seven consecutive patients [ three men and four women aged 15 - 77 ( mean , 42.7 ) years ] admitted to our hospital with hypoglycemia between april 1 , 2001 and september 31 , 2002 were retrospectively studied .
the time from the onset of neuroglycopenic symptoms to diagnosis ranged from 4 to 42 months .
the age , sex , and history of the patients are summarized in table 1 .
the inclusion criteria were coexisting hypoglycemic symptoms with low fasting serum glucose levels ( < 50 mg / dl ) and biochemical evidence of organic hyperinsulinemia , confirmed by a fasting test ( serum insulin : glucose ratio ( 0.3 , with high c - peptide levels ) .
symptomatic hypoglycemia was observed and documented [ plasma glucose range : 27 - 46 ( mean , 35 ) mg / dl ] after 24 - 72 hours of fasting .
concomitant insulin [ range : 10.9 - 33.6 ( mean , 18.4 ) iu / ml ] and c - peptide levels [ range : 1.95 - 5.67 ( mean , 3.95 ) ng / ml ] were not suppressed .
all these patients had pathologic glucose - insulin ratios ( range , 0.40 - 0.73 ; mean , 0.51 ) . thus , hyperinsulinemic hypoglycemia due to insulin - secreting tumors was proven in all cases .
radiological imaging modalities employed for the localization of these pancreatic adenomas are summarized in table 2 .
ultrasonography ( us ) was performed in three cases , endoscopic ultrasonography ( eus ) in two , computed tomography ( ct ) in seven , and intraoperative ultrasonography ( ious ) in four . in all cases ,
the detection rate of each study was evaluated . after obtaining informed consent from each patient
none of our patients was receiving cardiac glycosides , and none was suffering from sarcoidosis or renal failure , conditions considered relative contraindications to intra - arterial calcium injection .
all tests were carried out under local anesthesia and with continuous electrocardiographic and blood pressure monitoring . to avoid iatrogenic hypoglycemia ,
blood sugar levels were checked before the procedure . in patient 2 , this was 37 mg / dl , and 25 g of intravenous glucose were administered , using a 50% solution . prior to angiography , a 5-french ( f ) cobra catheter ( terumo , tokyo , japan ) was placed in the right hepatic vein close to its junction with the inferior vena cava through a puncture site in the right internal jugular vein ( fig .
the right femoral artery was then punctured , and a 5-f yashiro catheter ( terumo ) was advanced to the celiac trunk and the superior mesenteric artery ( sma ) .
occasionally , a 3-f progreat microcatheter ( terumo ) was used for coaxial superselective catheterization of the gastroduodenal ( gda ) and splenic artery ( spa ) .
selective presampling angiography was performed after selectively injecting nonionic contrast agent ( iomeron 300 ; ilsung , korea ) into the gda , spa , and sma . for angiographic studies , digital subtraction angiography ( dsa )
, a 5-ml bolus of calcium gluconate ( 0.025 meq ca / kg ) diluted in saline was rapidly injected through the proximally positioned catheter in each selectively catheterized artery .
the period between each injection was at least 5 minutes . before and 30 , 60 , and 120 seconds after calcium injection , 5 ml of hepatic venous blood was obtained .
each sample was labeled according to the time interval and artery of origin , and centrifuged , and the resulting serum was assayed for insulin concentration in all patients and c - peptide concentration in six .
all asvs results were analyzed by an individual blinded to all other preoperative imaging studies and operative findings . according to the findings of doppman
et al . , a positive finding is indicated by a twofold elevation of insulin levels in the 30- or 60-second samples ( or both ) obtained from the hepatic vein ( 1 ) . a twofold rise in insulin levels following calcium gluconate injection of the gda or
sma indicates that the tumor is located in the pancreatic head or uncinate process ; a twofold rise after injection into the spa suggests a corporeal or caudal location . for diagnostic accuracy , c - peptide gradients in all patients except patient 1
the diagnostic criteria for c - peptide have not been reported , but we supposed that such analysis would be useful if insulin gradients were equivocal .
the results of asvs in which insulin gradients only were determined , and in which additional c - peptide gradients were established , were compared .
comparisons were also made between the sensitivity of these modalities and that of other localizing modalities in terms of the operative findings and outcome of surgery .
the median follow - up time was 4 ( range , 1 - 10 ) months .
at these intervals , patient histories were obtained and plasma glucose levels were determined after 24 - 72 hours of fasting .
seven consecutive patients [ three men and four women aged 15 - 77 ( mean , 42.7 ) years ] admitted to our hospital with hypoglycemia between april 1 , 2001 and september 31 , 2002 were retrospectively studied .
the time from the onset of neuroglycopenic symptoms to diagnosis ranged from 4 to 42 months .
the age , sex , and history of the patients are summarized in table 1 .
the inclusion criteria were coexisting hypoglycemic symptoms with low fasting serum glucose levels ( < 50 mg / dl ) and biochemical evidence of organic hyperinsulinemia , confirmed by a fasting test ( serum insulin : glucose ratio ( 0.3 , with high c - peptide levels ) .
symptomatic hypoglycemia was observed and documented [ plasma glucose range : 27 - 46 ( mean , 35 ) mg / dl ] after 24 - 72 hours of fasting .
concomitant insulin [ range : 10.9 - 33.6 ( mean , 18.4 ) iu / ml ] and c - peptide levels [ range : 1.95 - 5.67 ( mean , 3.95 ) ng / ml ] were not suppressed .
all these patients had pathologic glucose - insulin ratios ( range , 0.40 - 0.73 ; mean , 0.51 ) . thus , hyperinsulinemic hypoglycemia due to insulin - secreting tumors was proven in all cases .
radiological imaging modalities employed for the localization of these pancreatic adenomas are summarized in table 2 .
ultrasonography ( us ) was performed in three cases , endoscopic ultrasonography ( eus ) in two , computed tomography ( ct ) in seven , and intraoperative ultrasonography ( ious ) in four . in all cases ,
after obtaining informed consent from each patient , asvs was performed according to the protocol proposed by doppmann et al .
none of our patients was receiving cardiac glycosides , and none was suffering from sarcoidosis or renal failure , conditions considered relative contraindications to intra - arterial calcium injection .
all tests were carried out under local anesthesia and with continuous electrocardiographic and blood pressure monitoring . to avoid iatrogenic hypoglycemia ,
blood sugar levels were checked before the procedure . in patient 2 , this was 37 mg / dl , and 25 g of intravenous glucose were administered , using a 50% solution .
prior to angiography , a 5-french ( f ) cobra catheter ( terumo , tokyo , japan ) was placed in the right hepatic vein close to its junction with the inferior vena cava through a puncture site in the right internal jugular vein ( fig .
the right femoral artery was then punctured , and a 5-f yashiro catheter ( terumo ) was advanced to the celiac trunk and the superior mesenteric artery ( sma ) .
occasionally , a 3-f progreat microcatheter ( terumo ) was used for coaxial superselective catheterization of the gastroduodenal ( gda ) and splenic artery ( spa ) .
selective presampling angiography was performed after selectively injecting nonionic contrast agent ( iomeron 300 ; ilsung , korea ) into the gda , spa , and sma . for angiographic studies , digital subtraction angiography ( dsa )
, a 5-ml bolus of calcium gluconate ( 0.025 meq ca / kg ) diluted in saline was rapidly injected through the proximally positioned catheter in each selectively catheterized artery .
the period between each injection was at least 5 minutes . before and 30 , 60 , and 120 seconds after calcium injection
each sample was labeled according to the time interval and artery of origin , and centrifuged , and the resulting serum was assayed for insulin concentration in all patients and c - peptide concentration in six .
all asvs results were analyzed by an individual blinded to all other preoperative imaging studies and operative findings . according to the findings of doppman
et al . , a positive finding is indicated by a twofold elevation of insulin levels in the 30- or 60-second samples ( or both ) obtained from the hepatic vein ( 1 ) .
a twofold rise in insulin levels following calcium gluconate injection of the gda or sma indicates that the tumor is located in the pancreatic head or uncinate process ; a twofold rise after injection into the spa suggests a corporeal or caudal location . for diagnostic accuracy , c - peptide gradients in all patients except patient 1 were also analyzed .
the diagnostic criteria for c - peptide have not been reported , but we supposed that such analysis would be useful if insulin gradients were equivocal .
the results of asvs in which insulin gradients only were determined , and in which additional c - peptide gradients were established , were compared .
comparisons were also made between the sensitivity of these modalities and that of other localizing modalities in terms of the operative findings and outcome of surgery .
the median follow - up time was 4 ( range , 1 - 10 ) months . at these intervals ,
patient histories were obtained and plasma glucose levels were determined after 24 - 72 hours of fasting .
the results of all localization studies and surgery are presented in table 2 . in no case
did asvs lead to complications , and procedural - related symptomatic hypoglycemia and hypercalcemia were not encountered .
insulin or c - peptide gradients were calculated as the ratios of hepatic venous insulin or c - peptide concentrations , respectively , at 30 , 60 , and 120 seconds after asvs to baseline . in patients 1 , 2 , 5 and 7 ,
significant insulin gradients were observed after calcium injection into the gda and in patient 6 after stimulation of the gda and sma , indicating the presence of insulinomas in the pancreatic head or uncinate process ( fig .
2b ) , and in patient 3 , both insulin and c - peptide gradients increased significantly after stimulation of the spa , suggesting that the pathological source of insulin might be the pancreatic body or tail ( fig .
peak insulin gradients in the gda 30 seconds after stimulation and in the spa at 60 seconds were not significantly different ( fig .
after 30 seconds , insulin gradients decreased gradually in the gda , but in the spa showed a gradual increase .
the analyst , blinded to all other preoperative imaging studies and operative findings , thus could not confidently determine the location of the insulinoma . in this case , additional c - peptide gradients were , however , helpful ( fig .
the c - peptide gradient peaked 60 seconds after stimulation of the spa , and in the gda was not more than 1.0 .
eight insulinomas , 5 - 25 ( mean , 12.5 ) mm in size , were found and confirmed histopathologically after enucleation ( table 2 ) . all tumors except in patient 3 were less than 2 cm in size .
three were in the head , two in the uncinate process and three in the tail . in patient 4 ,
the tumors were correctly localized by us in two of three patients ( sensitivity , 67% ) , by eus in one of two ( sensitivity , 50% ) , by ct in four of seven ( sensitivity , 57% ) , by angiography in three of seven ( sensitivity , 43% ) , and by ious in four of four ( sensitivity , 100% ) . for insulin gradients
only , the sensitivity of asvs was 86% ( 6 of 7 patients ) , but with additional c - peptide gradients , sensitivity was 100% ( 6 of 6 patients ) .
all patients were cured by enucleation of the insulinoma and remained free of hypoglycemia during the follow - up period .
the availability of methods to accurately determine circulating levels of insulin , c - peptide , and proinsulin has led to dramatic improvements in the preoperative diagnosis of insulinomas , and to exclusion of the surreptitious administration of insulin as the cause of hypoglycemia ( 3 ) .
preoperative localization of a tumor has , for this reason , moved to center stage as the main focus of interest . since daggett et al .
( 6 ) published their findings in 1981 , the question of whether imaging is necessary prior to initial insulinoma - related surgery has been a matter of debate ( 13 - 15 ) .
many surgical teams , meanwhile , do not rely exclusively on bimanual palpation of the pancreas combined with ious , but insist on meticulous preoperative localization , and it is to this that they attribute their high operative success rates ( 16 - 18 ) .
an average of 10% of insulinomas defy surgical exploration ( 4 , 16 ) and correct preoperative localization minimizes the extent to which this is necessary , thus reducing morbidity ( 13 ) .
recent developments in the laparoscopic resection of pancreatic insulinomas , a procedure increasingly described for tumors located in the body or tail of the pancreas , emphasize , furthermore , the need for an accurate preoperative localization procedure ( 19 , 20 ) . hence , even though they are controversial in terms of cost - effectiveness ( 3 , 22 ) , preoperative localization studies are recommended ( 13 , 15 - 17 , 21 ) . if such studies do not facilitate rational and safe surgical enucleation or resection , they are not , however , time- and cost - effective ( 23 ) .
the mean diameter of insulinomas is generally not more than 15 mm ( 2 , 11 , 15 , 24 ) , and non - invasive imaging modalities thus often fail to localize them .
non - invasive modalities such as us , ct , and mri have shown low sensitivities ( 8 , 9 , 13 , 14 , 16 , 21 , 25 ) , while ct and us will detect up to 60% of biochemically proven insulinomas .
relatively little has so far been reported about mri in the diagnosis of islet cell tumors , and its exact role is uncertain ( 4 ) . in our series
the mean size of insulinomas was 12.5 mm , a fact which could explain the low detection rate of adenomas at us and ct .
however , recent reports describing the findings of dynamic ct and mri have been promising ( 26 - 28 ) .
the sensitivities of other , invasive , localization techniques for detecting insulinomas were higher : 57 - 82% with eus ( 11 , 12 , 18 , 29 , 30 ) , 35% to 65% with angiography ( 9 , 10 , 31 , 32 ) , and 77 - 100% with transhepatic portal venous sampling ( tpvs ) ( 7 - 10 , 13 , 14 , 17 , 21 , 31 , 32 ) .
however , these techniques have certain disadvantages , including low sensitivity in the case of angiography and eus ( the sensitivity of eus depends on the location of the tumor ) and higher morbidity for tpvs ( 4 , 8 , 9 , 33 ) .
the sensitivity of ious combined with palpation was more than 80% in most reported series ( 2 - 4 , 14 , 16 , 31 , 34 ) .
however , insulinomas located in the pancreatic head or uncinate process , and thus deep within the parenchyma , were difficult or impossible to palpate , even where an experienced surgeon was involved ( 5 ) , and to detect at surgery , using ious , particularly at hospitals with limited experience of this modality ( 9 , 11 , 31 ) .
( 3 , 7 ) , the detection of insulinomas is based on their hormone production , not their appearance . the sensitivity of the technique is independent of lesion size . at the same time , however , since the lesion is identified by its hormone output , it is not visulalized directly and can not be located precisely .
its position can be confirmed only in terms of a region of the pancreas ( head / uncinate process versus body / tail ) .
adenomas to the left of the sma can be treated by enucleation and distal pancreatectomy , whereas those to the right require enucleation . in our series ,
moreover , asvs is far less invasive and complicated than tpvs and can be safely carried out in combination with a normal dsa procedure ( 5 , 8 , 9 ) .
complications of asvs are rare ( 33 ) , and major complications did not occur in our patients .
although hypoglycemia is a severe , even life - threatening potential complication of asvs , it has not previously been reported ( 4 ) .
insulin levels in the hepatic vein usually peaked in samples obtained 30 or 60 seconds after calcium stimulation , and were often returning toward baseline within 120 seconds of stimulation , suggesting that insulin release is confined to the short interval during which beta cells are exposed to high serum calcium levels ( 9 ) .
calcium should be administered cautiously to patients with sarcoidosis , or renal or cardiac disease , particularly to those receiving cardiac glycosides ( 7 ) .
the inotropic effects of cardiac glycosides and calcium are synergistic ; if both are administered simultaneously , dysrhythmia may thus occur ( 33 ) .
insulin gradients in the gda 30 seconds after stimulation and in the spa at 60 seconds were not significantly different , and while this gradient peaked 30 seconds after the start of calcium gluconate infusion into the gda , in the spa it increased gradually .
additional analysis of the c - peptide gradient showed that in the spa it peaked 60 seconds after stimulation , and in the gda it was not more than 1.0 .
the analyst localized the tumor to the pancreatic body or tail , and two small adenomas found in the tail were to the left of the sma .
elevated insulin levels in the hepatic veins after asvs did not always equate with correct localization ( 8) .
we assumed that additional analysis of c - peptide gradients would help assess the location of a tumor when insulin gradients are equivocal , basing our assumption on two factors : first , calcium gluconate administration led not only to hyperinsulinemia , but also to increased serum proinsulin and c - peptide levels ( 35 ) .
second , although the secretory ratio of c - peptide to insulin is 1:1 , the ratio in serum is about 5:1 to 15:1 ( 36 ) .
the molar concentration of c - peptide in blood is higher than that of insulin because of the hepatic clearance of the latter ( 36 ) .
approximately 50% of insulin is rapidly removed by its initial passage through the liver , but hepatic extraction of c - peptide is negligible ( 36 ) .
a relatively high concentration of c - peptide may thus reflect a subtle increase in its level , compared to that of insulin , after stimulation with calcium gluconate . in six of our patients ,
to our knowledge , this is the first report to describe the use of these gradients in asvs for the localization of insulinomas .
however , to confirm the efficacy of c - peptide gradients , in spite of the significant additional cost of multiple c - peptide assays , further investigation is needed .
a further point is that because catheterization of the left hepatic vein was technically more difficult , and also unnecessary , the right hepatic vein only was chosen ( 4 , 8 , 9 , 19 , 24 ) .
selective distribution of splenic and mesenteric venous blood to the left and right portal vein , respectively , may mask an adenoma in the body - tail region , but such portal flow dynamics have never been proven ( 24 ) .
( 19 ) reported that where asvs was used , there was no difference in the degree of step - up between right and left hepatic vein sampling .
, furthermore , observed that in patients with tumors in the body and tail of the pancreas , insulin levels in samples obtained from the right hepatic vein were always elevated ( 9 ) . in conclusion , asvs is a highly accurate and safe method for the preoperative localization of insulinomas .
additional c - peptide gradients seem to be helpful in assessing the location of a tumor , but additional investigation is needed .
 objectiveto determine the value of selective intra - arterial calcium stimulation with hepatic venous sampling using serum insulin and c - peptide gradients for the preoperative localization of insulinomas.materials and methodsseven consecutive patients [ three men and four women aged 15 - 77 ( mean , 42.7 ) years ] with hypoglycemia underwent selective intra - arterial calcium stimulation in conjunction with hepatic venous sampling . 
 insulin gradients were calculated by an individual blinded to all other preoperative imaging studies and operative findings . in all patients except one , 
 c - peptide gradients were also analyzed . 
 the results were compared with the preoperative findings of ultrasonography , computed tomography , arteriography and endoscopic ultrasonography , as well as with the intraoperative findings of ultrasonography and palpation at surgery.resultseight insulinomas ( mean diameter , 12.5 mm ) were diagnosed after surgery . in six patients , 
 the calcium stimulation test with insulin gradients allowed accurate localization of the pathologic source of insulin secretion . 
 both c - peptide and insulin gradients substantially increased diagnostic accuracy . in one patient , 
 c - peptide gradients were more helpful than insulin gradients for tumor localization.conclusionselective intra - arterial calcium stimulation with hepatic venous sampling is a highly accurate and safe method for the preoperative localization of insulinomas . 
 additional c - peptide gradients seem to be helpful in assessing tumor location , but further study is needed . 
MATERIALS AND METHODS
Patients
Imaging studies
ASVS technique and interpretation
Confirmative diagnosis and follow-up
RESULTS
DISCUSSION