Serous cystadenoma of the pancreas, also referred as microcystic adenoma, is an uncommon type of benign cystic pancreatic neoplasm.
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Epidemiology
There is a recognized strong female predilection (M:F ~ 1:4) and usually presents in middle age to elderly patients (>60 years of age).
Associations
von Hippel Lindau (vHL) disease: can be multiple or diffuse and present at a younger age
Clinical presentation
Most patients are asymptomatic 17. Some may present with pain, weight loss, jaundice, or a palpable mass 4,5.
Pathology
Pancreatic serous cystadenomas are benign neoplasms composed of numerous small cysts that are arrayed in a honeycomb-like formation. There can be significant variation in locule size (1-20 mm) 2-4.
Most individual cysts are typically <10 mm 12.
Three morphological patterns have been described 1:
polycystic: 70%
honeycomb: 20%
oligocystic (macrocystic variant): <10% (cysts can be larger than 20 mm)
The cysts are lined by glycogen-rich flat or cuboidal epithelium separated by fibrous septa that radiate from a central scar, which may be calcified. Lesions can be rather large at presentation (~5 cm).
Location
Lesions are distributed throughout the pancreas. In the largest series, they were found in the head/uncinate process 40% of the time, body 34%, and tail 26% 17.
Radiographic features
Plain radiograph
nonspecific and will usually be normal
may demonstrate amorphous central calcification overlying the pancreas
Ultrasound
nonspecific hypoechoic mass in the pancreatic head region, possibly with internal echoes indicating microcysts (the oligocystic subtype may demonstrate individually identifiable cysts 5)
CT
typically demonstrates a multicystic, lobulated mass in the pancreatic head sometimes described as a 'bunch of grapes'
the individual cysts are typically <20 mm in size and greater than six in number (except for the oligocystic variety)
a characteristic enhancing central scar may be present which can show associated stellate calcification (present in ~20% of cases)
MRI
Serous cystadenomas usually appear as a cluster of small cysts within the pancreas. There is no visible communication between the cysts and the pancreatic duct.
Signal characteristics include:
T1: typically low signal
T2: the central fibrous scar (if present) is of a low signal while cystic components themselves are of a high signal
T1 C+ (Gd): fibrous septa between them may enhance on delayed contrast-enhanced images
Excluding the absence of communication with the main pancreatic duct, visualization of the lesion will not be facilitated by secretin-enhanced MRCP (SMRCP or MRCP-S) 14,15.
Angiography
may show enhancement due to hypervascular components 4
Treatment and prognosis
Most lesions should be observed without treatment, unless there is diagnostic uncertainty or significant associated symptomatology 5,17. They are benign lesions and do not recur once resected 4.
Differential diagnosis
General imaging differential considerations on cross-sectional imaging include:
intraductal papillary mucinous tumor (IPMN) of the pancreas: communicates with pancreatic ducts
-
mucinous cystic neoplasm of the pancreas (e.g. mucinous cystadenoma)
calcification tends to be peripheral
usually unilocular
if multilocular type, individual cysts tend to be >20 mm in size
solid pseudopapillary tumor with cystic changes and necrosis 16