Macrocystic serous cystadenoma of the pancreas: importance of co-existent tiny cysts depicted by EUS

The case of a 38-year-old man with an unusual type of serous cystadenoma of the pancreas is reported. A multilocular cystic tumor in the head of the pancreas was detected on abdominal ultrasonography and computed tomography. On endoscopic ultrasonography, the major cysts ranged from 2.0 to 4.5 cm in size. In addition to these large cysts, a few small cysts were detected. Based on these findings, this tumor was diagnosed as a macrocystic type serous cystadenoma. Because endoscopic retrograde pancreatogram showed a compression of the main pancreatic duct around the tumor, and because the size of the tumor had been increasing over a 3-year period, surgical intervention was performed. The resected tumor consisted of macrocysts, with a few small cysts, and was histologically diagnosed as serous cystadenoma. Endoscopic ultrasonography appears to provide an excellent inside image of this unusual tumor, and because of its ability to detect small cystic lesions clearly, it could be useful in the diagnosis of macrocystic serous cystadenoma. Received: February 5, 1999 / Accepted: October 22, 1999     

Macrocystic type of serous cystadenoma with a communication between the cyst and pancreatic duct

A 42-year-old woman with a cystic lesion in the head of the pancreas was evaluated by using abdominal ultrasonography, a computed tomographic scan, magnetic resonance imaging and endoscopic retrograde pancreatography. Multiple cystic lesions, 5 cm in diameter, which had papillary protrusion inside the cyst in the head of the pancreas and had the communication between the cysts and pancreatic duct, were determined. Pylorus-preserving pancreaticoduodenectomy was performed under the diagnosis of mucinous cystic neoplasm of the pancreas. Although the cut surface of the tumor showed a macrocystic tumor of 3 cm in diameter, part of the cyst wall was cavernous. A histopathological examination showed single-layered cuboidal cells, which lead to the diagnosis as being serous cystadenoma of the pancreas. Serous cystadenoma is a rare, almost benign pancreatic tumor. The macrocystic subtype of serous cystadenoma is even more rare. We describe a patient who had this macrocystic subtype of serous cystadenoma with a communication between the cyst and pancreatic duct. This case illustrates the difficulty in the diagnosis of cystic lesions in the pancreas, and might support the single category of cystic lesions of the pancreas.     

A discrepant finding between magnetic resonance imaging and other imaging modalities suggests a microcystic serous cystadenoma of the pancreas

Summary Background. Serous cystadenoma of the pancreas is generally considered as having no malignant potential. Thus, of clinical importance is a differential diagnosis of this neoplasm from other solid tumors that are often malignant. Results. We report a case of microcystic serous cystadenoma of the pancreas. Abdominal ultrasonography, computed tomography, and endoscopic ultrasonography showed a solid mass in the body of the pancreas with a diameter of 15 mm, but magnetic resonance imaging revealed it as a unilocular cystic lesion. Histological examinations on the surgically resected tissue specimen showed a honeycombed tumor with innumerable tiny cysts appearing grossly as a solid mass. The discrepant finding between magnetic resonance imaging and other imaging modalities observed in this case is suggestive of and might be specific to microcystic serous cystadenoma of the pancreas. Conclusions. Magnetic resonance imaging is a mandatory modality to identify pancreatic serous cystadenoma that contains no visible cystic compartments on computed tomography and ultrasonography.     

A discrepant finding between magnetic resonance imaging and other imaging modalities suggests a microcystic serous cystadenoma of the pancreas.

BACKGROUND: Serous cystadenoma of the pancreas is generally considered as having no malignant potential. Thus, of clinical importance is a differential diagnosis of this neoplasm from other solid tumors that are often malignant. RESULTS: We report a case of microcystic serous cystadenoma of the pancreas. Abdominal ultrasonography, computed tomography, and endoscopic ultrasonography showed a solid mass in the body of the pancreas with a diameter of 15 mm, but magnetic resonance imaging revealed it as a unilocular cystic lesion. Histological examinations on the surgically resected tissue specimen showed a honeycombed tumor with innumerable tiny cysts appearing grossly as a solid mass. The discrepant finding between magnetic resonance imaging and other imaging modalities observed in this case is suggestive of and might be specific to microcystic serous cystadenoma of the pancreas. CONCLUSIONS: Magnetic resonance imaging is a mandatory modality to identify pancreatic serous cystadenoma that contains no visible cystic compartments on computed tomography and ultrasonography.     

A case of macrocystic serous cystadenoma of the pancreas

Summary A case of macrocystic serous cystadenoma of the pancreas is presented, and literature is reviewed. A 35-yr-old woman presented with mild upper abdominal pain. Abdominal ultrasonography and an abdominal computed tomography revealed a multiloculated and calcified cyst in the body of the pancreas. A T1-weighted image, using magnetic resonance imaging, revealed a low-intensity mutiloculated, pancreatic mass. In contrast, T2-imaging of the tumor showed a high-intensity mass. Endoscopic retrograde cholangiopancreatography showed no contact between the main pancreatic duct and the tumor. The preoperative diagnosis was a mucinous cystic neoplasm. Tumor enucleation was performed. Subsequent microscopic examination of this tumor suggested the diagnosis of a macrocystic serous cystadenoma of the pancreas.     

MRI对胰腺囊性肿瘤的诊断价值

目的探讨MRI对胰腺囊性肿瘤的诊断价值。方法回顾分析23例经手术病理证实的胰腺囊性肿瘤资料,总结其影像表现。结果黏液性囊性肿瘤10例,囊性肿块较大,肿块平均直径超过10 cm,由较厚的纤维壁分隔成多房囊肿,外壁光滑,边界清楚。浆液性囊腺瘤6例,病灶较小,囊内有分隔而呈放射状排列,中心瘢痕为其特征性表现。胰腺囊性转移瘤3例,均有肿瘤病史,表现不典型,需结合肿瘤病史定性。胰胚细胞瘤2例,幼儿发病,肿块巨大,肿瘤坏死囊变,形成假-假性囊肿。胰腺乳头状囊实性肿瘤1例,表现为边界清楚的囊实性肿块,囊壁上有壁结节。胰腺毛细血管瘤1例,表现与浆液性囊腺瘤相似,难以术前诊断。结论MRI对胰腺囊性肿瘤具有高度敏感性,不同病变有一定的特征性表现, 对术前定性极有价值。     

Macrocystic pancreatic cystadenoma: The role of EUS and cyst fluid analysis in distinguishing mucinous and serous lesions

BACKGROUND: Benign pancreatic serous cystadenoma usually is morphologically distinguishable from mucinous cystadenomas, which require resection because of their malignant potential. A macrocystic variant of serous cystadenoma recently has been described, rendering this important distinction more difficult. The aim of this study was to determine the EUS and tumor marker characteristics of mucinous cystadenoma compared with macrocystic serous cystadenomas. METHODS: Medical records for consecutive patients seen between 1995 and 2002, with a histopathologic diagnosis of mucinous cystadenoma or macrocystic serous cystadenoma after surgery, who had undergone a detailed EUS examination, including EUS-guided FNA, were retrospectively reviewed. RESULTS: A resection specimen was available for 32 mucinous cystadenomas and 9 macrocystic serous cystadenomas. No significant differences were observed with regard to clinical data (age, gender, presence of symptoms), lesion size, and location within the pancreas. All mucinous cystadenomas had a discernible cyst wall (thickened, 66%; focal parietal nodules, 25%) compared with 56% of macrocystic serous cystadenomas (p<0.0001). A thick echo content also was more frequent in mucinous cystadenoma (56% vs. 11%; p=0.04; statistical significance removed by the Bonferroni correction). Microcysts were only observed in macrocystic serous cystadenomas (44%; p=0.0008). The combination of a cyst wall that is thickened and the absence of microcysts had a sensitivity of 100% and specificity of 78% for the diagnosis of mucinous cystadenoma compared with macrocystic serous cystadenoma. Although intracystic carbohydrate-associated antigen 72-4 and mucins M1 were non-discriminatory, low carcinoembryonic antigen (<5 ng/mL) and carbohydrate-associated antigen 19-9 (<50,000 U/mL) values were found in macrocystic serous lesions (respectively, 100% and 100%; p=0.0002 and p=0.0002). CONCLUSIONS: Although there is considerable overlap, helpful EUS characteristics that differentiate mucinous cystadenoma from macrocystic serous cystadenoma include a thick cyst wall and microcysts. These features, coupled with analysis of aspirated fluid for tumor markers (especially carcinoembryonic antigen), should help to confirm the diagnosis.     

Serous cystic neoplasm of the pancreas-indications for surgery

BACKGROUND/AIMS: Serous cystic neoplasm is a rare pancreatic tumor. Almost all of these tumors are benign and only 9 cases of serous cystadenocarcinoma have been reported. Although serous cystic neoplasm is typically a microcystic lesion, there is a wide range of cyst sizes from micro to macro and even unilocular cysts have been reported. Thus, the diagnosis is difficult and indications for surgery are controversial. We aimed to elucidate the clinicopathological and imaging features of serous cystic neoplasm of the pancreas. METHODOLOGY: We investigated 15 cases of resected and 6 cases of nonresected cases of serous cystic neoplasm, evaluating the symptoms, imaging findings, preoperative diagnosis, macroscopic morphology, microscopic findings, and results of follow-up. RESULTS: Imaging diagnosis of serous cystic neoplasm was not easy, because not so many tumors had the typical microcystic pattern. Most of the resected serous cystic neoplasms were non-microcystic or were small tumors, which could not be precisely evaluated. CONCLUSIONS: Small serous cystic neoplasms, which can be diagnosed by imaging, do not need to be resected because serous cystadenocarcinoma is rare. Tumors of the pancreas that cannot be confirmed to be serous cystic neoplasm should be resected because of the possibility of pancreatic cancer, mucinous cystadenocarcinoma, or mucinous cystadenoma with malignant potential.     

Updates in diagnosis and management of pancreatic cysts

Incidental pancreatic cysts are commonly encountered with some cysts having malignant potential. The most common pancreatic cystic neoplasms include serous cystadenoma, mucinous cystic neoplasm and intraductal papillary mucinous neoplasm. Risk stratifying pancreatic cysts is important in deciding whether patients may benefit from endoscopic ultrasound (EUS) or surgical resection. Surgery should be reserved for patients with malignant cysts or cysts at high risk for developing malignancy as suggested by various risk features including solid mass, nodule and dilated main pancreatic duct. EUS may supplement magnetic resonance imaging findings for cysts that remain indeterminate or have concerning features on imaging. Various cyst fluid markers including carcinoembryonic antigen, glucose, amylase, cytology, and DNA markers help distinguish mucinous from nonmucinous cysts. This review will guide the practicing gastroenterologist in how to evaluate incidental pancreatic cysts and when to consider referral for EUS or surgery. For presumed low risk cysts, surveillance strategies will be discussed. Managing pancreatic cysts requires an individualized approach that is directed by the various guidelines.     

EUS in the evaluation of pancreatic cystic lesions

BACKGROUND: The differential diagnosis in pancreatic cystic lesions is often difficult despite the availability of various modern imaging modalities. This study assessed the role of EUS in the following: (1) discrimination of pseudocysts from pancreatic cystic tumors, (2) differential diagnosis between serous cystadenoma and mucinous cystic tumor, and (3) prediction of accompanying malignancy in intraductal papillary mucinous tumor. METHODS: EUS findings in 75 patients with pancreatic cystic lesions (58 cystic tumors, 17 pseudocysts) were evaluated. In the comparison of pseudocysts and cystic tumors, the latter included intraductal papillary mucinous tumor, mucinous cystic tumors, and serous cystadenomas, but not solid-pseudopapillary tumors. RESULTS: In univariate analysis, pseudocysts exhibited echogenic debris and parenchymal changes more often than cystic tumors did (respectively, 29% vs. 6%, p < 0.05; and 65% vs. 4%, p < 0.001). In contrast, septa and mural nodules were found more frequently in cystic tumors than pseudocysts (respectively, 69% vs. 12%, p < 0.001; 56% vs. 12%, p < 0.01). Multivariate analysis revealed that parenchymal changes (odds ratio [OR] = 83.59; p < 0.01); septa (OR = 30.75; p < 0.05); and mural nodules (OR = 21.38; p < 0.05) were independent predictors of differentiation between pseudocysts and cystic tumors. Serous cystadenoma exhibited diverse EUS features, as well as a honeycomb appearance. Mural nodules were found more often in mucinous cystic tumors than in serous cystadenomas (p < 0.05). There were no factors that predicted malignancy in intraductal papillary mucinous tumor. CONCLUSIONS: EUS is a useful complementary imaging method for differentiation of pancreatic cystic lesions.     

Pancreatic endocrine neoplasm can mimic serous cystadenoma

A 57-yr-old female patient was referred to our hospital with a cystic lesion of the head of the pancreas that had been noted on abdominal computed tomography (CT). Endoscopic ultrasonography (EUS) showed a 3.0 cm rounded mass in the head of the pancreas. EUS images showed that the tumor had a solid component consisting of multiple microcysts separated by septae and a cystic component consisting of a macrocystic lesion. Thus, the tumor was suspected of being a serous cystadenoma (SCA). However, the histopathological diagnosis based on endoscopic ultrasound- guided fine-needle-aspiration biopsy (EUS-FNAB) was that of a pancreatic endocrine neoplasm (PEN). Surgical resection was performed. Despite having very similar macroscopic findings to SCA, microscopic examination revealed that the patient's tumor was definitely a PEN. This case suggests that it is very difficult to distinguish PENs from SCAs based solely on imaging methods. EUS-FNAB is essential for determining the appropriate therapeutic strategy, as it provides the histopathological diagnosis.     

Serous cystadenoma of the pancreas communicating with a pancreatic duct

Summary Conclusion To differentiate serous cystadenoma from other cystic lesions communicating with the pancreatic duct, careful radiological examination is necessary. Background Communication between the cystic cavity and the pancreatic duct in an ordinary serous cystadenoma is uncommon, although it is not uncommon in other cystic lesions, such as pseudocyst, mucinous cystadenoma/adenocarcinoma, and intraductal papillary tumor. Methods A serous cystadenoma of the pancreas communicating with main pancreatic duct in a 76-yr-old male is reported. Results The communication was preoperatively demonstrated by endoscopic retrograde cholangiopancreatography and confirmed by histopathological examination of the resected specimen.     

Diagnosis of pancreatic cystic neoplasms: a report of the cooperative pancreatic cyst study

BACKGROUND & AIMS: Cysts of the pancreas display a wide spectrum of histology, including inflammatory (pseudocysts), benign (serous), premalignant (mucinous), and malignant (mucinous) lesions. Endoscopic ultrasonography (EUS) may offer a diagnostic tool through the combination of imaging and guided, fine-needle aspiration (FNA). The purpose of this investigation was to determine the most accurate test for differentiating mucinous from nonmucinous cystic lesions. METHODS: The results of EUS imaging, cyst fluid cytology, and cyst fluid tumor markers (CEA, CA 72-4, CA 125, CA 19-9, and CA 15-3) were prospectively collected and compared in a multicenter study using histology as the final diagnostic standard. RESULTS: Three hundred forty-one (341) patients underwent EUS and FNA of a pancreatic cystic lesion; 112 of these patients underwent surgical resection, providing a histologic diagnosis of the cystic lesion (68 mucinous, 7 serous, 27 inflammatory, 5 endocrine, and 5 other). Receiver operator curve analysis of the tumor markers demonstrated that cyst fluid CEA (optimal cutoff of 192 ng/mL) demonstrated the greatest area under the curve (0.79) for differentiating mucinous vs. nonmucinous cystic lesions. The accuracy of CEA (88 of 111, 79%) was significantly greater than the accuracy of EUS morphology (57 of 112, 51%) or cytology (64 of 109, 59%) (P < 0.05). There was no combination of tests that provided greater accuracy than CEA alone (P < 0.0001). CONCLUSIONS: Of tested markers, cyst fluid CEA is the most accurate test available for the diagnosis of mucinous cystic lesions of the pancreas.     

Endoscopic diagnosis of cystic lesions of the pancreas

Endoscopic methods are increasingly used in the diagnosis of cystic lesions of the pancreas. The two major endoscopic approaches are endoscopic ultrasonography (EUS) and transpapillary diagnosis. EUS‐guided fine‐needle aspiration cytology and EUS‐guided fine needle‐based confocal laser endomicroscopy have been used in the differential diagnosis of mucinous and non‐mucinous pancreatic cysts. EUS is the most sensitive modality for detecting mural nodules (MN) in intraductal papillary mucinous neoplasms (IPMN). Contrast‐enhanced harmonic EUS (CH‐EUS), as an add‐on to EUS, is useful for identifying and characterizing MN. Recent studies show that CH‐EUS has a sensitivity of 60–100% and a specificity of 75–92.9% for diagnosing malignant cysts. Intraductal ultrasonography and peroral pancreatoscopy are especially useful for detecting MN and IPMN. A recent meta‐analysis showed that cytological assessment of pancreatic juice using a transpapillary approach had a pooled sensitivity, specificity, and accuracy of 35.1%, 97.2%, and 92.9%, respectively, for diagnosing malignant IPMN. Further studies are warranted to determine the indications for each of these novel techniques in assessing cystic lesions of the pancreas.     

Cystic neoplasms of the pancreas

Cystic neoplasms of the pancreas, including 4 patients with serous cystadenoma and 11 with mucinous cystic neoplasm, were studied. Serous cystadenomas composed of epithelial cells with glycogen in the cytoplasm were benign in all, whereas mucinous cystic neoplasms consisted of four benign, two borderline, and five malignant lesions. The average size was 1.8 cm in the greatest diameter in benign mucinous cystadenomas, about 5 cm in borderline tumors, and more than 8 cm in mucinous cystadenocarcinomas. Histologically, in all borderline and malignant lesions, the cysts contained areas lined with epithelium and had a benign appearance, comparable with that of mucinous cystadenoma. These observations suggest a borderline or malignant disease in the case of a benign mucinous cystadenoma. An immunohistochemical study for carcinoembryonic antigen and carbohydrate antigen 19-9 showed denser and diffuse localizations of such materials in the cytoplasm and the stroma in the case of malignant lesions, as compared to findings in borderline and benign cases.     

Operative indications for cystic lesions of the pancreas with malignant potential--our experience

BACKGROUND/AIMS: There are still many important but unclear points regarding the differential diagnosis and operative indications of cystic lesions of the pancreas with malignant potential. Studies of the clinicopathological and molecular biological characteristics of such diseases are necessary. In this paper, we discuss operative indications for this condition based on a review of the literature and our own experience. METHODOLOGY: Seven cases of serous cystadenoma and 9 cases of mucinous cystadenoma or cystadenocarcinoma of the pancreas that were operated on or autopsied in our department from 1980 to 1996 were analyzed clinicopathologically. Small cystic lesions incidentally found in 300 autopsied cases were also studied. Finally, mucin-producing tumors described in several reports were reviewed, and the branch type of this tumor was especially investigated. RESULTS: A marked disappearance of pancreatic acini in the upstream pancreas was found when serous cystadenoma became large. Papillary projection was histologically found in all of the cases. Tumorous invasion to the interstitium was suspected in tumors more than 5 cm in diameter, and malignancy was reported when tumors were larger than 6 cm. As for mucinous cystadenocarcinoma, the patients had a poor prognosis. In 2 of 42 cases with a pseudocyst, small duct cell carcinoma was incidentally found adjacent to the pseudocyst on the duodenal side. With regard to branch-type intraductal papillary neoplasm, 80% of the tumors larger than 4 cm were malignant. Most of the small cystic lesions found in elderly autopsy cases were accompanied by hyperplastic epithelia without evidence of malignancy. CONCLUSIONS: Based on our experience, an operation should be considered and resection is recommended under the following circumstances: 1) cystic lesions in the body and tail of the pancreas in middle-aged women; 2) typical serous cystadenoma larger than 4 cm; 3) mucinous cystadenoma of any size; 4) branch-type intraductal papillary neoplasm larger than about 3 cm; and, 5) pseudocysts of unknown cause. Small cystic lesions in elderly patients should not necessarily be operated on, but should be followed-up carefully.     

Macrocystic form of serous pancreatic cystadenoma

OBJECTIVES: Macrocystic serous cystadenoma of the pancreas are benign lesions with sometimes difficult diagnostic issues. We aimed to describe clinicopathological and imaging features with cyst fluid analysis in a series of patients undergoing surgery for macrocystic serous cystadenoma. METHODS: Eight patients underwent pancreatic resection for a macrocystic lesion of the pancreas diagnosed on ultrasonography or CT. Endoscopic ultrasonography and preoperative fine-needle aspiration were performed in seven patients. Immunohistochemical analysis of the surgical specimen with antibodies to carcinoembryonic-antigen (CEA), carbohydrate antigen (CA) 19-9, estrogen receptor, and progesterone receptor antibodies was performed in all cases. RESULTS: Patients included seven women and one man, with a mean age of 48 yr. Lesions were incidentally discovered on ultrasonography in six patients and had a mean size of 3 cm (range, 1.5-5 cm). Endoscopic ultrasonography revealed millimetric cysts in three cases. In the seven aspirated cysts, cytological analysis was non-contributive, but biochemical analysis showed low content of CEA (< 5 ng/ml) and CA72.4 (< 40U/ml) in all but two. At histology, cysts were lined by clear cuboidal cells. They focally expressed CA19-9 but were negative for anti-CEA, antiestrogen receptor, and antiprogesterone receptor antibodies. Microscopic cysts in the wall of the lesions were demonstrated in five cases. CONCLUSIONS: Macrocystic serous cystadenoma is a particular variant of pancreatic serous cystadenoma. Endoscopic ultrasonography may be useful in detecting peripherally located millimetric cysts in unilocular lesions, and measurement of enzymes and tumor markers in cyst fluid may also contribute to the diagnosis showing low concentrations.     

Mucinous cystadenoma of the pancreas 17 years after excision of gallbladder because of a choledochal cyst

A 56-year-old woman who had undergone excision of the gallbladder because of a choledochal cyst had a tumorous lesion of the pancreas identified by upper abdominal ultrasonography, but an operation was not carried out, because there was no apparent increase in the cystic mass and no elevation of serum tumor markers. In October 2001, she was admitted to our hospital to check for malignancy because of elevated levels of the tumor marker Dupan-2. Abdominal enhanced computed tomography and upper abdominal ultrasonography revealed a large multilocular cystic mass in the body to tail of the pancreas. Endoscopic retrograde cholangiopancreatography showed elongation of the common duct that communicates with the common bile duct and the main pancreatic duct, indicating an anomalous arrangement of the biliary and pancreatic duct system. No apparent communications between the cystic mass and the main pancreatic duct were observed. In January 2002, the patient underwent a spleen-preserving distal pancreatectomy, and histopathological and immunohistochemical examinations led to the diagnosis of pancreatic mucinous cystadenoma with ovarian-like stroma. The mucinous cystadenoma was detected 17 years after the operation for the choledochal cyst. To the best of our knowledge, no documented case reports of mucinous cystadenoma of the pancreas associated with a choledocal cyst have been reported to date. We present here the first case report of pancreatic mucinous cystadenoma occurring in the body to tail of the pancreas, associated with a choledocal cyst.     

Risk of malignancy in serous cystic neoplasms of the pancreas

BACKGROUND: In contrast to mucinous cystic neoplasms of the pancreas, which are known to have considerable malignant potential, the serous variant is generally thought to be benign. There are, however, several reports of malignancy in serous cystic neoplasms of the pancreas. AIMS: To assess the risk of malignancy of serous cystic tumors of the pancreas and to investigate specific clinical and histological features. METHODS: Clinical and pathological characteristics of benign and malignant serous cystic neoplasms of the pancreas were investigated by a review of the literature and documented by a case of a serous cystadenocarcinoma and immunohistochemical analysis of a series of serous cystadenomas. Reviewing the literature prevalence, age and sex distribution of serous cystic neoplasms were analyzed. RESULTS: The prevalence of cancer among serous cystic neoplasms reported since 1989 was 3%. Serous cystadenoma of the pancreas present at an earlier age (61 years) than serous cystadenocarcinoma (66 years; p = 0.056) and are symptomatic in the majority of patients.Pathological examination of the primary tumor was not able to distinguish cystadenoma from cystadenocarcinoma in 38% of cases. In 25% the diagnosis of cancer was established only after growth of metachronous metastases. In the present case, nuclear atypia, papillary structures, proliferation marker Ki-67 and p53 protein were increased in the primary tumor and/or metachronous metastasis. CONCLUSION: Serous cystic neoplasms of the pancreas do have malignant potential with a risk of malignancy of 3% and should be surgically treated if the operative risk is acceptable. Routine analysis of genetic and proliferation markers may improve diagnosis of malignancy in these tumors.     

Mixed serous cystadenoma with mucinous cystadenoma of the pancreas

We report a case of serous cystadenoma of the pancreas mixed with mucinous cystadenoma. A 65-year-old woman was admitted to our hospital for evaluation of a palpable, elastic, hard mass measuring 6 cm in diameter in the right upper quadrant of the abdomen. A diagnosis of mucinous cystadenocarcinoma of the pancreas was made, and pancreatoduodenectomy was performed. The tumor was composed of a dominant compartment of macroscopic cyst, and its thick wall was filled with numerous microscopic cysts. The light microscopy findings with hematoxylin and eosin staining, and by the periodic acid-Schiff reaction, were almost perfectly consistent with the characteristics of microcystic or glycogen-rich cystadenoma, but the apical portion of the cytoplasm of the neoplastic cells was stained with Alcian blue at pH 2.4 and by the mucicarmine method. Neoplastic cells containing epithelial acidic mucin are usually found in mucinous cystadenomas. No K-ras point mutations were detected at the sites where neoplastic cells were present, whether or not they contained epithelial acidic mucin. Pancreatic serous cystadenomas that include a mucinous-cystadenoma component are extremely rare, and the difference between serous and mucinous cystadenomas is not always distinct.