Topography and Fascial Sheaths
The pancreas lies in the anteriormost of the three retroperitoneal compartments — the anterior pararenal space (anterior pararenal space). In addition to the pancreas itself, this space contains the ascending and descending colon, as well as the loop of the duodenum.
To understand where inflammatory exudate tracks in pancreatitis, one must clearly know the boundaries of this space:
- Anterior (ventral): posterior layer of the parietal peritoneum.
- Posterior (dorsal): anterior renal fascia (the well-known Gerota's fascia), separating the gland from the perirenal space.
- Lateral: lateroconal fascia.
Vascular syntopy on CT and ultrasound
On multidetector CT (MDCT) scans and sonograms, blood vessels serve as the main anatomical landmarks for locating parts of the gland:
- Head and uncinate process lie posterior (dorsal) to the superior mesenteric artery and vein.
- Body and tail are located anterior (ventral) to the splenic vein (v. splenica).
On ultrasound, the parenchyma of a healthy organ has a homogeneous echogenicity. Color Doppler mapping (CDM) clearly demonstrates the surrounding vascular network: the abdominal aorta, inferior vena cava, splenic vein, and portal vein confluence.
Embryogenesis and ductal system
The organ develops from the endoderm of the duodenum as two buds. The ventral bud gives rise to part of the head, and its main pancreatic duct (duct of Wirsung) empties into the major duodenal papilla. The dorsal bud forms the neck, body, tail, and the rest of the head; its accessory pancreatic duct (duct of Santorini) opens slightly higher, into the minor papilla.
During intrauterine development, the duodenum rotates, and the buds approach each other and fuse into a single organ. Their ducts merge at the junction of the head and body into the main pancreatic duct, which has a diameter of 1 to 2.5 mm (no more than 3.5 mm). Magnetic resonance cholangiopancreatography (MRCP) helps evaluate this architecture in detail.
Congenital anomalies
Disruptions in the fusion or rotation of the buds lead to anomalies that must be recognized:
- Pancreas divisum (Pancreas Divisum): The most common congenital anomaly (about 5% of the population). The buds do not fuse. The ventral duct drains only the head, while the dorsal duct is forced to drain secretions from the body and tail through the narrow minor papilla. This can provoke functional stenosis and pancreatitis.
- Annular pancreas (Annular Pancreas): Pancreatic tissue encircles the descending part of the duodenum, causing its narrowing. Clearly visible on MRCP, CT, or barium fluoroscopy.
- Agenesis and hypoplasia: As a rule, the dorsal bud is affected. On CT, we will see only the head, while the body and tail will be absent.
- Ectopia: The presence of pancreatic tissue islands in the wall of the stomach or duodenum. Resembles a polyp with a central umbilicated depression (the trace of a rudimentary duct).
Acute pancreatitis: imaging fundamentals
When the pancreas is injured (due to gallstones, alcohol, trauma, hyperlipidemia, or iatrogenic causes after ERCP), digestive enzymes are activated prematurely, causing destruction of the organ's own tissues.
Diagnosis requires at least 2 out of 3 criteria: characteristic pain, a threefold increase in amylase/lipase, and a specific imaging pattern. According to the revised Atlanta classification (2008), radiologists distinguish two main morphological types of acute inflammation: interstitial edematous pancreatitis and necrotizing pancreatitis.
Briefly: answers to topical questions
Where can ectopic pancreatic tissue be located?
Ectopic pancreatic tissue (Ectopic Pancreas) is most commonly located in the wall of the stomach or duodenum. It consists of islands of tissue located outside the pancreas itself. Macroscopically, such tissue appears as a polypoid nodule, often featuring a central umbilicated depression, which represents a rudimentary duct. This anomaly is usually an incidental finding during barium fluoroscopy or esophagogastroduodenoscopy (EGD).
What local complications of acute pancreatitis are distinguished according to the Atlanta classification?
The revised Atlanta classification distinguishes the following local complications of acute pancreatitis, presented as various fluid collections:
- Acute peripancreatic fluid collections (APFC) — contain no solid components and have no discernible wall.
- Pseudocyst (Pseudocyst) — a well-defined fluid collection with uniformly low X-ray attenuation, surrounded by a fibrous capsule.
- Acute necrotic collection (ANC) — a non-liquefied collection that matures over time.
- Walled-off necrosis (Walled-Off Necrosis - WON) — forms a thick wall between the area of necrosis and adjacent tissues, containing non-liquefied debris.
- Infected necrosis — a condition characterized by the appearance of gas bubbles within a necrotic collection.
How is the common bile duct positioned relative to the head of the pancreas?
The pancreatic segment of the common bile duct is located within the substance of the pancreatic head or on its posterior surface (in the retroduodenal groove). This duct also runs in the upper half of the cleft between the pancreatic head and the descending part of the duodenum. Topographically, it lies adjacent to the right margin of the inferior vena cava, while the portal vein crosses it obliquely from the left. Near the right margin of the pancreatic head, the common bile duct joins the main pancreatic duct to form the hepatopancreatic ampulla (ampulla hepatopancreatica).
The "C" rule helps quickly memorize the syntopy of the body and tail: Splenic vein runs Subsequent (posterior) to the body and tail of the pancreas.
Class and exam questions
Where exactly in the retroperitoneal space is the pancreas located?
It is located in the anterior pararenal space, which is posteriorly bounded by Gerota's fascia.
What is considered the normal maximum size of the main pancreatic duct?
The normal diameter ranges from 1 to 2.5 mm. The upper limit of normal is 3.5 mm, with the duct being widest in the region of the head.
What is Pancreas Divisum and why is it important?
This is an anomaly in which the dorsal and ventral ducts fail to fuse. It occurs in 5% of people and can lead to impaired drainage of pancreatic juice, causing recurrent pancreatitis.
What criteria are used to diagnose acute pancreatitis?
Requires the presence of two of the three features: typical abdominal pain, an amylase/lipase level exceeding the normal limit by 3 times, and characteristic signs of inflammation on ultrasound, CT, or MRI.
What else to study on this topic
- Fluid collections in pancreatitis according to the Atlanta classification (2008)
- Secretin-stimulated MRCP for duct function evaluation
- Anatomy and imaging of the major and minor duodenal papillae
- CT appearance of necrotizing pancreatitis
- Chronic pancreatitis: calcifications, fibrosis, and ductal changes
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