Electron Microscopy Renders the Diagnostic Capabilities of Cytopathology More Precise: An Approach to Everyday Practice

Cytology is a powerful diagnostic tool but to make definitive diagnoses, the use of ancillary techniques is imperative. By combining immunohistochemistry (IHC) and electron microscopy (EM), cytologic diagnoses can be as precise as those of surgical pathology. In the authors' daily practice of cytopathology they use all ancillary techniques available to them: histochemistry, IHC, EM, flow cytometry, and molecular pathology. IHC is frequently used as an ancillary technique in their daily practice but EM is many times their technique of choice. By the use of EM the authors can make specific final diagnoses, make the diagnosis more definitive, narrow the differential diagnosis, or determine the origin of a neoplasm with unknown primary site. Specimens obtained by fine-needle aspiration as well as all body fluids are suitable for EM. The limiting factor is to obtain the appropriate material with the diagnostic cells for ultrastructural examination. The common diagnostic dilemmas in the everyday practice of cytology are the following: mesothelioma vs. adenocarcinoma, neuroendocrine differentiation or not, the distinction of melanoma from adenocarcinoma and sarcoma, hepatocellular carcinoma vs. adenocarcinoma, and the origin of adenocarcinomas of unknown primary. The authors discuss how they approach these diagnostic problems in their everyday practice and how they incorporate EM in solving them.     

Electron microscopy renders the diagnostic capabilities of cytopathology more precise: an approach to everyday practice

Cytology is a powerful diagnostic tool but to make definitive diagnoses, the use of ancillary techniques is imperative. By combining immunohistochemistry (IHC) and electron microscopy (EM), cytologic diagnoses can be as precise as those of surgical pathology. In the authors' daily practice of cytopathology they use all ancillary techniques available to them: histochemistry, IHC, EM, flow cytometry, and molecular pathology. IHC is frequently used as an ancillary technique in their daily practice but EM is many times their technique of choice. By the use of EM the authors can make specific final diagnoses, make the diagnosis more definitive, narrow the differential diagnosis, or determine the origin of a neoplasm with unknown primary site. Specimens obtained by fine-needle aspiration as well as all body fluids are suitable for EM. The limiting factor is to obtain the appropriate material with the diagnostic cells for ultrastructural examination. The common diagnostic dilemmas in the everyday practice of cytology are the following: mesothelioma vs. adenocarcinoma, neuroendocrine differentiation or not, the distinction of melanoma from adenocarcinoma and sarcoma, hepatocellular carcinoma vs. adenocarcinoma, and the origin of adenocarcinomas of unknown primary. The authors discuss how they approach these diagnostic problems in their everyday practice and how they incorporate EM in solving them.     

The Utility of Electron Microscopy in Cytopathology

Background: The use of ultrastructural analysis in the diagnostic work-up of histologic specimens has been well studied but less is known about the utility of electron microscopy (EM) in cytopathology. Design: 149,006 non-gynecologic cytology cases at the Massachusetts General Hospital between the years 1993 and 2006 were searched to identify those in which material had been submitted for EM. Cytologic and EM diagnoses were correlated with available histologic diagnoses. The results were put into one of three categories: confirmatory, diagnostic, or insufficient material for diagnosis (IMFD). Results: Material for EM was obtained from 178 cytology cases that included 131 fine-needle aspirates (FNA) and 47 exfoliative specimens. EM provided additional diagnostic information beyond that offered by cytologic examination alone in 32% of cases, and in 48% of cases EM confirmed the cytologic findings. Insufficient material and discrepant results were noted for EM evaluation in 19% of cases and in 1% cases respectively. EM was most useful when applied to FNAs for subclassifying tumors as epithelial or mesenchymal (45.6%), for the diagnosis of non-neoplastic processes (15.7%) such as alveolar proteinosis and amyloidosis, and for the identification of microorganisms (12.2%). In our study, although EM was infrequently applied to exfoliative specimens to distinguish mesothelioma from adenocarcinoma, it proved to be very useful in this setting. Conclusion: When adequate material is obtained, EM can contribute significantly to the evaluation of both FNA and exfoliative cytology cases, including the diagnosis and subclassification of epithelial and mesenchymal tumors, non-neoplastic processes, and the identification of microorganisms.     

Molecular testing in cytology

In the era of personalized medicine, molecular testing plays a critical role in patient care. The rapid advance of molecular techniques, especially next-generation sequencing, makes molecular diagnosis feasible in daily practice. Molecular testing can be used as a valuable ancillary test to increase diagnostic sensitivity and specificity, especially in small biopsy or cytology samples. In addition, molecular testing plays an important role in selecting patients for appropriate treatment by detecting therapeutic and predictive biomarkers in tissue or cytology samples. Molecular studies can be applied in all cytology samples, sometimes with better results than histology. As molecular testing has become essential for patient care and is often requested to be performed in cytology samples, it is critical for cytopathologists to understand the basics of molecular diagnostic methods, indications for molecular testing, and how to best utilize different cytologic samples for this purpose. In this special issue, experts in various areas of cytopathology and molecular pathology review the literature and discuss the basics of molecular techniques and the application of molecular testing in various types of cytology samples. It is our hope that after reading the articles in this special issue, the readers can know better about the possibilities of molecular cytology, a very exciting field of pathology.     

Spindle-cell lesions of the mediastinum: Diagnosis by fine-needle aspiration biopsy

Spindle cells seen in fine-needle aspiration biopsy (FNAB) of the mediastinal lesions can be a component of a wide variety of benign and malignant conditions. Few of these conditions, however, are described in the FNA cytopathology literature. This review discusses the cytopathologic features, differential diagnoses, and potential pitfalls of a variety of lesions with a significant component of spindle cells encountered in mediastinal FNAB. The cytopathology files from four institutions were searched for cases of mediastinal FNAB containing a spindle-cell component that was a key or predominant cytologic feature of the diagnostic specimen. The cytomorphologic features of these cases were analyzed, and their differential features are discussed. Of 196 mediastinal FNABs, 22 (11%) were lesions with significant spindle-cell component: granulomatous inflammation (four); benign nerve sheath tumor (four); thymic cyst (two); spindle-cell thymoma (two); large-cell non-Hodgkin's lymphoma with sclerosis (two); nodular sclerosing Hodgkin's disease (two); liposarcoma (two); spindle-cell squamous carcinoma possibly arising in a teratoma (one); unspecified high-grade sarcoma (one); spindle-cell malignant melanoma (one); and nonspecific fibrous tissue (one). The cytologic features of each lesion were analyzed as an aid for accurate classification. These findings were correlated with radiologic and clinical information when available. The value of ancillary studies performed on aspirated material in selected cases was also reviewed. FNA of mediastinal lesions with significant spindle-cell morphology represents an infrequent and heterogeneous group of entities that may pose significant diagnostic challenges. This review presents the salient cytopathologic features of various spindle-cell lesions of the mediastinum with particular emphasis on differential diagnosis and pitfalls. The pathologist must use caution when interpreting these lesions and ancillary studies may be of significant value in selected cases. Diagn. Cytopathol. 1997;17:167–176. © 1997 Wiley-Liss, Inc.     

Fine-needle aspiration biopsy of nonteratomatous germ cell tumors of the mediastinum

We assessed the usefulness of fine-needle aspiration biopsy (FNAB) in the diagnosis of mediastinal germ cell tumors (GCTs). In the archives of 3 pathology departments, we found records of 7 patients with mediastinal GCTs who underwent mediastinal FNAB as part of the diagnostic workup. The FNAB smears, results of the immunocytochemical analysis, the corresponding histologic findings, and the clinical charts were reviewed. All patients were men (age range, 24-44 years; mean, 32 years). One patient had a history of testicular mixed GCT 10 years earlier. The 6 primary mediastinal GCTs consisted of 3 seminomas and 3 yolk sac tumors. Based on the cytologic features and immunocytochemicalfindings, a cytologic diagnosis of GCT was made in 5 cases, including the case of metastatic GCT In 2 cases, the differential diagnosis was between poorly differentiated carcinoma and GCT Results of ancillary studies were noncontributory in 1 case, and the aspirate of the second case demonstrated extensive necrosis. Our findings demonstrate that a diagnosis of mediastinal GCT, primary or secondary, can be established with a high degree of accuracy on the basis of FNAB. Immunocytochemical analysis helps confirm the diagnosis.     

The value of fine needle aspiration biopsy in the diagnosis and prognostic assessment of palpable breast lesions

In recent years there appears to be a growing movement toward the use of core needle biopsy (CNB) over fine needle aspiration biopsy (FNAB) for the detection of breast carcinoma. This tendency is caused in part by the idea that CNB can provide a more specific or definitive diagnosis as well as the belief that the assessment of prognostic/predictive factor is not possible or reliable on cytologic specimens. At our institution, FNAB of breast has been practiced for over 25 years with excellent cytologic-histological correlation. This practice has been beneficial not only for patients, but also for training physicians since nowadays a very small number of centers in the United States still routinely perform fine needle aspiration as a diagnostic tool in breast cases. To assess the diagnostic accuracy of FNAB in palpable breast lesions, we reviewed our experience during an 8-year-period and compared fine needle aspiration results with follow-up surgical specimens. From the cytology point of view, the lesions were divided as negative/benign, atypical/suspicious, positive, and insufficient. Only cases performed by pathologists were included. A total of 1,583 cases were retrieved from our archives. A definitive malignant diagnosis was reached in 357 cases. One-hundred and thirty-nine cases were classified as atypical/ suspicious, 135 cases had insufficient cells for establishing a diagnosis, and 952 were categorized as negative. A total of 408 follow-up surgical specimens were available for comparison with cytologic results. There were 19 false-negative, and no false-positive results were found. The majority of false-negative results were secondary to sampling errors. In 93% of the malignant cases, there was enough material obtained in cytological specimens to perform prognostic/predictive factors studies. Our data proves once again that FNAB is a reliable method for the initial evaluation and diagnosis of palpable masses of the breast. In addition, it also has the ability of providing necessary prognostic/predictive information, particularly for patients that may undergo neoadjuvant therapy.     

细胞病理学在经支气管镜超声引导针吸活检术中的作用

目的 探讨细胞病理学检查在经支气管镜超声引导针吸活检术(EBUS-TBNA)诊断中的作用及用于表皮生长因子受体(EGFR)基因突变分析的可行性.方法 回顾性分析复旦大学附属肿瘤医院2009年4月至2010年9月行EBUS-TBNA的连续病例200例,可取得细胞块的部分标本进行免疫组织化学染色(EnVision法),22例阳性病例还用细胞学标本进行EGFR基因突变分析.结果 200例中140例有组织学对照.细胞学诊断标本不充足24例(12.0％,24/200).良性病变42例(23.9％,42/176),可疑12例(6.8％,12/176),恶性肿瘤122例(69.3％,122/176).与组织学及临床共同诊断对照,细胞学的敏感度94.4％,特异度100％.细胞块及免疫酶标对准确分型及胸腔外转移性肿瘤的诊断有帮助.细胞学标本检测EGFR突变率36.4％ (8/22).结论 EBUS-TBNA细胞学是一种诊断肺癌及其纵隔淋巴结转移的准确、敏感和特异的方法.EBUS-TBNA细胞学标本是进行分子病理学检测的重要材料.     

Diagnostic accuracy of image-guided percutaneous fine needle aspiration biopsy of the mediastinum

Interpreting a fine needle aspiration biopsy (FNAB) from the mediastinum is challenging as this location may harbor many lesions, including primary and metastatic tumors. Image-guided transthoracic (percutaneous) FNAB is less invasive than mediastinoscopy or endoscopic-guided FNAB. The aim of this study was to determine the diagnostic accuracy of FNAB performed percutaneously for evaluating mediastinal lesions.A retrospective study of 157 consecutive CT-guided transthoracic FNAB of the mediastinum was performed (1988-2004). Direct smears (N = 145; average 13 slides/case), ThinPrep slides (N = 25), and adequate cell blocks (N = 131) were prepared from procured cytologic material. When needed, ancillary studies included immunocytochemistry (N = 53) and flow cytometry (N = 8). Subsequent histologic tissue diagnoses available for 68 cases were also reviewed.Patients were of average age 57 yr (range 1-88 yr), including 75 males and 82 females. A definitive diagnosis was rendered in 128 (82%) cases. Primary neoplasms (N = 38) included 24 lymphomas (6 Hodgkin and 18 non-Hodgkin), 7 thymomas, 1 thymic carcinoma, and 6 peripheral nerve sheath tumors. Metastases (N = 72) were mainly carcinomas (N = 71) and 1 melanoma. There were 4 non-neoplastic lesions (1 granulomatous process; 2 bronchogenic and 1 pericardial cyst), 1 case of undifferentiated malignant large cell neoplasm, 13 cases negative for malignancy, and 29 (18%) that were indeterminate, due largely to insufficient cellularity. Subsequent histologic diagnoses were concordant with FNAB diagnoses in 53/68 cases (78%). Nine FNAB were inadequate/nondiagnostic. There were 6 discordant cases, including 5 FNAB that were of adequate cellularity but interpreted as negative for malignant cells (on subsequent histology 2 turned out to be Hodgkin lymphoma, 2 carcinomas, and 1 diffuse large cell lymphoma), and 1 diagnosed as thymoma that on histologic evaluation was a thymic large cell lymphoma.Adequate diagnostic cytologic material was obtained by image-guided percutaneous FNAB of mediastinal lesions in 82% of our cases. Sufficient material was available to make cell blocks and perform ancillary studies when necessary. These data also show a high proportion of agreement (78%) between FNAB and subsequent histologic diagnoses for a wide variety of mediastinal lesions. The majority of discordant cases were primarily interpretive, with a final cytologic diagnosis negative for malignancy. Only one problematic case misdiagnosed on FNAB as thymoma was found on subsequent surgical excision to be a thymic large B cell lymphoma. Cases with nondefinitive FNAB diagnoses were largely due to sampling error and/or insufficient cellularity. Therefore, percutaneous FNAB of the mediastinum is a diagnostically helpful, minimally invasive procedure that can be performed in patients of all ages as part of the evaluation of a mediastinal mass lesion.     

Molecular techniques in cytopathology practice

In the last decade, new molecular techniques were introduced into pathology laboratories. Cytology also benefited from the innovations emerging from this new era. Molecular cytopathology (MCP) can be defined as molecular studies applied on all types of cytological specimens, namely gynaecology cytology, exfoliative non- gynaecology cytology and fine needle aspirates. The development of many new ancillary techniques has paralleled the emergence of clinical cytology as a major diagnostic specialty. Clinical applications of these techniques have been growing in the last decade. The widespread acceptance of liquid-based systems in gynaecological cytology emphasises the relation between cells and molecules. The increased use of morphology and molecular biology in human papillomavirus-induced lesions for example, showed the potential to optimise, in one single brushed sample, diagnosis and research. Cytology samples from serous effusions, the pulmonary tree, urine, and aspirations, among others, are now likely to be studied by different molecular techniques for diagnosis, prognosis, or even assessment of therapeutic targets. In this review, the main published results concerning the application of molecular techniques in different fields of cytopathology are highlighted, and their applications discussed.     

Hodgkin's disease mimicking suppurative lymphadenitis: a possible pitfall in fine-needle aspiration biopsy cytology

We report one case of nodular sclerosing Hodgkin's disease with uncommon pseudosuppurative presentations in fine-needle aspiration biopsy (FNAB) samples and on histopathologic material. The criteria for cytologic diagnosis include atypical mononuclear cells and diagnostic SR cells in the purulent exudate. This lesion is considered a possible pitfall in FNAB cytology of Hodgkin's disease.     

Neutrophil-rich Ki-1-positive anaplastic large cell lymphoma: a study by fine-needle aspiration biopsy

Fine-needle aspiration biopsy (FNAB) is an accurate, cost-effective method of evaluating lymphomas. The neutrophil-rich variant of anaplastic large cell lymphoma (NR-ALCL) is a rare non-Hodgkin lymphoma. To our knowledge, we present thefirst study of NR-ALCL by FNAB cytology. Histologic confirmation was available for both patients. Both cases were positive for Ki-1 (CD-30) and were either T-cell or null-cell phenotype. FNAB specimens were highly cellular with a single-cell pattern composed of pleomorphic tumor cells, "hallmark" tumor cells, and a background rich in neutrophils that occasionally obscured tumor cells. Diagnosis on FNAB is difficult owing to the rarity of this tumor, its resemblance to Hodgkin lymphoma and other non-Hodgkin lymphomas that express CD30, its similarity to an infectious process, and its occasional confusion with metastatic carcinoma and melanoma. Reproducible cytologic features usually are present, and the diagnosis can be made conclusively by FNAB in conjunction with ancillary studies.     

Monophasic parapharyngeal synovial sarcoma diagnosed by cytology, immunocytochemistry, and molecular pathology: case report and review of the literature

Synovial sarcoma (SS) of the head and neck region are rare, accounting for less than 10% of all head and neck soft tissue sarcomas. A limited number of SS have been reported in the parapharyngeal space and these reports have all been based on histological examination of resection material. The diagnosis of monophasic SS on cytology is extremely difficult. We report the first case where a SS was correctly diagnosed on a fine needle aspirate by cytology with the assistance of immunocytochemistry and fluorescence in situ hybridization. We will emphasize the importance of ancillary techniques, such as immunocytochemistry and cytogenetic/molecular pathology, in avoiding diagnostic pitfalls and correctly diagnosing monophasic SS on cytologic material. We will propose an algorithmic approach to accurately diagnose parapharyngeal spindle cell neoplasms with the use of appropriate ancillary studies in conjunction to morphological features.     

Value of ancillary studies in fine-needle aspiration biopsy

With growing interest in the application of fine-needle aspiration biopsy (FNAB) in primary diagnosis of benign and malignant lesions, there has been a significant increase in the use of ancillary studies in the aspirated material. To assess the value of such studies, we reviewed 254 morphologically difficult aspiration biopsy cases obtained from different sites that underwent ancillary studies which included microbiology (MC), special stains (SS), immunocytochemistry (ICC), electron microscopy (EM) and flow cytometry (FC). Correlation with available histologic material and/or pertinent clinical information was used as a “gold” standard. In some cases, more than one ancillary study was performed on a single aspirate. According to the impact of the ancillary studies on the final diagnosis, these studies were divided into three categories: confirmatory/ diagnostic (22%), helpful (41%), and non-helpful (37%). Overall, more studies had positive contributory effect to the diagnosis (63%) than those with non-helpful results (37%). Among these adjunct testings, ICC were the most commonly used tests (135/296, 46%), while the EM studies had more positive impact in establishing the diagnosis. These findings emphasize the usefulness of ancillary testings in FNAB and justify the more selective use of these studies in the aspirated material. © 1995 Wiley-Liss, Inc.     

The accuracy of fine-needle aspiration cytology in the diagnosis of canine skin and subcutaneous masses

A retrospective evaluation of cytologic and histopathologic specimens from 300 cutaneous and subcutaneous palpable lesions in dogs was performed. Preoperatively, specimens were obtained from each formation by fine-needle aspiration biopsy (FNAB). Samples for histopathology were obtained by surgical excision biopsy or at necropsy. The concordance and the accuracy of FNAB for the diagnosis of neoplasia were determined using histopathology as a gold standard. Fifty-two cases were considered as unsatisfactory and were excluded from the study (retrieval rate 82.66%, n = 248). Neoplasia was diagnosed in 193 cytologic specimens. In 190 cases, neoplasia was confirmed by histology (98.44% true positive). Fifty-five cytologic specimens were classified as non-neoplastic. In 35 (63.63%) cases, the cytologic diagnoses were in agreement with the histologic diagnosis (true negative), while in 20 (36.37%) cases, a false negative diagnosis of neoplasia was made by cytologic examination. Based on the results from our study, there was 88.7% (220/248) agreement between cytologic and histologic diagnoses. In diagnosing neoplasia cytology had a sensitivity of 90.47%, a specificity of 97.22%, a positive predictive value of 98.44%, and a negative predictive value of 63.63%.     

Cytologic-histologic correlation of nongynecologic cytopathology cases: separation of determinate from indeterminate cytologic diagnoses for analysis and monitoring of laboratory performance

Much of the literature on the quality-assurance aspect of cytologic-histologic correlation (CHC) has focused on gynecologic cytology. For nongynecologic cytopathology, the process is complicated by the use of determinate (positive for malignant cells, negative for malignant cells) and indeterminate (atypical, suspicious, or follicular lesion) diagnostic categories. Here, we illustrate our routine methodology for analyzing CHC data on nongynecologic cytopathology cases by separating determinate from indeterminate cases. A focused list of determinate and indeterminate cytopathology cases with surgical pathology correlation is generated each week. The determinate cases are ascertained as true positive (TP), true negative (TN), false positive (FP), or false negative (TN). The discrepant cases (FP and FN) are investigated to determine the cause (sampling, interpretation, or screening). For indeterminate cases, the surgical pathology outcome (benign, malignant) and suitability of the cytopathology category utilized are reviewed. For the focused period of 4 mo, sensitivity was 70% and specificity was 100%. The most common reason for false-negative diagnoses was a sampling problem in the cytologic specimen; there were no false-positive diagnoses. Malignant outcomes for follicular lesion, atypical, and suspicious diagnoses were 29%, 40%, and 76%, respectively. Data derived from regularly performed CHC are useful in reviewing the diagnostic performance of the laboratory.     

Accuracy of fine needle aspiration biopsy processed by cytologic smear and cell block techniques for the diagnosis of lacrimal gland tumors: a study of 48 cases

Objective: To study the accuracy of fine needle aspiration biopsy (FNAB) processed by smear cytology and cell block (CB) techniques for the diagnosis of lacrimal gland tumors (LGTs). Study Design: In a prospective study, we enrolled 48 consecutive patients with LGTs. Immediately after excision of LGTs, the tissues were underwent FNAB with 23-gauge needles. The FNAB samples were processed to produce cytologic smears and CB from which slides were cut for immunohistochemical staining. The remainders were submitted for routine histopathologic processing. The diagnostic value of FNAB was assessed by comparing the FNAB diagnoses to those made by routine histopathology. Results: Cytopathologic evaluations based on smear cytology and CB with sections stained immunohistochemically can distinguish non-epithelial lesions from epithelial ones in all cases. The diagnostic sensitivities, specificities, and accuracies for distinguishing benign from malignant lesions were: cytologic smears--76%, 68%, and 71%, respectively; CB with immunohistochemical staining--88%, 87%, and 88%, respectively. The accuracy of the tissue diagnosis compared to routine histopathology was less for cytologic smears (58%) than for CB with immunohistochemistry (81%; P < 0.05). Conclusions: FNAB of LGT processed using a CB technique capable of producing immunohistochemically stained slides results in a greater percentage of accurate tissue diagnoses than do cytologic smears, when compared to routine histopathology.     

Tissue Harvester with Functional Valve (THFV): Shidham's device for reproducibly higher specimen yield by fine needle aspiration biopsy with easy to perform steps

Background  

Fine needle aspiration biopsy (FNAB) cytology has been a highly effective methodology for tissue diagnosis and for various ancillary studies including molecular tests. In addition to other benefits, FNAB predominantly retrieves the diagnostic loosely cohesive cells in the lesion as compared to the adjacent supporting stroma with relatively higher cohesiveness. However, FNAB procedure performed with currently available resources is highly skill dependent with inter-performer variability, which compromises its full potential as a diagnostic tool. In this study we report a device overcoming these limitations.     

The minefield of indeterminate thyroid nodules: could artificial intelligence be a suitable diagnostic tool?

Artificial intelligence (AI) is assuming a central role in anatomic pathology for ancillary diagnosis in histology and cytology. AI techniques can analyse large amounts of data and identify patterns that may not be visible to the human eye.Several studies have explored the potential of such techniques to improve the accuracy and efficiency of thyroid nodule diagnosis and to increase the sensitivity and specificity of thyroid cytopathology. Specifically, the indeterminate categories of ‘the Bethesda system for reporting thyroid cytopathology’ (TBSRTC) represent a major diagnostic challenge, and articles reported in this review highlight the potential of new AI technologies in improving the accuracy and standardisation of the cytological diagnosis of indeterminate thyroid nodules.Although a large amount of data supports AI's utility in thyroid cytopathology, further research is needed to integrate and standardise AI-based diagnostic systems in clinical workflows.     

The utility of ancillary techniques in effusion cytology.

We believe that, in general, immunocytochemical studies when used as a panel are the most helpful of the ancillary techniques in the workup of a difficult effusion cytology case. Routine histochemical stains for mucin should also be employed due to their low cost and simplicity, but suffer from lack of sensitivity and specificity. EM examination is especially helpful in the differentiation of metastatic carcinoma from mesothelioma, but lacks specificity due to overlapping ultrastructural features, and is both costly and labor intensive. Immunophenotyping by flow cytometry is useful in the workup of problematic lymphoid proliferations, but DNA analysis by flow cytometry is not useful as a screening technique. Fortunately, most effusion cytology cases will not need the use of ancillary studies, since the diagnosis will be accurately rendered based on the cytomorphologic findings. However, occasional cases will benefit from the use of specific ancillary studies, which can aid in making an accurate, specific, and rapid diagnosis in an otherwise challenging case.