preoperative staging is crucial for the management of cancer patients . in colon cancer patients ,
extensive preoperative assessment of metastatic disease , especially liver metastases , plays a key role in the adequate clinical decision of surgical treatment . a wide range of imaging modalities , including ultrasound scan ( us ) , computed tomography ( ct ) , ct during arterial portography ( ctap ) and magnetic resonance imaging ( mri ) , are available for the detection of hepatic metastases . in terms of the ability to detect metastases in otherwise normal liver
, high diagnostic ability can be expected in each of the above techniques . however , when multiple focal lesions such as cysts , biliary hamartomas and hemangiomas exist as the background noise , the conventional screening strategy , which includes us , ct or non - enhanced mri , will not be sufficient for the accurate detection of metastatic lesions in most of the cases .
superparamagnetic iron oxide ( spio ) , such as ferumoxides and ferucarbotrans ( resovist ) , has recently been developed as a liver - specific mri contrast agent to improve the detectability of hepatic tumors [ 1 , 2 ] .
spios contain iron particles which are phagocytosed by kupffer cells and the reticuloendothelial system in normal liver and in most benign lesions .
since kupffer cells are not present in metastatic lesions , administration of the contrast agent will result in improvement of the mean lesion to liver contrast ratio , resulting in an increased lesion conspicuousness on mri .
thus , spio - enhanced mri provides excellent visualization of liver metastatic lesions in the preoperative assessment of colorectal cancer patients .
we describe a patient with sigmoid colon cancer in whom preoperative assessment by us and contrast - enhanced ct showed numerous cystic lesions of the liver , suspicious of von meyenburg complex , making difficult the visualization of other lesions .
a 56-year - old man was referred to our institution with advanced carcinoma of the sigmoid colon .
preoperative assessment of metastatic disease was performed by contrast - enhanced ct scan of the thorax and the abdomen .
contrast - enhanced ct demonstrated multiple , non - enhancing , irregularly defined hypodense structures ( < 1.5 cm ) in both lobes of the liver ( fig .
abdominal us also revealed many hypoechoic and hyperechoic lesions scattered in both hepatic lobes ( fig .
although the ct and us findings were highly suspicious of multiple bile duct hamartoma , also known as von meyenburg complex , to exclude disseminated liver metastases , mr examination was performed .
mri confirmed the presence of multiple hypointense and hyperintense hepatic nodules , on t1-weighted gradient echo images and t2-weighted fast spin echo images , respectively ( fig .
2a , b ) . on heavily t2-weighted images , the signal intensity increased ( fig .
these findings are characteristic mr features of von meyenburg complex [ 4 , 5 , 6 ] .
further resovist - enhanced images revealed two different lesions in hepatic segment vii and v , in addition to the numerous cystic lesions suspicious of von meyenburg complex . fast spoiled gradient echo sequence with a long te and a large flip angle ( so - called kupffer cell images ) detected two enhanced lesions except for cystic lesions with isointensity on this sequence ( fig .
these two lesions showed nodular peripheral enhancement similar to aortic attenuation on contrast - enhanced ct ( fig .
these hemangiomas and the multiple cystic lesions were both hypointense on t1- and hyperintense on t2-weighted images .
therefore , detection and characterization of such lesions by unenhanced mri is a difficult matter .
after injection of resovist , these two types of lesions revealed iso- and hypointensity , respectively , on t1-weighted images ( fig .
resovist - enhanced mr findings and other imaging modalities provided no obvious evidence of metastatic lesions .
the liver showed many tiny cystic lesions on its surface , and intraoperative us confirmed the presence of two hemangiomas , but no metastases .
the postoperative course was uneventful , and the follow - up ct 18 months later showed neither change in the findings of hepatic lesions nor recurrence .
if a curative resection is performed , a 5-year survival rate of 2530% has been shown in a large number of studies . therefore extensive preoperative investigation for liver metastases
previous studies have proved that spio definitely improves the detectability of hepatic metastases on unenhanced mr images up to the level of ctap . in our institution ,
us and contrast - enhanced ct are the first choice for screening of liver metastases , and spio - enchanced mri and intraoperative us are performed additionally when necessary . in the present case ,
the liver was diffusely occupied by cystic lesions , which led to the suspicion of von meyenburg complex .
von meyenburg complex , also known as multiple bile duct hamartomas or biliary hamartomas , is a benign malformation of the bile ducts in which the embryonal bile duct network has failed to involute .
the us appearance of von meyenburg complex varies between hypoechoic and hyperechoic lesions [ 5 , 6 ] , and some cases of von meyenburg complex have been noted to show homogenous enhancement on contranst - enhanced ct [ 5 , 9 ] .
therefore , it is quite difficult to exclude other hepatic lesions , such as tumor metastasis , by us and ct . on mri ,
the signal intensity on t2-weighted image progressively decreases from cysts and biliary hamartomas to hemangiomas and metastases , but the signal intensity , in most cases , overlaps , resulting in an inconclusive study .
further investigation is required on how to improve the detection ability of metastatic lesions behind the background noise of numerous cysts in oncologic patients , such as in the present case .
the most effective mr pulse sequence for the detection of metastatic lesions is not a fast spin echo t2-weighted sequence , but a gradient echo sequence with a long te , so - called t2 * -weighted sequence . on t2 * -weighted images , both cysts and metastases show hyperintensity compared to the normal hepatic parenchyma .
if t2 * -weighted sequence is modified with a larger flip angle , cysts and biliary hamartomas become isointense compared to liver parenchyma , whereas metastases and hemangiomas remain hyperintense because of relatively short t1 . this modified sequence , which is called  kupffer ( cell ) imaging , may be more suitable than the original t2 * -weighted sequence for the detection of lesions hidden among cysts . indeed , kupffer cell imaging was valuable to extract two hemangiomas from multiple cystic lesions in this patient . however
, when evaluating metastatic tumors , it is sometimes difficult to differentiate solid metastatic tumors from hemangiomas because both lesions shows high intensity on kupffer cell images .
recently , in addition to the lesion sensitivity , the lesion specificity can also be improved by combination of various mr pulse sequences , including t2-weighted sequence and post - contrast t1-weighted sequence with kupffer cell imaging [ 13 , 14 , 15 ] .
hemangiomas show high intensity on pre - contrast t2-weighted image , and a significant signal drop is observed on post - contrast t2-weighted images . on post - contrast
the intensity of metastases on pre - contrast t2-weighted images is usually lower than that of hemangiomas , and the signal intensity does not change on post - contrast t2-weighted image [ 13 , 14 ] .
metastases show hypointensity with the well - known  ring enhancement on post - contrast t1-weighted image . in our patient ,
two different lesions were diagnosed as hemangiomas with high intensity on pre - contrast t2-weighted image and a characteristic signal drop on post - contrast t2-weighted image . in this case , the biliary duct hamartomas were not histopathologically proven and the hemangioma was neither radiologically nor pathologically proven and the metastases were not excluded on solid base of biopsy , but the follow - up period was 18 months . during this follow - up period , the patient had no recurrence , and we are confident that these lesions are not metastatic lesions . moreover , in japan , it is not ethically feasible to perform biopsy of lesions suspected of hamartomas or hemangioma , and consequently the pathological diagnosis of such lesions is unfeasible . in conclusion ,
resovist - enhanced mr imaging was useful for the detection and characterization of hepatic lesions and preoperative staging of colorectal cancer . in cases where multiple focal lesions , such as cysts and biliary hamartomas , exist as the background noise
, spio - enhanced mri including kupffer cell imaging may improve the sensitivity and specificity of detection , especially of metastasic lesions .
in cases in whom the conventional imaging studies fail to give a diagnosis , resovist - enhanced mr imaging with various sets of pulse sequence is recommended for the differential diagnosis of benign and malignant hepatic lesions .
 extensive preoperative assessment of hepatic metastases is required in colon cancer patients . 
 we report a case in whom the preoperative investigation by ultrasound scan and contrast - enhanced computed tomography revealed numerous cystic lesions of the liver , suspicious of von meyenburg complex . 
 magnetic resonance and magnetic resonance cholangiographic images demonstrated typical features of von meyenburg complex . 
 further resovist - enhanced magnetic resonance imaging detected two hemangiomas in addition to the multiple cystic lesions . 
 so - called kupffer cell imaging strongly helped the detection of these hemangiomas , and a combination of various magnetic resonance pulse sequences was of great value for the differential diagnosis of cystic lesions and hemangiomas . in cases in whom conventional imaging studies fail to give a definite diagnosis , such as in the present case , superparamagnetic iron oxide - enhanced magnetic resonance imaging is meaningful for adequate preoperative staging . 
Introduction
Case Report
Discussion