.

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Figure 1 Maximum intensity projection image (a) of Fluorine-18 fluoro-D-glucose positron emission tomography-computed tomography (F-18 FDG PET/CT) showing 2 focal areas of abnormal FDG uptake in the thorax and left lumbar region (black arrows). Fused axial and coronal images localized them in the lower thoracic esophagus ([b] SUV_max-20) which was the primary malignant site (white arrow) and in the interpolar region of the left kidney (white arrow) ([c and d] SUV_max - 7.1). The PET/CT-guided biopsy from the left kidney (e and f) showing an invasive tumor, with individual cell keratinization and keratin pearls suggestive of metastatic squamous cell carcinoma

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Esophageal SCC usually metastasizes to the liver, lung, bone, brain, or adrenals.[1] Although renal metastases from E-SCC are found in 8%–13% of autopsy studies, clinical presentation with renal metastasis is very rare with only about 20 cases reported till date.[12345] Majority of these cases were Asian males with E-SCC, with the renal metastasis presenting metachronously. Solitary unilateral renal metastasis presenting in a synchronous fashion is extremely rare and has been reported only once before from China.[3] Renal metastases from E-SCC are usually small and asymptomatic and found in the highly vascular renal cortex in a subcapsular location, unlike primary renal malignancies which are symptomatic large masses with hematuria or pain.[34] F-18 FDG PET/CT has been reported to detect E-SCC metastases at unusual locations, and renal metastases have an intense FDG uptake.[678] This underlines the value of a baseline F-18 FDG PET/CT in E-SCC to detect small asymptomatic renal metastases and can lead to change in management. Once detected, the lesion should undergo targeted biopsy to confirm metastasis, as in our case. The treatment for isolated renal metastases in E-SCC is typically palliative chemotherapy, with a poor survival of 2 to 24 months.[1] The role of nephrectomy is uncertain and is only indicated when there is significant pain or massive hematuria.[9]