Mucinous Cystic Neoplasm of the Liver
Definition and Pathologic Features
Mucinous cystic neoplasm (MCN) of the liver is a rare cystic epithelial tumor lined by mucin-producing epithelium overlying ovarian-like hypercellular stroma, occurring predominantly in middle-aged women. 1
The two pathologic hallmarks that define MCN are:
- Presence of ovarian-like hypercellular stroma (the definitive diagnostic feature) 1
- Absence of communication with the bile duct (distinguishes MCN from intraductal papillary neoplasms) 1
These lesions were formerly called "biliary cystadenoma" or "biliary cystadenocarcinoma" but are now classified under the unified term MCN. 1
Epidemiology and Clinical Presentation
MCNs account for less than 5% of all liver cysts and occur predominantly in middle-aged women. 1, 2
86% of MCNs are symptomatic at presentation, manifesting as: 1
- Abdominal pain
- Abdominal fullness
- Early satiety (due to mass effect from large size)
Malignant Potential
The vast majority of MCNs are benign, but 3-6% harbor invasive carcinoma, typically in older patients. 1
MCNs may present with varying degrees of dysplasia: 1
- Low-grade dysplasia
- High-grade dysplasia
- Invasive carcinoma
Serum tumor markers (CEA and CA 19-9) may be elevated, particularly with invasive carcinoma, but lack good diagnostic accuracy. 1
Imaging Characteristics
MCNs are typically solitary, large, well-circumscribed cystic lesions that predominantly form in the left liver lobe. 1
Key imaging features include: 1
- Multiloculated appearance (90%) or unilocular
- No communication with the biliary tree (upstream ductal dilatation, if present, is from mass effect)
- Enhancing septa, mural calcifications, and mural nodules
- Mural nodules >1 cm are associated with malignancy 1
- Septa arise from the cyst wall without associated wall indentation 1
Worrisome Features for MCN
MRI should be used to characterize hepatic cysts with worrisome features, as it is more accurate than CT. 1
The combination of ≥1 major feature PLUS ≥1 minor feature carries 94-98% specificity for MCN: 1
Major worrisome features: 1
- Thick septations
- Nodularity
Minor worrisome features: 1
- Upstream biliary dilatation
- Thin septations
- Internal hemorrhage
- Perfusional change
- <3 coexistent hepatic cysts
Diagnostic Challenges
20-50% of MCNs are not properly identified before surgery, leading to inadequate resection. 1
Distinguishing MCNs from simple hepatic cysts remains challenging and requires multidisciplinary expertise involving hepatogastroenterologists, abdominal radiologists, abdominal surgeons, and expert pathologists. 1
Complicated hepatic cysts (infection or hemorrhage) may mimic MCNs on imaging, leading to misdiagnosis. 1
Invasive MCNs can only be differentiated from non-invasive MCNs by microscopic evaluation for ovarian-type stroma, making intraoperative biopsy and frozen section essential. 2
Management
Surgical resection with complete excision is the gold standard for all suspected MCNs of the liver. 1
Surgical Approach
Formal hepatic resection or enucleation with free margins is the preferred approach, with extended hemihepatectomy sometimes required for complete removal. 1
Fenestration is inadequate and associated with high tumor recurrence rates (0-26% recurrence after incomplete resection). 1
Complete surgical removal yields good long-term outcomes with very low recurrence rates. 1 The presence of malignancy at initial resection is the most significant factor associated with poorer outcomes. 1
Recurrence with malignant transformation in patients who initially had non-malignant MCNs is rare. 1
Rationale for Aggressive Surgical Management
Despite the difficulty in establishing reliable preoperative diagnosis and the low prevalence of MCNs, the current literature provides compelling evidence for complete surgical resection due to: 1