PCLs are commonly divided in three types: pseudocyst or encapsulated necrosis (EN), common cystic neoplasm (CN) and rare CN (figure 1).

Pseudocysts or (EN) are associated with pancreatitis or history of abdominal trauma.

Pseudocyst is a peripancreatic collection, often with a round shape and homogeneous content (water density). Some debris can be found, mostly on MRI. There is an enhanced, sometimes thick, pseudocapsule. Pseudocyst may communicate with the pancreatic ductal system but is never located within the pancreas (figure 2).

EN can be around or within the pancreas. Its content is heterogeneous and associated with necrosis of pancreatic tissue or adjacent structures (fat, digestive tract or vessels) (figure 3). It can be infected. This diagnosis is made in the presence of air inside the EN without recent drainage (figure 4).

Common CN include IPMN, mucinous cystadenoma (MC), and SC.

IPMN is the most common pancreas CN, mainly affecting men between 60 and 70 [3]. IPMN develops from the ductal system (main, secondary duct or mixed IPMN) and produce mucin.

Main duct IPMN identification may be challenging. Diagnosis is evoked when the main duct is dilated > 5 mm without an obvious cause (figure 5). Rarely there is a papilla bulging in the duodenal lumen. IPMN can be associated with upstream pancreatic atrophy.

Secondary duct IPMN appearance is broad: grape shaped, multicystic, unilocular or finger-shaped. This variant is often multiple and may involve the entire pancreas in up to 10% of cases [3]. Establishing connection with the ductal system is essential (figure 6). Calcifications are rare.

Mixed IPMN iconographic observation is a combination of main and secondary duct IPMN (figure 7).

MC is found almost exclusively in women of average age between 40 and 50. They are at high risk of malignancy (10-17%) [1]. 95% of cases occur in the pancreas body or tail [1]. These are typically solitary, unilocular and well-circumscribed lesions. Septations may be present with a “cyst within cyst” appearance (figure 8). The walls are often thick (>3 mm). In 25% of cases there are lamellar (egg-shell) and peripheral calcifications [1]. The content is homogeneous, commonly liquid, with the signal intensity on MRI depending on the protein concentration.

SC affects mostly women (75%) of average age between 60 and 70 [4]. There is an association (9-17%) with Von-Hippel-Lindau syndrome (VHLS) [5]. Four types of SC are described: microcystic (45%), macrocystic (32%), mixed (18%) and pseudosolid (5%) [3]. The majority of SC is found in the head of the pancreas [3]. Tumour septations are highly vascularized and are susceptible to haemorrhage.

Microcystic SC presents as a multilobulated lesion with a typical central scar (60%), sometimes calcified (18%) (figure 9) [4,5]. The cyst size varies from a few millimetres to 2 centimetres in diameter.

The macrocystic form corresponds to a cyst without or with a few septations only (figure 10).

The mixed form has caracteristics of both microcystic and macrocystic SC aspect (figure 11).

The pseudosolid SC consist of multiple and confluent tiny cysts, so small that they mimic a solid lesion (figure 12).

Uncommon CN include solid pseudopapillary neoplasm (SPN), neuroendocrine tumour (NET) with cystic degeneration and lymphoepithelial cyst (LEC).

SPN are considered as low-grade malignancy affecting mainly women between 20 and 30 years-old (figure 13) [1]. The average size is 9 cm at diagnosis. Predominant location is the pancreatic head or tail [3]. The content is often heterogeneous (necrotic or haemorrhagic). SPN may present a thick pseudocapsule (fibrosis and compressed pancreatic tissue). Calcifications are possible. Extension to adjacent structures is rare.

NET with cystic degeneration are rare and occur sporadically. It can be associated with multiple endocrine neoplasia type 1 (NEM1), neurofibromatosis, tuberous sclerosis (TS) or VHLS [1]. Arterial hyperenhancement is key to the radiological diagnosis (figure 14).

Pancreatic LECs are found in 0,5% of all PCLs. They predominantly affect middle-age men. The pancreatic body or tail are mainly affected with median size between 3,6 to 4,5 cm [6,7]. LECs are mostly exophytic and their content can be heterogeneous depending on their composition (figure 15). Some authors mentioned the presence of fat or even a diffusion restriction due to the presence of keratinised material inside the cyst. In some cases there is a solid component [6,7].

Other entities could mimic a CN of the pancreas, including ductal sequelae of pancreatitis, duodenal diverticulum, pancreatic cystosis in cystic fibrosis patients, pancreatic hydatid cysts, retroperitoneal lymphangioma and acinar cystic transformation (ACT) of the pancreas. The latter, formerly known as acinar cell cystadenoma, is a non-neoplastic cyst mainly affecting women. They are mostly found in the pancreatic head and ACT diagnosis should be evoked when there is: >5 cysts, clustered peripheral small cysts, cyst calcifications and no communication with the pancreatic duct (figure 16) [8].

Malignancy risk evaluation:

Malignancy risk can be divided in two categories: high and intermediate-risk features. High-risk malignancy signs at imaging include: enhanced nodule >5 mm (figure 18), biliary obstruction and/or main duct dilatation >10 mm. These signs have a predictive value for advanced neoplasia ranging from 56 to 89% [9]. Worrisome features consist of a cyst size > 30 mm, growth >5 mm in 2 years or >20% of cyst size, main duct dilatation between 5 and 9 mm, abrupt ductal size change with upstream pancreatic atrophy (figure 5), an enhanced or thickened wall/septations (figure 18), an enhanced nodule <5 mm, local lymphadenopathy and pancreatitis signs [10].

Symptoms should be considered as well. Jaundice caused by biliary obstruction is considered a high-risk feature. Pancreatitis due to ductal obstruction by the cyst or mucin overproduction, gastroduodenal obstruction, abdominal pain and weigh loss are considered intermediate-risk factors when they are related to the cyst, not always easy to certify.

An elevation of cancer antigen 19-9 (CA 19-9) or a new-onset diabetes in a laboratory test are associated with and intermediate-risk.

When the risk is uncertain, a cytology or biopsy can be performed.

How the radiologist should analyse a pancreatic cyst?

A systematic approach is resumed in figure 19. The first thing to verify is history of abdominal trauma or pancreatitis which could lead to a pseudocyst or an EN diagnosis. The second thing to assess is the connection with the pancreatic duct system which is typical of IPMN. Then the radiologist should evaluate the cyst morphology, location and look at the patient’s sex and age to determine if the cyst is a MC, SC or SPN. Finally he should evaluate the cyst wall vascularisation. If there is a hyperenhancement, the diagnosis of NET with cystic degeneration should be considered. Rarer diagnoses should be kept in mind to avoid unnecessary surgery.

What the surgeon and gastroenterologist want to know?

A standardized report is resumed in figure 20. To begin, the general aspect of the pancreas should be mentioned, especially if there is a pancreatic atrophy or chronic pancreatitis which may influence the surgery.

Cyst characteristics (location, size, growth, duct connection and dilatation and cyst composition) must be reported. They are of paramount importance to establish a precise diagnosis. In case of a solid component, vascular involvement should be evaluated. Lymph node and other metastatic dissemination must be looked for. As well as associated lesions in NEM1, neurofibromatosis, TS or VHLS.

Treatment and follow-up:

The only curative treatment for malignant PCL remain surgery (Whipple surgery or splenopancreatectomy). Patients should be selected carefully. An algorithm to approach PCL is resumed in figure 21.

There is six main guidelines recommendations regarding PCL follow-up (figure 22). It is important to understand that the majority of PCLs will not become malignant [10,11,12]. Most of the guidelines are about MC or IPMN (premalignant lesions). Indeed, SC are considered benign and don’t need follow-up. In case of a high risk feature, surgery should be considered if the patient is fit enough to benefit from this procedure. Surgery should also be considered if the patient has direct symptoms caused by the PCL (jaundice from biliary obstruction, nausea and vomiting caused by gastro-duodenal obstruction and of course if the lesion is thought to be the cause of recurrent pancreatitis). A less invasive strategy is preferred in case of absence of worrisome features in order to reduce the long term cost of follow-up.