Ultrasound‐guided fine needle aspiration cytology in the diagnosis of hepatic and pancreatic perivascular epithelioid cell tumors: A case series

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors that can affect any part of the body. They can be sporadic or arise in the setting of tuberous sclerosis (TSC). In this article, we report a series of three hepatic and two pancreatic PEComas diagnosed preoperatively with ultrasound‐guided fine needle aspiration (FNA). All patients were female (age range 28‐70), had no personal history of TSC and presented with a single, localized painless mass. Rapid on‐site evaluation (ROSE) of cytologic samples was performed for all cases to evaluate for cellular content and adequacy of specimens. Direct smears and cell block preparations revealed a proliferation of medium to large polygonal epithelioid cells, with abundant eosinophilic and vacuolated cytoplasm, arranged in sheets and nests. On immunohistochemistry (IHC), neoplastic cells showed co‐expression of melanocytic and smooth muscle markers and a diagnosis of PEComa was rendered. PEComas of the pancreas and liver are rare neoplasms, but should always be considered when examining “clear cell” neoplasms, especially in young female patients. If good quality cytologic samples are obtained by FNA, a correct diagnosis can be achieved with the help of IHC. This is of particular importance in order to plan adequate surgical strategy and to avoid overtreatment.     

Primary pancreatic leiomyosarcoma with metastasis to the liver diagnosed by endoscopic ultrasound‐guided fine needle aspiration and fine needle biopsy

Primary pancreatic leiomyosarcomas are rare tumors of the pancreas that are usually diagnosed after resection or by biopsy. One case in the literature has utilized endoscopic ultrasound‐guided fine needle aspiration (EUS‐FNA) cytology. We report a second case of a primary pancreatic leiomyosarcoma that yielded diagnostic material on EUS‐FNA cytology. A 72‐year‐old female presented with 3–4 months of abdominal pain. A CT scan showed a large heterogeneous, lobulated pancreatic head and uncinate mass and multiple hypoattenuating liver lesions. An EUS‐FNA was performed on one of the liver lesions with a 25‐gauge needle, yielding an adequate sample with lesional cells. The initial read was a spindle cell neoplasm. A subsequent endoscopic ultrasound‐guided fine needle biopsy with a 22‐gauge needle was performed on the pancreatic head mass to rule out two primaries and to provide tissue for a mitotic index in the case of gastrointestinal tumor. Both the cell block of the EUS‐FNA and the core biopsy were equally cellular and showed interlacing spindle cells that stained positive for SMA and negative for DOG‐1, CD 117, and CD34. In addition, the core biopsy of the pancreas stained positive for Desmin. A diagnosis of a primary pancreatic leiomyosarcoma was made and the patient was started on systemic chemotherapy. Primary pancreatic leiomyosarcomas are rare pancreatic tumors that may yield diagnostic material by EUS‐FNA with a 25‐gauge needle. Diagn. Cytopathol. 2016;44:1070–1073. © 2016 Wiley Periodicals, Inc.     

Primary pancreatic diffuse large B‐cell lymphoma diagnosed by endoscopic ultrasound guided FNAC: A rare entity

Primary pancreatic lymphoma (PPL) is an uncommon neoplasm which can clinico‐radiologically mimic carcinoma. But the management of these patients differs from that of a carcinoma. Endoscopic ultrasound (EUS) guided fine‐needle aspiration (FNA) serves as a potential tool to identify pancreatic lymphomas and thus prevent an invasive diagnostic test. This case report describes the presentation and diagnosis of primary pancreatic lymphoma. A 37‐year‐old female presented with nausea, vomiting with signs of icterus and elevated liver function test and Bilirubin. Abdominal computed tomography (CT) revealed a hypodense lesion in the head of the pancreas. EUS guided FNA was performed and cytological material was collected. The lesion was diagnosed as Non‐Hodgkin Lymphoma (NHL) and subtyped as diffuse large B‐cell lymphoma‐germinal centre (DLBCL‐GCB) base on immunohistochemistry on cell block. The patient was started on rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (RCHOP) regimen. EUS guided FNA along with ROSE, cell bock, and immunocytochemistry helps in the diagnosis of primary pancreatic lymphoma.     

Endoscopic ultrasound‐guided fine‐needle aspiration diagnosis of merkel cell carcinoma metastatic to the pancreas

Merkel cell carcinoma (MCC) is a rare and highly aggressive primary neuroendocrine carcinoma of the skin with a high propensity for local, regional, and distant spread. Distant metastasis of MCC to the pancreas is uncommonly seen and may impose a diagnostic challenge cytologically. Here we report a case of MCC with pancreatic metastasis, which was diagnosed by endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA). The aspirates revealed both single and clustered epithelial cells with scant cytoplasm and round nuclei with stippled chromatin and inconspicuous nucleoli. Immunocytochemically, the tumor cells were positive for CK20, synaptophysin, CD56, and CD117. The neoplastic cells were also identified by flow cytometry as non‐hematopoietic cells which were positive for CD56 and negative for CD45. To our knowledge, this is only the second case report of MCC metastatic to the pancreas diagnosed by EUS‐FNA. There have been several reports of MCC metastatic to the pancreas diagnosed only at the time of surgical resection. However, a preoperative diagnosis allows for appropriate management while sparing a patient the morbidity of unnecessary procedures. Diagn. Cytopathol. 2014;247–252. © 2012 Wiley Periodicals, Inc.     

Incidental perivascular epithelioid cell tumor in an inguinal hernia sac

Perivascular epithelioid tumors (PEComa) are uncommon mesenchymal neoplasms demonstrating positivity for muscular and melanocytic immuno-markers. Included in this category are angiomyolipoma, lymphangioleiomyomatosis, and clear cell sugar tumors. Lesions which do not fit into these categories are classified as “not otherwise specified”. We present a case of an incidentally discovered PEComa within inguinal hernia sac contents in a 70-year-old woman. It consisted of spindled and epithelioid cells with bland oval nuclei, small nucleoli and clear to light eosinophilic cytoplasm. There was no atypia or mitoses. The lesion was strongly positive for HMB45 and smooth muscle actin. Pelvic soft tissue and peritoneal PEComas are rarely reported in literature and very little is known about their prognosis. We discuss the immunohistochemistry, differential diagnosis, and pathogenesis of PEComas.     

Cytological findings and BCL10 expression in pancreatic acinar cell carcinoma

BCL10 was recently demonstrated to be a biomarker for pancreatic acinar cell carcinoma, but whether altered BCL10 expression can be detected in cell block specimens is unclear. Here, we report a pancreatic acinar cell carcinoma with cytological findings that showed BCL10 expression in a cell block. A 72‐year‐old man presented with a pancreatic tumor and underwent endoscopic ultrasound‐fine needle aspiration (EUS‐FNA) with additional passes performed for cell block preparation. The EUS‐FNA cytology showed loose cohesive clusters with focal acinar‐ or gland‐like‐structures and prominent nucleoli. The preoperative diagnosis was well differentiated adenocarcinoma, and he underwent a pancreaticoduodenectomy. Histological examination revealed an acinar tumor structure with tumor cells staining positive for BCL10 and trypsin. The cell block specimen also demonstrated strong and diffuse BCL10‐positive staining. Based on these findings, this tumor was diagnosed as acinar cell carcinoma of the pancreas. This case demonstrates that BCL10 expression within cell blocks facilitates a differential diagnosis of acinar cell carcinoma. Diagn. Cytopathol. 2017;45:247–251. © 2016 Wiley Periodicals, Inc.     

Metastatic tonsillar squamous cell carcinoma masquerading as a pancreatic cystic tumor and diagnosed by EUS‐guided FNA

Metastatic carcinoma to the pancreas is uncommon and head and neck squamous carcinoma metastatic to the pancreas is extremely rare. Metastatic squamous cell carcinoma to the pancreas presents a unique diagnostic challenge: in addition to mimicking the rare primary squamous cell carcinoma of the pancreas based on cytologic, histologic, and immunohistochemical features, it may be mistaken for a cystic neoplasm of the pancreas because of its high predilection for cystic degeneration in metastatic sites. Herein, we report a case of tonsillar squamous cell carcinoma with a cystic pancreatic metastasis diagnosed by ultrasound‐guided fine needle aspiration biopsy (EUS‐FNA). This represents a third reported case of metastatic squamous cell carcinoma to the pancreas from the head and neck region. Metastatic squamous cell carcinoma should be considered in the differential diagnosis of EUS‐FNA during evaluation of pancreatic cystic lesion.     

Pancreatic fine‐needle aspiration cytology in patients < 35‐years of age: A retrospective review of 174 cases spanning a 17‐year period

Pancreatic lesions in young patients are relatively rare and, to our knowledge, the clinical value of pancreatic fine needle aspiration (FNA) in patients < 35 years of age has not been previously established by any other large retrospective studies. All pancreatic endoscopic ultrasound‐guided FNA (EUS‐FNA) cases performed on patients < 35 years of age were identified for a 17‐year period (1994–2010). All FNAs and all available correlating surgical pathology reports were reviewed. There were a total of 174 cases of pancreatic FNA performed on 109 females and 65 males under the age of 35 (range: 8–34, mean: 27 years). The FNA diagnoses included 37 malignant, 114 negative, nine atypia/suspicious, and 14 cases that were nondiagnostic. Of the 37 malignant FNA cases, the diagnoses included 18 pancreatic neuroendocrine tumors (PanNeT), 11 solid pseudopapillary neoplasms (SPN), five adenocarcinomas and three metastatic neoplasms. Histologic follow‐up was available in 22 of the 37 malignant cases diagnosed by FNA, and the diagnosis was confirmed in 21 cases. One pancreatoblastoma was misclassified as SPN on EUS‐FNA. False negative diagnoses were noted in three cases of low‐grade mucinous cystic neoplasm and one case of PanNeT. The most common type of neoplasms diagnosed by EUS‐FNA in patients < 35‐year old is PanNeT, followed by SPN with both tumors accounting for 75% of all the neoplasms encountered in this age group. The sensitivity and specificity for positive cytology in EUS‐FNA of the pancreas to identify malignancy and mucinous neoplasms were 90% and 100%, respectively. Diagn. Cytopathol. 2014;42:297–301. © 2013 Wiley Periodicals, Inc.     

Fine‐needle aspiration diagnosis of high grade adenoid cystic carcinoma metastatic to the pancreas

Pancreatic tumors are mostly primary tumors, with only rare metastatic tumors described in the literature. Here we report an unusual case of fine‐needle aspiration (FNA) diagnosis of high grade adenoid cystic carcinoma of the parotid gland metastatic to the pancreas. The aspirate smears were moderately cellular and revealed numerous basaloid neoplastic cells. The cytomorphologic differential diagnosis included primary pancreatic tumor with small cell morphology as well as metastatic tumors. By immunocytochemistry, the tumor cells were positive for cytokeratins (AE1/AE3, CAM5.2, and CK7), and CD117 (C‐KIT), and negative for CD45, WT1, synaptophysin, chromogranin, CD56, TTF‐1, and CK20. The cytomorphologic features and immunoprofile in our case were consistent with high‐grade carcinoma metastases from patient's known salivary gland primary. To the best of our knowledge, this case is the first reported encounter of FNA diagnosis of pancreatic metastasis with small cell morphology from a salivary gland neoplasm as primary site. Diagn. Cytopathol. 2015;43:117–120. © 2014 Wiley Periodicals, Inc.     

Increased diagnostic yield of endoscopic ultrasound‐guided fine needle aspirates with flow cytometry and immunohistochemistry

Endoscopic ultrasound‐guided fine needle aspiration (EUS‐FNA) is the most sensitive and specific test for establishing a tissue diagnosis for many gastrointestinal malignancies; however, cytologic morphology alone may not be definitive for subsets of tumors. Our aim was to quantify the impact of the broad application of flow cytometry (FC) and immunohistochemistry (IHC) on EUS‐FNA diagnostic yield. A retrospective chart review was performed on EUS procedures at a tertiary referral, academic medical center. All EUS‐FNA cases performed over a 21‐month period were examined. Of 606 EUS procedures reviewed during the period of study, 264 utilized FNA. After pancreatic cyst cases were excluded, 235 EUS‐FNA cases for 221 patients were selected for analysis. For cases with subsequent histological evaluation, including the subset utilizing FC/IHC, the sensitivity of EUS‐FNA was 89%, specificity was 100%, and accuracy was 91%. One quarter (58/235, 25%) of the tissue specimens underwent further testing by FC/IHC. There were 48 definitive diagnoses made in the subset utilizing FC/IHC. In 20 of the 48 diagnoses (42%), FC/IHC was deemed critical to the diagnosis, and without FC/IHC testing in those cases, the overall sensitivity and accuracy of EUS‐FNA would be reduced to 74 and 77%, respectively. FC/IHC allowed for six diagnoses rarely or not previously described by EUS‐FNA. Application of FC/IHC improves characterization predominantly for nonadenocarcinoma tumor subtypes and may lead to a diagnostic result for tumors not previously characterized by EUS‐FNA. With an adequate tissue sample, broad application of FC/IHC increases the diagnostic yield of EUS‐FNA. Diagn. Cytopathol. 2013;41:1043–1051. © 2012 Wiley Periodicals, Inc.     

Diagnostic approach to pancreatic tumors with the specimens of endoscopic ultrasound‐guided fine needle aspiration

Endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA) has enabled clinicians to histologically diagnose pancreatic tumors. However, EUS‐FNA specimens often result in tiny fragmented tissues, so auxiliary utilities are necessary. Using immunostaining of CK7, CDX2, neuroendocrine markers and KRAS mutation analysis, we examined 57 FNA cell block sections and 61 surgically‐resected specimens (25 invasive ductal carcinomas, 25 endocrine tumors, and 11 acinar cell tumors). In the majority of the matched pairs, the diagnoses between EUS‐FNA and surgical specimens were concordant using the following criteria: neuroendocrine markers negative, CK7 positive, and mutated KRAS gene for invasive ductal carcinomas; neuroendocrine markers diffusely positive, CK7 and CDX2 negative, and wild‐type KRAS gene for well‐differentiated endocrine tumors; and neuroendocrine markers no more than focal positive, CK7 and CDX2 with various staining patterns, and wild‐type KRAS gene for acinar cell carcinomas. Expression of CK7 and/or CDX2 in addition to KRAS mutations were occasionally seen in endocrine carcinomas, but not in well‐differentiated endocrine tumors, suggesting that ductal differentiation in an endocrine tumor may be a predictor of aggressive disease. The usefulness of these markers was confirmed using 13 additional pancreatic tumors, prospectively. Although minimal in selection, these markers are helpful in making diagnosis from EUS‐FNA specimens of the major pancreatic tumors.     

Metastatic pheochromocytoma to the pancreas diagnosed by endoscopic ultrasound‐guided fine needle aspiration: A case report and review of literature

Pancreatic pheochromocytomas are rare and typically diagnosed by local resection. We present the first reported case of metastatic pheochromocytoma to the pancreas diagnosed by endoscopic ultrasound‐guided fine needle aspiration (EUS‐FNA) and cytology. A 67‐year‐old female presented with 2 to 3 months of abdominal pain. A CT scan showed a large mass in the head of the pancreas engulfing the superior mesentery artery and vein, along with a large mass in the left adrenal gland. An EUS‐FNA was performed on the pancreatic mass with a 22‐gauge needle, yielding an adequate sample. Papanicolaou stain, Diff‐Quik, and cell block showed loosely cohesive clustered tumor cells and singly dispersed pleomorphic naked tumor nuclei with anisonucleosis and cytoplasmic vacuolization. Tumor cells stained positive for synaptophysin, chromogranin A, and CD56 and negative for CK AE1/3 and CK AE1/3‐CAM5.2 cytokeratin cocktail. Because of cytokeratin negativity, diffusely positive neuroendocrine markers, and the presence of an adrenal mass, a metastatic malignant pheochromocytoma was suspected. Additional testing showed elevations in plasma metanephrines and normetanephrines, urine metanephrine‐to‐creatinine and normetanephrine‐to‐creatinine ratios, and serum chromogranin A. An iodine¹²³‐metaiodobenzylguanidine (MIBG) scan was obtained, which showed significantly increased MIBG uptake in the left adrenal lesion. A diagnosis of metastatic malignant pheochromocytoma was made. Surgical oncology was consulted, who recommended against resection of the adrenal mass in favor of outpatient management. Metastatic pheochromocytoma to the pancreas are rare tumors that may yield diagnostic material by EUS‐FNA with a 22‐gauge needle.     

The usefulness of S100P,mesothelin, fascin,prostate stem cell antigen,and 14‐3‐3 sigma in diagnosing pancreatic adenocarcinoma in cytological specimens obtained by endoscopic ultrasound guided fine‐needle aspiration

Endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA) of the pancreas is an efficient and minimally invasive procedure for the diagnosis and staging of pancreatic adenocarcinoma. Because of some limitations of EUS‐FNA in diagnosis of well‐differentiated or early stage cancers, the purpose of this study is to assess the added benefit of immunohistochemistry. We studied five proteins overexpressed in pancreatic adenocarcinoma, namely, prostate stem cell antigen, fascin, 14‐3‐3 sigma, mesothelin and S100P utilizing immunohistochemistry on paraffin sections from cellblocks obtained by EUS‐FNA. Sixty‐two cases of EUS‐FNA of the pancreas that had follow‐up histological and/or clinical diagnosis and sufficient material in cell blocks were included. Using histological diagnosis and/or clinical outcome as the reference standard, EUS‐FNA shows the highest sensitivity (95%) and specificity (91%) and is superior to any marker in this study. Among five antibodies, S100P reveals the best diagnostic characters showing 90% of sensitivity and 67% of specificity. Fascin shows high specificity (92%) but low sensitivity (38%). Mesothelin has a moderate sensitivity (74%) and low specificity (33%), PSCA and 14‐3‐3 show high sensitivity but zero specificity. S100P and mesothelin were useful in nine indeterminate cases. S100P correctly predicted six of seven cancers and one of one without cancer and mesothelin correctly diagnosed five of seven cancers and one of two noncancers in this group. EUS‐FNA cytomorphology is superior to any of the immunohistochemical markers used in this study. Use of S100P and mesothelin in cytologically borderline cases can increase the diagnostic accuracy in this group. Diagn. Cytopathol. 2014;42:193–199. © 2011 Wiley Periodicals, Inc.     

Fine‐needle aspiration findings of a rare hematopoietic neoplasm presenting as obstructive jaundice

A 51‐year‐old female who presented with obstructive jaundice was found to have masses in the pancreatic head and tail as well as suspicious liver and periaortic masses on imaging. Aspiration cytology of the pancreatic tail mass showed abundant large single cells with vacuolated eosinophilic cytoplasm, marked nuclear pleomorphism, large bizarre irregular nuclei, binucleation, and prominent nucleoli. Numerous cells also showed intracytoplasmic black to brown pigmentation. A cell block was obtained and extensive immunohistochemical staining was performed. S‐100, HMB‐45, Sox10, pancytokeratin, CK7, RCC antigen, synaptophysin, HepPar 1, inhibin, CD45, CD21, and CD123 were negative, making melanoma, epithelial malignancies, lymphoma, follicular dendritic and plasmacytoid dendritic cell neoplasms less likely. CD4 and CD56 showed partial positivity, and CD68, CD163, and CD14 were positive, supporting the diagnosis of histiocytic sarcoma. Surgical specimens and immunohistochemistry confirmed the cytologic findings. Histiocytic sarcoma is a rare aggressive malignancy of histiocytic origin with most cases presenting in adults in extranodal sites, most commonly the intestinal tract. Few cases are reported in the literature, presenting diagnostic challenges for cytopathologists when seen on fine‐needle aspiration. We present the first reported case of histiocytic sarcoma presenting as a pancreatic mass, diagnosed by endoscopic ultrasound guided fine‐needle aspiration (EUS‐FNA). This entity is rarely described on cytology and arose in a location in which EUS‐FNA is the diagnostic modality of choice. This case study highlights that cytopathologists should be aware of histiocytic sarcoma occurring in extranodal locations accessible by EUS‐FNA and be familiar with the cytomorphologic appearance.     

Malignant perivascular epithelioid cell tumour of the fibula: a report and a short review of bone perivascular epithelioid cell tumour

Perivascular epithelioid cell tumour (PEComa) is a term applied to a family of mesenchymal tumours composed of varying proportions of spindle and epithelioid cell components associated with HMB-45 expression. PEComa rarely arises in the soft tissue, visceral organs, skin and bone. This report details an instance when a purely epithelioid PEComa arose from the right fibula of a 52-year-old Chinese woman without features of tuberous sclerosis complex. The excision specimen disclosed an epithelioid tumour with a nested pattern associated with areas of nuclear pleomorphism, mitotic activity, necrosis and vascular invasion in addition to HMB-45 expression on immunohistochemistry. To the best of the authors' knowledge, this represents the first case of a histologically malignant PEComa of the bone. A short review of primary bone PEComas and potential problems in diagnosis is presented.     

Perivascular epithelioid cell tumor of the uterine cervix identified on a conventional cervical smear

Perivascular epithelioid cell tumors (PEComas) most frequently involve the uterus, particularly the uterine corpus and very occasionally the cervix. One case of PEComa identified using a conventional cervical smear has previously been documented. Herein, we present the second such case. The patient was a 51‐year‐old woman with abnormal genital tract bleeding. Samples collected for conventional cervical smears were submitted for cytopathological examination, which revealed discohesive monotonous tumor cells showing epithelioid morphology, ample cytoplasm that was pale to weakly eosinophilic, and mildly enlarged nuclei. The cytopathological features were well correlated with histopathological findings. Upon immunohistochemistry, the tumor cells were positive for both melanocytic and smooth muscle markers. Based on these findings, PEComa was diagnosed. Subsequently, a total hysterectomy with bilateral salpingo‐oophorectomy was performed, revealing that the tumor (28 × 22 × 12 mm) was located at the superficial part of the endocervix. We propose that the cytopathological findings described herein can guide the diagnosis of PEComa, even though this tumor is rare. Diagn. Cytopathol. 2015;43:1011–1016. © 2015 Wiley Periodicals, Inc.     

Diagnosis of metastatic pancreatic mesenchymal tumors by endoscopic ultrasound‐guided fine‐needle aspiration

Involvement of the pancreas by metastatic sarcoma is rare, and can prove challenging to differentiate from sarcomatoid carcinomas which occur more commonly. The endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA) technique has been successfully used for the diagnosis of pancreatic carcinomas whether primary or metastatic, and is now considered the most effective noninvasive method for the identification of pancreatic metastases. However, to date very few reports detail the diagnosis of mesenchymal neoplasms by EUS‐FNA. Herein, we report a series of four patients who underwent EUS‐FNA of the pancreas, where the diagnosis of metastatic sarcoma was made based on morphology and ancillary studies. The cases include metastases of leiomyosarcoma, liposarcoma, alveolar rhabdomyosarcoma, and solitary fibrous tumor. The history of a primary sarcoma of the chest wall, mediastinum, and respectively lower extremity was known for the first three of these patients while in the case of the solitary fibrous tumor a remote history of a paraspinal “hemangiopericytoma” was only elicited after the EUS‐FNA diagnosis was made. We conclude that EUS‐FNA is efficient and accurate in providing a diagnosis of sarcoma, even in patients without a known primary sarcoma, thus allowing institution of therapy without additional biopsies. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Large platelet aggregates in endoscopic ultrasound‐guided fine‐needle aspiration of the pancreas and peripancreatic region: A clue for the diagnosis of intrapancreatic or accessory spleen

Intrapancreatic and intraabdominal accessory spleens (IPIASs) are rarely encountered in endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA) biopsies. However, as incidentally discovered IPIAS can mimic a benign or malignant pancreatic neoplasm on imaging studies, a definitive diagnosis made by EUS‐FNA can avert an unnecessary surgical intervention or additional radiologic follow‐up. We report five cases of intrapancreatic splenules and one case of accessory spleen (AS) in which a definitive diagnosis was made on EUS‐FNA. Previously recognized FNA cytomorphologic features of splenic tissue, including ASs and splenosis, are endothelial cells and polymorphous lymphocytes admixed with neutrophils, eosinophils, plasma cells, histiocytes, and lymphoglandular bodies. We describe the additional finding of abundant large platelet aggregates as another distinguishing feature of splenic tissue on FNA. In all six cases, large platelet aggregates were identified along with polymorphous lymphoid cells, lymphoglandular bodies, loose aggregates of endothelial cells and scattered or aggregated bland spindle cells. A review of 10 consecutive cases of EUS‐FNA‐sampled benign intraabdominal lymph nodes showed that the presence of large platelet aggregates, three‐dimensional aggregates of lymphoid cells and of bland slender spindle cells and the absence of follicular germinal cell components (tingible body macrophages and lymphohistiocytic aggregates) are useful in differentiating IPIASs from reactive lymph nodes. Immunoperoxidase stains were useful to confirm a suspected IPIASs by showing CD31‐positive acellular flocculent material, consistent with large platelet aggregates and a rich CD8‐positive endothelial cell network between CD45‐positive lymphoid cells and CD68‐positive histiocytes in all six cases. Diagn. Cytopathol. 2013;41:661–672. © 2013 Wiley Periodicals, Inc.