J Clin Ultrasound 1063-66, February 1982

Appearance of Normal Pancreatic Duct: A Study Using Real-Time Ultrasound

Patrick J. Bryan, MB, FRCR

Abstract: Using a linear array real-time scanner and a video disc with slow-motion review capability, the pancreatic duct was seen in 86% of normal subjects. It appeared as a tubular structure in 65% of patients and as a single line echo in 21%. The normal pancreatic duct measures 2 mm in diameter or less. Indexing Words: Real-time ultrasound . Pancreatic duct . Video disc recorder

A dilated pancreatic duct has been recognized for some time as a sign of pancreatic There has been some controversy recently as t o whether the normal pancreatic duct can be seen, and if seen, whether it always appears as a single line or can be identified as a tubular structure with two distinct walls. It has been stated that the appear- ance of a tubular structure always indicated dila- tation of the pancreatic duct,3 while at least three workers have stated that the normal pancreatic duct can appear as a tubular ~ t r u c t u r e . ~ . ~ A study was undertaken to determine the frequency with which the normal pancreatic duct could be identified and to document its appearance (whether a single line echo or a tubular structure) and its size.

MATERIALS AND METHODS

An attempt was made to identify the pancreatic duct in 100 patients who were having an abdomi- nal sonogram for reasons other than biliary or pancreatic disease and in whom at least a portion of the pancreas could be seen. The patients were examined using a 3.5-MHz focused linear array real-time scanner (Toshiba Sonolayergraph, SAL-IOA)*. The video signals are fed into an analogue freeze-frame device which consists of a

*Toshiba Medical Systems, 1154 Dominquez, Carson, CA 90745.

From the Department of Radiology, Case Western Reserve University, Cleveland, Ohio. Manuscript received May 30, 1981; revised manuscript accepted July 30, 1981. For reprints contact Patrick J. Bryan, MB, FRCR, Department of Radiol- ogy, University Hospitals of Cleveland, 2074 Abington Road, Cleveland, Ohio 44106.

@ 1982 by John Wiley & Sons, Inc. 0091-27511821020063-04 $01 .OO

small video disc and a television monit0r.t Using this, it is possible to record 10 sec of scanning on the video disc and then to review it at actual speed, 1/7th of actual speed, or 1/15th of actual speed; or one may advance or reverse the images one frame at a time (Fig 1, 2). The recorder has been modified so that it can also be used as an analogue freeze-frame device.$

The patients ranged in age from 4 to 81 yr. Most patients had fasted overnight and had been given a laxative (magnesium citrate) the previous day. If the pancreas was nonvisualized due to overlying bowel gas, the patient was given water to drink and rescanned in an erect position after 5 to 10 min. Using this technique, the pancreas can be seen in over 9Wo of patient^.^,^

RESULTS

At least a portion of the pancreatic duct was seen in 86 patients but could not be identified in the remaining 14. This rate of visualization is almost identical to that reported by Ohto and co-workers in a recent study.4 The duct appeared as a tubular structure with two identifiable walls in 65 pa- tients (Fig l), while only a single line could be identified in 21. Of the 65 patients in whom a tubular structure could be identified, its diameter was 1 mm in 47 cases, 2 mm in 17, and 3 mm in 1 (Table 1).

The duct could be seen in both the body and head of the pancreas in 20 patients, the body alone in 64, and the head alone in 2 (Table 2). The patient’s body habitus in this study was charac-

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64

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PATRICK J. BRYAN

TABLE 3 Body Habitus of Patients in the Study

FIGURE 1. The pancreatic duct (arrows) is seen as a tubular structure in the head (A) and body (B) of the pancreas. The pancreatic duct in the head is seen approaching the common bile duct (arrowhead).

FIGURE 2. Transverse scan through the body of the pancreas (ar- row). The pancreatic duct (arrowheads) appears as a linear echo.

TABLE 1 Appearance of the Pancreatic Duct

Single line 1 mm 2 mm 3 mm Not seen

21 47 17 1

14

Total 100

TABLE 2 Segment of the Pancreatic Duct Seen

Body alone Head and body Head alone Not seen

64 20

2 14

Thin Average Obese

22 59 19

Total 100

TABLE 4 Body Habitus of Patients with Nonvisualized Ducts

Thin Average Obese

0 0 6

Total 14

70t

I

s o .

0 . 0 0

0

0

0 . 0

0 .

1 1 1 I _I

LINE Imm 2mm 3mm

FIGURE 3. The distribution of duct diameter in relation to age is shown. While there is a tendency for larger ducts to occur in older people, this finding was not statistically significant.

0 '

terized as thin, average, or obese. The series con- tained 22 people who were characterized as thin, 59 as average, and 19 as obese (Table 3). In those subjects in whom the duct was seen, there was no correlation between body habitus and visualized diameter. All of the 14 patients in whom the duct was seen were either of average build or obese, while none of the people with nonvisualized ducts were characterized as thin (Table 4).

The size of the duct was correlated with the age of the subjects. There was a tendency for younger people to have smaller ducts, either a single line echo or a 1-mm lumen, while most of the older subjects tended to have larger ducts (Fig 3). How- ever, if one ignores the measurements in children, who would be expected to have smaller ducts, the

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REAL-TIME APPEARANCE OF NORMAL PANCREATIC DUCT 65

variation of duct size with age was not statisti- cally significant.

DISCUSSION

This study shows that using high-resolution, real-time scanning, the normal pancreatic duct can be seen in the great majority of people, and it is usually identifiable as a tubular structure. Use of a real-time scanner makes the examination technically simple, and in this study the attempt to see the pancreatic duct took only two to three minutes. The pancreatic duct can also be seen with conventional B-scanning. Parulekar5 in a re- cent study reported seeing the normal pancreatic duct with conventional B-scanning in 82% of normal subjects. However, examination of the pancreas is much more time-consuming with the conventional B-scanner due to the inability to scan the entire gland continuously and the greater difficulty of aligning the plane of the scan with that of the pancreas and of the pancreatic duct. The addition of the video disc in our study helps when there is considerable respiratory mo- tion of the gland or intermittent visualization due to moving overlying bowel gas, as the slow motion or single-frame review enables one to see better a duct which is only briefly glimpsed in real-time.

The course and position of the duct in the head of the pancreas are quite variable. Because of this variability and also because the plane of the duct in the head of the pancreas is usually not perpen- dicular to the ultrasonic beam, the pancreatic duct is usually more difficult to identify in the head of the pancreas than it is in the body. This is particularly true when one is scanning with an articulated scanner, as it is very difficult to orient the plane of the scan to that of the duct. It is con- siderably easier to do this with a real-time scan- ner, as one can continuously alter the plane of the scan in search of the duct.

In this study, the body of the pancreas is taken to include that portion of the gland which is an- teromedial to the left kidney, in accordance with the definition in Gray’s Anatomy. This is at vari- ance with common usage in the radiological liter- ature, which describes all of the pancreas to the left of the vertebral body as the tail. According to Gray’s, the tail begins only when the pancreas en- ters the lienorenal ligament, and thus the portion of the pancreas anteromedial to the left kidney is still the body. The duct usually lies in a plane closer to the posterior surface of the pancreas than to its anterior surface, although this is vari- able, and it sometimes lies at or even slightly in front of the midplane of the gland.

VOL. 10, NO. 2, FEBRUARY 1982

The patient’s body habitus has considerable influence on the ease with which anatomical structures are identified by ultrasound. The best ultrasonic images are obtained in thin people, whereas obese subjects seldom provide such good anatomical definition. Reasons for this include at- tenuation of the beam by the fat, displacement of anatomical structures into the far field of the beam, and lack of contrast between the retro- peritoneal fat and the echogenic pancreas.

Since most of the patients in this study were fasting, could this condition have influenced the diameter of the pancreatic duct? It is doubtful that fasting causes an increase in the diameter since 1- and 2-mm ducts were seen in several pa- tients who were not fasting. Ohto and co-workers4 actually used injection of secretin to stimulate pancreatic secretion and demonstrated an in- crease in the diameter of the pancreatic duct fol- lowing secretin injections. They stated that the normal pancreatic duct was less than 0.8 mm in diameter, whereas in this study it was measured at up to 2 mm. It is difficult to decide where exactly to measure duct diameter, and this difficulty was alluded to by the Japanese workers. When distinct echogenic walls were seen, we used the beginning of the near-wall echo to the begin- ning of the far-well echo as a measurement, whereas the Japanese workers appeared to have used the inner lumen diameter. While measuring the inner lumen may be more technically repro- ducible, it probably underestimates the actual size of the duct. It is also difficult to make a pre- cise measurement of such a small structure when the scale available is centimeter markers. One duct in this study was measured at 3 mm, and no evidence of pancreatic disease was present either in the history or otherwise. Nevertheless, 2 mm should probably be taken as the upper limit of normal, and anything above this should be re- garded as dilated. Parulekar also considered 2 mm to be at the upper limit of normal in his study.5 Normal diameters as measured on pan- creatography are somewhat greater than this.g*10 However, there is probably not a true dis- crepancy, as the diameter of the duct on pancre- atography is increased by both radiographic magnification and distention of the duct due to in- stillation of the contrast medium.

CONCLUSION

In this study, the pancreatic duct was seen in 86% of normal subjects and, in the majority of cases, was identified as a tubular structure with two dis-

66 PATRICK J. BRYAN

tinct walls. The normal pancreatic duct measures 2 mm or less in diameter.

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3. Weinstein DP, Weinstein BJ: Ultrasonic demon- stration of the pancreatic duct An analysis of 41 cases. Radiology 130:729, 1979.

4. Ohto M, Saotome N, Saisho H, et al: Real-time sonography of the pancreatic duct: Application to percutaneous pancreatic ductography. AJR 134:647, 1980.

5. Parulekar SG: Ultrasonic evaluation of the pan- creatic duct. J Clin Ultrasound 8:457,1980.

6. Gibson JY Ultrasonic demonstration of the pan- creatic duct. Letter. Radiology 134:264, 1980.

7. Crade M, Taylor KJW, Rosenfeld AT: Water dis- tension of the gut in the evaluation of the pancreas by ultrasound. A m J Roentgen01 131:348, 1979.

8. MacMahon H, Bowie JD, Beezhold C: Erect scan- ning of the pancreas using a gastric window. AJR 132:587, 1979.

9. Rohrmann CA, Silvis SE, Vennes JA: Evaluation of the endoscopic pancreatogram. Radiology 113:297, 1974.

10. Millbourn E: Caliber and appearance of the pan- creatic ducts and relevant clinical problems. A roentgenographic and antomical study. Acta Schir Scand 118:286,1960.

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