14.2 Pancreas

Anatomy and Vascular Landmarks

The pancreas is a retroperitoneal organ lying transversely across the upper abdomen at roughly the L1-L2 level. It is divided into the head, neck, body, and tail, plus the uncinate process:

• Head — nestled within the C-loop of the duodenum, anterior to the inferior vena cava (IVC); the common bile duct courses through its posterior aspect
• Uncinate process — a medial extension of the head that curves behind the superior mesenteric vein (SMV)
• Neck — the short segment directly anterior to the SMV and the portal vein confluence
• Body — crosses anterior to the superior mesenteric artery (SMA) and the aorta
• Tail — extends leftward within the splenorenal ligament toward the splenic hilum

The vascular landmarks are how you find the gland, and they must be memorized:

Normal pancreatic echogenicity is equal to or slightly greater than the liver, becoming progressively more echogenic with age and fatty replacement. The main pancreatic duct (duct of Wirsung) appears as a thin echogenic line within the body and should measure no more than 2-3 mm.

Scan Technique

The patient fasts 6 to 8 hours to minimize gastric and duodenal gas. Begin with transverse epigastric scans, angling slightly so the plane runs from the head (lower, on the right) up toward the tail (higher, on the left), using the left lobe of the liver as an acoustic window. Deep inspiration pushes the gland below the costal margin. If gas obscures the body and tail, give the patient 300-500 mL of water to create a water-filled stomach window and rescan upright or in a right posterior oblique position. The tail can also be imaged coronally through the spleen and left kidney. A curvilinear 2-6 MHz transducer is standard, and gentle graded compression helps displace overlying gas. Document the gland in transverse and sagittal planes and measure the duct at its widest point.

Acute Pancreatitis

Acute pancreatitis is enzymatic autodigestion of the gland; the two leading causes are gallstones and alcohol. Sonographically the gland becomes enlarged and hypoechoic (edematous) with ill-defined margins, and the pancreatic duct may dilate. Look for peripancreatic fluid in the lesser sac, the anterior pararenal space, and around the splenic and portal veins. Ultrasound's biggest roles are identifying the cause (gallstones, biliary dilation) and following complications:

• Pseudocyst — the most common complication; a well-defined, encapsulated, anechoic collection with posterior acoustic enhancement that classically takes four or more weeks to develop after an acute episode and lacks an epithelial lining
• Abscess — a complex collection containing debris or gas (dirty shadowing)
• Pseudoaneurysm — enzymatic erosion of the splenic or gastroduodenal artery; Doppler shows swirling flow within the aneurysm sac
• Splenic vein thrombosis — echogenic intraluminal thrombus with absent Doppler flow and perisplenic collaterals

Chronic Pancreatitis

Chronic pancreatitis, most often caused by long-term alcohol use in adults, produces a small, atrophic, hyperechoic gland with coarse parenchymal calcifications that cast acoustic shadows — the most specific finding. The pancreatic duct becomes irregularly dilated with alternating strictures (the 'chain of lakes' appearance) and may contain calcified stones. Chronic pseudocysts are common. A focal inflammatory mass of chronic pancreatitis can be sonographically indistinguishable from carcinoma and may require biopsy.

Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma, a ductal malignancy, accounts for about 90% of pancreatic cancers, and roughly 60-70% occur in the head. The typical appearance is a poorly defined hypoechoic solid mass. Head tumors obstruct both the common bile duct and the pancreatic duct, producing the double-duct sign, and patients classically present with painless jaundice and a distended gallbladder (the Courvoisier gallbladder). Assessment of vascular involvement — encasement or thrombosis of the SMV, portal vein, SMA, and celiac axis — is critical because it determines resectability. Also survey the liver for hypoechoic metastases and the peripancreatic region for lymphadenopathy. Tumors of the body and tail present late and are usually large at diagnosis.

Other Pancreatic Masses

• Islet cell (neuroendocrine) tumors — small, solid, hypoechoic, often hypervascular masses; insulinomas are the most common functioning type and may be tiny
• Mucinous cystadenoma/cystadenocarcinoma — a multiloculated cystic mass with thick septations, typically in the body or tail of middle-aged women; considered premalignant
• Serous (microcystic) cystadenoma — a cluster of tiny cysts, sometimes with a central calcified scar, seen in older women; benign
• Metastases and lymphoma — uncommon; lymphoma tends to be markedly hypoechoic