Pancreatic serous oligocystic adenomas: clinicopathologic features and a comparison with serous microcystic adenomas and mucinous cystic neoplasms.

INTRODUCTION: The preoperative distinction between serous cystic neoplasms (SCNs) and mucinous cystic neoplasms (MCNs) is essential, as all MCNs are considered malignant or potentially malignant and should be surgically resected, whereas SCNs are almost always benign. However, the radiologic distinction between SCNs and MCNs is frequently difficult especially with serous oligocystic adenoma (SOA), a morphologic variant of SCN, as both SOA and MCN appear on cross-sectional imaging as a solitary macrocystic lesion in the pancreas. We reviewed all SOAs managed at our institution to determine if any clinicopathologic features would prove useful for establishing a preoperative diagnosis. METHODS: Over a 15-year period, 64 patients with a pathologically confirmed diagnosis of a pancreatic cystadenoma or cystadenocarcinoma treated at Singapore General Hospital were retrospectively reviewed. There were 27 MCNs and 37 SCNs including 12 SOAs. In addition, 40 cases of SOA previously reported in the literature were reviewed and analyzed together with the 12 patients, making this a series of 52 SOAs. RESULTS: In our experience, SOAs comprised 32.4% of the SCNs, and females predominated (7/12). The median age of the patients was 42.5 years (range 22-74 years), and only 4 of the 12 patients were symptomatic. Most of the cysts were located in the body or tail of the pancreas (9/12), and the median cyst size was 52.5 mm (range 10-190 mm). When the clinicopathologic features of SOAs and serous microcystic adenomas (SMAs) were compared, there was no difference between the patients with SOAs and SMAs in terms of age, sex, presence of symptoms, cyst size, or site of the lesion. However, SOAs occurred in the women less frequently (67.3% vs. 96.3%, P=0.004), were smaller [40 mm (range 10-190 mm) vs. 95 mm (range 25-180 mm), P<0.001], and occurred more commonly in the head of the pancreas [25 (48.1%) vs. 2(7.4%)] compared to MCNs. None of the SOAs were frankly malignant compared to the 29.6% of MCNs that were. CONCLUSIONS: SOAs and SMAs have similar clinicopathologic features. On the other hand, SOAs differ from MCNs by their relatively higher male/female ratio, higher frequency of tumors occurring in the head of the pancreas, and smaller cyst size. Knowledge of these distinguishing clinical features when used in combination with other diagnostic modalities such as endoscopic ultrasonography/fine-needle aspiration will enable clinicians to better differentiate these two pathologic entities preoperatively.