sinusoidal obstruction syndrome ( sos ) is a severe adverse event of long - term chemotherapy in patients with colorectal cancer .
in contrast , it sometimes appears as a liver mass occurring with local parenchymal hemorrhaging , and is often misdiagnosed as liver metastasis .
a 40-year - old woman with rectal cancer underwent high anterior resection and partial liver resection of segment 7 due to synchronous liver metastasis .
she received oxaliplatin - based chemotherapy ( mfolfox6 ) as adjuvant chemotherapy for 6 months .
a 13-mm irregular low - echoic mass was detected by ct in segment 3 of the liver 12 months after the operation .
the mass was again resected as a liver metastasis because it had increased in size .
the pathological diagnosis was focal sos , which showed sinusoidal dilation and congestion by hepatocyte trabeculae in the liver parenchyma .
atypical irregular tumors should be considered as sos when the patient has received oxaliplatin - based chemotherapy . a qualitative imaging modality diagnosis , such as with diffusion - weighted mri , is superior to a morphological diagnosis in focal sos .
synchronous and metachronous liver metastases are found in 20% - 25% and 35% - 55% of patients with advanced colorectal cancer , respectively ( 1 , 2 ) .
liver resection provides a 30% - 40% increase in the 5-year survival rate when metastasis is found only in the liver ( 3 ) .
oxaliplatin - based chemotherapy is effective and is the first treatment choice for advanced colorectal cancer .
recently , liver damage from long - term chemotherapy has arisen as a new clinical problem for colorectal cancer treatment .
sinusoidal obstruction syndrome ( sos ) is diffuse liver damage that causes liver congestion ( 5 ) .
however , focal sos mimics metastatic liver tumors and has been ineffectively treated by surgery in three previous reports ( 6 - 8 ) .
we report a case of synchronous colorectal metastasis and metachronous focal sos within one year .
we found that a qualitative imaging modality , such as diffusion - weighted mri , can lead to an accurate diagnosis .
a 40-year - old woman underwent high anterior resection for rectal cancer , with partial liver resection of segment 7 for synchronous liver metastasis .
on ct , a 13-mm irregular tumor was found in segment 3 of the liver 12 months after the operation .
the laboratory data showed a slight decrease in the platelet count ( 12.8     10/mm ) , with otherwise normal findings ( albumin 3.8  g / dl , total bilirubin 0.8  mg / dl , aspartate transaminase 34  iu / l , alanine transaminase 22 
all tested tumor markers remained normal after the first operation ( carcinoembryonic antigen 1.8  ng / ml , carbohydrate antigen 19 - 9 13  u / ml , and -fetoprotein 1.7  ng / ml ) .
ultrasonography showed a 17-mm isoechoic tumor that was surrounded by a low - echoic area in the liver metastasis at the first operation .
the pseudotumor of sos was unclear on conventional ultrasonography ( figure 1a ) , whereas sonazoid contrast - enhanced ultrasonography in the kupffer phase visualized a 13-mm low - echoic mass ( figure 1b ) .
enhanced ct at the early phase showed a ring - enhanced tumor in segment 7 ( figure 2a ) , whereas the metachronous pseudotumor presented as an unclear hypodense mass without surrounding enhancement ( figure 2b ) . a , the pseudotumor of sos presented as an unclear isoechoic tumor ; b , the pseudotumor was clearly visualized as a low - echoic mass on the kupffer phase of sonazoid contrast - enhanced ultrasonography .
a , enhanced ct in the portal phase clearly visualized a ring - enhanced tumor of primary liver metastasis ; b , the pseudotumor presented as an irregular hypodense mass without any surrounding enhancement .
mri revealed that the primary liver metastasis was a low - intensity mass on t1-weighted images and a high - intensity mass on t2-weighted images .
the hepatocyte phase of gd - eob mri and diffusion - weighted mri clearly showed the mass to be a tumor .
the pseudotumor by sos also presented as a low - intensity mass on t1-weighted images ( figure 3a ) .
however , the tumor was not detected by diffusion - weighted mri ( figure 3b ) .
therefore , the standardized uptake value of the pseudotumor was approximately equal to that of the liver parenchyma .
a , the pseudotumor revealed a low - intensity mass on the hepatocyte phase of gd - eob mri ; b , the pseudotumor was not detected on the diffusion - weighted mr images . during the surgery ,
therefore , we performed sonazoid contrast - enhanced ultrasonography intraoperatively , and a low - echoic mass in segment 3 was resected .
an irregular , non - solid , brown - colored mass was confirmed in the resected specimen ( figure 4a ) .
histopathologically , the tumors showed sinusoidal dilation and congestion by hepatocyte trabeculae , compatible with sos ( figure 4b ) .
a , an irregular , non - solid , brown - colored mass was confirmed in the resected specimen ; b , a massive hemorrhage in the liver parenchyma was observed ( original magnification : 20  ) .
morphological imaging modalities , such as ct or us , are not suitable for the diagnosis of a pseudotumor caused by sos , which always mimics liver metastasis and may be misdiagnosed with conventional ct or us alone .
consideration of the pathophysiology of sos , which is congestion in the liver parenchyma , can lead to an accurate diagnosis .
qualitative imaging modalities , such as diffusion - weighted mri , have diagnostic power superior to that of morphological imaging modalities .
the  blue liver  caused by oxaliplatin - based chemotherapy is a specific adverse event that reflects the peripheral obstruction of hepatic vessels .
sos is recognized as sustained sinusoidal endothelial cell injury , which results in centrilobular hemorrhagic necrosis .
sos widely affects the liver parenchyma , but the clinical symptoms are nonspecific ; elevated transaminase levels , jaundice , hepatomegaly , splenomegaly , and ascites are characteristic clinical manifestations
. moreover , occult parenchymal damage due to chemotherapy results in increased intraoperative blood loss , a high complication rate , and delayed liver regeneration after liver resection ( 4 , 5 ) .
all cases had a history of advanced colorectal cancer surgery and adjuvant chemotherapy ( table 1 ) .
gd - eob mri , which was considered to be the most reliable modality in colorectal liver metastasis , showed a defect in the hepatocyte phase , similar to imaging findings of colorectal liver metastasis .
therefore , a qualitative imaging modality , such as diffusion - weighted mri , may be superior because the cellular density is higher in cancer than in pseudotumors ( 9 ) .
additionally , pseudotumors do not show uptake on pet , whereas 90% - 94% of liver metastases are detected with pet / ct ( 10 ) .
abbreviations : crm , colorectal metastasis ; dwi , diffusion - weighted image ; eob , gadoxetic acid - enhanced magnetic resonance imaging ; n.d . , not detected . in the present case ,
two different tumor etiologies were treated within a year in a patient who underwent postoperative chemotherapy .
one of the options was to perform a needle biopsy before the operation ; however , due to a fear of tumor - seeding from the biopsy , an inappropriate treatment was performed .
 introductionsinusoidal obstruction syndrome ( sos ) is a severe adverse event of long - term chemotherapy in patients with colorectal cancer . 
 it usually develops as liver congestion due to diffuse microscopic obstruction in liver parenchyma . 
 in contrast , it sometimes appears as a liver mass occurring with local parenchymal hemorrhaging , and is often misdiagnosed as liver metastasis.case presentationa 40-year - old woman with rectal cancer underwent high anterior resection and partial liver resection of segment 7 due to synchronous liver metastasis . 
 she received oxaliplatin - based chemotherapy ( mfolfox6 ) as adjuvant chemotherapy for 6 months . 
 a 13-mm irregular low - echoic mass was detected by ct in segment 3 of the liver 12 months after the operation . 
 the mass was again resected as a liver metastasis because it had increased in size . 
 the pathological diagnosis was focal sos , which showed sinusoidal dilation and congestion by hepatocyte trabeculae in the liver parenchyma.conclusionsatypical irregular tumors should be considered as sos when the patient has received oxaliplatin - based chemotherapy . a qualitative imaging modality diagnosis , such as with diffusion - weighted mri , is superior to a morphological diagnosis in focal sos . 
 this imaging modality can prevent unnecessary operations . 
Introduction
Case Presentation
Conclusions
1. Introduction
2. Case Presentation
3. Discussion