Fine needle aspiration cytomorphology of mucinous nonneoplastic cyst of the pancreas

[Simple mucinous cyst of the pancreas: Case-report and literature review]

Simple mucinous cyst of the pancreas is an unusual pancreatic cyst, first described by Kosmahl et al. in 2002 with 5 cases. We describe a case of simple mucinous cyst of the pancreas, followed by a literature review. The physiopathology of this cyst is still unclear. It is an epithelial cyst, presenting as unilocular cystic lesion of the pancreatic body or tail, with a clear content, and no communication with the pancreatic duct. Microscopically, the cyst is lined by mucin-producing cells with mild atypia, and contains a fibrous wall without ovarian-like stroma. The prognosis is excellent, as no recurrent disease and progression to malignancy have been described. The non neoplastic origin of this lesion is debated, as cases with KRAS mutation and intra-epithelial neoplastic lesions have been recently reported. It is important to distinguish this lesion from macrocystic serous cystadenoma, mucinous cystic neoplasms and intraductal papillary mucinous neoplasms, by clinical, radiological and pathological features, as the treatment varies from simple surveillance to surgical resection.

Mucinous nonneoplastic cyst of the pancreas: CT and MRI appearances

PURPOSE

The purpose of this retrospective study was to evaluate imaging features of mucinous nonneoplastic cyst (MNNC) of the pancreas.

MATERIALS AND METHODS

Three (0.9%) patients with MNNC of the pancreas were found in 335 surgically resected pancreatic cystic lesions. Three MDCT and two MRI/MRCP studies were retrospectively reviewed.

RESULTS

Three cases of MNNC were found in the pancreatic neck, body, and tail, respectively. All the three cases were multilocular without communication with the main pancreatic duct (MPD), although upstream MPD dilatation was seen in two of the three cases. The signal intensity of the cyst fluid was low on T1-weighted, high on T2-weighted, and low on diffusion-weighted images. Cyst wall was thin in two cases, and the remaining case with obstructive pancreatitis showed visible cyst wall enhancement.

CONCLUSION

Imaging findings of MNNC of the pancreas were nonspecific without communication with the MPD. Cyst wall is typically thin without visible enhancement.

Simple Mucinous Cyst of the Pancreas: Review and Update

CONTEXT

- According to the 2014 Baltimore Consensus Meeting, simple mucinous cysts are defined as macroscopic cysts that are greater than 1 cm in size with gastric-type flat mucinous lining and minimal cytologic atypia without ovarian-type stroma. This lesion has not been widely recognized and has undergone a recent nomenclature change owing to unclear pathogenesis and biologic behavior. Mucinous pancreatic cystic lesions are generally considered precursor lesions of pancreatic adenocarcinoma. However, simple mucinous cysts generally have benign behavior with no recurrence or malignant transformation during short follow-up periods.

OBJECTIVE

- To provide a brief update and summary of the evolving nomenclature and current knowledge of simple mucinous cysts with an overview of their clinical, histopathologic, immunohistochemical, and molecular characteristics, as well as discussion of their differential diagnoses and biological behavior.

DATA SOURCES

- Analysis of the pertinent literature (PubMed) and authors' clinical practice experience based on institutional and consultation materials.

CONCLUSIONS

- Simple mucinous cyst has undergone a nomenclature evolution from mucinous nonneoplastic cyst to the current recommended name of simple mucinous cyst to reflect its unclear pathogenesis and progression. The malignant potential of simple mucinous cyst is still debatable. Recent molecular studies support a neoplastic process, but these cysts generally exhibit benign behavior without recurrence or malignant transformation. Therefore, accurate diagnosis of simple mucinous cysts is critical to distinguish them from other more common and aggressive mucinous pancreatic cysts. Studies with larger cohorts and longer clinical follow-up data are needed to further determine the biologic behavior of this cyst and implications for prognosis.

Molecular analysis of mucinous nonneoplastic cyst of the pancreas

Although a mucinous nonneoplastic cyst (MNNC) of the pancreas is defined as a benign nonneoplastic lesion with no malignant potential, its histogenesis and etiology are still uncertain. To explore the origin and development of MNNC, we searched for neoplasia-associated mutational change in oncogene and tumor suppressor genes. Specifically, we analyzed KRAS oncogene mutations by polymerase chain reaction/dideoxy DNA (Sanger) sequencing and tumor suppression gene deletion by loss of heterozygosity (LOH) using polymerase chain reaction/capillary gel electrophoresis for a panel of 16 polymorphic microsatellite repeat markers targeting common tumor suppression gene loci at 1p, 3p, 5q, 9p, 10q, 17p, 17q, 18q, 21q, and 22q on DNA isolated from the cystic lining epithelium microdissected from 15 surgically diagnosed MNNCs by microdissection of unstained histologic sections of fixed resection specimens. DNA mutations were demonstrated in 4 of 15 cases: 1 with KRAS mutation at codon 12 glycine (G) substitution by aspartic acid (D) (G12D), 1 with KRAS mutation at 12 glycine (G) substitution by arginine (R) (G12R), 1 with LOH at 10q (PTEN), and 1 with LOH at 17q (RNF43). Therefore, although the genomic mutation rate detected in MNNC is relatively low, our results indicate that MNNCs may acquire genetic alteration similar to low-grade pancreatic intraepithelial neoplasia, furthering debate of the true nature of these lesions.

Rare nonneoplastic cysts of pancreas

Pancreatic cysts represent a small proportion of pancreatic diseases, but their incidence has been recently increasing. Most pancreatic cysts are identified incidentally, causing a dilemma for both clinicians and patients. In contrast to ductal adenocarcinoma, neoplastic pancreatic cysts may be cured by resection. In general, pancreatic cysts are classified as neoplastic or non-neoplastic cysts. The predominant types of neoplastic cysts include intraductal papillary mucinous neoplasms, mucinous cystic neoplasms, serous cystic neoplasms, and solid pseudopapillary neoplasms. With the exception of serous type, neoplastic cysts, have malignant potential, and in most cases requires resection. Non-neoplastic cysts include pseudocyst, retention cyst, benign epithelial cysts, lymphoepithelial cysts, squamous lined cysts (dermoid cyst and epidermal cyst in intrapancreatic accessory spleen), mucinous nonneoplastic cysts, and lymphangiomas. The incidence of nonneoplastic, noninflammatory cysts is about 6.3% of all pancreatic cysts. Despite the use of high-resolution imaging technologies and cytologic tissue acquisition with endosonography, distinguishing nonneoplastic from neoplastic cysts remains difficult with most differentiations made postoperatively. Nonetheless, the definitive distinction between non-neoplastic and neoplastic cysts is crucial as unnecessary surgery could be avoided with proper diagnosis. Therefore, consideration of these rare disease entities should be entertained before deciding on surgery.

Endoscopic ultrasound-guided pancreatic fine-needle aspiration: potential pitfalls in one institution's experience of 1212 procedures

BACKGROUND

Endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) has emerged as the diagnostic modality of choice for mass lesions in the pancreas. The objective of the current study was to determine the accuracy and pitfalls of EUS-FNA in the diagnosis of pancreatic lesions in cases that involved follow-up surgical resection.

METHODS

Cases of EUS-FNA of pancreatic lesions performed from 2007 to mid-2012 for which subsequent surgical resection was performed were retrieved from the department's database. The accuracy of the cytologic diagnosis was assessed using the histological diagnosis as the gold standard. The sensitivity, specificity, positive predictive value, and negative predictive value were calculated. "Neoplastic," "suspicious," and "malignant" were classified as a positive cytologic diagnosis. In one calculation method, "atypical" was also included as a positive cytologic diagnosis whereas in another it was not considered to be a positive cytological result. The cases with a cytologic-histological discrepancy were reviewed to identify sources of errors.

RESULTS

A total of 1212 cases from 1104 patients (518 women and 586 men; age range, 18-94 years [average age, 63.5 years]) were identified. Cytologic diagnoses included 52 unsatisfactory, 224 benign, 129 atypical, 140 neoplasm, 35 suspicious, and 632 malignant diagnoses. Of these cases, 397 patients had histological follow-up information available. The sensitivity, specificity, positive predictive value, and negative predictive value were 83.2%, 85.9%, 95.9%, and 56.1%, respectively, with atypical cases excluded from the analysis. When atypical cases were included as a positive cytologic diagnosis, the sensitivity, specificity, positive predictive value, and negative predictive value were 86.7%, 67.9%, 90.7%, and 58.5%, respectively, and were 73.7%, 87.7%, 95.6%, and 48.0%, respectively, when atypical cases were included as a negative cytologic diagnosis. The major difficulty in EUS-FNA cytology was to differentiate pancreatic mucinous neoplasms from contaminants of gastric mucosa. Other pitfalls included differentiating mucinous neoplasm from extensive pancreatic intraepithelial neoplasia, and endocrine tumor from nesidioblastosis versus acinar cell carcinoma or intrapancreatic spleen.

CONCLUSIONS

EUS-FNA is a valuable tool for the diagnosis of pancreatic lesions, especially solid malignant tumors. Cytologic-radiological correlation is essential in differentiating pancreatic mucinous neoplasms from gastric mucosa, because the former usually are found to have characteristic features on imaging. Pathologists should be aware of the pitfalls in the cytologic diagnosis of pancreatic lesions that may significantly change the clinical management of the patients.