Introduction

A pancreatic serous cyst neoplasm (SCN) is a relatively rare tumor, accounting for 1–2 % of all pancreatic tumors and 10 % of surgically resected cystic lesions of the pancreas [1–4]. It typically consists of small cysts surrounded by a thin capsule and the inner surface of the cyst is composed of columnar or cuboidal cells with glycogen-rich cytoplasm. In rare cases, this type of tumor can exhibit subtotal cystic degeneration [5]. We report a surgical case of pancreatic serous cystadenoma (SCA), which shrank remarkably with cystic degeneration before surgery, over a period of only 3 weeks.

Case report

A 29-year-old woman was referred to our hospital for investigation of epigastric pain and jaundice. Laboratory test results included the following: total bilirubin, 3.1 mg/dL; alkaline phosphatase, 376 IU/L; AMY, 82 U/L; C-reactive protein, 15.54 mg/dL; and normal carcinoembryonic antigen and carbohydrate 19-9 levels. Contrast-enhanced computed tomography (CT) showed a 6-cm monolocular tumor in the pancreatic head (Fig. 1a). Magnetic resonance cholangiopancreatography (MRCP) revealed that the upper part of the extrahepatic bile duct was dilated because the tumor was compressing the inferior part of the duct (Fig. 1b). Endoscopic retrograde cholangiopancreatography (ERCP) showed stenosis and deviation of the inferior part of the bile duct (Fig. 1c), and there was no communication between the main pancreatic duct and the tumor in the pancreatic head. We performed endoscopic retrograde biliary drainage using a plastic stent, after which the abdominal symptoms resolved and the serum total bilirubin level returned to within the normal range. We suspected either a mucinous cystadenoma (MCA) or a macrocystic SCA, and the patient underwent surgery 3 weeks after ERCP. At laparotomy, the tumor was not detected around the pancreatic head and had apparently disappeared; however, intraoperative ultrasonography revealed a 1.5-cm low-echoic tumor in the pancreatic head. The tumor was very close to the intrapancreatic bile duct but was not compressing it (Fig. 2a). Complete tumor excision was performed using Whipple procedure (operative duration 191 min; blood loss 50 mL). Macroscopically, it was a 1.5-cm monolocular tumor (Fig. 2b). Microscopically, the cystic tumor was composed of a thick fibrous wall with granulation tissue and hemorrhage (Fig. 2c). Although epithelial cells were not found inside the cystic wall, at its periphery, there were numerous grossly invisible microcysts with glycogen-containing epithelial cells (Figs. 2c, 3a). Periodic acid–Schiff staining was positive in the cytoplasm of the epithelial cells of the microcysts (Fig. 3b). The residual epithelial foci accounted for approximately 10 % of the tumor volume. We did not observe an ovarian-type stroma suggestive of MCA. On the basis of these findings, the tumor was diagnosed as SCA with subtotal cystic degeneration (Fig. 4). The patient recovered well without complications and was discharged on postoperative 11. There were no signs of recurrence at her 8-month follow-up.

Fig. 1
figure 1

Preoperative imaging findings. a Computed tomography showed a 6-cm monolocular tumor in the pancreatic head (arrow). b Magnetic resonance cholangiopancreatography revealed that the upper part of the extrahepatic bile duct was dilated as a result of being compressed by the tumor. c Endoscopic retrograde cholangiopancreatography (ERCP) revealed stenosis and deviation of the inferior part of the bile duct (arrows)

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Fig. 2
figure 2

a Intraoperative ultrasonography revealed a 1.5-cm low-echoic tumor in the pancreatic head (black arrow), very close to the intrapancreatic bile duct (white arrow). b Macroscopically, the growth was found to be a 1.5-cm monolocular tumor (black arrow). c Microscopically, the cystic tumor was composed of a thick fibrous wall with granulation tissue and hemorrhage (black arrow). Epithelial cells were not found inside the cystic wall (blank arrow), but at its periphery, there were numerous, grossly invisible microcysts (dotted arrow) (hematoxylin–eosin; ×10)

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Fig. 3
figure 3

Microscopic findings of the microcysts. a The microcysts were composed of glycogen-containing epithelial cells (hematoxylin–eosin; ×100). b Periodic acid–Schiff (PAS) staining was positive in the cytoplasm of the epithelial cells (PAS staining; ×100)

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Fig. 4
figure 4

Morphology of the tumor before and after cystic degeneration. a Prior to degeneration, the tumor was composed of a central large cyst (black arrow), surrounded by numerous invisible microcysts (dotted arrow). b The tumor shrank remarkably degree after degeneration. The degenerative change was thought to have involved the large central cyst. After degeneration, the central cyst was composed of a thick fibrous wall (black arrow)

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Discussion

Pancreatic SCN is a relatively rare tumor that occurs most frequently in middle-aged women [6]. It has been morphologically classified into two types: microcystic and macrocystic, according to the World Health Organization classification system, and a solid variant also exists, although it is uncommon [7]. With respect to the malignant potential of this tumor, most SCNs are benign and there have been very few reports on malignant serous cystadenocarcinoma [1]. Because it is not associated with highly malignant behavior, the indication for surgery is still controversial. A recent multi-institutional study of the Japan Pancreas Society concluded that resection should be considered when differentiation from other neoplasms is difficult; when the patient has symptoms or mass effects on the main pancreatic duct; and when the tumor size is large or increasing [1]. In the present case, the cystic tumor was suspected preoperatively of being an MCA or a macroscopic SCA of the pancreas. We did not think it could be a pseudocyst because the serum AMY level was within the normal range and CT showed no sign of pancreatitis. Furthermore, the patient denied any history of alcohol consumption or gallstones, either of which could cause pancreatitis. If preoperative endoscopic ultrasonography had been performed, the peripheral, numerous small microcysts might have been detected because this technique has been reported to be superior to any other modality with respect to spatial resolution and the ability to detect small pancreatic lesions [8–10]. However, both MCA and symptomatic SCA are indications for surgery, so laparotomy was planned without further examination.

At laparotomy, the tumor was found to have shrunk markedly, and although local excision would have been a less invasive option, the Whipple procedure was adopted because of the close proximity of the tumor to the intrapancreatic bile duct, which might have been damaged during local tumor excision.

According to some reports on other solid pancreatic neoplasms, including adenocarcinoma or neuroendocrine tumors, cystic degeneration is rare [11, 12]. Kosmal et al. [11] reported degenerative cystic cavities in only 8 (1.7 %) of 483 pancreatic adenocarcinomas. With respect to SCA, we found only a single report from the Memorial Sloan-Kettering Cancer Center and Johns Hopkins Hospital, describing subtotal cystic degeneration in only 8 among 397 resected SCAs (2.0 %) [5]. Microscopically, all of these eight tumors were composed of cysts with thick fibrous walls showing chronic inflammation and containing reactive myofibroblasts and hemorrhage. The innermost layer of the cystic tumors had no epithelial lining; thus, resembling a pseudocyst. The epithelial foci were often arranged in strands at the periphery of the large cyst, and accounted for 5–60 % of the total tumor volume. The microscopic findings of the SCA in the present case were identical to those described previously.

We speculate that the tumor in the present case originated as a multilocular tumor composed of a central 6-cm cyst surrounded by numerous, macroscopically invisible small cysts, although it appeared to be a monocyst on preoperative CT and MRCP (Fig. 1a, b). Over the 3 weeks before surgery, degenerative changes were thought to be occurring in the large central cyst and the tumor was grossly monolocular, even after degeneration. Similarly, four of the eight previously reported SCAs with cystic degeneration were found to be grossly monolocular, although all had microcysts on the periphery of the cystic wall. Although the reason for the tumor shrinkage remains unknown, it is thought that degenerative change caused this remarkable morphological alteration (Fig. 4). No other events that might have caused tumor shrinkage, such as tumor rupture or trauma, were noted. To our knowledge, this is the first reported case of pancreatic SCA in which morphological changes were observed before and after cystic degeneration.