Beyond the Inflamed Appendix: Low-Grade Appendiceal Mucinous Neoplasm—Emphasis on Macroscopic Findings

Low-grade appendiceal mucinous neoplasms (LAMNs) are uncommon epithelial tumors that frequently present with symptoms indistinguishable from acute appendicitis, yet may progress to pseudomyxoma peritonei with significant long-term morbidity. We report the case of a 51-year-old male who presented with periumbilical pain, nausea, and fever. Although clinical findings suggested acute appendicitis, abdominal ultrasound demonstrated cystic dilation of the appendix, raising suspicion for appendiceal mucocele. Appendectomy revealed a markedly cystic, pearly appendix with multifocal wall discontinuities and mucinous exudate, resulting in complete distortion of normal anatomy. Histological examination reflected LAMN with extra-appendiceal spread. Early postoperative reoperation due to free intra-abdominal fluid revealed pseudomyxoma peritonei. This case underscores the diagnostic challenge of LAMN, highlights the critical role of meticulous gross examination and complete embedding, and emphasizes that subtle macroscopic findings may herald clinically significant peritoneal dissemination.