Natural course of an untreated metastatic perirectal lymph node after the endoscopic resection of a rectal neuroendocrine tumor

Abstract

Lymph node metastasis is rare in small (i.e., <10 mm) rectal neuroendocrine tumors (NETs). In addition to tumor size, pathological features such as the mitotic or Ki-67 proliferation index are associated with lymph node metastasis in rectal NETs. We recently treated a patient who underwent endoscopic treatment of a small, grade 1 rectal NET that recurred in the form of perirectal lymph node metastasis 7 years later. A 7-mm-sized perirectal lymph node was noted at the time of the initial endoscopic treatment. The same lymph node was found to be slightly enlarged on follow-up and finally confirmed as a metastatic NET. Therefore, the perirectal lymph node metastasis might have been present at the time of the initial diagnosis. However, the growth rate of the lymph node was extremely low, and it took 7 years to increase in size from 7 to 10 mm. NETs with low Ki-67 proliferation index and without mitotic activity may grow extremely slowly even if they are metastatic.

Keywords: Lymph node; Metastasis; Neuroendocrine tumor; Rectum.

Fig. 1. Endoscopic findings. (A) A 5-mm-sized subepithelial tumor in the rectum. (B and C) Endoscopic mucosal resection was performed.

Fig. 2. Histopathological findings of the rectal neuroendocrine tumor. (A) The endoscopically resected specimen mostly consisted of a relatively well-demarcated tumor. The tumor involved the mucosa and submucosa, and it measured 8 mm across the greatest dimension. The deep resection margin characterized the tumor (H&E, ×10). (B) The tumor cells formed nests or cords in the sclerotic stroma and demonstrated histological patterns typical of a neuroendocrine tumor. The tumor cell nuclei are round or ovoid and demonstrate fine salt-and-pepper chromatin (H&E, ×200).

Fig. 3. Abdominopelvic CT findings. (A) The initial CT imaging showed perirectal lymph node. (B) Seven years later, the perirectal lymph node had slightly enlarged from 7 to 10 mm.

Fig. 4. Histological findings of the perirectal lymph node. (A) The metastatic node was located in the pericolic adipose tissue, but there was no recognizable lymph node structure. The node demonstrated a stellate shape (H&E, ×10). (B) Lymphovascular invasion was noted in the peripheral part of the metastatic node (H&E, ×100). (C) Some parts of the tumor demonstrated neural and perineural invasion (H&E, ×100).