Urine cytology in the detection of renal cell carcinomas - a territory-wide multi-institutional retrospective review of more than 2 decades.

INTRODUCTION: Compared with urothelial lesions of the upper urinary tract, the diagnostic performance of urine cytology in detection of renal cell carcinomas is underreported. This study aims to establish the role of urine cytology in the assessment of renal carcinomas by a multi-institute review of urine cytology from nephrectomy confirmed renal cell carcinomas, referenced against renal urothelial and squamous cell carcinomas. METHODS: Records of nephrectomy performed from the 1990s to 2020s at three hospitals were retrieved and matched to urine cytology specimens collected within 1 year prior. Patient demographics, specimen descriptors, and histology and staging parameters were reviewed and compared against cytologic diagnoses. RESULTS: There were 1147 cases of urine cytology matched with renal cell carcinomas, with 666 renal urothelial/squamous carcinomas for comparison. The detection rate for urothelial/squamous (atypia or above [C3+]: 63.1%; suspicious or above [C4+]: 24.0%) were higher than renal cell carcinoma (C3+: 13.1%; C4+: 1.5%) (p < 0.001). The positive rate for upper tract urine exceeded other collection methods at 45.0% (C3+) and 10.0% (C4+) (p < .01). Other factors associated with increased positive rates were male sex, collecting duct carcinoma histology, nuclear grade, and renal/sinus involvement (p < .05). Multivariate analysis revealed additional positive correlations with presence of sarcomatoid tumor cells, lymphovascular invasion, and perinephric fat involvement (p < .05). Larger lesion size and higher urine volume did not improve detection rates (p < .05). CONCLUSIONS: The detection rate of renal cell carcinomas is suboptimal compared with urothelial carcinomas, although urine samples collected from cystoscopy or percutaneous nephrostomy significantly outperformed voided urine specimens.

Urinary IL-6 and IL-8 as predictive markers in bladder urothelial carcinoma: A pilot study.

BACKGROUND: Cytokines are known to be a key a factor in numerous malignancies and to exert an important regulatory role in the tumor microenvironment. Interest has grown in understanding how cytokines modulate the tumor microenvironment and which cytokines may serve as markers of the tumor process; however, a complete picture of the cytokine landscape in bladder cancer remains unclear. METHODS: Fresh urine specimens with sufficient volume were collected at random intervals. The urine concentrations of IL-8 (CXCL8), CCL18, and CXCL9 were determined using the standard commercially available enzyme immunoassay. The urine concentrations of IL-6 were determined using the high sensitivity enzyme immunoassay kit. Urinary cytokine concentrations were normalized with urinary creatinine concentrations. RESULTS: Significantly elevated concentrations of IL-6 and IL-8 were detected in the urine from patients with urothelial carcinoma on follow-up compared to patients with benign follow-up. The presence of both IL-6 and IL-8 in the urine samples from the high grade urothelial carcinoma (HGUC) cohort revealed a clear discrimination when compared to samples from patients with benign follow-up. The presence of the combination of both IL-6 and IL-8 had a sensitivity of 90.0% and a specificity of 81.25%. Similar data were obtained when receiver operating characteristic analysis was performed on both IL-6 and IL-8 concentrations in the urine from patients with HGUC vs. the hematuria cohort. CONCLUSIONS: The presence of IL-6 and IL-8 in urine specimens may have predictive value for urothelial carcinoma. However, a large longitudinal study is required to statistically eliminate confounding factors and support this theory.

The Implementation of Nongynecologic Reporting Systems in Cytopathology Laboratories Is Highly Variable: Analysis of Data From a 2020 Supplemental Survey of Participants in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology.

CONTEXT­: In recent years, several reporting systems have been developed by national and international cytopathology organizations to standardize the evaluation of specific cytopathology specimen types. OBJECTIVE­: To assess the current implementation rates, implementation methods, and barriers to implementation of commonly used nongynecologic reporting systems in cytopathology laboratories. DESIGN­: Data were analyzed from a survey developed by the committee and distributed to participants in the College of American Pathologists Nongynecologic Cytopathology Education Program mailing. RESULTS­: Nongynecologic reporting systems with the highest rate of adoption were the Bethesda System for Reporting Thyroid Cytopathology, 2nd edition (74.1%; 552 of 745); the Paris System for Reporting Urinary Cytology (53.9%; 397 of 736); and the Milan System for Reporting Salivary Gland Cytopathology (29.1%; 200 of 688). The most common reason given for not adopting a reporting system was satisfaction with a laboratory's current system. Implementation varied among laboratories with regard to which stakeholders were involved in deciding to implement a system and the amount of education provided during the implementation process. CONCLUSIONS­: The implementation of nongynecologic reporting systems in cytopathology laboratories was highly variable.

Urine cytology in patients with gender confirmation surgery and hormone therapy: evaluation of urine cytology performance in an underserved patient population.

INTRODUCTION: There is a practice gap and educational need regarding urine cytology (UC) performance in patients with history of gender confirmation surgery (GCS) and/or hormone therapy (HT). This potentially impacts diagnostic accuracy in this medically underserved population. We report a methodology that identifies relevant cases and evaluates the performance of UC in this cohort. MATERIALS AND METHODS: Two institutional pathology archives from 2000 to 2021 were searched using relevant keywords to identify UC specimens from patients with GCS and/or HT for this retrospective study. For each specimen, patient demographics, relevant clinical history, and history of HT and/or GCS were noted. Each case was blindly reviewed by a cytopathologist according to The Paris System. RESULTS: A total of 32 UC specimens from 15 patients with history of GCS and/or HT were identified. There were 13 male to female and 2 female to male transgender patients. The original diagnosis was negative for high-grade urothelial carcinoma (NHGUC) in 24 of 32 (75%) and atypical urothelial cells (AUC) in 8 of 32 (25%) cases. The most common atypical features were irregular nuclear membranes and prominent small nucleoli in 7 of 8 (87.5%). Degenerative changes were present in 5 of 8 (62.5%). On re-review, with relevant clinical history, 100% of cases were re-classified as NHGUC. CONCLUSIONS: The original diagnosis of AUC in these cases likely reflects reactive changes post GCS and/or HT. This cohort may be at risk of AUC overdiagnosis, particularly if the pathologist is unaware of this clinical history. Pathologists need to recognize reactive cytomorphologic changes in these patients. Further multi-institutional studies are warranted to expand knowledge about UC performance in these patients.

Quality metrics in non-gynecologic cytology: results from the 2022 American Society of Cytopathology survey.

INTRODUCTION: Rapid advancements in minimally invasive techniques and the discovery of molecular biomarkers have resulted in major changes in the practice of non-gynecologic cytology and have highlighted a need for novel quality assurance (QA) metrics. MATERIALS AND METHODS: To obtain data regarding the current and desired usage, methods of collection, and barriers to the implementation of non-gynecologic cytopathology QA, an 18-question survey was constructed by the Clinical Practice Committee of the American Society for Cytopathology. RESULTS: A total of 206 responses were received. Respondents included 112 (54.4%) cytopathologists, 81 (39.3%) cytotechnologists, and 13 others. Almost all (97%) acknowledged the value of assessing QA metrics in cytology. The most commonly used QA metrics were cytotechnologist-pathologist diagnostic agreement and pathologist amendment rates. The desire to implement non-gynecologic QA metrics was significantly higher among academic hospitals, relative to nonacademic facilities. A combined manual and electronic approach to collect QA data was generally used (70% of institutions). QA metrics were more often collected by the cytology laboratory supervisors (59.5%), while the evaluation was most often performed by the cytology laboratory director (76.5%). Limited staffing and laboratory information system (LIS) capabilities were cited as major challenges in the implementation of novel QA metrics. CONCLUSIONS: While the collection of quality data might be perceived as an onerous task, a thoughtful selection of quality indicators, with an inbuilt search option in LIS, can contribute to the successful implementation of non-gynecologic QA metrics.

Nuclear membrane irregularity in high-grade urothelial carcinoma cells can be measured by using circularity and solidity as morphometric shape definitions in digital image analysis of urinary tract cytology specimens.

BACKGROUND: The Paris System for Reporting Urine Cytology defines objective (elevated nuclear/cytoplasmic ratio ≥0.7) and subjective (nuclear membrane irregularity, hyperchromicity, and coarse chromatin) cytomorphologic criteria to identify conventional high-grade urothelial carcinoma (HGUC) cells. Digital image analysis allows quantitative and objective measurement of these subjective criteria. In this study, digital image analysis was used to quantitate nuclear membrane irregularity in HGUC cells. METHODS: Whole-slide images of HGUC urine specimens were acquired, and HGUC nuclei were manually annotated using the open-source bioimage analysis software QuPath. Custom scripts were used to calculate nuclear morphometrics and perform downstream analysis. RESULTS: In total, 1395 HGUC cell nuclei were annotated across 24 HGUC specimens (48.1 ± 6.0 nuclei per case) using both pixel-level and smooth annotation approaches. Nuclear membrane irregularity was estimated by calculating nuclear circularity and solidity. Annotating at pixel-level resolution artifactually increases nuclear membrane perimeter, thus smoothing is necessary to better approximate a pathologist's assessment of nuclear membrane irregularity. After smoothing, nuclear circularity and solidity discriminate between HGUC cell nuclei with visually apparent differences in nuclear membrane irregularity. CONCLUSIONS: Nuclear membrane irregularity defined by The Paris System for Reporting Urine Cytology is inherently subjective. This study identifies nuclear morphometrics that visually correlate with nuclear membrane irregularity. HGUC specimens show intercase variation in nuclear morphometrics, with some nuclei appearing remarkably regular while others show marked irregularity. A small population of irregular nuclei generates most of the intracase variation in nuclear morphometrics. These results highlight nuclear membrane irregularity as an important, but not definitive, cytomorphologic criterion in HGUC diagnosis.

The international system for reporting serous fluid cytopathology: The initial project survey.

OBJECTIVE: An international panel in the field of body fluid cytology, supported by the International Academy of Cytology and the American Society of Cytopathology, conducted a survey to identify opinions and explore existing practice patterns regarding body fluid cytopathology. METHODS: The study group, formed during the 2018 European Congress of Cytology in Madrid, generated a survey of 54 questions related to the practice and taxonomy of body fluid cytology. The survey was available online from 28 August 2018 until 10 December 2018. Participants were invited through the websites and listserves of the professional societies. RESULTS: The survey collected 593 international participant responses. Questions pertained to practice patterns and diagnostic language. Information was collected regarding credentials, work setting, work volume (4-10,000 samples) and years in practice (0-60 years). The responses revealed variations in diagnostic practice and sample management. Direct smears and ThinPrep® preparations are the most popular methods, followed by Cytospin® and SurePath®. Most (70%) respondents perform ancillary studies on their material, with over 50% preferring a cell block preparation. Approximately 32% indicated that they are capable of performing genetic studies on the samples. Nearly 78% of participants would accept a two-stage cytology report, with a preliminary assessment followed by a final diagnosis that accounts for ancillary studies to generate a more precise cytological interpretation. Approximately one-third (36%) never report adequacy on body fluid samples. Most (78%) report a general category result (negative, atypical, suspicious, or positive) and 22% provide a detailed surgical pathology type report. Most (73.6%) participants believe that both Papanicolaou stains and a modified Giemsa stain (eg Diff Quik) should be standard preparations for all serous fluid cytology. CONCLUSIONS: The results of the survey demonstrated strong support for the development of a unified system for reporting body fluid cytopathology among respondents.

Cell blocks in cytology: review of preparation methods, advantages, and limitations.

Cell blocks are cytologic preparations that are processed as paraffin embedded blocks in a manner comparable to formalin-fixed paraffin-embedded tissue in surgical pathology. In addition to serving as an adjunct to other cytologic preparations for morphologic diagnosis, cell blocks play an increasingly important role as they yield tissue sections that can be utilized for ancillary testing such as immunohistochemical stains and molecular studies. While essentially universally viewed as playing a pivotal role in cytopathology practice, there are various factors that limit their use in practice and contribute to dissatisfaction with cell block quality. Cell block preparation, as opposed to tissue processing in surgical pathology, is more variable with many different protocols in use today. This review explores the most commonly used cell block preparation techniques currently in use with review of the unique advantages and limitations each method presents. The goal of this work is to serve as a resource that can aid in making more informed decisions about which cell block protocol may work best for individual laboratories.

The Diagnostic Challenge of Evaluating Small Biopsies from the Pancreatobiliary System.

Examination of fine needle aspirations and small core biopsies of the pancreas can be an extremely difficult and treacherous area for the diagnostic pathologist. The pancreas often yields small and often fragmented specimens, which, in combination with the morphologic overlap between numerous neoplastic and nonneoplastic mimickers, generate multiple potential diagnostic pitfalls. The authors review this challenging topic and provide insight into resolving these pitfalls using morphologic pattern recognition and ancillary testing.

High-risk human papillomavirus testing in cytology aspiration samples from the head and neck part 1: a review of the literature on available testing options.

Human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma is increasing in incidence and is often first diagnosed on a cytology fine needle aspiration (FNA) specimen of metastatic nodal disease of the neck. In the setting of oropharyngeal squamous cell carcinoma, HPV status defines the disease with HPV-associated tumors having better overall prognosis than those that are HPV negative. Furthermore, metastatic squamous cell carcinoma of the neck of unknown origin requires testing for HPV as a positive result suggests an oropharyngeal primary. As a result, HPV testing in aspirate samples is increasingly important for the proper diagnosis and treatment of patients with head and neck squamous cell carcinoma. Although HPV testing in cervicovaginal cytology specimens is common and well-established, testing in head and neck FNA samples remains challenging. p16 immunohistochemistry is an excellent surrogate marker for HPV in tumors of known or suspected oropharyngeal origin, but the criteria used in histologic specimens may not be appropriate in cytology samples. FNA samples are more frequently hypocellular, and cytology cell blocks have variable fixation and processing steps, limiting the utility of p16 immunohistochemistry. Other potential testing options have been reported in the literature including staining of aspirate smears and molecular testing of liquid-based samples. The American Society of Cytopathology Clinical Practice Committee recently surveyed the American Society of Cytopathology membership to determine the current state of HPV testing in aspirate samples, and this review article is designed to provide a summary of the current literature on various testing options in FNA samples.

High-risk human papillomavirus testing in cytology aspiration samples from the head and neck part 2: a survey of the American Society of Cytopathology community.

INTRODUCTION: High-risk human papillomavirus (HR-HPV) status is critical in the diagnosis of oropharyngeal squamous cell carcinoma, informing prognosis and choice of therapy. HR-HPV status additionally plays a key role in the evaluation of squamous cell carcinoma of unknown origin metastatic to cervical lymph nodes. Thus, HR-HPV testing of fine needle aspirate (FNA) specimens from the head and neck is invaluable for accurate diagnosis, prognostication, and treatment planning. MATERIALS AND METHODS: American Society of Cytopathology members were surveyed to understand the current state of HR-HPV testing on FNA samples from the head and neck. The survey focused on 3 main topic areas: practice setting of respondents, methods of collection and processing of aspirate specimens for HR-HPV testing, and validation of HR-HPV testing methodologies on aspirate samples. RESULTS: The survey reveals that laboratories employ various methods to detect HR-HPV in FNA samples, most commonly p16 immunohistochemical staining of cell block sections. Although some laboratories have independently validated their HR-HPV detection method, such validation is not universal. Finally, not all respondents currently have HR-HPV testing available, but approximately half of those without a testing method desire to make HR-HPV testing of FNA samples available. CONCLUSIONS: Survey responses highlight that various testing modalities are utilized for HR-HPV detection in aspirate samples. However, internal laboratory validation of HR-HPV testing for FNA specimens is not ubiquitous despite professional society recommendations.

Cross-contamination in cytology processing: a review of current practice.

INTRODUCTION: New cytopreparatory technologies decrease the need for direct smears in favor of an increased use of liquid-based cytology methods. Despite these practice changes, Clinical Laboratory Improvement Amendments continue to require that cytopathology laboratories have procedures to prevent cross-contamination (CC). While the incidence of CC is not well documented, specific cytologic preparations and specimens with a high potential for CC have not been generally defined by professional guidelines or consensus. The American Society of Cytopathology Clinical Practice Committee surveyed cytology practitioners to better understand current practice related to CC in cytology. MATERIALS AND METHODS: The survey focused on four topics: (1) practice settings and demographic data; (2) current practice for meeting CC requirements; (3) practice for rapid on-site evaluation; and (4) preparation types considered high risk for CC. The survey was sent to all American Society of Cytopathology and American Society for Cytotechnology members from July 1 to August 14, 2020. RESULTS: Ninety-eight percent of laboratories had a written CC policy, with 66.18% of the policies addressing rapid on-site evaluation CC procedures. Documented cases of CC were rare. Alcohol-fixed, direct smears of Pap-stained fluids were deemed the most likely to be impacted by CC. Cell block contamination during the histologic processing were reported by 56.20% of respondents. CONCLUSIONS: Changes in practice has resulted in decreased preparation types associated with a high potential for CC. Laboratories should follow a risk-based approach to define these cases. Knowledge of practice patterns among laboratories can guide the development and refinement of policy and procedures.

The Diagnostic Dilemma of Urothelial Tissue Fragments in Urinary Tract Cytology Specimens.

Since the release of The Paris System for Reporting Urinary Cytology (TPS), the assessment of urine cytology specimens has primarily focused on the detection of high-grade urothelial carcinoma (HGUC) and carcinoma in situ (CIS). Fortunately, the malignant cells in these lesions tend to be loosely cohesive, resulting in the natural exfoliation of individual malignant cells into the urine. However, HGUC/CIS lesions occasionally exfoliate larger fragments which can be difficult to assess due to cellular overlap and fragment three-dimensionality. Furthermore, reactive benign urothelial fragments and fragments from low-grade urothelial neoplasms (LGUN) may also be seen in urine specimens and contain atypical cytomorphologic features. As a result, the significance of urothelial tissue fragments (UTFs) is often unclear. Herein, we discuss the literature on UTFs before and after the implementation of TPS, as well as strategies to help overcome this diagnostic challenge.

The cytologic diagnosis of "atypical": Criteria and controversies.

Historically, the word "atypia" has been applied as a descriptor for cytomorphologic changes that deviate from what is expected; the assessment of deviant vs. expected cytomorphology is in the eye of the beholder. "Atypia" has been used to define a spectrum of changes which includes reactive changes known to be benign, but also for those concerning for malignancy, as well as everything in-between. The absence of a standardized reporting system and/or the lack of communication with clinicians can lead to the overutilization of the atypical category. When faced with a high rate of atypical diagnoses, clinicians are unable to distinguish patients who need more aggressive follow up from those that do not. Patients accessing their test results may not understand what an "atypical" diagnosis means; this can lead to unnecessary patient anxiety. Finally, atypical diagnoses can trigger reflex ancillary testing. This impacts ancillary test performance, as performance depends upon the pre-test probability of the cohort being tested. The inappropriate testing of low-risk patients can result in an increased number of false positive tests, which in turn lead to unnecessary procedures. Given these challenges, we present this special issue on "atypical" diagnoses in the field of cytopathology. In this issue, experts in various areas of cytopathology review the literature and discuss the diagnostic dilemmas of rendering "atypical" cytologic diagnosis, associated controversies, the effect on patient management, and abuse of ancillary studies. This issue also includes brief commentaries from clinicians from four different medical specialties who often encounter indeterminate cytologic diagnoses.

Indeterminate atypia in urinary tract cytology: Does it really matter?

The study of atypia in urinary cytology has been ongoing for decades but most studies have focused primarily on test performance in patients with concurrent biopsies and/or limited follow-up periods. While these data are useful, many studies fail to consider patient factors that may alter the pretest probability, which can subsequently affect test performance. An isolated diagnosis of malignancy in urinary cytology usually has a high positive predictive value and allows a urologist to conduct a rigorous workup of the patient to establish a tissue diagnosis. However, it is less certain how an atypical diagnosis impacts patient care, given that many patients have a history of bladder cancer and are already under surveillance with cystoscopy at regular screening intervals. Furthermore, a discrete negative urine cytology is unlikely to allow a patient to forego a cystoscopy procedure due to limitations in the sensitivity of urine cytology. Over the last several years, the introduction of The Paris System for Reporting Urinary Cytology (TPS) has improved the predictive value of atypical diagnoses, but additional studies are needed to evaluate the performance of these diagnoses in specific clinical situations. Such data could better inform urologists on how to manage patients with atypical diagnoses. This review discussed the diagnosis of atypia in urinary cytology and the impact of such a diagnosis in various clinical contexts.

A Review of Effusion Cytomorphology of Small Round Cell Tumors.

BACKGROUND: Small round cell tumors (SRCTs) are a broad category of diverse malignant tumors composed of monotonous undifferentiated cells. Involvement of serous fluids by SRCT is rare; however, the identification of exfoliated malignant cells is a crucial component of management and has significant implications for treatment and prognosis. The most common effusion tumors with SRCT morphology include Ewing sarcoma, synovial sarcoma, rhabdomyosarcoma (RMS), small-cell neuroendocrine carcinoma (SCNC), and desmoplastic SRCT, and the cytomorphologic distinction between these tumors is challenging. The purpose of this article is to describe the morphologic features of the most common SRCT in fluids and propose helpful ancillary testing. SUMMARY: Effusion SRCTs display similar primitive and undifferentiated morphologic features although each has subtle variations. Ewing sarcoma is a mesenchymal neoplasm and harbors characteristic translocations t(11;22) (EWSR1-FLI1) or t(21;22) (EWSR1-ERG). In fluids, Ewing sarcoma shows poorly differentiated cells of variable size with round to oval nuclei, prominent nucleoli, and scant cytoplasm. In contrast, synovial sarcoma typically involves extremities and expresses a fusion transcript in t(X;18) (SS18-SSX). This soft tissue neoplasm demonstrates uniform cells with irregular nuclear contours, characteristic nuclear folding, and scant cytoplasm. RMS is a neoplasm arising from skeletal muscle, and the alveolar subtype demonstrates a translocation in t(2;13) (PAX3-FOXO1). The malignant cells show a spectrum of small round cells and pleomorphic large cells with rhabdoid morphology. RMS cells characteristically express myogenin and MyoD1, markers of skeletal muscle differentiation. Although SCNC is not a classic SRCT, the morphology is similar. SCNC demonstrates tight clusters of malignant cells with nuclear molding and salt-and-pepper chromatin. This tumor classically has neuroendocrine differentiation and is positive for synaptophysin and chromogranin on immunohistochemistry. And last, desmoplastic SRCT typically presents as an intra-abdominal mass in young men and characteristically harbors the translocation t(11;22) (p13;q12) (EWSR1-WT1). Cytomorphologically, the tumor shows small monomorphic cells occasionally arranged as rosette-like structures. KEY MESSAGE: The diagnosis of SRCT can be made in effusion samples and is best achieved with a combination of morphologic features, clinical history, and ancillary testing.

Continuing Undergraduate Pathology Medical Education in the Coronavirus Disease 2019 (COVID-19) Global Pandemic: The Johns Hopkins Virtual Surgical Pathology Clinical Elective.

CONTEXT.­: In the early months of the response to the coronavirus disease 2019 (COVID-19) pandemic, the Johns Hopkins University School of Medicine (JHUSOM) (Baltimore, Maryland) leadership reached out to faculty to develop and implement virtual clinical clerkships after all in-person medical student clinical experiences were suspended. OBJECTIVE.­: To develop and implement a digital slide-based virtual surgical pathology (VSP) clinical elective to meet the demand for meaningful and robust virtual clinical electives in response to the temporary suspension of in-person clinical rotations at JHUSOM. DESIGN.­: The VSP elective was modeled after the in-person surgical pathology elective to include virtual previewing and sign-out with standardized cases supplemented by synchronous and asynchronous pathology educational content. RESULTS.­: Validation of existing Web communications technology and slide-scanning systems was performed by feasibility testing. Curriculum development included drafting of course objectives and syllabus, Blackboard course site design, electronic-lecture creation, communications with JHUSOM leadership, scheduling, and slide curation. Subjectively, the weekly schedule averaged 35 to 40 hours of asynchronous, synchronous, and independent content, approximately 10 to 11 hours of which were synchronous. As of February 2021, VSP has hosted 35 JHUSOM and 8 non-JHUSOM students, who have provided positive subjective and objective course feedback. CONCLUSIONS.­: The Johns Hopkins VSP elective provided meaningful clinical experience to 43 students in a time of immense online education need. Added benefits of implementing VSP included increased medical student exposure to pathology as a medical specialty and demonstration of how digital slides have the potential to improve standardization of the pathology clerkship curriculum.

Cytomorphologic Features Found in Cerebrospinal Fluid Specimens of Hemophagocytic Lymphohistiocytosis Patients.

OBJECTIVES: Central nervous system involvement is present in 70% of patients with hemophagocytic lymphohistiocytosis (CNS-HLH). CNS-HLH is defined by neurologic deficits, neuroimaging abnormalities, or positive cerebrospinal fluid (CSF) findings. The CSF cytomorphologic spectrum of CNS-HLH, however, has not been well investigated. METHODS: A retrospective review was performed on 64 CSF specimens from pediatric and adult patients with HLH. Ten patients had clinicoradiologic evidence of CNS involvement. RESULTS: We identified five CSF cytomorphologic patterns: (1) hemophagocytosis, (2) vacuolated macrophages without evidence of hemophagocytosis, (3) monocytes and/or nonvacuolated macrophages, (4) acellular specimens, and (5) bloody specimens. Patterns 1 and 2 were common in CNS-HLH and rare in patients without CNS involvement. The CSF cytomorphologic patterns did not correlate well with WBC counts or protein concentration. CONCLUSIONS: Our study offers a comprehensive view of the cytomorphologic features seen in CSF specimens from patients with HLH.