Mucinous Appendiceal Adenocarcinoma Mimicking a Bladder Tumor: A Case Report

Background: Appendiceal mucinous adenocarcinoma is a rare malignancy with nonspecific clinical manifestations, making early diagnosis challenging. Most localized tumors are diagnosed incidentally following appendectomy, whereas advanced disease may present with fistula formation or involvement of adjacent organs. Case Presentation: A 56-year-old nonsmoking male with no significant comorbidities presented with dysuria, gross hematuria with passage of amorphous clots for six months, and pneumaturia for three months. He denied abdominal pain, melena, or bowel obstruction symptoms. Clinical Findings and Investigations: Urinalysis revealed numerous red blood cells and pus cells, while urine culture grew Escherichia coli. Ultrasonography demonstrated a solid mass along the right lateral bladder wall with extravesical extension. Following treatment of urinary tract infection, cystoscopy revealed a mucin-covered tumor involving the right lateral and anterior bladder walls with evidence of fistula formation. Histopathological examination of cystoscopy biopsy demonstrated mucinous adenocarcinoma of appendiceal origin. Colonoscopy was unremarkable. Contrast-enhanced CT of the chest, abdomen, and pelvis showed a 6.3 × 4.7 cm heterogeneous mass involving the right lateral and anterior bladder walls with both endophytic and exophytic components and loss of fat planes with an adjacent ileal loop. Intervention and Outcome: Exploratory laparotomy revealed an appendiceal tumor encasing the ileum and infiltrating the urinary bladder, forming a complex fistulizing mass. En bloc appendectomy, partial cystectomy, and ileal resection with primary anastomosis were performed. Histopathology confirmed pT4bN0M0 mucinous adenocarcinoma arising in a tubulovillous adenoma, with direct invasion of the bladder detrusor muscle and ileum. Surgical margins were negative. Follow-up imaging at three months showed no evidence of recurrence. Conclusion: Appendiceal mucinous adenocarcinoma may rarely present with urological symptoms due to fistula formation and adjacent organ invasion. A multidisciplinary approach is essential for accurate diagnosis and optimal management in such complex cases. Keywords: Appendiceal Mucinous Adenocarcinoma; Hematuria; Pneumaturia; Fistula, Urinary Bladder Invasion.