Description
Pancreatic serous cystadenomas (SCAs) are benign neoplasms that account for approximately 1-2% of all pancreatic tumours. They are predominantly microcystic lesions filled with a clear, serous fluid and characterised by the presence of numerous small cysts, giving them a honeycomb or spongy appearance.
Pathogenesis
The precise pathogenesis of SCAs is not fully understood. They are thought to arise from the replication of ductal epithelial cells. SCAs can occur in any part of the pancreas, though they are most frequently found in the body or tail.
Subtypes
Pancreatic serous cystadenomas are typically classified into two main subtypes based on their morphology on imaging:
- Microcystic serous cystadenoma: The most common type, characterised by many small cysts giving it a honeycomb appearance.
- Macrocytic (oligocystic) serous cystadenoma: Characterised by larger cysts and may mimic a mucinous cystic neoplasm or pseudocyst on imaging. This type is relatively rare.
Epidemiology, Risk Factors & Associations
- SCAs are more commonly diagnosed in women, with a female-to-male ratio of approximately 4:1.
- The median age at diagnosis is in the sixth decade of life, thus it is commonly referred to as the “grandmother tumour”.
- There is no established association with smoking, alcohol, or chronic pancreatitis.
- Most SCAs are sporadic.
- Around 75-80%% of patients with von Hippel–Lindau (VHL) syndrome develop pancreatic cystic lesions, 10% of which are serous cystadenomas.
Clinical Features
- Most patients with SCAs are asymptomatic.
- When symptoms do occur, they are typically nonspecific and often related to the mass effect of the tumour, including abdominal pain or discomfort, early satiety, and weight loss.
- Rarely, SCAs may cause obstructive jaundice if they compress the common bile duct.
Complications
Complications are rare but can include haemorrhage, rupture, and obstructive jaundice. The rate of malignant transformation is extremely low, estimated at less than 1%.
Pathological Features
Histopathology
SCAs are characterised by numerous small cysts lined by a single layer of cuboidal, glycogen-rich, clear cells that stain positive for periodic acid-Schiff (PAS).
Immunohistochemistry
Cells show positive staining for cytokeratin and are negative for mucin, differentiating them from mucinous cystic neoplasms.
Radiological Features
General Imaging Features
- Typically found in the body or tail of the pancreas, although they can occur anywhere within the organ
- SCAs typically appear as well-defined lesions with a polycystic or microcystic pattern giving a honeycomb or spongy appearance. Usually more than 6 cysts ranging from a few mm to 2 cm is seen.
- Macrocystic or oligocystic pattern is uncommon.
- A fibrous central scar with or without a characteristic stellate pattern of calcification is virtually pathognomic (seen in 30% of cases)
- Fine, external lobulations are a common feature
- Enhancement of septa and the cyst wall may be seen
- Pancreatic ductal dilatation is uncommon.
- Does not communicate with pancreatic duct
CT
- SCAs appear as hypodense lesions.
MRI
- Lesion appears hypointense on T1-weighted images and hyperintense on T2-weighted images.
Differential Diagnosis
- Mucinous cystic neoplasm (MCN): MCNs typically occur in the body or tail of the pancreas and are almost exclusively found in females. Unlike SCAs, these typically have a macrocystic appearance and are often associated with ovarian-type stroma. They often have a thickened wall with a peripheral calcified rim (eggshell), distinguishing them from SCAs (central stellate calcification). On pathology, they are filled with mucin, and the cysts are lined by columnar mucin-producing epithelium.
- Intraductal papillary mucinous neoplasm (IPMN): IPMNs are typically located in the head of the pancreas and are associated with cystic dilatation of the main pancreatic duct or its side branches. The presence of communication with the main pancreatic duct helps distinguish IPMN from SCAs. IPMNs often show an “enhancing mural nodule” which is not characteristic of SCAs.
- Pseudocysts: Pseudocysts usually present after acute pancreatitis or trauma and do not have an epithelial lining which distinguishes them from SCAs. They are often unilocular and lack the “honeycomb” or “microcystic” appearance of SCAs. They also have higher protein and amylase content on cyst fluid analysis.
- Solid pseudopapillary neoplasm (SPEN): This is a rare, low-grade malignant neoplasm that predominantly affects young female and often appears as well encapsulated, mixed solid and cystic masses. They lack the central scar and calcifications typical of SCAs.
- Pancreatic ductal adenocarcinoma: Though predominantly solid, it can become necrotic and mimic a cystic lesion. However, pancreatic adenocarcinoma often has a more irregular outline, and a dilated main pancreatic duct upstream (double duct sign), which are not seen in SCAs.
Management
- For asymptomatic, small SCAs, surveillance with imaging is often the preferred management strategy due to the benign nature of these tumours.
- For larger, symptomatic lesions, surgical resection may be indicated, often involving a distal pancreatectomy for tumours in the body or tail, or a pancreaticoduodenectomy for tumours in the head of the pancreas.