Solitary Lymph Node Metastasis of Sigmoid Colon Cancer to Posterior Site of Inferior Vena Cava: A Case Report.

Colorectal cancer (CRC) remains a leading cause of cancer-related mortality worldwide. Despite advances in surgical and systemic treatments, recurrence continues to impact prognosis. Paraaortic lymph node metastasis (PALM) is an uncommon site of recurrence, occurring in only 1-2% of CRC cases. Among PALMs, solitary lymph node metastasis located posterior to the inferior vena cava (IVC) is exceptionally rare and challenging to diagnose. We present the case of a 66-year-old woman initially diagnosed with sigmoid colon cancer and multiple liver metastases. Following laparoscopic sigmoidectomy for tumor-related bleeding, the cancer was staged as pT3, pN3, cM1 (H), Stage IV. Chemotherapy resulted in significant regression of liver lesions. However, fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) revealed increased FDG uptake in a solitary 5-mm lymph node (LN) located posterior to the IVC. The patient subsequently underwent hepatic resection and lymphadenectomy. Histopathological examination confirmed metastatic adenocarcinoma in both the hepatic lesions and the solitary LN; however, the liver lesions showed a marked therapeutic response, while the LN did not. The discrepancy in therapeutic response between the liver metastases and the LN may be attributed to variable drug distribution and tissue-specific responses to chemotherapy. Solitary metastasis to the LN posterior to the IVC is extremely rare and difficult to diagnose. This case highlights the diagnostic and therapeutic challenges of solitary PALM in CRC. Accurate diagnosis of PALM is limited due to the difficulty for performing biopsy and imaging sensitivity, particularly for small LNs. Multidisciplinary evaluation, including PET/CT and surgical biopsy, is essential to guide treatment decisions.