• Distal pancreatectomy is the primary surgical treatment for benign and malignant etiologies arising from the pancreatic body and tail
• Several variations in surgical technique have been described with similar outcomes and complications
• CT is routinely performed in the post-operative evaluation of patients who underwent distal pancreatectomy
• Knowledge of normal postoperative anatomy, expected post-operative findings and common complications is critical for the interpreting radiologist to arrive at the correct diagnosis and facilitate proper management

• Purpose of this exhibit is to provide a general overview of distal pancreatectomy for the radiologist
• This exhibit will:
  • Review the regional anatomy surrounding the pancreatic body and tail
  • Review the indications and surgical approaches for distal pancreatectomy
  • Differentiate the expected post-operative CT appearances from common to life-threatening complications through a case review

• A derivative of the embryologic foregut, the pancreas is an elongated, endocrine and exocrine organ located in the epigastric region
  • Approximately 15-22cm in length
• Often oriented slightly oblique to the left and cranially
• Organ is divided into the head, neck, body and tail
• Confined to the retroperitoneum in the anterior pararenal space2
  • Except for the pancreatic tail, which is intraperitoneal, loosely associated with the peritoneal folds which comprise the splenorenal ligament

• Head: Located medial to the C-loop of the duodenum, right of the superior mesenteric vessels
  • Uncinate process is a posterior and medial continuation of the pancreatic head, located posterior to the superior mesenteric vessels
• Neck: Located deep to the pylorus of the stomach and ventral to the portal confluence
• Body: Located deep to the lesser peritoneal sac and the stomach, ventral to the left kidney and splenic vasculature
• Tail: Located intraperitoneal, within the splenorenal ligament, adjacent to the splenic hilum
• No consensus on anatomic division of the pancreatic body and tail
  • Can be denoted by measuring one-half of the distance between the pancreatic neck and tip of the pancreas

• Pancreas has a rich, complex arterial vascular supply from numerous branches off the celiac axis and SMA
• Considerable variations exist in arterial supply, particularly for the pancreatic head
• Most common arterial supply:
  • Head and neck are supplied by branches of the superior pancreaticoduodenal artery (arise from GDA) and dorsal pancreatic artery (arise from splenic artery)
  • Inferiorly, these anastomose with branches of the inferior pancreaticoduodenal artery (often arise from SMA) and retropancreatic arcades
  • Body is supplied by the dorsal and greater pancreatic arteries (arise from splenic artery)
  • Tail is supplied by inferior and caudal pancreatic arteries (arise from splenic artery)

• Compared to arterial supply, less variation exists for the venous drainage of the pancreas
• Four primary veins drain the head and neck of the pancreas
  • Anterior and posterior branches of the superior and inferior pancreaticoduodenal veins coalesce into branches that drain into the SMV or main portal vein directly (posterior SPDV)
• Body and tail are drained by numerous collateral branches, inferior and caudal pancreatic veins, all of which drain into the splenic vein

• Distal pancreatectomy is the surgical treatment of choice for a wide range of benign and malignant etiologies arising in the pancreatic body and tail
• Most common indications are benign (mucinous and serous cystic neoplasms) and malignant (adenocarcinoma and neuroendocrine tumors) pancreatic neoplasms
• Two, large single-institution retrospective reviews demonstrated the most common indications:
  • Goh et al: Serous cystadenoma (14%), ductal adenocarcinoma (13%), mucinous cystic neoplasm (11%), neuroendocrine tumors (9%)
  • Lillemoe et al: Chronic pancreatitis (24%), serous cystadenoma (22%), ductal adenocarcinoma (18%), neuroendocrine tumors (14%)
    • Mucinous cystic neoplasms were not reported in this series
• Collective review on laparoscopic distal pancreatectomy by Borja-Cacho et al9 had similar results:
  • Mucinous cystic neoplasm (20%), serous cystadenoma (16.5%), neuroendocrine tumor (16.2%), ductal adenocarcinoma (9.8%)

• May be performed via open and laparoscopic approaches
• Open approach is classically performed for malignancies
  • Due to relatively late stage of presentation for cancers in the body and tail
  • Lack of sufficient literature on oncologic safety of laparoscopic approach
• Laparoscopic approach is generally performed for benign lesions and small pancreatic malignancies
  • Preoperative EUS for lesion tagging or intraoperative ultrasound-guidance may be utilized to aid detection of small, intraparenchymal lesions

• Distal pancreatectomy traditionally performed with en bloc splenectomy
  • Given close relationship of pancreatic tail with splenic hilum and vasculature
• Spleen preservation can be considered on an individual case basis for benign or low malignant potential lesions
  • Aims to reduce the infectious and hematologic complications associated with splenectomy
• Two primary spleen preserving techniques
  • May be performed by dividing the splenic vasculature distal to the pancreatic tail, consequently the spleen is vascularized by short gastric vessels
    • Shorter, easier technique but can lead to gastric varices
  • Alternatively, entire splenic artery and vein can be conserved
• Several techniques exist for closure of the pancreatic remnant following resection
  • Anastomotic (pancreaticojejunostomy), suture or staple closure with or without main pancreatic duct ligation

• Distal pancreatectomy with en bloc resection of the celiac axis
• Radical operation performed for subset of locally advanced cancers of the pancreatic body which involve the celiac trunk or common hepatic artery14 Often performed after neoadjuvant chemotherapy
• Flow to proper hepatic artery is achieved via retrograde flow from the GDA and collateral pathways from the SMA Preoperative common hepatic artery embolization can be performed to increase collateralization
• Closure of pancreatic stump is similar to conventional distal pancreatectomy

• Parenchyma sparing procedures, such as enucleation, may be considered on an individual basis for small lesions of low malignant potential including neuroendocrine tumors, serous and mucinous cystadenomas
• Consideration criteria for enucleation include:
  • Free of major vessels
  • 2-3mm away from main pancreatic duct
  • Peripherally located or exophytic

• Standard practice is to obtain initial surveillance CT at 3 to 6 month intervals
• Patients are scanned in the immediate post-operative period only if there is clinical suspicion of a post-op complication
• Dual-phase MDCT is performed with arterial and venous phase images obtained approximately 30-40 and 60-70 seconds following contrast injection, respectively
• Positive oral contrast material is not utilized
  • Unlike pancreaticoduodenectomies, no enteric anastomoses to evaluate
  • Streak artifact can obscure pancreatectomy bed and possible bowel hemorrhage
• Alternatively, water or neutral contrast is used as an oral contrast agent
• In addition to standard MPRs, maximum-intensity-projects (MIPs) and volume rendered images are important to review for complete evaluation of the surgical anatomy
  • Particularly in evaluating for vascular complications or fistula formation

• Considerable variability exists in the post-operative appearance depending on the time since surgery
• Immediate post-operative scan can be used as a baseline for future, surveillance scans
• In the acute, perioperative setting, small fluid collections, fat stranding and edema are typical, particularly in the lesser sac and splenectomy bed
  • Stability and regression over follow-up scans favors benign inflammatory process
  • Persistence or organization of fluid may indicate fistula formation or evolution of abscess
• Small fluid collections adjacent to pancreatic stump are visualized in nearly half of distal pancreatectomy patients on the first follow-up study (43%)16
  • Often <5cm, asymptomatic, and resolve without intervention by 18 months post-op

• Distal pancreatectomy morbidity and mortality ranges between 31-47% and 0.25-3%, respectively
• No significant differences for open versus laparoscopic9,18 and splenectomy versus spleen preservation
• Most common complications:
  • pancreatic fistula (5-12%)
  • intra-abdominal abscess (4-5%)
  • post-operative hemorrhage (4%)
  • small bowel obstruction (4%)
• Risk factors for complications include: high ASA score, obesity, multivisceral resection, and malignant lesion

• Pancreatic fistula is the most common complication following distal pancreatectomy and carries a high morbidity
• In general, fistula refers to leakage of amylase-rich fluid, usually adjacent to the pancreatic remnant
  • Persistent fluid collection intimately associated with the pancreatic stump
• Numerous definitions exist in the literature, therefore reported rates vary dramatically (0-64%)
• International Study Group of Pancreatic Fistula (ISGPF) definition was introduced in 2005 with the hopes to standardize pancreatic resection results regarding complications20
  • Pancreatic fistula was defined as any drain output with an amylase content more than 3 times the upper limit of normal serum amylase (>300 IU/L) at post-op day 3 or later
  • PFs graded A through C, where Grade A PFs are asymptomatic with only elevated drain amylase levels, Grade B are symptomatic, suspicious fluid collections not requiring treatment, and Grade C are clinically severe collections, requiring radiologic or surgical intervention

• Another common complication is intra-abdominal abscess formation (4-5%)
  • Often associated with pancreatic fistula formation or superinfection of small fluid collection
  • Successfully treated with percutaneous drain placement
• Post-operative hemorrhage, while rare (3-4%), is one of the most common reasons for reoperations and mortality7,8,17
  • Acute post-operative hemorrhage is often associated with ligated vasculature (eg, splenic artery)
  • Chronic bleeding is frequently associated with irregularity or erosion of the mesenteric vasculature with pseudoaneurysm formation

• Distal pancreatectomy is the main surgical treatment for a wide range of benign and malignant pathology in the pancreatic body and tail
• Several surgical approaches exist for distal pancreatectomy and pancreatic remnant closure with no clear consensus on superiority of any technique
• Small fluid collections, fat stranding and omental/fat necrosis are all common post-operative findings which should evolve or regress on subsequent surveillance CTs
• Among the common complications, pancreatic fistulae, intra-abdominal abscesses and hemorrhage account for the highest morbidity
• Radiologists need to have a detailed understanding of normal post-operative findings as well as knowledge of common to life-threatening complications in order to arrive at the correct diagnosis and guide management

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Acknowledgements

• Ryan A. Stephens, MD
• Franco Verde, MD
• Hima Tadimeti, MD
• Elliot K. Fishman, MD