most gallbladder carcinomas show histological evidence of the capacity to produce mucin , but the tumors which secrete clinically detectable amounts of mucin are extremely rare ( 1 , 2 ) ; these tumors have been labeled as " mucin - producing carcinoma of the gallbladder ( mpgbc ) " ( 3 , 4 ) .
there have been several reports describing the imaging findings of mpgbc on ultrasonography ( us ) , computed tomography ( ct ) and endoscopic retrograde cholangiopancreatography ( 3 - 5 ) .
however , to the best of our knowledge , there has been only one case report until now that contains at least a short description of the findings on magnetic resonance cholangiopancreatography ( mrcp ) ( 6 ) .
the purpose of this report is to characterize the magnetic resonance ( mr ) findings of mpgbc , especially the findings on mrcp and to correlate their appearance with the histopathologic features .
we also discuss the usefulness of mrcp in the diagnosis of this tumor in comparison with that of us and ct .
a 59-year - old man was referred to our hospital for a gallbladder tumor detected by abdominal us during a health check - up .
laboratory results showed some abnormalities , including elevated levels of aspartate and alanine aminotransferase , as well as gamma - glutamyl transpeptidase , but the levels of tumor markers such as carcinoembryonic antigen ( cea ) and carbohydrate antigen ( ca ) 19 - 9 were within normal limits .
ultrasonography revealed a 17-mm protruding mass and hyperechoic streaks with spontaneous wave - like movements in the enlarged gallbladder ( fig .
ct showed a mild increase in attenuation of the gallbladder content and a localized thickened wall with enhancement ; however , tumors were not visualized even on contrast - enhanced ct . using a 1.5-t mr system with a torso phased - array coil , we performed t1-weighted gradient - recalled echo ( gre ) images before and after the administration of gadopentetate dimeglumine , and t2-weighted fast spin echo ( fse ) images .
both thick - slab and thin - section mrcp images were obtained with a single - shot fse sequence .
mrcp disclosed some streaks of hypointensity extending from the tumor to the neck of the gallbladder ( fig .
1b ) . unenhanced t1-weighted gre images and t2-weighted fse images did not show the tumor or any other findings in the enlarged gallbladder .
a cholecystectomy with wedge resection of the liver bed ( cwl ) and regional lymphadenectomy were performed and the gallbladder was found to be filled with 100 ml of greenish viscous mucin . a papillary tumor 4 cm in size was found in the fundus .
histologically , adenocarcinoma cells were demonstrated to have proliferated intraluminally with papillary formation , shallow invasion into the mucosa , and a few muscular and subserosal layers .
many striations protruded from the papillary proliferation of the adenocarcinoma , and the striations consisted of thick mucus bundle with detached cells ( fig .
a 53-year - old woman was referred to our hospital with pain in the right hypochondrium .
laboratory tests were normal except for an elevated cea level . both ct and mr images revealed a 3-cm eccentric mass in the fundus of the dilated gallbladder and lymph node adenopathy in the hepatoduodenal ligament .
mrcp showed many hypointense striations in the lumen , running from the tumor surface to the neck and along the long axis of the gallbladder ( fig .
us also depicted a mass and many hyperechoic striations moving in a wave - like manner ( fig . 2c ) .
cholecystectomy with wedge resection of the liver bed and pylorus - preserving pancreatoduodenectomy with regional lymph node dissection were performed .
histologically , the intraluminal nodular tumor , whose luminal surface was covered by mucin , consisted of the papillary adenocarcinomatous proliferation .
the adenocarcinoma had also infiltrated into the subserosal connective tissue , where the tumor was a mucinous carcinoma partly associated with tubular adenocarcinoma .
no recurrence has been observed 72 months after the operation . a 48-year - old woman presented with pain in the right abdomen .
ct showed an enlarged gallbladder filled with irregular septa with varying degrees of thickening near the center of the body .
mrcp showed an octagonal gallbladder with heterogeneous hyperintensity and some hypointense streaks running from the gallbladder to the abdominal cavity ( fig .
on coronal thin - section mrcp , the outer wall of the fundus was partially discontinuous and surrounded by an irregular - shaped hyperintense area , which was suspected to be a mucin collection caused by a perforation ( not shown ) .
the gallbladder had a 3-cm diameter hole in the fundus , from which yellowish and glistening mucus material was overflowing ( fig .
histologically , the original gallbladder cavity was not so enlarged and the papillary adenocarcinoma was present on the fundus .
it contained mucus nodules of varying sizes , which were demonstrated in the histology of the mucinous carcinoma .
a 59-year - old man was referred to our hospital for a gallbladder tumor detected by abdominal us during a health check - up .
laboratory results showed some abnormalities , including elevated levels of aspartate and alanine aminotransferase , as well as gamma - glutamyl transpeptidase , but the levels of tumor markers such as carcinoembryonic antigen ( cea ) and carbohydrate antigen ( ca ) 19 - 9 were within normal limits .
ultrasonography revealed a 17-mm protruding mass and hyperechoic streaks with spontaneous wave - like movements in the enlarged gallbladder ( fig .
ct showed a mild increase in attenuation of the gallbladder content and a localized thickened wall with enhancement ; however , tumors were not visualized even on contrast - enhanced ct . using a 1.5-t mr system with a torso phased - array coil , we performed t1-weighted gradient - recalled echo ( gre ) images before and after the administration of gadopentetate dimeglumine , and t2-weighted fast spin echo ( fse ) images .
both thick - slab and thin - section mrcp images were obtained with a single - shot fse sequence .
mrcp disclosed some streaks of hypointensity extending from the tumor to the neck of the gallbladder ( fig .
1b ) . unenhanced t1-weighted gre images and t2-weighted fse images did not show the tumor or any other findings in the enlarged gallbladder .
a cholecystectomy with wedge resection of the liver bed ( cwl ) and regional lymphadenectomy were performed and the gallbladder was found to be filled with 100 ml of greenish viscous mucin . a papillary tumor 4 cm in size was found in the fundus .
histologically , adenocarcinoma cells were demonstrated to have proliferated intraluminally with papillary formation , shallow invasion into the mucosa , and a few muscular and subserosal layers .
many striations protruded from the papillary proliferation of the adenocarcinoma , and the striations consisted of thick mucus bundle with detached cells ( fig .
a 53-year - old woman was referred to our hospital with pain in the right hypochondrium .
laboratory tests were normal except for an elevated cea level . both ct and mr images revealed a 3-cm eccentric mass in the fundus of the dilated gallbladder and lymph node adenopathy in the hepatoduodenal ligament .
mrcp showed many hypointense striations in the lumen , running from the tumor surface to the neck and along the long axis of the gallbladder ( fig .
us also depicted a mass and many hyperechoic striations moving in a wave - like manner ( fig . 2c ) .
cholecystectomy with wedge resection of the liver bed and pylorus - preserving pancreatoduodenectomy with regional lymph node dissection were performed .
histologically , the intraluminal nodular tumor , whose luminal surface was covered by mucin , consisted of the papillary adenocarcinomatous proliferation .
the adenocarcinoma had also infiltrated into the subserosal connective tissue , where the tumor was a mucinous carcinoma partly associated with tubular adenocarcinoma .
ct showed an enlarged gallbladder filled with irregular septa with varying degrees of thickening near the center of the body .
mrcp showed an octagonal gallbladder with heterogeneous hyperintensity and some hypointense streaks running from the gallbladder to the abdominal cavity ( fig .
on coronal thin - section mrcp , the outer wall of the fundus was partially discontinuous and surrounded by an irregular - shaped hyperintense area , which was suspected to be a mucin collection caused by a perforation ( not shown ) .
the gallbladder had a 3-cm diameter hole in the fundus , from which yellowish and glistening mucus material was overflowing ( fig .
histologically , the original gallbladder cavity was not so enlarged and the papillary adenocarcinoma was present on the fundus .
it contained mucus nodules of varying sizes , which were demonstrated in the histology of the mucinous carcinoma .
mucin - producing carcinoma of the gallbladder is considered to be a subtype of two major histological types of gallbladder carcinoma : well - differentiated adenocarcinoma ( intracystic papillary adenocarcinoma ) and mucinous carcinoma ( 4 ) .
gallbladder carcinomas are commonly biologically aggressive tumors , whereas the biological behavior of mpgbc itself is still unknown .
some authors consider it to be highly aggressive and invasive , as demonstrated in one of our reported cases with perforation ( 1 , 4 , 6 ) .
however , the majority of the reported mpgbc cases so far have presented with clinical symptoms linked to enlargement of the gallbladder and the viscous mucin , such as abdominal pain , discomfort , fever and jaundice ( 3 - 7 ) . as a result , it may be possible to detect these tumors at an earlier stage , while the prognosis still remains reasonable . in our series with mpgbc
, mrcp showed linear or curvilinear striations in the gallbladder , running more or less along the long axis of the gallbladder .
the signal intensity of these striations was less than that of the bile in the lumen , but greater than that of the liver .
we called this characteristic pattern of striations a " mucus thread " sign , which corresponded microscopically to a thick mucus bundle including some cellular components .
huang et al . ( 6 ) also reported visualizing laminated streaks of fluid inside the gallbladder without evidence of obstruction of the cystic duct in their case on mrcp .
we speculated that this finding is associated with the flow of the highly viscous mucin secreted from the surface of the tumor in the gallbladder cavity .
in addition , we observed some threads showing an irregular arrangement in a mucus lake associated with mucinous carcinoma .
the mucus thread sign was observed on mrcp with a single - shot fse sequence in all the three patients in our series , and was seen more clearly on mrcp images than on t2-weighted fse images . on the other hand , visualization of mucus material from mucin - producing tumors , such as
intraductal papillary mucinous tumors of the pancreas , has not been reported on mrcp using a fse sequence in previous publications ( 7 ) .
we speculate the reasons for our successful visualization of the mucus thread sign as follows : first , the parameters used for mrcp using a single - shot fse sequence in this study relied on more heavily - t2 weighted imaging than on fse imaging ( 8 , 9 ) .
second , we used a phased - array torso coil and a large matrix size to obtain higher space resolution ( 8 , 9 ) .
in addition , mrcp allows a direct optimized plane of acquisition , enabling precise evaluation of this sign ; this plane should be arranged with its long axes parallel to the long axis of the gallbladder .
the papillary projections and solid components of the tumors were more clearly visualized on the gadolinium - enhanced mr images , by virtue of their moderate to marked enhancement , than by other modalities in all the three patients . since unenhanced t1- or t2-weighted images
sometimes do not show thin papillary projections in the gallbladder , as in case 1 , it would appear that gadolinium - enhanced mr imaging is essential to confirm the diagnosis of mpgbc .
moreover , since mucus threads do not show enhancement , gadolinium - enhanced mr imaging could be useful for differentiating them from tumorous lesions .
two patients preoperatively examined by us with a 5.0 or 9.0 mhz probe showed a linear or curvilinear hyperechoic bundle of streaks .
intraoperative us with a 7.5 mhz probe in the three patients demonstrated a bundle of mucus threads within the lumen of the gallbladder in two patients and a mucus lake - destroyed wall in one .
( 5 ) reported the same findings , called tree - like sludge echoes , in intraoperative us , although they missed them in conventional extracorporeal us .
therefore , higher frequency echo probes of 5.0 mhz or more may be useful for a detailed visualization of the structure of not only the tumor itself , but also of the hypersecreted mucus and its course , although it might still may be possible in thin patients only . on the other hand , intraoperative us with a high - frequency probe may be more helpful , regardless of patient body type .
computed tomography demonstrated mpgbc as a solid mass of 3-cm or more in size that shows enhancement in the enlarged gallbladder in two patients .
however , in the remaining patient with thin papillary projections , both unenhanced and contrast - enhanced ct failed to show the projections or the tumor itself .
since the tumors are thin projections and contain significant mucin , it may be difficult on ct images to distinguish between a low - attenuation lesion similar to water and bile - containing gelatinous mucin ( 10 , 11 ) .
radiologists must bear in mind that the diagnosis of mpgbc may be easily missed by ct alone .
differentiating mucus threads from stones , sludge or hematomas , which can obstruct the cystic duct and are often associated with the retention of mucus , is important in clinical practice .
usually show higher intensity than dilute bile on t1-weighted images and layers beneath the dilute bile due to its greater specific gravity .
the mucus thread sign of mpgbc should be carefully evaluated for the size and length of the mucus bundle , the appearance of the arrangement and direction , and the continuity with tumorous lesions . in conclusion
careful assessment of this sign can be helpful for early detection and accurate preoperative diagnosis of this type of malignancy of the gallbladder .
also , gadolinium - enhanced mr imaging is mandatory for precise characterization of the lesions .
 we report three cases of mucin - producing carcinoma of the gallbladder , along with the magnetic resonance ( mr ) findings , especially the findings on a mr cholangiopancreatography . in our cases , 
 linear or curvilinear streaks were detected running along the long axis of an enlarged gallbladder ( mucus thread sign ) . 
 when such findings were seen , a mucin - producing carcinoma of the gallbladder should be included as a differential diagnosis . 
 thus , gadolinium - enhanced mr imaging is mandatory for the precise diagnosis of the mucin - producing carcinoma of the gallbladder . 
INTRODUCTION
CASE REPORTS
Case 1
Case 2
Case 3
DISCUSSION