Taurine

Variation of enterohepatic circulation observed with 75SeHCAT images in the first three hours. Scintigraphic patterns and analysis of their association with the diagnosis of bile acid malabsorption6

A. Brontea,∗, J.F. Bastidasa, Juan J. Rosalesa, J. Zuaznabarb, M. Herraizc, J.A. Richtera
a Department of Nuclear Medicine, Clinica Universitaria de Navarra, Pamplona, Navarra, Spain
b Department of Internal Medicine, Clínica Universidad de Navarra, Pamplona, Spain
c Department of Digestive, Clínica Universidad de Navarra, Pamplona, Spain

A R t i c l E I N f o A B s t R A C t

Article history:
Received 29 June 2020
Accepted 25 January 2021 Available online xxx

Keywords:75 SeHCAT,Chronic diarrea,Biliar acid malabsorption Enterohepatic circulation

Objetive: To evaluate the enterohepatic circulation of 75-Selenium turoselecolic acid (75 Se-SeHCAT) dur- ing the first 3 h and its correlation with the abdominal retention at the 7th day (AR7), as contribution to the clinical study of biliar acid malabsorption (BAM).
Materials and methods: 38 patients with chronic diarrhea were retrospectively studied. Acquisition pro- tocol included static abdominal images at 1st, 2nd and 3rd hour and the 7th day after oral administration of the radiopharmaceutical. Images of 1–3 h determined 5 patterns of enterohepatic circulation that, due to their location, were characterized as: 1) gallbladder 2−3 h, 2) gallbladder 3 h, 3) gallbladder-abdomen 2−3 h, 4) abdomen, 5) upper left abdomen. The association of these patterns with the AR7 (Fisher,STATA) were investigated. Patients were classified as Non BAM (AR7 > 15%), mild-BAM (AR7 15−10%), moderate-BAM (AR7 10−5%) or severe-BAM (AR7 < 5%). Results: 19 patients had an AR7 diagnostic of BAM (7 mild-BAM, 5 moderate-BAM, 7 severe-BAM). The pattern “gallbladder at 2−3 h” was statistically associated with Non BAM (p 0,008), while “gallbladder- abdomen at 2−3 h” was correlated with having BAM (p 0,029). Conclusion: Variations detected at the abdominal level in images during the first 3 h were associated with changes in intestinal absorption and the incorporation of the radiopharmaceutical into the pool of bile acids, so visual interpretation of the images at 2nd and 3rd hour could be useful in the final assessment of the study. © 2021 Sociedad Espan˜ola de Medicina Nuclear e Imagen Molecular. Published by Elsevier Espan˜a, S.L.U. All rights reserved. Introduction Bile acid malabsorption (BAM) is the cause of 6% of chronic diarheas.1,2 Primary bile acids are synthetized and conjugated in the liver, after which they are secreted by the bile and stored in the gallbladder during fasting. After fasting they are excreted to the duodenum where they facilitate the absorption of liposoluble vita- mins and contribute to the digestion of fats. In normal conditions, on arrival to the terminal ileon approximately 95% are reabsorbed and transported by the portal tract to the liver. This process is called enterophepatic circulation, which has a mean recycling time of 3.4 h, with a total of 4.6 cycles daily. In normal conditions, only 5% of primary bile salts reach the colon.1,3–5 When there is a loss greater than 5% in each enterohepatic cir- culation, a patient is considered to have BAM.6 This loss may be due to ileal dysfunction by both resection and an inflammatory alteration (type 1 BAM), by an idiopathic condition in which the ileum is structurally normal (type 2 BAM) or it may be secondary to gastrointestinal diseases which interfere in the physiology of bile acid reabsorption: post cholecystectomy, chronic pancreatitis, or bacterial overgrowth, among others (type 3 BAM).1,3–5 75Se-Homocholic acid taurine (75SeHCAT) scintigraphy is the study of reference in Europe for the diagnosis of BAM. Tau- rodeoxycholic acid is a synthetic bile acid conjugate labeled with 75-selenium. When administered orally it is absorbed in the termi- nal ileum and by enterohepatic circulation becomes part of the pool of bile acids. In order to be accurate in the quantification of abdom- inal retention of 75SeHCAT, the methodology for study acqusition is very demanding in regard to patient preparation and the acqui- sition of background and static abdominal images at 3 h and on the 7th day after administration of the radiopharmaceutcial. Using these images, quantitiative analysis is performed to calculate the percentage of abdominal retention of radiopharmaceutical activity at day 7 (RA7), which determines whether there is or is not BAM.1,3,7 The images made at 3 h can present variable uptake patterns which can lead to doubts as to the correct centering of the abdom- inal image. Since there is no literature on this finding, it has been proposed that this study be directed at detecting changes in abdom- inal uptake during the first 3 h after the administration of the radiopharmaceutical with the aim of optimizing the procedure of image acquisition of the 75SeHCAT study. Material and methods The present study was approved by the Ethical Committee of Investigation of the Universidad de Navarra. Study population We retrospectively analyzed a cohort of 38 patients (23 women and 15 men) ranging in age from 18 to 81 years. All the patients presented chronic diarrhea and had undergone 75SeHCAT scintig- raphy in the Clínica Universidad de Navarra between June 2019 and April 2020. Table 1 shows the characteristics of the patients, the diagnostic procedures performed and the presence of other diagnosed dis- eases which could be the cause of chronic diarrhea. Acquistion equipment and parameters The images were acquired using a Symbia (Siemens) gamma camera with 2 detectors with parallel hole collimators, low energy and high resolution, centered in two windows of 20% over 2 energy peaks of 75Se (136 and 264 KeV), a matrix of 128 × 128 and zoom of 1. Scintigraphic study: exploration protocol Study on day 1 After at least 4 h of fasting, an oral capsule of 0.37 MBq (0.01 mCi) of 75SeHCAT was administered. Fasting was maintained during the following 3 h.Five-minute images were acquired in anterior (ANT) and pos- terior (POST) projection in the 1st, 2nd and 3rd hours after the administration of the radiopharmaceutical. The patient was supine for all the images, and the detectors were centered over the abdominal region, maintaining the distance of the upper detector at more than 15 cm from the patient and the lower detector as close as possible to the gurney.Before and after the image at 3 h, 2 background images of 5 min in duration were obtained in ANT (F1) and POST (F2) projec- tion. These 2 images, together with the abdominal ANT and POST images at 3 h, constituted the registry of the initial or time zero (AA0) activity. Study on day 7 The same acqusition as that performed a 3 h (background and abdomen) was performed, obtaining the registry of abdominal activity on day (AA7). Quantitative 75SeHCAT analysis Abdominal retention was calculated on day 7 (RA7), by calculation of AA0 and AA7 applying the formula AA0/7: ([ANT-meanF1] + [POST-meanF2])/2 and afterwards RA7: (AA7/AA0) × 100.1,6 The following diagnoses were considered: no-BAM when RA7 was > 15%, mild-BAM when RA7 was 15−10%, moderate-BAM when RA7 was 10−5% or severe-BAM when RA7 was < 5%, according to Arasaradnam et al. in the guidelines for the study of chronic diarhhea in adults. Qualitative 75SeHCAT analysis To determine the patterns of uptake, qualitative analyses of the abdominal images performed in the first part of the study were carried out (ANT and POST images at the 1st, 2nd and 3rd hour), and are shown in image A of Figs. 1–5; figures and the antomical limits are shown in image B of these figures. Five patterns were determined based on the distribution of the images: 1) Gallbladder 2−3 h: when focal uptake was visualized in the gallbladder at both 2 and 3 h (Fig. 1); 2) Gallbladder 3 h: focal uptake in the gallbladder only at 3 h (Fig. 2); 3) Gallbladder- abdomen 2−3 h: low uptake in the gallbladder with diffuse abdominal uptake at 2 and 3 h (Fig. 3); 4) Abdomen: diffuse uptake in the abdomen at 2 and 3 h or only at 3 h (Fig. 4); and 5) Upper left abdomen: when the uptake was localized in the upper left abdomen at 2 and 3 h (Fig. 5). Statistical analysis The STATA® was used to investigate the possible association between the 5 enterohepatic circulation patterns of the radiophar- maceutical in the first 3 h and RA7 as well as the type of BAM. When the expected value was less than 5 in any of the observations, the non parametric Fisher test was used. On the other hand, the RA7 percentage of each pattern was expressed as mean ± standard devi- ation (SD) and as interquartile ranage (IQR) when the distribution did not follow normality. Results Table 2 shows the classification of the patients in the 5 patterns of enterohepatic circulation of the radiopharmaceutical as well as the definitive diagnosis and the results of the statistical analyses.Of the 38 patients included, 19 (50%) presented an RA7 diagnos- tic of BAM (7 mild-BAM, 5 moderate-BAM and 7 severe-BAM), and in the other 19 patients (50%) RA7 was diagnostic of no-BAM.Seven patients presented pattern 1 (gallbladder 2−3 h), with all being diagnosed as no-BAM with a mean RA7 of 31.15% (± 4.61). This pattern was statistically significantly associated with a final diagnosis of no-BAM (p 0.008). Eight patients were classified as pattern 2 (gallbladder 3 h), and the mean RA7 was 20.49% (± 5.02). Four of these patients were diag- nosed as BAM, all with type 2 BAM: 3 with mild-BAM and 1 with severe-BAM.Pattern 3 (gallbladder-abdomen 2−3 h) was observed in 11 patients with a mean RA7 of 8.66% (3.66−11.34). Nine of these patients were diagnosed with BAM: 3 mild-BAM (2 type 2 BAM and 1 type 3 BAM who had received treatment with lenalidomide, which is known to be a possible cause of BAM, although the molec- ular mechanism is unknown9), 3 moderate-BAM (1 type 1 BAM diagnosed as possible Crohn disease and 2 type 2 BAM) and 3 severe-BAM (all with type 2 BAM). This pattern was significantly associated with the final diagnosis of BAM (p 0.029), and in turn, was significantly associated with presenting type 2 BAM (p 0.005). Nine patients were classified as having pattern 4 (abdomen), with a mean RA7 of 17.58% (± 4.93). Four were diagnosed with BAM: 1 moderate-BAM (type 3 BAM by cholecystectomy) and 3 severe- BAM (3 patients with type 3 BAM, all due to cholecystectomy). This pattern was significantly associated with presenting type 3 BAM (p 0.041).Finally, pattern 5 (uppper left abdomen) was classified in 3 patients, with a mean RA7 of 17.87% (± 6.61). Two patients were diagnosed with BAM: 1 mild-BAM (type 3 BAM by pancreatic insuf- ficiency) and 1 moderate-BAM (type 3 BAM by gastrectomy). Discussion The results of the qualitative analysis showed a clear variability in the location of the radiopharmaceutical in the first 3 h asssociated with the dynamics of the enterohepatic circulation of each patient. The image obtained in the first hour was not essential for deter- mining the 5 patterns and classifying the patients into each pattern. This image shows diffuse abdominal uptake corresponding to the radiopharmaceutical in the small intestine prior to incorporation into the enterohepatic circulation, requiring more time to adequately evaluate the distribution of the radiopharmaceutical. If the different patterns are analyzed based on these results it can initially be noted that pattern 1 (gallbladder 2−3 h) is associ- ated with an RA7 diagnostic of no-BAM. This may be explained by two premises. The first is that the gallbladder stores the bile acids during the period of fasting which is the state of the patient during the first part of the study.11 The second is that to achieve this stor- age it is necessary for the enterohepatic circulation to be intact with no bile acid loss greater than 5%. This implies that the ileum is not altered (inflammation or resection), that the transporters are act- ing adequately, that there is a gallbladder (no cholecystectomy), and that there is no other gastrointestinal disease affecting the absorption.1,4,12,13 Fig. 1 shows that in the first hour there is diffuse abdominal uptake that corresponds with the radiopharmaceutical in the small intestine prior to incorporation into the enterohepatic circulation. The images of the second and third hour show focal uptake in the gallbladder which corresponds with progressive stor- age of bile acids without excretion to the duodenum due to the fasting period. This helps to understand that this pattern is statis- tically significantly associated with the diagnosis of no-BAM, since a physiological distribution of the bile acids in the enterohepatic circulation can be visualized early. On the other hand, pattern 3 (gallbladder-abdomen 2−3 h) presents a statistically significant association with the diagnosis of BAM, specifically with presenting type 2 BAM; that is, there is no gastrointestinal disease producing the malabsorption, and the mucosa of the ileum is intact. Following the previous reasoning, in the images of the second and third hours this pattern could be present as low intensity uptake in the gallbladder due to less progressive accumulation of bile acids. This could be due to reabsorption of less than 95% in the terminal ileum due to incapacity of the transporters to perfrom their function or by accelerated intesti- nal transit that reduces the possibility of resabsorption of the bile acids.1,4,8,14 This accelerlated excretion of stored bile acids gen- erates the presence of bile acids in the small intestine before the absorption in the terminal ileum or colon, thereby visualizing dif- fuse abdominal uptake. This explains that within this pattern we can find one type 1 BAM patient diagnosed with possible Crohn disease, which is an inflammatory intestinal disease that can affect the ileum and impede adequate absorption of bile acids,1,15 7 patients with type 2 BAM, which seems to be related to an alteration of the transporters,4 and one patient treated with lenalidomide, of which the molecular mechanisms of its production remain unknown.9 On the other hand, it is possible that due to the slower enterohep- atic circulation during the first 3 h, the radiopharmaceutical has not yet finished the first cycle, and there is still radiopharmaceutical in the small intestine that is still being absorbed in the terminal ileum (abdominal uptake) and incorporated into the gallbladder. This would explain why in this pattern 2 patients were classified as no-BAM. Figure 1. Pattern 1 (gallbladder 2–3 h). Abdominal uptake in the 1st hour and focal activity in the gallbladder after the 2nd and 3rd hours. Figure 2. Pattern 2 (gallbladder 3 h). Abdominal uptake in the 1st and 2nd hour and focal uptake in the gallbladder in the 3rd hour. Figure 3. Pattern 3 (gallbladder-abdomen 2–3 h). Low abdominal uptake in the 1st hour, and after the 2nd hour low uptake in the gallbladder with diffuse abdominal uptake. Figure 4. Pattern 4 (abdomen). Diffuse abdominal uptake at the 1st, 2nd and 3rd hour. Figure 5. Pattern 5 (upper left abdomen). Diffuse abdominal uptake in the 1st hour and in the upper left abdomen in the 2nd and 3rd hours. Pattern 2 (gallbladder 3 h) could be scarcely different from pattern 1 and even similar statistical results could be expected. Nonetheless, visualization of focal uptake only in the image at 3 h could be due to several factors. On one hand, the enteroheptic cir- culation could be slower and the radiopharmaceutical has not yet completed the first cycle, remaining in the small intestine without having reached the terminal ileum where absorption takes place (abdomoinal uptake in the second hour), and then the absorption and storage in the gallbladder is produced after the third hour (bilary uptake at 3 h). It may also be that there is an alteration in the secretion of bile acids from the liver and they are therefore stored more slowly in the gallbladder, which would mean that BAM is not present.11 Another possible explanation is that the reabsorption in the enterohepatic circulation is altered due to malfunctioning of the transporters or an accelerated intestinal transit which could lead to BAM. Pattern 4 (abdominal) is not present in any of the images uptake in the biliary tract. This may be due to the presence of slower entero- hepatic circulation. It may also be due to slow primary bile acid secretion from the liver to the gallbladder, which would not pro- duce BAM. On the other hand, it could be due to the absence of the gallbladder which impedes the storage of bile acids producing a continuous flow to the duodenum,13,15 or lastly, it could be due to an enterohepatic circulation with altered reabsorption as explained above, which would produce BAM. For example, there were 4 chole- cystectomized patients with this pattern, which would explain the absence of uptake in the gallbladder and the statistical association with type 3 BAM.Finally, pattern 5 (upper left abdomen) could be explained in the same way as pattern 4. Despite the atypical and persistent localiza- tion in the upper left level of the abdomen, it may be due to other digestive diseases or to surgical interventions of the digestive tract that have modified the anatomy.Limitations of the study mainly include the small number of patients which precludes obtaining robust conclusions, as well as the subjective nature of the determnation of the 5 patterns of uptake. Conclusions In this study we performed a physiopathological evaluation of BAM and made an in depth study of the differences between the 5 patterns defined and their possible association with a final diagno- sis of no-BAM or BAM as well as their relationship with the three type s of BAM, in which 75SeHCAT imaging studies provided added value to the interpretation of the study.Despite the small number of cases studied, it can preliminar- ily be stated that pattern 1, showing uptake in the gallbladder at 2−3 h, is significantly associated with the diagnosis of no-BAM, while pattern 3, with low uptake in the gallbladder at 1 h and dif- fuse abdominal uptake at 2−3 h, is significantly associated with a diagnosis of BAM and specifically with type 2 BAM.Studies including a larger number of patients are needed to establish more robust associations and to perform a more in depth investigation in this line with the final objective of evaluating whether the current protocol can be modified and optimize the image acquisition procedure. 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