Description
Pancreatic mucinous cystadenomas (MCNs) are a type of cystic neoplasm in the pancreas characterised by the production of mucin. They represent about 10-45% of all cystic pancreatic neoplasms. Their malignant counterpart is known as a mucinous cystadenocarcinoma.
Pathogenesis
The precise pathogenesis of MCNs is unknown, but they are thought to arise from the pancreatic ductal epithelium. MCNs possess an ovarian-type stroma, suggesting a possible hormonal influence on their development.
Epidemiology, Risk Factors & Associations
- MCNs predominantly occur in middle-aged women (over 90% of cases) with a median age of presentation around 50 years old. Thus is known as the mother tumour.
- There is no known strong genetic association.
Clinical Features
- Many patients are asymptomatic with the cysts discovered incidentally during imaging for unrelated conditions.
- Symptoms can arise due to the mass effect of the cysts causing abdominal pain or discomfort, nausea, and vomiting.
Complications
- Complications can occur from the cyst itself growing in size, causing compression of surrounding structures and subsequent pain or obstruction.
- There is also a risk of infection within the cyst.
- Of significant concern is the potential for malignant transformation to mucinous cystadenocarcinoma. The overall risk of malignancy associated with MCNs is estimated to be about 10-20%.
Subtypes
MCNs do not have any specific subtypes. However, they can be subclassified based on the presence or absence of high-grade dysplasia or invasive carcinoma.
Pathological Features
Histopathology
MCNs are characterised by cysts filled with mucin and lined by a columnar, mucin-producing epithelium. These cysts are surrounded by a distinctive ovarian-type stroma.
Biochemistry
Fluid from MCNs often has a high concentration of mucin and carcinoembryonic antigen (CEA), which can be diagnostically helpful.
Radiological Features
General Features
- MCNs are typically located in the body or tail of the pancreas (approximately 95% of cases), with cysts tending to be larger compared to other cystic pancreatic neoplasms.
- Usually thick-walled, unilocular or oligolocular mass and often demonstrate a wall of eggshell calcification.
- The mass demonstrates variable signal intensity based on cyst content
US
- Usually well-defined, anechoic lesions with occasional internal septations or mural nodules.
- Detection of a peripheral calcified rim can be challenging using ultrasonography alone.
CT
- Appear as low-attenuation cystic masses with a capsule, sometimes with a peripheral calcified rim (seen in approximately 20% of cases).
- CT can demonstrate the size and number of cysts, as well as the presence of septa, nodules, or a thickened wall.
MRI
- T2: Typically hyperintense fluid-containing cystic spaces
- T1: Variable signal; depending on the protein content of the mucin and haemorrhage.
- Gd+: Enhancement of septations and cyst wall is common
EUS
- EUS is highly sensitive (90%) and specific (98%) for diagnosing MCNs.
- EUS allows for the evaluation of cyst size, internal architecture (including the presence of septa or nodules), and wall thickness.
- Enables fluid aspiration for cytological and biochemical analysis, helping differentiate MCNs from other cystic lesions of the pancreas.
PET
Positron emission tomography (PET) is typically not used in the routine evaluation of pancreatic cysts, but it may provide additional information in selected cases, particularly when malignancy is suspected. FDG uptake in MCNs is generally low unless there is malignant transformation.
Grading and Staging
The grading and staging of MCNs depend on the degree of dysplasia and whether there is invasive carcinoma. The World Health Organization (WHO) has a classification system that grades MCNs into low-grade, intermediate-grade, and high-grade dysplasia.
Differential Diagnosis
- Pancreatic Serous cystadenoma (SCA): SCAs usually have a honeycomb appearance and are commonly located in the head of the pancreas. They can be differentiated by the lack of a peripheral calcified rim and an often central calcified scar.
- Intraductal papillary mucinous neoplasm (IPMN): IPMNs often show an “enhancing mural nodule”, and they are commonly located in the head of the pancreas, which helps differentiate them from MCNs.
- Pseudocyst: These lesions typically have a history of pancreatitis, do not have an epithelial lining, and often contain high amylase content.
- Solid pseudopapillary neoplasm (SPEN): Predominantly in young females, these masses have mixed solid and cystic components, which differentiates them from MCNs.
Management
- The management of MCNs usually involves surgical resection, given the risk of malignant transformation.
- The extent of surgery depends on the size and location of the cyst.
- Asymptomatic small MCNs with no features suggesting malignancy may be managed conservatively with surveillance.
- Endoscopic ultrasound-guided fine-needle aspiration may be required for diagnostic purposes, particularly when radiographic features are indeterminate.