Pancreatic pseudocyst

Pancreatic pseudocysts are common sequela of acute pancreatitis, and the most common of cystic lesion of the pancreas ⁹. They are important both in terms of management and differentiation from other cystic processes / masses of the region.

Clinical presentation

Pancreatic pseudocysts are frequently found on imaging follow-up of acute pancreatitis, and may in themselves be asymptomatic for some time. Presentations attributable to the pseudocyst include:

• mass effect
  • biliary obstruction
  • gastric outlet obstruction
• secondary infection

Pathology

Pseudocysts occur from disruption of pancreatic duct structure with resulting leakage and accumulation of pancreatic juice. A severe inflammatory reaction that this incites results in encapsulation of the cyst with fibrous tissue. This usually takes 4-6 weeks ^8-9. In approximately 50% of cases the cyst retains a communication with the pancreatic duct ². Such cysts are more problematic to treat, and are more likely to recur.

Radiographic features

Pseudocysts are fluid filled oval or round collection with a relatively thick wall. They can be multiple and are most commonly located in the pancreatic bed. However, they can be found anywhere from the groin to the mediastinum and even in the neck, having ascended in the retroperitoneum via the diaphragmatic hiatuses into the mediastinum ⁵. 

It is not possible to reliably distinguish infected from non infected pseudocysts on imaging alone ⁹.

Ultrasound

Hypoechoic or anechoic collections with low level echos are often seen dependently representing debris ⁸.

CT

Fluid density rounded mass with wall thickening.  While the wall thickness is variable between patients, a cyst will usually have a uniformly thick wall that demonstrates some enhancement ⁹

MRI

• T1
  • hypo intense (fluid signal) centre
  • wall demonstrates mild early enhancement, which progressively becomes more intense ⁷
• T2
  • hyper intense (fluid signal)
  • layering / dependent debris highly specific ⁶

Treatment and prognosis

Treatment of pseudocysts depends on size and presence of superimposed infection, as well as local mass effect (usually related to size). If the cysts are small (less than 4 - 6 cm) then most resolve spontaneously. Approximately half of all pseudocysts resolve spontaneously ^2,3. Indications for drainage include ¹:

• infection
• large size : > 4-6 cm
• mass effect
  • gastric outlet obstruction
  • hydronephrosis
  • biliary obstruction
• growth on serial scanning

Treatment options include:

• open surgical debridement, or cystenterostomy with a Roux-en-Y jejunal loop ³
• endoscopic drainage into the stomach (or duodenum) ³
• percutaneous drainage
  • remains somewhat controversial, although increasingly accepted ^1-2
  • many centres report high safety and efficacy ¹
  • critics raise concern in regards to potential reaccumulation and fistula formation to the skin (especially in patients with severe pancreatitis) ⁴
• Octerotide infusion : decreases amount of pancreatic secretions

Cysts that do not communicate with the pancreatic duct usually do not recur, and are unlikely to create fistulae ².

Differential diagnosis

General imaging differential considerations include

• cystic lesions of the pancreas
  • do not usually have internal debris
  • may be microcystic in the case of serous cystadenoma
  • dilated duct with communication with side branch may indicate an IPMN
  • often requires endoscopic FNA for definitive diagnosis ⁶
• choledochal cyst (especially for ultrasound)
• mesenteric duplication cysts
  • very thin walls
• peripancreatic collection of acute pancreatits
  • will not be round, but rather take on the contours of the space in which they are located
  • pseudocysts take approximately 4 weeks to form
• pancreatic abscess