Perforated Appendiceal Mucinous Neoplasm With Long-Term Progression to Pseudomyxoma Peritonei in an Elderly Patient: A Case Report.

Low-grade appendiceal mucinous neoplasms (LAMNs) are rare tumors that may present as appendiceal mucoceles, with perforation carrying the risk of mucin dissemination and subsequent pseudomyxoma peritonei (PMP). We report the case of an 83-year-old female who presented with lower abdominal pain and was found on CT imaging to have an appendiceal mucocele. Laparoscopic appendicectomy revealed a perforated appendiceal mucocele with disseminated mucin, and histopathology confirmed a pT4a LAMN with perforation at the tip and a clear base. Despite its initially indolent course, surveillance over two and a half years demonstrated progressive intra-abdominal mucin accumulation and omental nodularity, culminating in radiological features of PMP with large-volume ascites and enhancing septations. Given her age and comorbidities, the patient declined cytoreductive surgery and was managed palliatively. This case emphasizes the indolent but progressive nature of perforated LAMNs, the importance of long-term surveillance, and the need to tailor management according to patient preference and surgical risk, particularly in elderly individuals. Clinicians should maintain a high index of suspicion for malignancy in appendiceal mucoceles and ensure ongoing surveillance following perforated LAMN to detect and manage progression to PMP.