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Ultrasonography |
1 From the Department of Radiology, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, Iowa City, IA 52242. From the 1999 RSNA scientific assembly. Received January 5, 2000; revision requested February 22; revision received May 10; accepted May 22. Address correspondence to M.M.A.Y. (e-mail: monzer-abu-yousef@uiowa.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Seventy patients in whom visualization of the pancreatic tail was poor at US were reevaluated in the upright position after ingesting 2 cups (500 mL) of water with 80 mg of simethicone followed by rotating three times on the examination table. In a few patients, the right posterior oblique position was used. Pancreatic tail visualization and disbursement of gastric gas were evaluated. Seventy patients who received 500 mL of distilled water only served as control subjects.
RESULTS: Pancreatic tail visualization in patients versus control subjects was complete in 55 (79%) versus five (7%) of 70 patients and control subjects, partial in 10 (14%) versus 38 (54%), and not improved in five (7%) versus 27 (39%). The effect on diminishing gastric air was closely correlated with the degree of improved visualization in most patients. All patients tolerated the procedure well, with no side effects. The technique added a mean of 8 versus 5 minutes to the examination in patients versus control subjects. The full acoustic window effect of the simethicone-water mixture lasted approximately 10 minutes.
CONCLUSION: The simethicone-water-rotation technique is simple, safe, inexpensive, and effective for improving pancreatic tail visualization in ambulatory patients and is superior to the use of water alone.
Index terms: Contrast media, comparative studies, 773.12988 • Pancreas, US, 773.1298, 773.12988 • Simethicone • Ultrasound (US), contrast media, 773.1298
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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In 1978, a technique involving the use of methylcellulose and glucagon was described (7). It was claimed to improve pancreatic visualization, but no data on improvement were provided. More recently, the introduction of cellulose-based gastrointestinal contrast agents has resulted in remarkable improvement in US of the pancreas. The contrast agents emulsify the air in the stomach with cellulose particles to form a variably echogenic medium that acts as an acoustic window for use in imaging the pancreas (8–12). However, the relatively high cost of this cellulose-based contrast material proved prohibitive for use in routine upper abdominal US.
Simethicone is a well-known emulsifying agent that has been used previously in upper gastrointestinal barium examinations to break down large gas pockets by changing their surface tension. It also improves the coating of the gastric mucosa with barium (13,14). Patient rotation also is a well-known technique used to improve gastric coating with barium, although no articles have been published on this technique, to our knowledge. The purpose of our study was to determine whether it is possible to improve US visualization of the pancreatic tail with the use of degassed water, simethicone, and patient rotation.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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We also retrospectively reviewed, for the control group, US images of the pancreatic tail in 70 consecutive patients with incomplete visualization of the pancreatic tail in whom previous upper abdominal US was performed before and after the administration of degassed water. These patients did not receive simethicone and did not rotate. We excluded from the control group postprandial patients, patients who could not or were not supposed to drink water, and those who could not stand upright. Patients who were unable to drink the full amount, however, were not excluded. Fifty-two of these were men, and 18 were women, ranging in age from 18 to 83 years (mean, 49 years).
Technique
In the prospective study group, patients were asked to ingest 2 cups (500 mL) of degassed (distilled) water mixed with 80 mg of simethicone (Goldline Laboratories, Miami, Fla) while in the sitting position. They were then asked to rotate 360° on the examination table three times and were reexamined by means of US while in the upright position. There was no waiting period after the simethicone was mixed with water or before imaging could be started. In the latter part of our experience, a few patients were initially examined in the right posterior oblique position; of these patients, only those who had incomplete visualization were reexamined in the upright position. Because of their small number, no attempt was made to assign these patients to a separate subgroup.
In the retrospective control group, patients with poor pancreatic tail visualization had been given 2 cups (500 mL) of degassed water only and were reexamined in the upright position. US was performed with use of a 4-MHz vector or curvilinear transducer (Acuson, Mountain View, Calif). The time gain compensation curve was adjusted to reduce the enhancing effect of the water-filled stomach on the pancreas to produce an image with even brightness.
We estimated the mean time our technique adds to routine US and compared this time with the estimated mean time the water technique adds to such an examination. We estimated the number of repeated examinations performed by the sonologist (M.M.A.Y.) in the study group alone. We also evaluated patients for potential complications from the simethicone mixture, such as nausea, vomiting, abdominal cramps, aspiration, and exhaustion. We did not perform long-term evaluation of patients for diarrhea since simethicone is not known to cause this complication. We looked at the potential causes of partial and no improvement in pancreatic tail visualization in both groups. In addition, we evaluated whether the simethicone technique helped to clarify the presence of disease seen prior to the use of the technique.
Image Analysis
The images from the two studies were evaluated by two experienced radiologists (M.M.A.Y., Y.E.Z.), and the differences were resolved by consensus. All pancreatic US examinations, including those performed before and after administration of water and the water-simethicone mixture, were graded according to the degree of pancreatic tail visualization as follows: grade 0, no visualization of the pancreatic tail; grade 1, visualization of only the proximal (horizontal) segment; grade 2, visualization of the area up to the proximal descending segment; grade 3, visualization of the area up to the distal descending segment; and grade 4, complete visualization, including the distal horizontal segment, often landmarked by the anterior surface of the left kidney and/or the distal splenic vein near the hilum of the spleen.
US findings were also divided into five grades depending on the amount of gas in the stomach as follows: grade 0, no gastric air; grade 1, minimal gastric air with no interference; grade 2, small amount of gastric air with mild interference; grade 3, moderate amount of gastric air; and grade 4, stomach totally filled with air.
Patients were then assigned to three categories depending on the degree of improvement in pancreatic tail visualization. Group 1 showed no improvement; that is, no change in the visualization grade. Group 2 showed partial improvement; that is, improved visualization degree but parts of the tail were still obscured. Group 3 had complete improvement with visualization of all segments of the pancreatic tail. The echotexture of the gastric contents also was evaluated after use of the simethicone-water-rotation technique and was compared with the echotexture after use of the water-only technique. We did not compare our clinical findings with findings at either CT or MR imaging, since not all patients underwent these examinations.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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In 28 patients, the water in the stomach had a homogeneous, hyperechoic, finely speckled appearance resulting from tiny bubbles of gas fragmented by the simethicone (Fig 1), while in 25 the appearance was hypoechoic and mildly speckled (Fig 3). In 17 patients, the medium was totally anechoic without speckles (Fig 4b).
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All patients tolerated the procedure well. A few patients had mild fatigue after the rotation. None of the patients from group 1 or 2 experienced nausea, vomiting, aspiration, cramps, or other side effects or complications.
The most common causes of our inability to fully visualize the pancreas with use of this technique were low-lying stomach followed by incomplete mixing of the gastric air. Attenuation due to severe fatty infiltration of the pancreas, colonic gas, and body fat were less common causes of incomplete pancreatic visualization. With severe fatty infiltration of the pancreas, this organ was extremely hyperechoic and attenuating, which prohibited visualization of its posterior aspect.
In 18 patients, the whole pancreas was totally obscured prior to the ingestion of the simethicone-water mixture. In 15 of these, complete visualization of the pancreas including the tail was possible, while in two there was partial improvement in visualization of the tail, and in one there was no improvement. In one of the 15 patients, visualization of intraparenchymal calcifications facilitated the diagnosis of chronic pancreatitis (Fig 3). In two other patients suspected of having pancreatic tail enlargement at preliminary US, the simethicone-water-rotation technique helped in clearly depicting a normal pancreatic tail (Fig 4), while in two others a diffusely hypoechoic pancreatic tail was normal (Fig 1). In one patient, the technique helped in the depiction of a pancreatic head mass (Fig 5).
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There was no effect on the gas interference in 25 (36%) of 70 control subjects, partial clearing in 39 (56%), and complete clearing in six (8%). Before water ingestion, the number of studies with grade 0, 1, 2, 3, or 4 gas interference was 0, 3, 7, 12, or 48, respectively. After ingestion, the number of studies in each grade was 6, 11, 18, 20, or 15, respectively. Figure 2d shows the mean gas interference grade before and after the ingestion of water.
The fine, hyperechoic, speckled appearance seen in the study group was not seen in any of the control subjects, and the medium was anechoic. The estimated time for control subjects to complete the study, including drinking and undergoing imaging, was 5 minutes. The most common cause of our inability to fully visualize the pancreas with use of this technique was persistence of gas pockets in the stomach.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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While some study findings (2) have confirmed the superiority of the sensitivity (0.87) and specificity (0.90) of CT relative to those of US (0.69 and 0.82, respectively), other study findings (3,4) have shown CT to be either more sensitive or more specific, but not both. Several methods, including the use of water and glucagon (5) or examination of the patient in the upright position (6), have been advocated to improve pancreatic US. More often than not, shadowing from persistent gas pockets in the stomach interfered with improved visualization despite the use of those methods.
Recently, cellulose-based orally administered US contrast agents have been shown to improve imaging of the upper abdominal organs, particularly the pancreas (8–12). In a study (8) in which 10 volunteers were evaluated, cellulose suspensions were found to be far superior, compared with degassed water, in improving visualization of the upper abdomen, including the pancreas, with a P value for improved visualization after oral administration of contrast medium of less than .05. The results of studies by other investigators (9) were similar, although the degree of improvement in pancreatic visualization varied. In one study (9), the mean score after the administration of cellulose-based contrast medium was 3.1 of 4, compared with 1.8 for water and 1.6 before the administration of contrast medium. Harisinghani et al (10) also noted improvement in pancreatic tail visualization, with a P value of less than .05. In another study (11), pancreatic tail visualization improved in only 67% of the patients after a cellulose-based contrast agent was used.
In our study, the mean score after the administration of the simethicone-water mixture was 3.56 of 4 compared with a score of 1.39 after the administration of water alone and a score of 0.57 of 4 before the administration of contrast medium. Furthermore, the use of simethicone, water, and rotation in our study improved pancreatic tail visualization in 93% of the patients, with complete visualization in 79%.
There is disagreement about the effect of the cellulose fiber size on the degree of image improvement. While some investigators (8) have found the greatest degree of improvement to occur with a cellulose fiber size of 18 µm, others (11) found the best imaging with a fiber size of 22 µm. Differences also were noted between articles on the effect of cellulose concentration in the suspension. While some investigators (8) found that the concentration affected the quality of the images, with the best visualization achieved with the use of the 2% suspension, others (9) found no change in improved visualization with concentrations of 1%–3%.
There were no clinically important complications following the administration of cellulose-based contrast agents; however, in most studies, a small percentage of patients complained of nausea and vomiting. In one study (8), one of 10 volunteers experienced nausea, and another had diarrhea. In another study (11), nausea was the main side effect, with no statistically significant difference between cellulose and the control agent. Other side effects reported were upper abdominal discomfort and aspiration. In our study, there were no such side effects or complications. The only side effect that some of our patients reported was mild fatigue following rotation, which did not interfere with the examination.
In most studies, substantial time is needed to allow the cellulose-based contrast medium to settle in vivo after it is shaken. More time also is needed after the patients ingest the contrast material before US may begin. In one study (8), each patient required more than 15 minutes to drink the agent and 10 more minutes to wait before imaging started. Other investigators (9–12) had similar experiences. The mean time for us to prepare the contrast medium and for the patients to ingest it and to rotate in our study was 5 minutes. Furthermore, our patients did not have to wait before they ingested the contrast agent or before imaging could start after ingestion.
The retail cost of one dose of cellulose-based contrast agent for oral administration in today’s market is about $30. Because of their relatively high cost, thus far such agents have not been routinely used at upper abdominal US. Our technique, in which we use 2 cups (500 mL) of degassed water mixed with a few drops of simethicone, is much less expensive.
A few limitations to our technique do exist. The technique cannot be used for bedridden patients who are unable to rotate themselves on the examination table, patients who cannot or are not supposed to ingest the required amount of water (especially those with acute pancreatitis), patients who underwent previous gastrectomy, or patients who have just eaten. The latter three limitations, however, are also shared by techniques involving the use of cellulose-based agents.
The contrast effect of our agent lasts for only 10 minutes, compared with more than 30 minutes for the cellulose-based contrast agents. In our study, 10 minutes was sufficient to complete the examination. Additional amounts of the mixture could be given without notable side effects, due to the low toxicity of simethicone. Furthermore, this rapid transit helps in making our technique more acceptable than the use of cellulose-based contrast media for patients who will be undergoing endoscopic procedures, barium studies, or CT on the same day.
Lack of complete improvement of pancreatic tail visualization in our study occurred in patients with a low-lying stomach, in patients with severe obesity (because there was interference from excessive mesenteric fat or attenuation due to fatty infiltration of the pancreas), and occasionally in patients with incomplete fragmentation of large air bubbles in the stomach.
Our study also had some limitations. There was inherent bias toward the study group, since the examinations in this group were more closely supervised. Patients who did not drink the 2 full cups (500 mL) of water and those who did not perform three full rotations were not included in the study. On the other hand, all consecutive patients in the control group who were reexamined in the upright position after ingesting water were included. Although patients were typically postprandial and had to drink 2 cups (500 mL) of water, it was difficult to identify and exclude patients who may have ingested less than the required amount, due to the retrospective nature of this part of the study. In addition, a few of the patients in the study group were reexamined in the right posterior oblique position, which may have constituted another bias toward the study group. The fact that the author (M.M.A.Y.) who enrolled the patients in the study group participated in the review process could potentially cause some bias skewed toward the study group.
In conclusion, the use of a simethicone-water mixture and patient rotation is simple, inexpensive, safe, and effective in improving pancreatic tail visualization and thus obviates additional expensive CT or administration of US contrast agents in many patients. Although this technique is tolerated by most, its use is limited to ambulatory patients. Prospective studies in which this technique is compared with the administration of cellulose-based contrast media may be necessary for better evaluation of the role of both methods in improving upper abdominal US imaging.
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FOOTNOTES |
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