Cystic Lesion of Dissected Pararectal Lymph Node in a Female Patient With Rectal Carcinoma: A Rare Pattern of Nodal Metastasis Mimicking a Serous Inclusion Cyst.

Nodal metastatic foci of colorectal carcinoma are usually solid nodules. Serous inclusions are occasionally found in lymph nodes, particularly in female patients, and they occasionally form cysts. An 86-year-old woman was treated with laparoscopic low anterior resection and D3 lymph node dissection for advanced rectal carcinoma. A cyst with serous fluid and no necrotic debris was found within one of the dissected pararectal lymph nodes. Histologically, the cyst was lined by low columnar-to-cuboid epithelium with mild nuclear atypia, mimicking a serous inclusion cyst. Immunohistochemically, the epithelial cells were positive for caudal type homeobox 2 and negative for Wilms' tumor suppressor gene1. Immunohistochemistry for p53 showed a diffuse strong positivity, indicating a mutant as seen in primary rectal carcinoma. Thus, the nodal cystic lesion was confirmed to be a metastatic lesion. It is important to carefully assess a nodal cystic lesion to confirm whether it is benign or malignant.