Synchronous Low-Grade Appendiceal Mucinous Neoplasm, Perforated Ascending Colon Diverticulitis, and Mature Ovarian Cystic Teratoma Treated in a Single Operation: A Case Report

Abstract

Background: Low-grade appendiceal mucinous neoplasm (LAMN) is found in about 0.13%–0.30% of appendectomy specimens and can cause pseudomyxoma peritonei (PMP) after rupture. Its coexistence with perforated ascending colon diverticulitis and an ovarian mature cystic teratoma complicates diagnosis and surgical planning.

Objective: To describe the presentation, imaging pitfalls, single-stage surgical management, and 90-day outcome of this combination.

Methods: Following the CARE guideline, we report a 52-year-old postmenopausal woman treated at Klungkung Regional General Hospital, Indonesia (protocol No. 2026/0418) and followed from symptom onset (day −30) to postoperative day 90.

Results: On admission she had leukocytosis (white blood cells 19.18 × 10³/µL; neutrophils 91.0%; neutrophil-to-lymphocyte ratio 21.67) and pre-renal azotemia (creatinine 1.40 mg/dL). Ultrasonography and computed tomography showed a 10.20 × 10.44 × 10.46 cm (583.2 cm³) right ovarian teratoma and a right lower quadrant phlegmon containing a tubular structure that was read as an abscess. At laparotomy, this proved to be a 9.50 × 3.00 × 2.50 cm (37.31 cm³) mucinous appendix; two ascending colon diverticula had perforated (50.0 mL of pus). Single-stage oncologic right hemicolectomy, end ileostomy, transverse colon stump closure, and total abdominal hysterectomy with bilateral salpingo-oophorectomy achieved R0 resection of a pT4a LAMN. White blood cells (8.42 × 10³/µL; −56.1%) and creatinine (0.88 mg/dL; −37.1%) normalized by day 5; at day 90, there was no clinical, biochemical, or CT evidence of PMP.

Conclusion: In this patient, a large ovarian teratoma and a diverticular phlegmon obscured a coexisting LAMN on imaging; systematic intraoperative exploration allowed all three lesions to be treated in one operation.