Pancreatic Cyst

The higher detection of cystic pancreatic lesions on cross-sectional radiography has resulted in an increase in pancreatic operative resections. However, because many cystic lesions are considered to be benign, excision may not be necessary in some cases. As a result, it's essential to differentiate cystic neoplasms from pseudocysts and to describe cystic neoplasms of the pancreas. Although several histologic forms of cystic pancreatic neoplasms have been discussed in the literature, 90% of all primary cystic pancreatic neoplasms are serous cystadenomas, mucinous cystic neoplasms, and intraductal papillary mucinous neoplasms (IPMNs). Most mucin-producing lesions have malignant potential and necessitate surgical removal in asymptomatic individuals, whereas serous cystadenomas are usually benign that do not necessitate surgical removal in asymptomatic patients.

Solid tumors of the pancreas, such as islet cell tumors and adenocarcinomas, can sometimes have a cystic element or degenerate, mimicking a cystic neoplasm on imaging. It's crucial to distinguish cystic neoplasms from pancreatic adenocarcinomas since malignant cystic neoplasms have a more favorable prognosis than ductal adenocarcinomas. As a result, precise preoperative characterization of the lesions enhances prognosis and directs therapeutic decision-making. In the assessment of patients with cystic pancreatic lesions, imaging is critical. Multidetector computed tomography (CT) provides for pancreatic cyst thin-section imaging and has become the preferred imaging technique for both early detection and description.

Magnetic resonance imaging (MR) cholangiopancreatography properly shows the cyst's morphologic characteristics and has the added benefit of revealing the cyst's relationship to the pancreatic duct. Although cross-sectional imaging using CT and MRI can accurately identify cysts in a significant number of patients, morphologic overlap can occasionally cause confusion. However, endoscopic ultrasonography can help to solve this problem to a large extent. This approach can help further describe the cyst by guiding cyst fluid aspiration and biopsy from questionable locations, in addition to providing high-resolution information regarding the morphologic aspects of the cyst.

The most common cystic pancreatic lesions include pseudocysts, serous cystadenomas, mucinous cystic neoplasms, and IPMNs, which account for more than 91% of cystic pancreatic lesions. Doctors created a simple imaging-based categorization system for cystic pancreatic lesions that is based on the lesion's morphologic characteristics. A systematic method that incorporates these characteristics with the patient's clinical manifestations might be used as a practical guide for treating these patients.

 

Epidemiology

The true frequency and incidence of pancreatic cysts are unidentified; however, in a surgical case series of resected pancreatic cysts, the frequency was 27 percent branch duct IPMN, 24 percent main duct IPMN, 12 percent to 24 percent serous cystadenoma, 12 percent to 17 percent mucinous cystic neoplasm, 4 to 7 percent cystic pancreatic neuroendocrine tumor, and 2 percent solid pseudopapillary neoplasm.

 

Pancreatic Cyst Causes

The cause of pancreatic cysts differs depending on whether they are non-neoplastic or cancerous. Furthermore, they are frequently discovered by chance. Pancreatic cysts are more likely to develop if you have a history of pancreatic cancer or pancreatitis. IPMN, mucinous cystic neoplasm, solid pseudopapillary neoplasm, and cystic pancreatic neuroendocrine tumors are all examples of neoplastic cysts. Serous cystadenoma, lymphoepithelial cysts, and mucinous non-neoplastic cysts are examples of non-neoplastic cysts.

 

Pancreatic Cyst Pathophysiology

Main duct, branch duct, and mixed IPMN are the three types of IPMN. IPMN of the main pancreatic duct is defined by segmental or diffuse dilatation of the duct to a diameter more than 5 mm without any other obstruction. Cysts larger than 5 mm in diameter that connect with the main pancreatic duct without dilatation of the main duct indicate branch duct IPMN. Cysts in mixed IPMN satisfy the definition for both main and branch duct IPMN.

Mucin-producing cysts that do not connect with the ductal system are known as mucinous cystic neoplasms. This lesion can be identified by the presence of an ovarian-type stroma.

Solid pseudopapillary neoplasm comprises cystic and solid tumors that are large and well-defined.

A cystic pancreatic neuroendocrine tumor is smaller and more likely non-functional and may be related to a variety of endocrine neoplasia type 1.

Microcystic type serous cystadenoma and macrocystic type serous cystadenoma are two subtypes of serous cystadenoma. A honeycomb appearance formed of tiny septated cysts around a central stellate scar is pathognomonic for microcystic type serous cystadenoma. Macrocystic serous cystadenomas might be mistaken for other pancreatic mucinous tumors on radiography.

Lymphoepithelial cysts contain non-dysplastic squamous cells with sheets of benign lymphocytes. Simple cysts have non-dysplastic squamous cells with layers of benign lymphocytes.

A mucinous non-neoplastic cyst is a mucin-producing cyst with no malignant potential, distinguished from mucinous cystic neoplasm by the absence of ovarian-type stroma and IPMN by the absence of ductal connection.

 

Pancreatic Cyst Classification

Bosniak's morphologic-based categorization for renal cysts is well-established and has proven to be a fairly accurate way of determining the risk of malignancy in renal cysts. Researchers propose a classification strategy for pancreatic cysts based on the imaging morphologic aspects of the cyst, using a similar approach. Unilocular cysts, microcystic lesions, macrocystic lesions, and cysts with a solid component are the four different forms of pancreatic cysts.

 

Unilocular Cyst

Unilocular cysts are pancreatic cysts that lack internal septa, have a solid component, or have calcification on the central cyst wall. The most frequent and commonly encountered cystic lesion in this group is pseudocyst. IPMNs, unilocular serous cystadenomas, and lymphoepithelial cysts are some of the less common unilocular cysts. The lack of clinical, biochemical, and radiological evidence of pancreatitis distinguishes these lesions from pseudocysts. A pseudocyst is nearly invariably a unilocular cyst in a patient with a history of pancreatitis. Pancreatic inflammation, atrophy or calcification of the pancreatic stroma, and dilatation of and calculi in a normally thin-walled pancreatic duct are all radiological findings that support the diagnosis.

On MRCP or CT, the connection of the pseudocyst with the pancreatic duct can be observed, especially on curved reformatted images. Cyst connection with the pancreatic duct can also be seen in IPMNs; however, on CT scans or MRCP, IPMNs have a narrow neck at the cyst-duct junction. In the absence of pancreatitis or evident cyst connection with the pancreatic duct, precise identification of a unilocular cyst on the basis of imaging evidence alone can be challenging. A unilocular macrocystic serous cystadenoma should be considered when a unilocular cyst with a lobulated shape is found in the head of the pancreas. In a unilocular cyst, the presence of uneven wall thickening indicates a more aggressive biological tendency. When imaging does not allow for distinction, symptomatic individuals might be managed further with endoscopic US-guided cyst aspiration or surgical excision. CT or MR imaging can be used to monitor asymptomatic thin-walled unilocular cysts, particularly if they are modest.

When several unilocular cysts are found, they are almost always pseudocysts caused by the previous pancreatitis. Von Hippel–Lindau disease and, in rare cases, IPMN are other causes of numerous cysts. The pancreas is otherwise healthy in von Hippel–Lindau disease, although cysts in the kidneys or liver may also be found.

 

Microcystic Lesions

Serous cystadenoma is the only cystic lesion listed in the class of microcystic lesions. In 71% of cases, these benign tumors have a polycystic or microcystic structure, which consists of a group of cysts (typically more than 5) ranging in size from a few millimeters to 2.5 cm. Fine, outer lobulations are prevalent, and septa and cyst wall enhancement may be visible. In 32% of instances, a fibrous central scar with or without a characteristic stellate arrangement of calcification is found, and when seen on CT or MR imaging, it is extremely specific and practically pathognomonic for serous cystadenoma. In these people, pancreatic ductal dilatation is a rare occurrence.

Microcysts in a honeycomb pattern makes up 22% of these tumors, which look as well-marginated, "spongy" lesions with soft-tissue or heterogeneous attenuation and a sharp interface with vascular structures on CT. Further characterization with MRI or the endoscopic US may be performed in patients with equivocal CT findings. On T2-weighted MRI, the microcysts appear as numerous isolated foci with strong signal intensity. Endoscopic ultrasound can also be used to adequately describe these microscopic microcysts as distinct small anechoic regions. The macrocystic or oligocystic type of these tumors is extremely rare, accounting for fewer than 10% of all occurrences.

Either of these types can be a single dominating macrocavity that appears as a unilocular cyst, or it can be a collection of smaller cysts. The latter type is referred to as a macrocystic tumor, and it might be difficult to distinguish from a mucinous cystic tumor. Because serous cystadenomas are benign, some doctors believe that imaging surveillance of microcystic tumors is adequate in asymptomatic individuals. Although the exact rate of growth for serous cystadenomas is unclear, early findings acquired during a three-year follow-up period suggest that the average rate of growth is around 4 mm per year.

 

Macrocystic Lesions

Multilocular cysts with fewer compartments are examples of macrocystic lesions. Individual compartments are also larger than in serous cystadenomas. Mucinous cystic neoplasms and IPMNs are examples of cystic tumors in this class. Mucinous cystic neoplasms mostly affect the body and tail of the pancreas and can cause partial pancreatic ductal blockage despite the fact that they do not connect with the pancreatic duct. These neoplasms present as multilocular macrocystic lesions on cross-sectional radiography. Sometimes, the cysts may comprise debris or bleeding. On MRI and the endoscopic US, the cyst's complex internal structure, which includes septa and an internal wall, is best viewed, allowing distinction from serous cystadenomas.

Despite the fact that peripheral eggshell calcification is uncommon on CT, it is specific for a mucinous cystic neoplasm and highly indicative of malignancy. In up to 74 percent of instances, these tumors are asymptomatic. Symptoms are generated by the bulk effect of these frequently massive malignancies when they are present. Surgical excision is frequently recommended because mucinous cystic neoplasms have a significant risk of becoming cancerous. The prognosis for benign or borderline malignant tumors is good, while 50 percent to 74 percent of patients with fully removed malignant tumors can expect long-term survival. Depending on the location and degree of involvement, IPMNs can be classed as main duct, branch duct, or mixed IPMNs.

IPMN of the main duct is a morphologically different entity that cannot be addressed alongside pancreatic cysts. A side-branch IPMN or a mixed IPMN might, however, have the morphologic characteristics of a complicated pancreatic cyst, making differentiation from a mucinous cystic neoplasm challenging. The presence of a septated cyst communicating with the main pancreatic duct strongly suggests the presence of a side-branch or mixed IPMN. It's worth noting, however, that a lack of connection with the main pancreatic duct during imaging does not rule out the possibility of an IPMN. 

For demonstrating the morphologic characteristics of the cyst, establishing the existence of communication between the cystic lesion and the pancreatic duct, and assessing the extent of pancreatic ductal dilatation, MRCP is presently the modality of choice. For the diagnosis of an IPMN, endoscopic retrograde cholangiopancreatography (ERCP) is no longer required.

 

Cysts with Solid Component

Unilocular or multilocular cysts with a solid component are also possible. This group includes true cystic tumors as well as solid pancreatic tumors with a cystic component or cystic degeneration. Islet cell neoplasm, solid pseudopapillary neoplasm, pancreatic adenocarcinoma, and metastasis are all solid tumors that have a cystic component. Surgical removal is the accepted technique of care because all of the tumors in this category are either malignant or have a high malignant risk. For the detection of small mural nodules, MRI using MRCP is thought to be better than single CT.

On T2-weighted MRI, a mural nodule appears as a low-signal region, and contrast material enhancement after administration of gadopentetate dimeglumine is indicative of its presence. On MRCP, inspissated mucin or calcification in the cyst may seem to be a mural nodule. Small mural nodules may go unnoticed on thin-section CT and MRI, but high-resolution endoscopic US is quite sensitive in detecting them.

 

Pancreatic Cyst Symptoms

A substantial proportion of pancreatic cysts are discovered by chance during imaging work-up for a medical ailment that is unrelated. More than one-third of patients with cystic pancreatic lesions seen in a surgical practice during a 5-year period were found to be asymptomatic, according to Fernandez-del Castillo et al. The majority of unintentionally discovered pancreatic cysts were cystic neoplasms, and asymptomatic patients were less likely to have pseudocysts. Abdominal pain is the most common symptom of symptomatic cysts. When a lesion communicates with the pancreatic ductal system or obstructs the pancreatic or biliary duct, it causes jaundice or recurrent pancreatitis. Patients with advanced cystic malignancies may experience symptoms that are comparable to pancreatic cancer. Pseudocysts are most common in acute pancreatitis, but they can also develop slowly in chronic pancreatitis.

 

Pancreatic Cyst Diagnosis

Pancreatic cysts are generally discovered by accident during a CT or MRI scan. The results of various imaging modalities, as well as symptomatology, will be used to guide further examination. Furthermore, as improved diagnostic technologies such as endoscopic ultrasound are developed, standards for the evaluation of pancreatic cysts continue to evolve.

For patients with asymptomatic, accidental pancreatic cysts, the American Gastroenterology Association provides guidelines. On the basis of imaging and patient history, incidental cysts should be categorized as high risk or low risk for cancer. A symptomatic patient, lymphadenopathy, a main pancreatic duct diameter higher than 5 mm, and cyst features such as a sudden transition in main pancreatic duct diameter, mural nodule, enhancing solid component, thickened walls, and a cyst size greater than 3 cm are all considered high-risk.

Cysts are graded as either surveillance only, urgent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA), or surgery depending on these risk factors. If at least two of the following conditions are present: size larger than 3 cm, solid component, or primary pancreatic duct dilatation, EUS-FNA is recommended.

Surgical excision is the recommended treatment for symptomatic pancreatic cysts, not only because it relieves symptoms but also because pain is related to a higher risk of premalignant or malignant disease.

Resection is advised for high-risk pancreatic cysts with the high-risk features listed above or a main pancreatic duct dilatation, probable mucinous cystic neoplasm, or presumptive branch duct IPMN more than 3 cm.

Low-risk pancreatic cysts, such as microcystic serous cystadenoma, are likely to be observed regardless of size because their malignant propensity is relatively low. On imaging, however, macrocystic serous cystadenomas might be difficult to identify from mucinous lesions, necessitating examination by EUS-FNA, which involves testing the fluid for carcinoembryonic antigen levels (CEA).

EUS-FNA is a method that is gaining popularity as a way to characterize lesions more thoroughly and avoid misdiagnosis. Mucin, CEA, and cytology can all be tested in cyst fluid. Mucinous lesions are related to higher CEA levels. Fluid cytology can also clearly differentiate between malignant and nonmalignant lesions.

 

Pancreatic Cyst Treatment

The outcome of treatment is ultimately determined by the initial imaging and symptom observations. Initial care for asymptomatic unintentional cysts can be divided into three groups, according to the American Gastroenterological Association: surveillance, the necessity for EUS-FNA, or surgery. If the cyst is smaller than 3 cm in diameter, has no solid component, and has no dilatation of the main pancreatic duct, surveillance is advised. If at least two of the following criteria are met: size larger than 3 cm, solid component, or primary pancreatic duct dilatation, EUS-FNA is advised. If there is a solid component as well as main pancreatic duct dilatation or questionable results on EUS-FNA, surgery is suggested. If monitoring is the recommended treatment, an MRI should be performed after one year and then every two years thereafter.

Surveillance can be ceased after 5 years if the cyst does not change. EUS-FNA should be performed if there is a change. If surgical removal was the first choice and the histology revealed high-grade dysplasia or malignancy, an MRI should be done every two years after that.

All IPMN, mixed IPMN, and mucinous cystic neoplasms in the main duct should be removed. The presence of an enhancing solid cyst component, a main pancreatic duct diameter greater than 5mm, a mural nodule, cyst fluid cytology showing suspicious or positive findings of neoplasm, or a change in main pancreatic duct diameter with distal pancreatic atrophy all influence branch duct IPMN surgical excision.

 

Conclusion

CT and MRI are useful tools for detecting and characterizing cystic pancreatic lesions in the early stages. Endoscopic US-guided aspiration and biopsy are effective in circumstances where cross-sectional imaging is inconclusive or where observation is required. The classification of cystic pancreatic lesions based on imaging morphologic characteristics might help with differential diagnosis and therapy. The presence or absence of symptoms and high-risk characteristics on cross-sectional radiography must be used to risk-stratify pancreatic cysts for malignant propensity. Because pancreatic cysts are becoming increasingly common, physicians should apply a methodical approach to making a diagnosis and deciding which patients need treatment.