Fine-needle aspiration of intrapancreatic accessory spleen, mimic of pancreatic neoplasms.
The patient was a 67-year-old asymptomatic man who had a 1.3-cm pancreatic tail mass incidentally detected by computed tomography. The mass was round, well-circumscribed, hyper-vascular with uniform enhancement. The image findings were highly suggestive of a pancreatic endocrine neoplasm. Other differential diagnoses included acinar cell carcinoma, solid pseudopapillary neoplasm, and, less likely, adenocarcinoma or lymphoma. To further classify the mass, the patient underwent endoscopic ultrasound (EUS)-guided transgastric fine-needle aspiration (FNA) and a total of 7 passes were performed. Two direct smears were made from each pass and the needle was then rinsed in CytoLyt solution (Cytyc Corporation, Marlborough, Massachusetts) for a cell block. One smear was air dried and stained with Diff-Quik stain (StatLab, McKinney, Texas) for onsite rapid assessment. The other smear was quickly fixed with Spray Fix (Surgipath Medical Industries, Inc, Richmond, Illinois) and stained with Papanicolaou stain before final evaluation. The on-site review of the Diff-Quik-stained smears revealed a polymorphous population of lymphocytes admixed with a subset of other inflammatory cells that included neutrophils, monocytes, plasma cells, and a few eosinophils. In addition, the presence of lymphoglandular bodies in the background was appreciated (Figure 1, A). The latter finding is compatible with a lesion of lymphoid origin. After confirming correct placement of the needle into the mass and the similarity of signal intensity between the mass and the spleen, a preliminary diagnosis of intrapancreatic accessory spleen (IPAS) was rendered. Review of the Papanicolaou-stained smears (Figure 1, B) showed cellular components that were identical to those of the Diff-Quik-stained smears. Further, the hematoxylin-eosin-stained cell block sections showed conspicuous thin-walled blood vessels in addition to the mixtures of lymphocytes and other inflammatory cells. Immunostaining with antibody against CD8 (Novocastra, Newcastle Upon Tyne, United Kingdom) was performed and showed strong positivity in endothelial cells of the thin-walled vessels (Figure 1, C). This immunoprofile was consistent with the origin of splenic sinuses. Overall, the cytologic findings and the result of immnuostaining supported a final diagnosis of IPAS, which was in agreement with the preliminary interpretation.
Accessory spleen is a congenital abnormality with normal pancreatic tissue in ectopic sites due to the fusion failure of splenic anlage. (1,2) It is estimated to occur in approximately 10% to 15% of the general population. (3) Most accessory spleens (80%) are located at the splenic hilum, while fewer than 20% are in the pancreatic tail. Other uncommon sites have also been reported, such as the wall of the jejunum, mesentery, and pelvis. The patients are usually asymptomatic and have an incidental, image-detected mass during an unrelated workup. Computed tomography and/or magnetic resonance imaging commonly identify the lesion as a round to oval, hypervascular mass with sharp borders and homogenous intensity. The enhancement pattern is similar to that of the spleen on contrast computed tomography and/or magnetic resonance imaging. However, radiographic features of accessory spleens are not specific and similar features may be observed in many neoplasms. (4,5) Review of the literature by Uchiyama et al (6) revealed that, among 11 cases of surgically removed IPAS, only 1 case was correctly diagnosed preoperatively owing to the presentation of idiopathic thrombocytopenic purpura. On the contrary, the remaining 10 cases were misdiagnosed as pancreatic endocrine neoplasms and patients therefore underwent surgical resection. (6) Currently, there are no clinical or radiographic criteria to distinguish IPAS from pancreatic neoplasms.
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What About the Role of EUS-Guided FNA in the Diagnosis of IPAS?
There are a few case reports of thoracic splenosis diagnosed by FNA cytology. (7,8) Schreiner et al (9) recently reported the first series of IPAS diagnosed by EUS-guided FNA. Accordingly, the cytologic features of IPAS were nonspecific and included predominantly small lymphocytes with a subset of histiocytes, conspicuous eosinophils, and plasma cells. The cell block sections showed conspicuous thin-walled blood vessels. Immunocytochemical staining of CD8 specifically highlighted endothelial cells of the thin-walled blood vessels. The authors stated that the latter findings were characteristic of splenic sinuses, as immunostaining of CD8 is negative in systemic endothelial cells and hemangioma. (9,10) Overall, EUS-guided FNA with the aid of CD8 immunostaining may make it possible to diagnose IPAS preoperatively and thus avoid unnecessary surgery.
Cytologic Differential Diagnoses of IPAS
Neoplasms mimicking IPAS include pancreatic endocrine neoplasm (PEN), acinar cell carcinoma (ACC), solid pseudopapillary neoplasm, well-differentiated adenocarcinoma, as well as lymphoma. Among these entities, PEN is the most common mimic of IPAS. (6) Pancreatic endocrine neoplasm is uncommon and represents 2% of pancreatic neoplasms. (11) There is no sex predilection. The tumor commonly occurs in older adults, although it may affect individuals in a broad age range. It may be associated with hereditary syndromes such as multiple endocrine neoplasia type I and von Hippel-Lindau syndrome. Pancreatic endocrine neoplasm often involves the pancreatic tail and is identified incidentally by radiologic imaging. A specimen of PEN prepared from FNA is hypercellular with single and loosely cohesive groups of cells. Some groups may exhibit a configuration of pseudorosettes. Commonly, the tumor cells appear relatively uniform with a round, polygonal, or plasmacytoid shape, although other cell types, that is, clear, oncocytic, and spindled, may be seen. Some cells may show binucleation or multi-nucleation. Classic salt-and-pepper chromatin pattern is easily appreciated and nucleoli may be conspicuous (Figure 2, A and B).
Acinar cell carcinoma is a rare malignant exocrine pancreatic neoplasm, which accounts for less than 2% of pancreatic malignancy. (12) Acinar cell carcinoma occurs in older adults, with a male predominance. It commonly involves the head of the pancreas. Smears of ACC prepared from FNA are cellular with tumor cells and naked nuclei in a clean background. The cells are arranged either singly or in loose clusters with acinar formation. The cytoplasmic borders are indistinct and cytoplasm is abundant, with granular, clear, or vacuolated appearance. The nuclei are either centrally or eccentrically located and prominent nucleoli are appreciated (Figure 3, A through C).
Solid pseudopapillary neoplasms compose 1% to 2% of pancreatic tumors. It is a disease of young women, with uncertain cellular differentiation. (13) Fine-needle aspiration smears are hypercellular with single and/or loose clusters of cells, as well as branching papillary fronds with central fibrovascular cores surrounded by 1 to several layers of cells. The cells appear monotonous and bland with scant to moderate amount of delicate cytoplasm and mildly atypical nuclei. The chromatin is granular with indistinct nucleoli. Intranuclear grooves are commonly identified (Figure 4, A and B). Myxoid, metachromatic stroma, and hyaline globules may be present. Rarely, necrotic debris may be seen when cystic degeneration occurs in the tumor.
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Adenocarcinoma is the fifth leading cause for cancer-related death in the United States, with a 5-year survival rate of 5% despite the progress of chemotherapy regimens and the increased success rate of pancreatoduodenectomy. Adenocarcinoma accounts for up to 85% to 90% of all pancreatic neoplasms. It is a disease of older adults with a male predominance. More than 50% occur in the head of the pancreas, 15% in the body, 5% in the tail, and the remaining 20% are multifocal. Although FNA cytologic diagnosis of moderately or poorly differentiated adenocarcinoma of pancreas is commonly straightforward, well-differentiated adenocarcinoma may present a diagnostic dilemma owing to the subtle, atypical features. With regard to the latter, the aspirates are hypercellular, with numerous, large, 2-dimensional sheets of neoplastic cells with well- to ill-defined cytoplasmic borders. The nuclei are unevenly distributed within the sheets and thus present a "drunken honeycomb" appearance. Nuclear atypia varies from mild to severe and N/C ratios range from low to high (Figure 5, A and B). It is not uncommon to see scattered, isolated cells with severe atypia.
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It is noteworthy to mention that distinguishing well-differentiated pancreatic adenocarcinoma from chronic pancreatitis may be extremely difficult not only for clinicians and radiologists but also for pathologists. Reports (14,15) indicate that chronic pancreatitis accounts for up to 75.9% of false-positive diagnoses. Cellularity of smears prepared from FNA of patients with chronic pancreatitis is variable. Fibrotic stromal fragments, along with variable amount of acinar tissue and mixed inflammatory infiltrates, may be seen. The background may contain prominent chalky calcific debris. Despite the cytologic atypia, normal architecture of honeycombing is maintained. Moreover, the lack of single atypical cells makes the diagnosis of adenocarcinoma less likely.
The role of ancillary studies, such as immunostaining, in establishing a definitive diagnosis of pancreatic epithelial neoplasms has been previously discussed. (11) In this regard, PEN is positive for pancytokeratin as well as neuroendocrine markers such as chromogranin and synaptophysin. The presence of diastase-resistant, periodic acid-Schiff-positive zymogen granules is characteristic of ACC. Acinar cell carcinoma is also immunoreactive for the antibody to cytokeratin, as well as enzymes such as trypsin, lipase, chymotrypsin, and a1-antitrypsin. (11) Solid pseudopapillary neoplasm reacts variably with neuroendocrine markers, cytokeratin, and pancreatic enzymes. In addition, nuclear staining of [beta]-catenin is characteristic for solid pseudopapillary neoplasm. (16)
Last but not least, the neoplastic entity that needs to be differentiated from IPAS is lymphoma. Like the smears of IPAS, those prepared from aspirations of lymphoma may contain a lymphoglandular bodies in the background. However, aspirates of non-Hodgkin lymphoma commonly contain monomorphous population of lymphocytes. On the other hand, identification of rare atypical cells resembling Reed-Sternberg cells, with a background polymorphous population of lymphocytes, should raise concerns for Hodgkin lymphoma. When in doubt during the on-site rapid assessment of FNA, collecting additional material for ancillary studies, such as flow cytometry and/or immunostaining, is highly recommended.
Epidermoid cysts may occur in IPAS, (5,6,17) which raises concerns for distinguishing IPAS from lymphoepithelial cyst, a nonneoplastic pancreatic lesion of unknown etiology. Aspirates of lymphoepithelial cyst reveal squamous cells, keratinous materials, lymphocytes, histiocytes, and cholesterol crystals.
Most patients with IPAS do not require surgical treatment unless IPAS becomes symptomatic owing to torsion, spontaneous rupture, or hemorrhage or causes hematologic disorders such as idiopathic thrombocytopenic purpura. (18) In contrast, virtually all pancreatic neoplasm/malignancies require surgery if the lesions are resectable. Therefore, the distinction between IPAS and pancreatic neoplasm/malignancy is extremely important. The use of EUS-guided FNA may provide a reliable diagnosis, thus preventing unnecessary surgery.
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Jingmei Lin, MD, PhD; Xin Jing, MD
Accepted for publication June 10, 2010.
From the Department of Pathology, University of Michigan Health System, Ann Arbor. Dr Lin is now located at the Department of Anatomic Pathology, The Cleveland Clinic, Ohio.
The authors have no relevant financial interest in the products or companies described in this article.
Presented at New Frontiers in Pathology: An Update for Practicing Pathologists, University of Michigan, Ann Arbor, Michigan, October 9, 2009.
Reprints: Xin Jing, MD, Department of Pathology, University of Michigan Health System, 1500 E Medical Center Dr, Rm 2G332, Ann Arbor, MI 48109 (e-mail: email@example.com).
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|Author:||Lin, Jingmei; Jing, Xin|
|Publication:||Archives of Pathology & Laboratory Medicine|
|Date:||Oct 1, 2010|
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