The Dilated Pancreatic Duct

Background and Definitions

The pancreas arises in utero from the fusion of the ventral and dorsal pancreatic buds. The dorsal pancreatic bud gives rise to the pancreatic body and tail, and the ventral pancreatic bud gives rise to the pancreatic head and uncinate process. The main pancreatic duct (also known as the duct of Wirsung) forms when the dorsal and ventral pancreatic buds fuse at the genu (or neck), with the primary location for pancreatic drainage into the duodenum being the major papilla, also referred to as the ampulla of Vater. A remnant of the dorsal pancreatic bud that is in continuity with the minor papilla contains the duct of Santorini. In patients with pancreas divisum, occurring in approximately 7% to 10% of the population, the major route of pancreatic drainage is through the duct of Santorini and the minor papilla rather than the major papilla.

The average dimension of the pancreatic duct varies from patient to patient and with respect to its location within the pancreas. In general, the main pancreatic duct diameter is approximately 3 to 4 mm in the head, 2 to 3 mm in the body, and 1 to 2 mm in the tail. Pancreatic duct dilation would then refer to a ductal dimension that exceeds the accepted upper limit of normal at each anatomic section. Causes for dilation of the pancreatic duct can broadly be divided into those associated with benign conditions and those associated with malignant or premalignant conditions ( Box 37.1 ). In some patients the pancreatic duct can dilate physiologically with age in the absence of a disease state.

When a duct is distended relative to the downstream duct, it can be considered dilated even if it falls within the normal range. In other words, the pancreatic duct should taper as one moves from head to body to tail. When this pattern is not seen, underlying pathology may be present. This frequently occurs in the setting of a focal stricture or obstructing mass lesion. In contrast, it is normal to have a focal narrowing at the genu without upstream dilation, as this represents the location of fusion between the dorsal and ventral pancreatic ducts.

Several clinical and autopsy studies have suggested that the pancreatic duct likely dilates with age in the absence of underlying pancreatic pathology. In one autopsy study of 112 patients without known pancreatic disease, 18 (16%) had pancreatic duct diameters greater than 4 mm. This becomes important when a physician is asked to evaluate a patient with an asymptomatic dilated pancreatic duct—a very common reason for consultation. Hastier and colleagues compared pancreatograms obtained at endoscopic retrograde cholangiopancreatography (ERCP) from 105 subjects older than 70 years with those obtained from a control group of patients younger than 50 years. Subjects with pancreatic pathology were excluded from both cohorts. These authors found that the mean main pancreatic duct diameter in the head of the pancreas was 2 mm wider (5.3 mm compared with 3.3 mm, p < 0.05) in the older cohort and that 20% of the subjects in the elderly group had pancreatic duct diameters that were more than two standard deviations above normal. In a prospective endoscopic ultrasonography (EUS) study of age-related changes in the pancreas, patients older than 60 years had wider pancreatic ducts in the head of the pancreas [median diameter in mm (interquartile range) = 2.9 (2.2 to 3.5)] than patients younger than 40 years [2.0 (1.6 to 2.2)]. Similarly, duct diameters in the pancreatic body were greater in patients older than 60 years, at 1.8 (1.3 to 2.1), compared with 1.5 (1.2 to 2.0) in patients younger than 40 years, whereas duct diameters in the tail of the pancreas did not differ significantly between these two groups.

Evaluation

Clinical

A patient with a dilated pancreatic duct may present with abdominal pain, acute or chronic pancreatitis, exocrine insufficiency, or a pancreatic duct leak, or may be completely asymptomatic. Often the dilated pancreatic duct is detected as an incidental finding on a cross-sectional imaging study that was ordered to investigate a completely different problem, such as a computed tomography (CT) scan to evaluate for nephrolithiasis.

The most important aspect is the clinical setting (patient characteristics, symptoms, associated imaging features) in which the abnormality is found, and thus a detailed history is imperative. Abdominal pain associated with pancreatic ductal dilation is thought to result from increased pressure within the duct, as well as the related parenchymal hypertension and localized ischemia and inflammation. If a dilated duct is found in the setting of concomitant weight loss, a double-duct sign (biliary duct dilation in concert with pancreatic duct dilation), presence of pancreatic atrophy found on imaging studies, and other “red flag” symptoms such as new-onset or worsening diabetes mellitus or depression, the chance of malignancy being present is substantial ( Fig. 37.1 ). Alternatively, if the patient has significant pain with pancreatic calcifications on imaging tests, then a diagnosis of chronic pancreatitis with associated pancreatic duct distension with or without a downstream stricture is more likely. In this case a history of recurrent bouts of acute pancreatitis is reassuring, although patients with chronic pancreatitis can harbor malignancy.

If the patient is truly asymptomatic, it may influence the decision regarding further treatment or investigation. This is particularly true if the patient is of an advanced age or has multiple and/or significant comorbidities, wherein a potential endoscopic procedure or surgical resection may not affect the natural history of the disease or improve the length or quality of life. In contrast, because one-third of patients with isolated pancreatic duct dilation without chronic pancreatitis are diagnosed with an underlying pancreatic malignancy, it is generally prudent to obtain further diagnostic information in the majority of patients.