Pancreas: Tumors: Spiral CT following the Whipple Procedure: Distinguishing Normal Post-Operative Findings from Complications

Introduction

Spiral computed tomography is the imaging modality of choice in the diagnosis and staging of pancreatic adenocarcinoma with an overall accuracy of greater than 90 percent. Although the majority of patients have unresectable disease at the time of diagnosis, the 10-15 percent of patients with resectable disease that undergo pancreaticoduodenectomy (Whipple procedure) have a greater than 30 percent 5-year survival compared to an overall survival rate of less than 2 percent at 3 years for those with unresectable disease . For those patients who undergo a Whipple procedure, dynamic spiral CT is the study of choice to monitor for postoperative complications as well as local recurrence and metastatic disease.

The postoperative appearance in patients who have undergone a Whipple procedure has been described and is often complex with characteristics that emulate both benign and malignant processes. The diagnosis of recurrent disease is further complicated by postoperative complications and changes due to treatment with radiation and chemotherapy. Accurate interpretation of these complex postoperative exams requires knowledge of the type of surgery performed including surgical anastamoses, the interval between surgery and imaging and whether or not the patient has received any ancillary treatment such as radiation or chemotherapy. Optimizing scanning techniques and possessing a strong familiarity with the postoperative exam is essential to the early detection of recurrent and metastatic disease and to avoid false positive or false negative interpretations.

Technique

Until recently, it was common practice at our institution to perform post Whipple CT exams within 30 days of surgery to establish a postoperative baseline for future comparison as well as monitor for postoperative complications. However, the standard practice at this time is to image patients in the early postoperative period only when there is clinical suspicion of postoperative complications. Follow up imaging is generally performed at 3-6 month intervals.

We recommend administration of 750 cc or water soluble oral contrast beginning approximately 1 hour prior to imaging, with an additional 250 cc just prior to the start of spiral CT. Additionally, 120 cc of nonionic contrast is administered intravenously at a rate of 2-3 cc/second. Patients are asked to hyperventilate for several breaths during the injection, and spiral CT scanning is begun approximately 45 seconds after the contrast injection. Scanning parameters include a 5 mm collimation, pitch of 1.6 and images reconstructed at 5 mm intervals for a single detector CT scanner . For multidetector CT we use 3 mm collimation, a pitch of 6 and images reconstructed at 3mm intervals.

The Normal Post Whipple Exam

A Whipple procedure at our institution entails a duodenectomy, antrectomy, as well as removal of the common bile duct and resection of the head of the pancreas. Surgical anastamoses result in a gastrojejunostomy, hepaticojejunostomy and a pancreaticojejunostomy . The Whipple procedure is often modified depending on the patient’s extent of disease. When possible, a pylorus sparing procedure is performed creating a duodenojejunostomy rather than a gastrojejunostomy.

On postoperative spiral CT, the most common finding is pneumobilia. The presence of pneumobilia is often useful in identifying the hepaticojejunostomy . By following the intrahepatic ductal air into the region of the porta hepatis, the anastamosis becomes more obvious. Adequate opacification of jejunal loops with oral contrast is important, to distinguish recurrent or residual tumor from bowel . The pancreaticojejunostomy is often difficult to identify, particularly when the remnant gland becomes atrophic. Typically, jejunum is anastamosed to the right side of the remnant gland. The gastrojejunostomy is best identified following adequate gastric distention just prior to imaging. It is usually identifiable to the right of the gastric remnant, and there is often significant edema at the anastomotic site .

Small lymph nodes measuring less than 1 cm often appear in the immediate postoperative period and should regress on follow up imaging. Additionally, soft tissue stranding in the mesenteric fat within the operative bed and surrounding the celiac axis, superior mesenteric and hepatic arteries is often evident on postoperative CT exam . Although this is not a specific finding, the development of acute mesenteric stranding following surgery is likely inflammatory when negative surgical margins are achieved. Correlation with prior CT exams demonstrating stability or regression over time as well as a normal serum CA 19-9 level favor a benign inflammatory process. Studies have shown that postoperative inflammatory changes remain stable or regress over a 6 month period and usually resolve within 13 months.

Nearly all patients undergoing a Whipple procedure are offered and receive postoperative chemotherapy and radiation treatment. Common postradiation affects include thickening of the gastric antrum or gastrojejunostomy , fatty infiltration of the liver, stranding of the mesenteric fat within the radiation port and occasionally decreased function within the medial portions of the kidneys depending on the depth of the radiation port.

Complications

Early, accurate diagnosis of postoperative complications is imperative as multivariate analysis has documented that reoperation is one factor associated with a poor outcome. In fact, the absence of reoperation is an independent predictor of long term survival. Common indications for reoperation include hemorrhage, abscess and fascial dehiscence .

The postoperative complication rate following a Whipple procedure for periampullary masses at our institution is approximately 41- 47%. The most common complication is early delayed gastric emptying, occurring in 19-23% of patients. This is more prevalent following surgery for duodenal masses. Although gastric outlet obstruction is traditionally assessed by gastrograffin swallow exam, it is manifested on CT by a distended stomach or gastric remnant with narrowing of the gastric outlet .

The second most common complication in series from our institution and a leading cause of patient morbidity and mortality is pancreatic fistula . Pancreatic fistulae occur in up to 17% of patients and occur more commonly following Whipple procedure performed for periampullary masses . The diagnosis is made clinically by detection of greater than 50 cc of amylase-rich fluid in the drainage from the surgical bed on or after the 10th postoperative day. Treatment does not necessarily require surgery.

Other less common immediate postoperative complications include wound infection (9-10 %), wound dehiscence, abdominal abscess , breakdown of the surgical anastamoses leading to peritonitis and pancreatitis. Vascular complication are relatively uncommon and include hepatic artery injury, portal vein thrombosis and splenic infarction.

Recurrent and Metastatic Disease

Following a Whipple procedure, pancreatic cancer may occur within the surgical bed or metastasize to distant sites. Within the liver, metastatic disease is characterized by single or multiple low density lesions with minimal or delayed enhancement . Regional lymph nodes measuring less than one centimeter commonly appear in the immediate postoperative period but should continually decrease in size and number when free of tumor involvement. We commonly see metastatic lung and peritoneal carcinomatosis . Recent studies at our institution show the most common site for recurrent disease is within the pancreatic bed (53 % of patients) which occurs at an increased rate in patients with known residual disease at the time of surgery . . Soft tissue encasing the peripancreatic vessels or within the mesentery is often seen during the postoperative period and may have an identical appearance to postoperative inflammatory changes. Ancillary clues to recurrent disease would include a history of positive margins, an elevated CA-19-9, an increase in size of the soft tissue mass or a newly appearing soft tissue mass outside of the perioperative period.

Conclusion

For those patients who present with resectable pancreatic cancer, the Whipple procedure provides a significant increase in survival. Careful interpretation of the post operative CT examinations is essential, to detect post operative complications and early recurrent disease.

References

Coombs RJ, Zeiss J, Howard JM et al. CT of the Abdomen After the Whipple Procedure: Value in Depicting Postoperative Anatomy, Surgical Complications, and Tumor Recurrence. AJR 154: 1011-1014, May 1990.

Lepanto L, Gianfelice D, Dagenais M et al. Postoperative Changes, Complications, and Recurrent Disease After Whipple's Operation: CT Features AJR 1994; 163: 841-846.

Yeo CJ, Cameron JL, Sohn TA et al. Six Hundred Fifty Consecutive Pancreaticoduodenectomies in the 1990s: Pathology, Complications and Outcomes. Annals of Surgery 226(3): 248-260, 1997.

Yeo CJ, Cameron JL, Sohn TA et al. Periampullary Adenocarcinoma: Analysis of 5-year Survivors. Annals of Surgery 227(6): 821-831, June 1998.

Friess H, Wagner M et al. Pancreatic Fistula After Pancreatic Head Resection. British Journal of Surgery 87(7): 883-889, July 2000.

Based on an article by Pamela T. Johnson, Charlene A. Curry, MD, Bruce A. Urban, Elliot K. Fishman