Appendiceal mucocele on imaging masking invasive goblet cell adenocarcinoma

A woman in her late 60s presented with right lower quadrant abdominal pain suggestive of acute appendicitis. Cross-sectional imaging demonstrated a dilated, fluid-filled appendix with mural enhancement, interpreted as concerning for appendiceal mucocele. Laparoscopic appendectomy was performed. Histopathologic examination revealed goblet cell adenocarcinoma invading into the subserosa (pT3) with involvement of the proximal resection margin. Completion right hemicolectomy was subsequently undertaken for definitive oncologic management and lymph node staging and revealed no residual carcinoma, with nine negative lymph nodes. Postoperative staging imaging showed no evidence of metastatic disease, and the patient was managed with oncologic surveillance. This case highlights the diagnostic limitation of imaging in differentiating appendiceal mucocele from invasive malignancy and underscores the importance of histopathologic evaluation and appropriate oncologic resection in goblet cell adenocarcinoma.