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Multiple von Meyenburg complexes mimicking diffuse liver metastases from esophageal squamous cell carcinoma.

Von Meyenburg complexes are benign liver lesions consisting of adenomatous bile duct proliferates. We present two patients suffering from esophageal cancer accompanied by the occurrence of von Meyenburg complexes. Preoperative computerized tomography (CT) of the liver had not shown these lesions. In one of the patients, diffuse nodular manifestation was found in both liver lobes, mimicking diffuse hepatic metastases. Intraoperative frozen section revealed the benign nature of the lesions in both cases. The patients underwent esophageal resection without complications. To the best of our knowledge, the coincidence of von Meyenburg complexes and esophageal cancer has never been reported before. This uncommon entity should be taken into consideration as a differential diagnosis of liver lesions in malignancies. It underlines the importance of intraoperative frozen section for liver lesions of unknown origin.


Abstract
Von Meyenburg complexes are benign liver lesions consisting of adenomatous bile duct proliferates. We present two patients suffering from esophageal cancer accompanied by the occurrence of von Meyenburg complexes. Preoperative computerized tomography (CT) of the liver had not shown these lesions. In one of the patients, diffuse nodular manifestation was found in both liver lobes, mimicking diffuse hepatic metastases. Intraoperative frozen section revealed the benign nature of the lesions in both cases. The patients underwent esophageal resection without complications. To the best of our knowledge, the coincidence of von Meyenburg complexes and esophageal cancer has never been reported before. This uncommon entity should be taken into consideration as a differential diagnosis of liver lesions in malignancies. It underlines the importance of intraoperative frozen section for liver lesions of unknown origin. www.wjgnet.com

DISCUSSION
Esophageal cancer is an important cause of cancer death, with an incidence of about 8-10/100 000 and 13 300 deaths in the United States in 2004 [8] . About 35% of all patients already suffer from liver metastasis by the time of diagnosis of the primary tumor. Since patients are excluded from potentially curative resection of the tumor when metastases are present, the diagnosis of liver metastases plays a crucial role for further treatment. The prognosis of these patients is also highly dependant on the respectability of the tumor.
Distant metastases, especially liver metastasis, can be diagnosed by CT scan or MRI with high sensitivity and specificity [6] . Sensitivities of these diagnostic means range between 74% and 85% [9] . In these series, almost all falsenegative results occurred when lesions were less than 1.5 cm in diameter. Therefore, non-invasive detection of small metastases can be difficult or even impossible.
When suspicious lesions are found by CT scan, further differentiation is possible by additional MRI imaging [5] . Differential diagnosis of liver metastases includes benign liver lesions, including hemangiomas, adenomas, von Meyenburg complexes or infectious lesions e.g. miliary tuberculosis [5] .
Bile duct hamartomas (von Meyenburg complexes) of the liver are usually detected during laparotomy or autopsy as an incidental finding. Multilocular occurrence is possible although they are rarely spread throughout the whole liver, as it was observed in our first patient. They may be found in normal liver tissue, but also in association with Caroli's syndrome, congenital hepatic fibrosis (CHF) or autosomal dominant polycystic kindney disease (ADPKD) [10] . Histology of von Meyenburg complexes consists of a variable number of dilated small bile ducts, embedded in a fibrous, sometimes hyalinizing stroma (Figure 3).
If detected by CT scan or MRI, von Meyenburg complexes appear as small intrahepatic cystoid lesions. The lesions are frequently located adjacent to the portal veins, although the lesions can also be located everywhere else [5] . However, it remains difficult to differentiate between metastases and benign liver lesions. Moreover, small liver lesions with a diameter of less than 1.5 cm are often not detected by CT or MRI [9] .
Since the treatment of metastatic disease is completely different from resectable esophageal cancer, liver lesions need to be identified and characterized as early as possible. In our presented patients, the preoperative staging did not reveal any liver metastases. This underlines the importance of exact diagnostic measures in cases of unexpected intraoperative findings. Besides intraoperative ultrasound of the liver, frozen section is the gold standard for further differentiation of liver lesions of unknown origin. Von Meyenburg complexes are defined as innocuous lesions. However, there are about 10 reported cases of neoplastic transformation of von Meyenburg complexes resulting in cholangiocarcinomas [2,3] .
In conclusion, von Meyenburg complexes are an important differential diagnosis of hepatic metastases. As the existence of liver metastases is crucial for therapeutic decision making in malignant diseases, this differential diagnosis must be carefully clarified. Since von Meyenburg complexes are usually less than 5 mm in size, they can escape preoperative radiologic diagnostics. The macroscopic appearance of von Meyenburg complexes can mimic liver metastasis as demonstrated in our reported patients. This underlines the importance of intraoperative frozen sections to make the correct diagnosis.