What is the differential diagnosis for a septated liver cyst?

Differential Diagnosis for Septated Liver Cyst

A septated liver cyst requires MRI characterization to distinguish between benign entities (complicated simple cyst with hemorrhage, polycystic liver disease, Caroli disease) and mucinous cystic neoplasm (MCN), which mandates surgical resection when worrisome features are present. 1

Key Diagnostic Entities

Benign Septated Cysts

Hemorrhagic Simple Cyst

• Most common benign cause of septations in an otherwise simple cyst 2
• Presents with sudden severe abdominal pain in ~80% of cases 3
• MRI shows heterogeneous hyperintense signal on both T1- and T2-weighted sequences, with fluid-fluid levels representing blood-filled lakes between septa 2, 3
• Ultrasound demonstrates heterogeneous hyperechoic mobile material (clots) and thin mobile septations 3
• Critical distinction: Lacks contrast enhancement on contrast-enhanced ultrasound, unlike malignant lesions 2

Polycystic Liver Disease (PLD)

• Defined as >10 hepatic cysts (some sources use >20) 2, 4
• Multiple cysts may have septations from prior hemorrhage or infection 2
• Associated with autosomal dominant polycystic kidney disease (ADPKD) in most cases 4
• Ultrasound screening of liver and both kidneys combined with family history is diagnostic 4

Caroli Disease

• Characterized by segmental intrahepatic saccular or fusiform cystic dilatations of bile ducts 2
• Pathognomonic "central dot sign" represents fibrovascular bundles within dilated ducts 2
• Magnetic resonance cholangiopancreaticography (MRCP) has highest diagnostic accuracy by visualizing continuity between cystic lesions and bile ducts 2
• Must differentiate from Caroli syndrome, which includes congenital hepatic fibrosis and kidney cysts 2

Malignant/Premalignant Septated Cysts

Mucinous Cystic Neoplasm (MCN)

• This is the diagnosis you cannot miss—carries 3-6% risk of invasive carcinoma 1
• Predominantly affects middle-aged women, typically in left liver lobe 1
• Symptomatic in 86% of cases (pain, fullness, early satiety) 1
• Worrisome features requiring surgical resection: ≥1 major feature (thick septations, mural nodularity) PLUS ≥1 minor feature (upstream biliary dilatation, thin septations, internal hemorrhage, perfusional changes, or <3 coexistent hepatic cysts) 2, 1
• This combination carries 94-98% specificity for MCN 1
• CEA and CA 19-9 may be elevated, particularly with invasive carcinoma 1

Infectious Septated Cysts

Infected Hepatic Cyst

• Septations may develop from inflammatory debris and fibrin deposition 2
• Enhanced wall thickening and perilesional inflammation on imaging 3
• May show gas within the cyst on CT 3
• Clinical signs: fever, elevated WBC, elevated CRP 3
• Neutrophil debris and/or microorganisms in cyst aspirate confirms diagnosis 2

Echinococcal (Hydatid) Cyst

• Septations represent daughter cysts within the mother cyst 4, 5
• Serodiagnostic tests are invaluable for diagnosis 4
• Contrast-enhanced ultrasound (CEUS) helps differentiate from other entities when conventional imaging is ambiguous 4

Diagnostic Algorithm

Step 1: Initial Characterization with MRI

• MRI is superior to CT for characterizing septated cysts 2, 1
• Assess for worrisome features systematically 1
• CT is NOT recommended for diagnosing cyst hemorrhage (91% consensus) 2, 3

Step 2: Risk Stratification

• If ≥1 major + ≥1 minor worrisome feature present → Proceed directly to surgical resection 1
• If simple cyst with hemorrhage features (hyperintense T1/T2, no enhancement) → Conservative management 1, 3
• If multiple cysts (>10) → Evaluate for PLD with renal ultrasound and family history 2, 4
• If communicating with bile ducts with central dot sign → Diagnose Caroli disease with MRCP 2

Step 3: Adjunctive Testing When Diagnosis Unclear

• Contrast-enhanced ultrasound to identify vascularized septations (present in malignancy, absent in benign lesions) 2, 4
• Serodiagnostic tests if echinococcosis suspected 4
• Tumor markers (CEA, CA 19-9) if MCN suspected 1
• Cyst fluid analysis for TAG-72 may help distinguish simple cysts from MCNs 2

Critical Pitfalls to Avoid

Do not mistake hemorrhagic septations for malignancy

• Hemorrhage causes granulation tissue in septa with neovascularization that can mimic malignant hypervascularity 6
• Key differentiator: True MCNs have thick septations and nodularity, not just thin mobile septations from clots 1, 3

Do not use CT as primary modality

• CT is less accurate for assessing cyst contents and may miss hemorrhagic or proteinaceous material 2
• CT cannot reliably differentiate benign from malignant septations 3

Do not assume all septated cysts in women are MCNs

• While MCNs predominantly affect middle-aged women, hemorrhagic simple cysts are far more common 1
• Require the specific combination of worrisome features before proceeding to surgery 1

Giant cysts with septations warrant lower threshold for resection

• When imaging cannot definitively exclude malignancy in large septated cysts, surgical resection should be considered given the inability to exclude MCN 6
• Incomplete resection of MCN results in high recurrence rates 1