Detection of an Isolated Solitary Brain Metastasis from Colon Adenocarcinoma via 18F-FDG PET/CT: A Rare Case and Its Multimodal Management

Background: Brain metastasis (BM) is observed in approximately 1–4% of cases involving metastatic colon cancer and is almost invariably associated with extracranial dissemination. The occurrence of isolated intracranial disease in the absence of systemic metastases is, therefore, exceedingly rare. Case presentation: We report a 74 year-old female who presented with new-onset focal seizures 18 months after curative surgery for stage IIIC sigmoid adenocarcinoma. The F18 FDG PET/CT scan revealed increased F18 FDG uptake in an 18x19 mm hyperdense lesion located in the right temporal lobe, accompanied by a substantial edematous region in the surrounding area (SUV max:8.0) but no abnormal F18 FDG accumulation elsewhere, confirming isolated BM. Brain MRI revealed a 28x30 mm contrast-enhancing lesion in the right temporal lobe with vasogenic edema. The patient underwent gross-total resection followed by adjuvant stereotactic radiosurgery (SRS, 18 Gy single fraction). Histopathology showed metastatic moderately-differentiated colon adenocarcinoma (CK20+, CDX-2+, CK7+, P53+). Post-operative capecitabine plus bevacizumab was given for six cycles. At 12-month follow-up the patient remains disease-free on surveillance MRI and F18 PET/CT. Conclusion: This case illustrates the diagnostic value of F18 FDG PET/CT in excluding extracranial disease and supports an aggressive local-therapy strategy (surgery ± SRS) for solitary kolon adenocarsinoma BM, which may confer prolonged survival.