How to manage hypodense liver lesions in a patient with Mirizzi syndrome?

Management of Hypodense Liver Lesions in Mirizzi Syndrome

In patients with Mirizzi syndrome presenting with hypodense liver lesions, proceed immediately with multiphasic contrast-enhanced MRI or CT to differentiate benign inflammatory changes from malignancy, as Mirizzi syndrome can mimic gallbladder and biliary malignancies and requires surgical management regardless of the liver lesion etiology. 1, 2

Understanding the Clinical Context

Mirizzi syndrome occurs when an impacted gallstone in the cystic duct or gallbladder infundibulum causes chronic inflammation and extrinsic compression of the common hepatic duct, eventually leading to cholecystobiliary fistulation in advanced cases. 3 The condition presents a diagnostic challenge because:

• The clinical presentation mimics malignancy: Patients typically present with obstructive jaundice and can have markedly elevated CA 19-9 levels (reported as high as 21,068 u/mL) even in the absence of malignancy. 4
• Preoperative diagnosis is achieved in only 56% of cases despite multiple imaging modalities, with the majority diagnosed intraoperatively. 5
• The condition occurs in less than 1% of patients with gallstones, making it an uncommon but important consideration. 6

Initial Imaging Strategy for Hypodense Lesions

For any hypodense liver lesion with density >20 HU on initial imaging, obtain multiphasic contrast-enhanced imaging immediately, as this indicates solid tissue or complex fluid rather than simple cyst. 1

Recommended Imaging Protocol:

• MRI with contrast is the preferred modality because it provides superior soft tissue characterization and can differentiate Mirizzi syndrome from gallbladder malignancy by showing the extent of inflammation around the gallbladder. 7
• MRCP should be included as it is increasingly important in Mirizzi syndrome, showing typical findings of a shrunken gallbladder, impacted stone(s) in the cystic duct, dilated intrahepatic tree, and common hepatic duct with normal-sized common bile duct. 7
• Triphasic CT achieves 80-90% sensitivity and 90-95% specificity for differentiating benign from malignant lesions if MRI is unavailable or contraindicated. 1

Distinguishing Inflammatory from Malignant Lesions

The enhancement pattern is critical for diagnosis:

• Inflammatory changes from Mirizzi syndrome typically show periportal edema and inflammatory enhancement without the characteristic arterial hyperenhancement and washout pattern of hepatocellular carcinoma. 1
• CT's main role is to differentiate Mirizzi syndrome from malignancy in the porta hepatis or liver parenchyma. 7
• If imaging shows peripheral enhancement with early central washout, consider intrahepatic cholangiocarcinoma, which can coexist with chronic biliary inflammation. 1

When to Perform ERCP

ERCP is the gold standard for diagnosing Mirizzi syndrome and should be performed when:

• Imaging suggests biliary obstruction with uncertain etiology 7
• You need to delineate the cause, level, and extent of biliary obstruction 7
• Therapeutic intervention is needed, such as stone extraction or biliary stent placement 7

ERCP has the advantage of identifying ductal abnormalities including fistula and can provide therapeutic options. 7

Role of Liver Biopsy

Biopsy is indicated when diagnosis remains uncertain after optimal imaging AND the result will change management. 1 Specifically:

• Core needle biopsy is required (fine needle aspiration is insufficient) with 90-95% sensitivity. 1
• Use CEUS or fusion imaging guidance for lesions with poor conspicuity, achieving 96-100% technical success. 1
• Biopsy is particularly important if the patient is proceeding to systemic chemotherapy, radiation, or clinical trial enrollment. 1

Critical Management Considerations

Surgical Planning:

• Open cholecystectomy remains the standard for managing Mirizzi syndrome, with good short- and long-term results and low mortality/morbidity. 7
• Laparoscopic management is increasingly viable for less severe stages, but the presence of dense adhesions and distorted anatomy at Calot's triangle increases the risk of bile duct injury. 3
• For Type I lesions (without cholecystobiliary fistula), partial cholecystectomy alone is safe and appropriate. 5
• For Type II lesions (with fistula), depending on fistula size, either primary closure over a T-tube or bilioenteric anastomosis (preferably Roux-en-Y) is appropriate. 5

Preoperative Preparation:

• Endoscopic treatment can serve as a temporizing measure to provide biliary drainage in preparation for elective surgery, particularly in elderly patients or those with multiple comorbidities. 7
• Maintain high index of suspicion for malignancy in elderly patients with elevated CA 19-9, as Mirizzi syndrome and cholangiocarcinoma are difficult to distinguish. 4

Common Pitfalls to Avoid

• Do not rely on CA 19-9 levels alone to diagnose malignancy, as markedly elevated levels can occur in Mirizzi syndrome without cancer. 4
• Do not attempt laparoscopic cholecystectomy if dense adhesions or distorted anatomy is suspected, as this increases morbidity and mortality risk. 7, 3
• Do not use Tc-99m sulfur colloid scans, as they have no role in modern evaluation of indeterminate liver lesions. 2
• Recognize that the majority of cases are diagnosed intraoperatively, so maintain vigilance during surgery even with negative preoperative imaging. 5, 8