Low-grade Appendiceal Mucinous Neoplasm with Appendiceal Reduction and Re-expansion Over a Two-year Period: A Case Report.

A 71-year-old woman was found to have submucosal tumor-like lesion on colonoscopy (CS) before gastric surgery, and computed tomography (CT) showed a 12-mm structure at the base of the appendix. The lesion could not be clearly detected on CT nine months later, but it had enlarged again on CT one year later; therefore, CS and endoscopic ultrasound (EUS) were performed. The lesion was determined to be cystic with viscous contents, and laparoscopic appendicectomy was performed. This is the first report of low-grade appendiceal mucinous neoplasm (LAMN) diagnosed by a histopathologic examination of a resected specimen showing shrinkage and re-expansion of the appendix.