MRI features of serous oligocystic adenoma of the pancreas: differentiation from mucinous cystic neoplasm of the pancreas

Objectives

The purpose of this study was to describe the MRI features of the benign pancreatic neoplasm serous oligocystic adenoma (SOA) that differ from those of mucinous cystic neoplasm (MCN), a neoplasm with the potential for malignant degeneration.

Methods

Seven patients with SOA (seven women; mean age 36.6 years) and eight patients with MCN (eight women: mean age 39.9 years) were included. Several imaging features were reviewed: mass size, location, shape, wall thickness, cyst configuration (Type I, unilocular; Type II, multiple clustered cyst; Type III, cyst with internal septation) and signal intensity of the lesion with heterogeneity.

Results

SOA lesions were smaller (3.4 cm) than those of MCN (9.3 cm) (p=0.023). The commonest lesion shape was lobulated (85.7%) for SOA, but oval (50.0%) or lobulated (37.5%) for MCN (p=0.015). The most common cyst configuration was Type II (85.7%) for SOA and Type III (75.0%) for MCN (p=0.008). Heterogeneity of each locule in T₁ weighted images was visible in all cases of MCN, but in no case for SOA (p=0.004).

Conclusion

SOA could be differentiated from MCN by identifying the imaging features of lobulated contour with multiple clustered cyst configurations and homogeneity of each locule in T₁ weighted MR images.Serous oligocystic adenoma (SOA) is a recently described rare, benign pancreatic neoplasm and a morphological variant of serous microcystic adenoma, because it contains six or fewer cysts and the cysts are large (>2 cm) 1,2]. Pathologically, SOA is a benign pancreatic neoplasm composed of a few relatively large cysts uniformly lined with glycogen-rich cuboidal epithelial cells 3]. According to the World Health Organization classification, SOA is a subgroup of pancreatic serous cystic tumours and the term SOA is a synonym for macrocystic serous cystadenoma 3,4].The CT and MRI features of SOA of the pancreas are documented 2]. On CT and MRI, SOA typically appears as a small unilocular or bilocular cyst (<5 cm) with a thin wall (<2 mm) that lacks mural nodules or calcifications 2]. Because the cystic spaces are >2 cm, SOA images can be mistaken for mucinous cystic neoplasm (MCN), pseudocyst or intraductal papillary mucinous tumour 2,5-7]. It is very difficult to differentiate SOA from MCN by clinical and radiological features 2,6,8,9]. SOA does not require resection unless it causes symptoms, but MCN should be resected because of a potential for malignant degeneration 5,7,8]. Endoscopic ultrasound and cyst fluid aspiration have a role in distinguishing mucinous and serous lesions, but it is an invasive procedure with a risk of complications such as pancreatitis 10]. Therefore, it is clinically valuable to determine characteristic imaging findings that can distinguish SOA from MCN.Recently, Kim et al 6] and Cohen-Scali et al 5] described characteristic CT findings that can be used to differentiate SOA from MCN. MRI can demonstrate septa within a lesion with greater sensitivity than CT; therefore, MRI provides a better evaluation of tissue characteristics than CT 1,11]. However, few studies have described the MRI features of SOA 1,2]. The purpose of this study was to describe the differences in the MRI features of SOA and MCN in the pancreas.