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Korean J Gastroenterol  <  Volume 78(2); 2021 <  Articles

Korean J Gastroenterol 2021; 78(2): 138-143  https://doi.org/10.4166/kjg.2021.044
Pancreatic Acinar Cell Cystadenoma Mimicking Pancreatic Serous Cystadenoma
Jong Hyun Lee, Soo Jin Jung1, Yo Han Park2, Sung Jae Park3, Jung Sik Choi3
Department of Internal Medicine, Green Hospital, Seoul; Departments of Pathology1, Surgery2 and Internal Medicine3, Busan Paik Hospital, Inje University College of Medicine, Busan, Korea
Correspondence to: Jung SikChoi, Division of Gastroenterology, Department of Internal Medicine, Busan Paik Hospital, Inje University College of Medicine, 75 Bokji-ro, Busanjin-gu, Busan 47392, Korea. Tel: +82-51-890-6270, Fax: +82-51-892-0273, E-mail: jschoi@paik.ac.kr, ORCID: https://orcid.org/0000-0002-4235-0522
Received: March 15, 2021; Revised: May 3, 2021; Accepted: May 5, 2021; Published online: August 25, 2021.
© The Korean Journal of Gastroenterology. All rights reserved.

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Acinar cell cystadenoma, also known as an acinar cystic transformation of the pancreas, is an exceedingly rare but benign pancreatic lesion. A 51-year-old woman was transferred to Inje University Busan Paik Hospital because of an 8 cm-sized calcified, multiseptated, and multilocular cystic mass in the pancreatic tail observed during abdominal CT performed at another hospital. The patient did not complain of abdominal pain or other symptoms, and her laboratory findings were normal. MRI showed that the cyst was not connected to the main pancreatic duct. A pancreatic serous cystadenoma was suspected, and a laparoscopic distal pancreatectomy was performed. The resected mass was composed of variable sized multilocular cysts with incomplete septa and focally lined by epithelium with acinar differentiation. The patient was diagnosed with acinar cell cystadenoma and is currently being followed up regularly. No complications or recurrences have been observed.
Keywords: Acinar cells; Cysts; Cystadenoma; Pancreas
INTRODUCTION

Acinar cell neoplasms of the pancreas are quite rare and include acinar cell carcinoma, acinar cell cystadenocarcinoma, and acinar cell cystadenoma.1 Among them, acinar cell cystadenoma, also known as an acinar cystic transformation of the pancreas, is a cystic lesion of the pancreas that is very uncommon, benign, and shows evidence of acinar differentiation.1,2 This paper reports a case of acinar cell cystadenoma, which was misrecognized as a serous cystadenoma of the pancreas.

CASE REPORT

A 51-year-old woman with no significant medical history other than dyslipidemia was transferred to gastroenterology of Inje University Busan Paik Hospital after an 8 cm-sized calcified, multiseptated, and multilocular cystic mass was observed in the pancreatic tail on a CT scan performed in another hospital (Fig. 1).

Figure 1. Abdominal computed tomography revealed an 8 cm-sized calcified, multiseptated, and multilocular cystic mass in the pancreatic tail (arrow).

There were no abdominal symptoms, such as pain, and the tumor marker test was negative at CEA 0.904 ng/mL (reference value ≤4.7 ng/mL), CA 19-9 12.8 U/mL (reference value ≤34 U/mL). The patient was neither a drinker nor a smoker and had no significant family history.

An 8 cm-sized lobulated and multilocular cyst was observed in the pancreatic tail, which was not connected to the main pancreatic duct on MRI performed after she was transferred (Fig. 2).

Figure 2. Pancreatic magnetic resonance imaging (T2-weighted axial image) revealed an 8 cm-sized lobulated multilocular cyst in the pancreatic tail (arrow).

Serous cystadenoma of the pancreas as large as 8 cm was suspected, and as the patient was anxious, surgery was requested for postoperative confirmation.

The preoperative blood test results were in the normal range as follows: white blood cell count 5,770/mm3 (reference value 4,000-10,000/mm3), hemoglobin 13.9 g/dL (reference value 12.0-16.0 g/dL), total bilirubin 1.1 mg/dL (reference value 0.2-1.2 mg/dL), AST 21 U/L (reference value 13-33 U/L), ALT 16 U/L (reference value 6-27 U/L), ALP 200 U/L (reference value 115-359 U/L), urea nitrogen 19 mg/dL (reference value 8-22 mg/dL), creatinine 0.52 mg/dL (reference value 0.6-0.9 mg/dL), sodium 145 mmol/L (reference value 138-145 mmol/L), potassium 4.2 mmol/L (reference value 3.6-4.8 mmol/L), and chloride 105 mmol/L (reference value 101-108 mmol/L).

Laparoscopic distal pancreatectomy was performed, and a 7.0×4.0×3.0 cm-sized multilocular cystic tumor was observed during a visual examination. The tumor was well distinguished from the normal pancreatic tissue, and the cyst wall was thin and translucent (Fig. 3).

Figure 3. Distal pancreatectomy specimen showed well delineated mutilocular cystic mass measuring 7.0×4.0×3.0 cm (arrows indicate mass boundaries).

Microscopically, the tumor was composed of variable sized multilocular cysts with incomplete septa. The cysts were interconnected and focally lined by epithelium with acinar differentiation (Fig. 4). The patient was diagnosed with acinar cell cystadenoma based on a histologic findings. The patient is currently being followed up regularly, and there have been no complications or recurrence since surgery.

Figure 4. (A) Microscopic findings revealed variable sized multilocular cysts with incomplete septa (H&E,×100), and (B) focally linned by epithelium with acinar differentiation (arrows) (H&E,×100).
DISCUSSION

Acinar cell cystadenoma is a benign cystic lesion of the pancreas that shows acinar cell differentiation defined as the generation of zymogen granules, including the pancreatic exocrine enzyme.3 The condition is also known as an acinar cystic transformation of the pancreas and is very rare.

Klöppel4 described an acinar cystic transformation in 2000, and Albores-Saavedra5 proposed acinar cell cystadenoma to describe a 9 cm-sized multilobular pancreatic cyst found during the autopsy of a 58-year-old woman in 2002. The etiology of acinar cell cystadenoma is unclear; it is more prevalent in women and occurs across different age groups.2,6 It can occur in any part of the pancreas but tends to be found more commonly in the head. It is mostly localized but may exist as diffuse lesions in approximately 10% of patients.2,7 Acinar cell cystadenoma is diagnosed based on a combination of the clinical features, radiological features, and histopathological findings. Clinically, abdominal pain is the most common symptom, but it is often discovered incidentally during an imaging test.2,8

The imaging features are not specific, but Delavaud et al.9 suggested that they are more closely related to acinar cell cystadenoma than to branch duct intraductal papillary mucinous neoplasia based on the following imaging findings: 1) five or more cysts, 2) clustered small, peripheral cysts, 3) presence of cyst calcification, and 4) absence of communication with the main pancreatic duct. The modality showed 100% sensitivity and 60% specificity when at least one criterion is satisfied, 100% sensitivity and 85% specificity when at least two criteria are satisfied, 85% sensitivity and 100% specificity when at least three criteria are satisfied, and 60% sensitivity and 100% specificity when all four criteria are satisfied. This case satisfied three of the imaging findings: five or more cysts, presence of cyst calcification, and absence of communication with the main pancreatic duct.

Although EUS-guided fine needle aspiration (FNA) is used to diagnose approximately 75% of pancreatic cystic tumor patients, it may show false-negative results because of small specimen size, sampling error, and lack of preservation of the tissue architecture. EUS-guided FNA may be helpful in a differential diagnosis before surgery, but the diagnosis is mostly confirmed based on the histopathological testing of the surgical specimen.3

Histopathologically, the cyst wall consists of cells with acinar cell differentiation that lack nuclear mitotic figures, distinct cellular atypia, necrosis, and infiltrative growth.3 The presence of intracellular eosinophilic zymogen granules is an excellent pathological indicator that the lesion may be an acinar cell cystadenoma.10

Acinar cell cystadenoma and serous cystadenoma are difficult to distinguish, especially those with a multilocular and microcystic pattern, as in the present case. Acinar cell cystadenoma is characterized by interconnected and dilated acinar epithelium. The cysts are lined by 1-2 layer flatten or cuboidal epithelium with acinar differentiation.

In immunohistochemical staining, cells in the cyst wall differ from the normal cells. They are positive for acinar cell differentiation markers, such as trypsin and chymotrypsin, and also for CK7, which is negative in normal acinar cells.11

Caution should be taken when distinguishing acinar cell cystadenoma from acinar cell cystadenocarcinoma during a differential diagnosis. Acinar cell cystadenoma can be distinguished from acinar cell cystadenocarcinoma because it shows very low positivity in Ki-67 staining, no dysplasia, and no infiltration into the surrounding tissues.2

A surgical resection is recommended to exclude other cystic neoplasms associated with malignant tumors, prevent local expansion or malignant transformation of the cyst, and relieve the symptoms.8 The prognosis is good, and malignant transformations or recurrences have not been reported.3

The PubMed database was searched from 2000 until the present using a keyword search for “acinar cell cystadenoma” and “acinar cystadenoma” and 69 patients with acinar cell cystadenoma were identified (Table 1).1,3,5-8,10,12-23

Table 1 . Clinical Features of the Reported Cases of Pancreatic Acinar Cell Cystadenoma

Case no.Age (years)SexSize (cm)LocationAbdominal painTreatment
139F2.5Entire pancreasPresentTotal pancreatectomy
257M5.7BodyPresentDistal pancreatectomy
327F15.0Entire pancreasPresentTotal pancreatectomy
452F6.0HeadPresentPancreaticoduodenectomy
559F1.8HeadPresentPancreaticoduodenectomy
653F9.3HeadPresentPancreaticoduodenectomy
736F4.0HeadPresentPancreaticoduodenectomy
818F10.0HeadPresentPancreaticoduodenectomy
927F7.5TailPresentLaparoscopic distal pancreatectomy
1041F6HeadPresentPancreaticoduodenectomy
1152F5.1Body and tailPresentDistal pancreatectomy
1239M17.8TailPresentDistal pancreatectomy
1367F9.7HeadPresentPancreaticoduodenectomy
1433M6.5NeckPresentPancreaticoduodenectomy
1556F14.2TailPresentDistal pancreatectomy
1662M5.3Neck and bodyAbsentCentral pancreatectomy
1748F19.7Body and tailPresentDistal pancreatectomy
1865F3.0BodyPresentDistal pancreatectomy
1933F10HeadPresentPancreaticoduodenectomy
2046F4 (head); 10 (tail)Head and tailPresentInternal drainage
2116F7.5HeadPresentPancreaticoduodenectomy
2244F0.1-1.5Entire pancreasAbsentTotal pancreatectomy
2347F2.5 (head); 0.5 (tail)Head and tailPresentPancreaticoduodenectomy
2439F4HeadPresentPancreaticoduodenectomy
2549F0.5TailAbsentDistal pancreatectomy
2657M0.5TailAbsentDistal pancreatectomy
2766M0.2HeadAbsentDistal pancreatectomy
2861M0.2HeadAbsentDistal pancreatectomy
2952M5Head and bodyAbsentDistal pancreatectomy
309M11.7Entire pancreasAbsentLaparoscopic biopsy
3152M5BodyPresentPancreaticoduodenectomy
3258F9Body and tailAbsentAutopsy
3325M6HeadPresentPancreaticoduodenectomy
3454F1.5Body and tailAbsentLaparoscopic distal pancreatectomy
3550F7.5Head and neckAbsentPancreaticoduodenectomy
3633M1.7TailNINI
3738M2.4HeadNINI
3846F3BodyNINI
3933M4.6HeadNINI
4063F2HeadNINI
4119F3.6TailPresentDistal pancreatectomy
4225MNIEntire pancreasPresentTotal pancreatectomy
4346FNIEntire pancreasAbsentTotal pancreatectomy
4462FNIHeadAbsentPancreaticoduodenectomy
4561MNIEntire pancreasAbsentTotal pancreatectomy
4652M5BodyPresentDistal pancreatectomy
4740F4HeadPresentPancreaticoduodenectomy
4852M5Head and bodyAbsentPancreaticoduodenectomy
4913F4.6Body and tailNINI
5047F1.1TailNINI
5165F2.1HeadNINI
5242F3.0HeadNINI
5377M2.5NeckNINI
5459F0.5TailNINI
5537M3.0Head, body, and tailPresentDistal pancreatectomy
5640F4.5Entire pancreasNIPancreaticoduodenectomy
5722F6.3TailPresentDistal pancreatectomy
5814M2.6TailPresentLaparoscopic distal pancreatectomy
5942FUp to 2Head and bodyAbsentPancreaticoduodenectomy
6023F6HeadPresentPancreaticoduodenectomy
6165M6.9HeadPresentPancreaticoduodenectomy
6225F2.9BodyPresentCentral pancreatectomy
6368M3.5TailAbsentLaparoscopic distal pancreatectomy
6471F5.1Head and neckAbsentPancreaticoduodenectomy
6567F5HeadAbsentPancreaticoduodenectomy
6659F3.2Head and neckAbsentPancreaticoduodenectomy
6757F1.5TailPresentDistal pancreatectomy
6853F5.8HeadAbsentPancreaticoduodenectomy
6925F6.2HeadPresentPancreaticoduodenectomy
7051F7.0TailAbsentLaparoscopic distal pancreatectomy

Patient 70 is our additional experience.

F, female; M, male; NI, not identified.



This was the case of an 8 cm-sized cystic tumor in the pancreatic tail that was detected accidentally during an abdominal imaging test in a 51-year-old woman without any symptoms. The diagnosis of acinar cell cystadenoma was made after surgery, while serous cystadenoma of the pancreas was suspected from the image. Although only a few cases are being reported as acinar cell cystadenoma, which is a very rare disease, it should be considered in a differential diagnosis of cystic tumors of the pancreas. Here, the authors report one case of acinar cell cystadenoma that was misrecognized as a serous cystadenoma of the pancreas.

Financial support

None.

Conflict of interest

None.

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