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Mucinous cystadenoma is a benign epithelial ovarian tumor composed of cysts lined by mucin-secreting columnar epithelium, histologically resembling endocervical or intestinal epithelium. It is one of the most common benign ovarian neoplasms.

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Etiopathology

• Cell of origin: Ovarian surface (coelomic) epithelium with mucinous (endocervical/intestinal) differentiation.
• Epidemiology:
  • Occurs most commonly in 30–50 years (reproductive and perimenopausal).
  • Less frequently bilateral (~5–10%, vs ~20% in serous cystadenoma).
• Molecular biology: Some tumors show KRAS mutations, similar to mucinous borderline and carcinoma.
• Biological behavior: Benign, but forms part of the adenoma–borderline–carcinoma sequence.

Clinical Features

• Frequently asymptomatic, discovered incidentally.
• Large tumors cause abdominal distention, pelvic mass effect, pain, urinary or bowel symptoms.
• May rupture, leading to pseudomyxoma peritonei if associated with appendiceal mucinous tumor.
• Risk of torsion in giant cysts.

Gross Pathology

• Usually very large (can reach 20–30 cm, occasionally >40 cm; larger than serous).
• Unilateral in ~90–95%.
• Smooth surface, often multiloculated with thin septations.
• Contents: viscous, gelatinous, mucin-rich fluid.
• Papillary excrescences are rare (seen in borderline/malignant forms).