Increased detection of cystic lesions of the pancreas at cross-sectional imaging has led to a rise in the number of pancreatic surgical resections. However, because many cystic lesions are known to be benign, in several instances resection may be unjustified.

Differentiating cystic neoplasms from pancreatic adenocarcinomas is important, since the prognosis for malignant cystic neoplasms is better than that for ductal adenocarcinomas.

The prevalence of cystic lesions of the pancreas has been estimated to range from 2.4% to 24% in imaging and autopsy studies. Decisions regarding surgical treatment of cystic lesions of the pancreas are based on the projected risk of malignancy or the presence of symptoms relatable to the cyst or both. CT and MR imaging are only 40%–60% accurate in determining the correct histologic diagnosis of cystic lesions of the páncreas but they can differentiate aggressive from nonaggressive lesions in 75%–90%.

The imaging approach of pancreatic cystic lesions includes:

 -US: it is considered that the pancreas is difficult to explore due to its deep retroperitoneal location, but sometimes US is the first diagnostic technique used.

 -CT evaluation of pancreatic lesions is best performed with a multiphasic technique consisting of a precontrast scan, an early arterial angiographic phase, a pancreatic parenchymal phase (35–45 seconds after initiation of injection of contrast agent) and a portal venous phase.

-MRI: represents the best noninvasive method for the morphologic evaluation of cystic lesions of the pancreas. The helpful distinguishing characteristics of cystic pancreatic lesions (specifically their internal septal enhancement patterns and whether they communicate with the pancreatic ductal system) are easier to elucidate at MR imaging and MR cholangiopancreatography (MRCP) than at CT, thus allowing a more narrowed list of differential diagnoses.

Standard sequences include T1-weighted gradient echo; T2-weighted axial and coronal, including fat saturation to help elucidate acute inflammation; 2D and 3D MRCP; and three-dimensional T1-weighted gradient echo before and after administration of a gadolinium contrast agent. The emerging use of diffusion-weighted imaging may provide even more diagnostic confirmation.

-       - EUS with FNA and cyst fluid analysis is an effective method of classifying cystic lesions of the páncreas. 

Classification:

 Common cystic lesions of the pancreas are:

• Ø   intraductal papillary mucinous neoplasms (IPMNs),
• Ø  mucinous cystic neoplasms,
• Ø  serous cystadenomas,
• Ø  pseudocysts,  
• Ø  true epithelial cysts
• Several solid tumors may contain cystic components related to degeneration, including neuroendocrine tumors, solid pseudopapillary tumors, and, rarely, adenocarcinoma and its variants.

SEROUS CYSTADENOMA (“THE GRANDMOTHER LESION”)

They are generally benign neoplasms of the pancreas and 80% of these occur in women over 60 years old.

There is a slight predominance of localization in the pancreatic head.

The tumor tends not to cause many clinical symptoms or present with abdominal pain, vomiting or weight loss.

The typical microcystic form of serous cystadenoma consists of a cluster of several small cysts , each typically less than 1 cm in diameter. The cysts may be arranged around a central fibrous scar in a “sunburst pattern”. The cysts are filled with serous fluid similar to water and the scar tend to have áreas of coarse calcification in tumors greater tan 5cm in size.

Imaging findings:

• Ø    US: well-circumscribed, lobulated .

        The fibrous portion of the lesión is hyperechoic, while the cystic portions are hypoechoic.

• Ø   CT: lobular shape, hypodense on NECT

       may demonstrate sunburst calcification of the central scar, which is seen in approximately 30% of cases.

       On CECT, the fibrous portions of the lesión enhance. Serous microcystic adenomas are the only hypervascular cystic pancreatic tumor, and its enhancement pattern is a distinguishing feature that differentiates it from other cystic neoplasms.

• Ø  MRI: cluster of tiny cysts with high T2 signal intensity, with intervening septa and a central scar that may enhance on delayed imaging. There is no communication with the pancreatic ductal system.

The cystic portions are hypointense on T1 but may have areas of hyperintensity if there has been previous intracystic hemorrhage.

Enhancement of the fibrous septations on early and late imaging, with persistent enhancement of the central scar.

• Ø  EUS-guided FNA: Cyst fluid amylase and CEA concentrations are low to undetectable, and a cyst fluid CEA concentration of less than 5 ng/mL virtually excludes a mucinous lesion and support  the diagnosis of serous cystadenoma.  ( Fig. 1,2 and 3)

MUCINOUS CYSTIC TUMOR (“THE MOTHER LESION”)

They represent 10% of cystic lesions of the páncreas and range from the benign, slow growing mucinous cystadenoma to aggessive and invasive mucinous cystadenocarcinoma.

These lesions usually do not communicate with the pancreatic duct, and approximately 95% are located in the pancreatic body or tail. In 15% of cases present peripheral calcifications.

Clinical symptoms: from asymptomatic to nonspecific abdominal pain, nausea weight loss and back pain.

Imaging findings:

Ø  CT: unilocular or septated hypoattenuating cystic lesion, often with a thick wall that enhances at delayed imaging. The páncreas distal to the lesión could present changes as seen in chronic pancreatitis.

Ø  MRI: cystic lesion that is hyperintense on T2-WI with different intensities on T1 based on the proteinaceous content of the mucin.

   -enhancement of the wall and any septations or areas of nodularity.

Ø  EUS-guided FNA: The cyst fluid is viscous and CEA levels are   elevated (>192 ng/dL), and amylase levels are low (indicating no communication with the main pancreatic duct.

  Approximately 17.5% of mucinous cystic neoplasms contain carcinoma.

  Imaging features suggestive of malignancy include:

-        presence of nodules or a tumor diameter greater than 6cm.

-        eggshell calcification,

-         increased wall thickness or irregularity,

-         obstruction or displacement of the main pancreatic duct.

Treatment: Resection, because of their malignant potential.

Surveillance:

-        If benign mucinous cystic neoplasms – no

-        If malign mucinous cystic neoplasms – yes, at 6-month intervals.

          ( Fig. 4,5 and 6).

SOLID PSEUDOPAPILLARY TUMOR (“THE DAUGHTER LESION”)

SPT occurs almost exclusively in younger women

Commoly located in the tail and is a benign or a low-grade malignant tumor that can cause symptoms related to extrinsec compression on surroounding structures.

Tumors may be solid or cystic, well-circumscribed and peripheral calcifications may be present in approximately 30% of cases.

Imaging findings:

Ø     CT: encapsulated, large, cystic /solid masses.

        The capsule and solid components can enhance.

Ø MRI: well-defined, heterogeneous mass with áreas of hemorrhage.

         Peripheral, mild enhancementduring the arterial phase with progressive enhancement of the solid portions durig the portal and delayed phases.

Key diagnosis: presence of a fibrous capsule.

INTRADUCTAL PAPILLARY MUCINOUS NEOPLASM (IPMN)

IPMN are characterized by intraductal papillary growth and abundant mucin production, leading to ductal dilatation.

Clinical symptoms: from asymptomatic to abdominal pain, weight loss, pancreatitis, and pancreatic insufficiency.

Classification: on the basis of site of origin of the pancreatic ductal system:

-        main-duct IPMN, which can be diffuse or segmental;

-        side-branch IPMN;

-        mixed IPMN involving both the main duct and side branches.

They are variable in aggressivity : slow growing, local lesions or invasive and mtastatic tumors.

Imaging findings:

• Ø  CT

v Main pancreatic duct: diffuse/segmental dilation of the duct

v Side branch IPMN:  hypodense  lesion in close proximity to the pancreatic duct; normally in the uncinate process.

• Ø  MRI:

v main-duct IPMN: diffuse or segmental ductal dilatation, with hypointense T1 and hyperintense T2 signal with /without mural nodules or parenchymal atrophy. ( Fig. 7,8,9),  (Fig. 10 ,11).

v side-branch IPMN: small round or oval lobulated masses. (Fig. 12,13,14)

• Ø  EUS:

v    - Main-duct IPMN: diffuse or segmental dilatation, often with cystic side-branch dilatation as a result of secondary mucin obstruction in side branches; +/- mural nodules. Intraductal papillary growth, can be identified as isoechoic to hyperechoic frondlike projections from the duct wall.

v - Side-branch IPMN: simple unilocular anechoic lesion to a complex multiseptated multilocular lesion

• Ø  cyst fluid analysis: elevated CEA concentration (>192 ng/ dL), with normal to high amylase levels.

  Treatment: based on symptoms and the malignant potential of the lesion.

1.     Resection if:

o   -  Symptomatic

o   - all main-duct and mixed-type IPMNs

o   - all side-branch IPMNs greater than 3 cm in diameter.

o   - side-branch IPMNs smaller than 3 cm in the presence of high

-ririsk features (mural nodules, positive cytologic findings) or rapid

cycyst growth (>2 mm per year)

2.     Control if:

o   Annual imaging follow-up for lesions smaller than 1 cm;

o   6–12-month follow-up for lesions between 1 and 2 cm;

o   3–6-month follow-up for lesions larger than 2 cm.

There is risk of recurrence, so, surveillance imaging after resection of an IPMN is recommended:

·       every 6-months if malignant IPMNs,

·       annual imaging for benign IPMNs.

PSEUDOCYST

The  pancreatic pseudocyst is a nonneoplastic cystic lesion of the pancreas associated with pancreatitis or trauma.

They are the most common cystic lesion of the páncreas.

Imaging findings:

Ø  CT: unilocular round or oval fluid collection with a wall that can range in thickness from barely perceptible early in its formation to thick and enhancing after time.

Ø    MRI: simple fluid hyperintense on T2-WI

                            Hypo intense on T1-WI or  hyperintense on T1-W1, if blood products and proteinaceous fluid are present within the lesion.

Ø    EUS: thin-walled unilocular anechoic cystic lesions.

Ø  cyst fluid analysis: low viscosity and dark color; CEA concentrations are typically low; amylase and lipase concentrations are characteristically elevated.

(Fig. 19,20), ( Fig. 21,22,23,24).

Treatment:

Drainage if there are of symptoms (gastric outlet obstruction, obstruction of the extrahepatic biliary tree, and infection).

 Absolute size itself is not considered an indication for drainage

CYSTIC NEUROENDOCRINE TUMOR

ü  17% of all neuroendocrine tumors and is  secondary to tumor degeneration.

ü  They are larger, more often symptomatic, and more likely to be nonfunctional  than solid neuroendocrine.

ü  The propensity for metastasis is the same in patients with cystic tumors as in those with solid tumors.

ü  most commonly occur in the body and tail of the pancreas.

ü   

    Imaging findings:

• Ø  EUS: well-circumscribed, heterogeneous

Ø  cyst fluid analysis:  can be diagnostic when small homogeneous cells with round nuclei that stain positive for chromogranin and synaptophysin are identified. Cyst fluid CEA concentrations are noted to be low to undetectable, and amylase concentrations are also low.

 Treatment:

-        complete resection because of their malignant potential.

 ( Fig. 15,16,17,18)

CYSTIC METASTATIC DISEASE

They occur in cases of aggressive metastatic tumors such as sarcomas, melanomas, ovarian carcinomas.