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1 All authors: Department of Radiology, Our Lady of Mercy Hospital, The Catholic University of Korea, College of Medicine, 665 PupyungDong, PupyungGu, Inchon 403-720, South Korea.
Received September 5, 2001;
accepted after revision November 12, 2001.
Presented at the annual meeting of the American Roentgen Ray Society,
Seattle, April—May 2001.
Abstract
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SUBJECTS AND METHODS. Unenhanced abdominal CT was performed before and then 1 hr to 1 hr 30 min after Gastrografin ingestion in 30 patients 7 days after gastric surgery and in 19 healthy adults who served as the control group. CT scans were reviewed for the opacification of the renal collecting system or urinary bladder after Gastrografin ingestion, a finding that represents renal excretion of the ingested contrast medium.
RESULTS. In the control group, four (21 %) of the 19 healthy adults showed renal excretion of ingested Gastrografin visualized as opacification of the urinary tract on CT scans obtained 1 hr to 1 hr 30 min after ingestion of the substance. Renal excretion of the ingested Gastrografin was seen in 19 (63%) of the 30 patients, a significantly larger percentage than in the control group (z score, p < 0.01). No patient showed either radiologic or clinical evidence of leakage from the anastomotic site.
CONCLUSION. Renal excretion of ingested Gastrografin is frequently visualized on CT in patients without anastomotic leakage during the early postoperative period after gastric surgery, and this phenomenon is not rare, even in healthy adults. Therefore, renal excretion seen on CT should not be regarded as a sign of anastomotic leakage in early postoperative patients.
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However, urinary excretion of enteral Gastrografin visualized on CT in patients who have various bowel diseases without gastrointestinal perforation has been sporadically reported [4,5,6,7]. To our knowledge, no reports have described this phenomenon on CT in patients during the early recovery period after gastric surgery. We investigated the prevalence of urinary excretion of ingested Gastrografin seen on CT scans in patients who had recently undergone gastric surgery and in healthy adults and correlated it with the clinical data of the patients to reassess the clinical relevance of this phenomenon on CT in patients during the early postoperative period.
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The protocol for the patient group included unenhanced CT scanning of the abdomen at the level of kidneys and urinary bladder (four images each), a fluoroscopic gastrointestinal study with ingestion of 100 mL of undiluted Gastrografin, and rescanning of the entire abdomen 1 hr to 1 hr 30 min after the gastrointestinal study. For the control group, abdominal CT was performed before and then 1 hr to 1 hr 30 min after ingestion of 100 mL of undiluted Gastrografin. Fluoroscopic gastrointestinal studies were not performed for the control group. IV contrast material was not used in either group. For both groups, CT was performed (Somatom Plus 4; Siemens, Erlangen, Germany) using a 10-mm collimation at a 10-mm interval.
Two radiologists retrospectively interpreted the CT scans, and decisions were made by consensus. CT scans were reviewed specifically for the presence of urinary excretion of ingested Gastrografin. Evidence of contrast medium leakage, free air, abscess formations, and the presence of ileus was also carefully sought, and clinical data of each patient were correlated with the imaging findings. Urinary excretion of the ingested contrast medium was regarded as being present if opacification of the renal collecting system or urinary bladder was visible on the CT scans obtained after Gastrografin ingestion (Figs. 1A,1B and 2A,2B). The CT attenuation coefficient was measured from the dependent portion of the urinary bladder on both unenhanced and enhanced CT scans to calculate the difference. We regarded the attenuation difference in the dependent portion of the urinary bladder as a maximal attenuation difference after ingestion of the contrast medium.
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For statistical analysis, we used a z-score to compare the incidence of urinary excretion of orally ingested Gastrografin among the early postoperative patients who had undergone gastrointestinal surgery with that of healthy adults in the control group.
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In the patient group, 19 (63%) of the 30 patients showed renal excretion of Gastrografin, a significantly larger percentage than in the control group (z score, p < 0.01). The mean maximal attenuation difference of the urinary bladder was 105.3 ± 92.8 H (n = 17) in the patients showing renal excretion of the contrast medium and 14.6 ± 8.1 H (n = 8) in the patients showing no renal excretion of the medium. In five patients, the attenuation coefficient of the urinary bladder was not measurable. As for the type of surgery, seven of the eight patients who had undergone total gastrectomy showed renal excretion of ingested Gastrografin. Of the patients who had undergone subtotal gastrectomy, 11 of 21 showed renal excretion of the contrast medium. The one patient who had undergone Whipple's operation also showed renal excretion of the medium.
Definite leakage of the contrast medium from the anastomotic site, free air, or abscess formation was not seen on the CT scans obtained in the patient group. The CT scans of 27 (90%) of 30 patients showed no major ileus, a finding confirmed by transit of the contrast medium through the loops of the large bowel visible on delayed CT. One patient had some ascites caused by hypoalbuminemia. None of the patients showed direct leakage from an anastomotic site on the fluoroscopic gastrointestinal study, and none had clinical data suggestive of anastomotic leakage, not even the five patients with a maximal attenuation difference of more than 100 H in the urinary bladder.
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Increased absorption of an enteral water-soluble contrast medium is now known to be a nonspecific sign of mucosal injury or increased permeability of the bowel, and it is not necessarily accompanied by perforation [5, 7]. Animal studies on the pathophysiology of this phenomenon have shown that urinary excretion occurs in cases of induced ischemia, radiation injury of the intestine, and small-bowel obstruction [8,9,10]. In human beings, increased intestinal permeation due to mucosal damage has been found to occur in patients with various intestinal diseases. Hay and Cant [5] described seeing urinary contrast medium on CT in a patient with an ischemic bowel disease associated with abscess formation but without evidence of intraperitoneal perforation. Laerum et al. [11] and Halme et al. [12] investigated the increased intestinal mucosal permeability in patients with small-bowel obstruction and with ileal Crohn's disease. An abdominal emergency, such as postoperative obstruction accompanied by vomiting, dehydration, and diminished speed of transit of the contrast medium through the gut, may result in increased absorption of the contrast medium and a greater concentration in the urine of this absorbed contrast material than would be found in healthy subjects [4].
Our study found that on CT, urinary excretion of ingested Gastrografin was visualized in 63% of the patients scanned 7 days after gastrointestinal surgery, which is a significantly larger percentage than the 26% of the control group in whom urinary excretion of the medium was visualized. However, no patient had clinical findings suggestive of postoperative complications, such as anastomotic leakage, abscess formation, or major obstruction, and no patient showed direct leakage from the anastomotic site during the gastrointestinal study. The increased absorption of enteral Gastrografin in these patients could be due to increased mucosal permeability with inflamed and edematous mucosa after gastrointestinal operation. Ileus or diminished speed of the contrast material through the gut may account for the increased absorption of enteral Gastrografin in postoperative patients. However, because Gastrografin stimulates bowel peristalsis and most (90%) of the patients in this study showed no substantial ileus, the change in the mucosal permeability was believed to be the main cause for the increase in the absorption of enteral Gastrografin.
Apter et al. [7] found that study participants who were free of bowel disease did not show urinary excretion of Gastrografin on CT. However, in our study, urinary excretion of ingested Gastrografin was seen on CT in 21% of healthy adults. This discrepancy might be caused by the difference of concentration of Gastrografin ingested: Undiluted Gastrografin was used in our study, whereas diluted Gastrografin was used in the study performed by Apter et al.
In this study, the patients who had undergone total gastrectomy showed a higher frequency of urinary excretion of enteral Gastrografin than the patients who had undergone subtotal gastrectomy. This finding may be related to the greater amount of tension applied and the greater degree of mucosal damage that occurs during the total gastrectomy procedure than during the sub-total gastrectomy. The presence of more contrast material in the intestinal tract after the waiting period (1 hr to 1 hr 30 min) that would be caused by the lack of any remnant stomach could be another reason that more absorption was seen in patients who had undergone total gastrectomy.
Our study is limited in that the cause of renal excretion of ingested Gastrografin was not surgically confirmed, nor was the mucosal change evaluated on endoscopy. However, no clinical need for further invasive study or surgical intervention was present because there was no radiologic or clinical data suggestive of anastomotic leakage.
In summary, this study showed that renal excretion of ingested Gastrografin was frequently visualized on CT at postoperative day 7 in the patients who had undergone gastric surgery and who had no radiologic or clinical data suggestive of anastomotic leakage. We concluded that intestinal absorption of enteral Gastrografin could be considerably greater in early postoperative patients after gastrointestinal surgery than in healthy subjects but that such absorption is not rare, even in healthy adults. Therefore, renal excretion of orally administered Gastrografin seen on CT should not be regarded as a sign of anastomotic leakage in a patient during the early postoperative period unless direct leakage is identified. Increased intestinal mucosal permeability and increased bowel transit time in such patients could account for the increased absorption of enteral Gastrografin.
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