Mucinous cystic neoplasms of the liver: current insights into epidemiology, diagnosis, and treatment.

Mucinous cystic neoplasms of the liver (MCN-L) are rare cyst-forming epithelial tumors defined by mucin-producing epithelium and characteristic ovarian-type stroma. Once grouped with other biliary cystic lesions, MCN-L are now recognized as a distinct premalignant entity with potential for progression to invasive carcinoma. Accurate preoperative diagnosis remains difficult because imaging findings frequently overlap with those of other cystic liver lesions, including simple hepatic cysts, hydatid cysts, and intraductal papillary neoplasms of the bile duct. Laboratory markers, cyst fluid analysis, and biopsy have limited diagnostic reliability and cannot confidently exclude malignancy. Given the risk of malignant transformation and diagnostic uncertainty, complete surgical excision is recommended for all suspected MCN-L irrespective of symptom status or lesion size. Resection with negative margins is associated with excellent long-term outcomes, whereas non-definitive procedures such as cyst fenestration or drainage are associated with high recurrence rates. In selected cases, intraoperative findings-particularly the presence of the "peeling sign"-may allow safe parenchyma-sparing excision while preserving functional liver tissue. Prognosis is generally favorable in non-invasive disease but significantly worse when invasive carcinoma is present, a feature that cannot be reliably predicted before surgery. This review synthesizes current evidence on the epidemiology, diagnostic approach, imaging characteristics, pathology, surgical management, and prognosis of MCN-L, and proposes a practical framework for the evaluation and management of cystic liver lesions suspicious for MCN-L.