The spectrum of malignant diagnoses in cerebrospinal fluid cytology from an adult population: a multi-institutional retrospective review.

INTRODUCTION: Limited updated literature exists about the prevalence and spectrum of malignancies involving cerebrospinal fluid (CSF). In this multi-institutional study, we review our experience with focus on first time malignancy diagnosis in CSF samples of adults. MATERIALS AND METHODS: Institutional databases at 4 academic centers were queried retrospectively for CSFs over a 10-year period. The following data elements were collected: total # of CSFs, total # of CSFs with a malignant diagnosis; for each patient with a first time CSF diagnosis of malignancy: age, gender, diagnosis, prior history of malignancy, and ancillary studies. RESULTS: Twenty-four thousand one hundred forty-two CSFs were collected with a positive for malignancy rate of 2.3% (n = 551). Out of 347 (1.4%) adults with a first-time diagnosis of CSF malignancy 182 (52%) were female (age range: 19-89/mean: 57) and 165 (48%) were male (age range: 20-95/mean: 60). Hematolymphoid malignancies (48%, n = 168) were overall the most common neoplasm. In women, metastatic carcinomas (63%, n = 114) were the leading malignancy, of which the majority were breast primaries. In men, lymphomas/leukemias (64%, n = 106) were the leading malignancy, of which the majority were B-cell lymphomas. Ancillary studies aided the final diagnosis in 110 (32%) cases. For 286 (82%) cases, a prior history of malignancy was available to correlate CSF findings. CONCLUSIONS: A malignancy diagnosis in the CSF of adults is rare. The most common malignancies in females and males are metastatic breast carcinoma and hematolymphoid malignancies, respectively. Metastatic neoplasms account for the majority, with primary central nervous system neoplasms being quite uncommon. History of malignancy and ancillary tests can be helpful.

Oil Red O Staining of Pulmonary Macrophages in Bronchoalveolar Lavage Specimens Is Not Specific for Vaping-Associated Lung Injury.

OBJECTIVES: Oil Red O (ORO) positivity in bronchoalveolar lavage (BAL) fluid macrophages in the setting of e-cigarette, or vaping, product use-associated acute lung injury (EVALI) has been frequently requested by clinicians based on rare reports and subsequent US Centers for Disease Control and Prevention guidelines. The aim of this study was to determine the specificity of ORO staining in BAL specimens with disease states other than EVALI. METHODS: Consecutive BAL specimens (October-December 2019) were stained with ORO. The lipid-laden macrophage index (LLMI) was calculated for each case. RESULTS: We studied BAL samples from 50 patients. Indications for BAL were surveillance bronchoscopy for lung transplantation (27/50), suspected infection (12/50), sarcoidosis/suspected sarcoidosis (3/50), nodules or ground-glass opacities (3/50), hemoptysis (2/50), asthma or eosinophilic pneumonia (2/50), and idiopathic pulmonary fibrosis (1/50). ORO staining was seen in BAL fluid macrophages in 45 of 50 cases (focal in 18, moderate in 23, diffuse in 4); LLMI ranged from 0 to 218. Using a threshold of LLMI of 85 or higher as positive, ORO was positive in 7 of 50 (14%) cases (range, 85-218). CONCLUSIONS: ORO staining in BAL fluid macrophages is not specific for EVALI. Even when an LLMI of 85 or higher is used as a threshold for positivity, ORO positivity occurs in a significant subset of non-vaping-related cases.

Does histological assessment accurately distinguish separate primary lung adenocarcinomas from intrapulmonary metastases? A study of paired resected lung nodules in 32 patients using a routine next-generation sequencing panel for driver mutations.

AIM: Various approaches have been reported for distinguishing separate primary lung adenocarcinomas from intrapulmonary metastases in patients with two lung nodules. The aim of this study was to determine whether histological assessment is reliable and accurate in distinguishing separate primary lung adenocarcinomas from intrapulmonary metastases using routine molecular findings as an adjunct. METHODS: We studied resected tumour pairs from 32 patients with lung adenocarcinomas in different lobes. In 15 of 32 tumour pairs, next-generation sequencing (NGS) for common driver mutations was performed on both nodules. The remainder of tumour pairs underwent limited NGS, or EGFR genotyping. Tumour pairs with different drivers (or one driver/one wild-type) were classified as molecularly unrelated, while those with identical low-frequency drivers were classified as related. Three pathologists independently and blinded to the molecular results categorised tumour pairs as related or unrelated based on histological assessment. RESULTS: Of 32 pairs, 15 were classified as related by histological assessment, and 17 as unrelated. Of 15 classified as related by histology, 6 were classified as related by molecular analysis, 4 were unrelated and 5 were indeterminate. Of 17 classified as unrelated by histology, 14 were classified as unrelated by molecular analysis, none was related and 3 were indeterminate. Histological assessment of relatedness was inaccurate in 4/32 (12.5%) tumour pairs. CONCLUSIONS: A small but significant subset of two-nodule adenocarcinoma pairs is inaccurately judged as related by histological assessment, and can be proven to be unrelated by molecular analysis (driver gene mutations), leading to significant downstaging.

e-Cigarette or Vaping Product Use-Associated Lung Injury: Clinical, Radiologic, and Pathologic Findings of 15 Cases.

Since mid-2019, > 2,000 cases of e-cigarette or vaping product use-associated lung injury (EVALI) have been reported. Although initial reports suggested that this entity may be a form of inhalation-related lipoid pneumonia, subsequent studies indicate that EVALI represents various patterns of acute lung injury. Cases of EVALI continue to be reported, and public awareness of the epidemic is increasingly high. However, evidence surrounding optimal management of EVALI remains limited. In this case series, we report 15 cases of EVALI across a spectrum of severity, highlighting key radiologic, pathologic, and cytologic findings, and discuss management implications. In line with national findings, most patients with EVALI in the series vaped liquids containing tetrahydrocannabinol. Our imaging and pathologic findings support the notion that EVALI is a form of acute lung injury.

Leveraging Technology for Remote Learning in the Era of COVID-19 and Social Distancing.

The ongoing global pandemic of coronavirus disease 2019 (COVID-19) has rapidly disrupted traditional modes of operation in health care and education. In March 2020, institutions in the United States began to implement a range of policies to discourage direct contact and encourage social distancing. These measures have placed us in an unprecedented position where education can no longer occur at close quarters-most notably, around a multiheaded microscope-but must instead continue at a distance. This guide is intended to be a resource for pathologists and pathologists-in-training who wish to leverage technology to continue collaboration, teaching, and education in this era. The article is focused mainly on anatomic pathology; however, the technologies easily lend themselves to clinical pathology education as well. Our aim is to provide curated lists of various online resources that can be used for virtual learning in pathology, provide tips and tricks, and share our personal experience with these technologies. The lists include videoconferencing platforms; pathology Web sites; free online educational resources, including social media; and whole slide imaging collections. We are currently living through a unique situation without a precedent or guidebook, and we hope that this guide will enable the community of pathology educators worldwide to embrace the opportunities that 21st century technology provides.

INSM1 Is a Highly Specific Marker of Neuroendocrine Differentiation in Primary Neoplasms of the Gastrointestinal Tract, Appendix, and Pancreas.

OBJECTIVES: INSM1 has been described as a sensitive and specific neuroendocrine marker. This study aims to compare INSM1 with traditional neuroendocrine markers in gastrointestinal neuroendocrine neoplasms. METHODS: Retrospective review (2008-2018) was used to retrieve paraffin-embedded tissue from 110 gastrointestinal neuroendocrine neoplasms and controls that was subsequently stained with INSM1, synaptophysin, chromogranin, CD56, and Ki-67. RESULTS: INSM1 was positive in 16 of 17 (94.1%) gastric, 17 of 18 (94.4%) pancreatic, 13 of 18 (72.2%) small bowel, 17 of 21 (81.0%) colonic, and 26 of 36 (72.2%) appendiceal tumors. INSM1 was positive in 58 of 70 (82.9%) well-differentiated neuroendocrine tumors, 17 of 20 (85.0%) poorly differentiated neuroendocrine carcinomas, 8 of 11 (72.7%) low-grade goblet cell adenocarcinomas (grade 1), and 6 of 9 (66.7%) high-grade goblet cell adenocarcinomas (grade 2/3). INSM1 sensitivity for neuroendocrine neoplasms (80.9%) was less than that of synaptophysin (99.1%), chromogranin (88%), and CD56 (95.3%); specificity was higher (95.7% vs 86.0%, 87.3%, and 86.0%, respectively). CONCLUSIONS: INSM1 is a useful marker of neuroendocrine differentiation in gastrointestinal neuroendocrine and mixed neuroendocrine neoplasms. Compared with traditional neuroendocrine markers, INSM1 is less sensitive but more specific.

#EBUSTwitter: Novel Use of Social Media for Conception, Coordination, and Completion of an International, Multicenter Pathology Study.

CONTEXT.­: Social media sites are increasingly used for education, networking, and rapid dissemination of medical information, but their utility for facilitating research has remained largely untapped. OBJECTIVE.­: To describe in detail our experience using a social media platform (Twitter) for the successful initiation, coordination, and completion of an international, multi-institution pathology research study. DESIGN.­: Following a tweet describing a hitherto-unreported biopsy-related histologic finding in a mediastinal lymph node following endobronchial ultrasound-guided transbronchial needle aspiration, a tweet was posted to invite pathologists to participate in a validation study. Twitter's direct messaging feature was used to create a group to facilitate communication among participating pathologists. Contributing pathologists reviewed consecutive cases of mediastinal lymph node resection following endobronchial ultrasound-guided transbronchial needle aspiration and examined them specifically for biopsy site changes. Data spreadsheets containing deidentified data and digital photomicrographs of suspected biopsy site changes were submitted via an online file hosting service for central review by 5 pathologists from different institutions. RESULTS.­: A total of 24 pathologists from 14 institutions in 5 countries participated in the study within 143 days of study conception, and a total of 297 cases were collected and analyzed. The time interval between study conception and acceptance of the manuscript for publication was 346 days. CONCLUSIONS.­: To our knowledge, this is the first time that a social media platform has been used to generate a research idea based on a tweet, recruit coinvestigators publicly, communicate with collaborating pathologists, and successfully complete a pathology study.

Primary salivary gland-type tumors of the tracheobronchial tree diagnosed by transbronchial fine needle aspiration: Clinical and cytomorphologic features with histopathologic correlation.

BACKGROUND: Primary salivary gland-type tumors of the tracheobronchial tree are rare; their cytologic features have been seldom reported. We aim to describe the clinical and cytomorphologic features of tracheobronchial salivary gland-type tumors diagnosed by transbronchial fine needle aspiration (TBNA) at our institution, and correlate the findings with a corresponding surgical specimen. METHODS: We searched our laboratory information system to identify patients with a primary salivary gland-type neoplasm of the tracheobronchial tree diagnosed by TBNA and with a corresponding surgical pathology specimen, over 10 years. RESULTS: The study cohort consisted of 11 patients (7F/4M; mean age 58 years, range 41-78). Presenting symptoms included hemoptysis (4), cough (3), dyspnea (1), stridor (1), and shoulder pain (1). Most had a tracheal mass (5), while 3 had mainstem bronchi masses and 3 had lung masses. Radiographically, the masses were lobulated, rounded, or polypoid in six patients. All underwent TBNA with a 21- or 22-gauge needle and endobronchial biopsy. The most frequent diagnosis was adenoid cystic carcinoma (4/11, 36%), followed by mucoepidermoid carcinoma (3/11, 27%), epithelial-myoepithelial carcinoma (2/11, 18%), oncocytoma (1/11, 9%), and hyalinizing clear cell carcinoma, salivary gland type (1/11, 9%). The surgical pathology specimens confirmed the diagnosis in all cases. CONCLUSIONS: To our knowledge, this is one of the largest cytomorphologic studies of primary salivary gland tumors of the tracheobronchial tree in the literature. Salivary gland tumors of the tracheobronchial tree are rare, and recognizing cytomorphologic changes that occur in salivary gland-type tumors is important for establishing a definitive diagnosis.

Molecular Testing of Non-Small Cell Lung Carcinoma Diagnosed by Endobronchial Ultrasound-Guided Transbronchial Fine-Needle Aspiration: The Cleveland Clinic Experience.

CONTEXT.­: Given the increasing demand for molecular testing of non-small cell lung carcinoma specimens to guide therapeutic decision-making and the trend toward minimally invasive techniques for obtaining diagnostic tissue, cytopathology laboratories must devise strategies to maximize DNA yield for necessary molecular testing. OBJECTIVE.­: To describe our experience at Cleveland Clinic with epidermal growth factor receptor (EGFR) mutation testing by next-generation sequencing and anaplastic lymphoma kinase (ALK) gene rearrangement testing by fluorescence in situ hybridization of non-small cell lung carcinomas diagnosed by cytology, with an emphasis on specimens obtained by endobronchial ultrasound-guided transbronchial fine-needle aspiration. DATA SOURCES.­: Data sources include a review of the current literature, including published articles from our institution. CONCLUSIONS.­: At our institution, liquid-based cytology specimens are the primary resource used for molecular testing of non-small cell lung carcinomas; in most instances, adequate DNA can be extracted from the residual cell pellet for next-generation sequencing, and ThinPrep slides can be used reliably for fluorescence in situ hybridization testing for ALK gene rearrangements. In occasional cases where the cell pellet material is not adequate for molecular testing, cell blocks and/or surgical pathology specimens are secondary options. The cytopathologist's role in specimen handling and triage is essential to ensure that molecular testing can be carried out successfully.

Displaced Cartilage Within Lymph Node Parenchyma Is a Novel Biopsy Site Change in Resected Mediastinal Lymph Nodes Following EBUS-TBNA.

Biopsy site changes in mediastinal lymph nodes (LNs) attributable to prior endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) have not been studied in a systematic manner. Twenty-four contributors from 14 institutions in 5 countries collaborated via social media (Twitter) to retrospectively review consecutive cases of resected mediastinal LNs from patients with prior EBUS-TBNA. Resected LNs were reexamined by submitting pathologists for changes attributable to EBUS-TBNA. Patients who received neoadjuvant therapy were excluded. Cases with suspected biopsy site changes underwent central review by 5 pathologists. A total of 297 mediastinal LN resection specimens from 297 patients (183 male/114 female, mean age: 65 y, range: 23 to 87) were reviewed. Biopsy site changes were most common in station 7 (10 cases) followed by 11R, 4R, and 10R, and were found in 34/297 (11.4%) cases, including displacement of tiny cartilage fragments into LN parenchyma in 26, intranodal or perinodal scars in 7, and hemosiderin in 1. Cartilage fragments ranged from 0.26 to 1.03 mm in length and 0.18 to 0.62 mm in width. The mean interval between EBUS-TBNA and LN resection was 38 days (range: 10 to 112) in cases with biopsy site changes. A control group of 40 cases without prior EBUS-TBNA, including 193 mediastinal LN stations, showed no evidence of biopsy site changes. Biopsy site changes are identified in a subset of resected mediastinal LNs previously sampled by EBUS-TBNA. The location of the abnormalities, temporal association with prior EBUS-TBNA, and the absence of such findings in cases without prior EBUS-TBNA support the contention that they are caused by EBUS-TBNA.

Evaluation of Carcinoma of Unknown Primary on Cytologic Specimens.

Carcinoma of unknown primary is defined as metastatic carcinoma without a clinically obvious primary tumor. Determining the tissue of origin in carcinoma of unknown primary is important for site-directed therapy. Immunohistochemistry is the most widely used tool for the work-up of metastases, but molecular profiling assays are also available. This review provides an overview of immunohistochemical stains in the work-up of metastatic carcinoma, with a focus on newer site-specific markers, and discusses the role of gene expression profiling assays for determining tissue of origin. The utility of cytopathology specimens in the evaluation of carcinoma of unknown primary also is highlighted.

Insulinoma-associated protein 1 is a sensitive and specific marker of neuroendocrine lung neoplasms in cytology specimens.

BACKGROUND: Recent studies suggest that insulinoma-associated protein 1 (INSM1) is a sensitive and specific marker of neuroendocrine neoplasms. The aims of this study were to determine whether INSM1 can be reliably used in cytology (Cellient) cell blocks, to ascertain whether staining correlates with paired surgical pathology specimens, and to compare its sensitivity and specificity with those of synaptophysin (SYN), chromogranin (CHR), and CD56 for neuroendocrine lung tumors. METHODS: Seventy-four primary lung neoplasms diagnosed on cytology were stained with INSM1, SYN, CHR, and CD56: 41 small cell lung carcinomas (SCLCs), 1 large cell neuroendocrine carcinoma (LCNEC), 10 carcinoid tumors, 11 adenocarcinomas, 9 squamous cell carcinomas, 1 mesothelioma and 1 poorly differentiated non-small cell lung carcinoma, not otherwise specified. In 20 cases, a paired surgical pathology specimen was also stained with INSM1. RESULTS: INSM1 was positive in 48 of 52 primary lung neuroendocrine neoplasms (92%), including 38 of 41 SCLCs (93%), the only LCNEC (100%), and 9 of 10 carcinoid tumors (90%), and it was negative in all 22 non-neuroendocrine primary lung tumors. For SCLC, the sensitivity of INSM1 (93%) was lower than the sensitivity of CD56 (100%), equal to the sensitivity of SYN (93%), and higher than the sensitivity of CHR (35%). For carcinoid tumors, the sensitivity of INSM1 (90%) was lower than the sensitivity of all other markers (100% each). The specificity of INSM1 for neuroendocrine neoplasms as a group was 100%. INSM1 staining was concordant with surgical pathology specimens in all 20 paired cases. CONCLUSIONS: INSM1 can be used in cytopathology cell blocks, and it is sensitive and highly specific for neuroendocrine lung tumors. INSM1 staining in cytology cell blocks correlates well with surgical pathology specimens. Cancer Cytopathol 2018;126:243-52. © 2018 American Cancer Society.

HER2 FISH concordance in breast cancer patients with both cytology and surgical pathology specimens.

INTRODUCTION: Fluorescence in Situ Hybridization (FISH) for Human Epidermal Growth Factor Receptor 2 (HER2) is traditionally performed on histologic specimens; there are no guidelines for validation of HER2 testing on cytology specimens. Our aim was to correlate HER2 FISH results on cytologic and histologic specimens. MATERIALS AND METHODS: A retrospective search was conducted to identify breast carcinomas with HER2 FISH testing on both cytologic and histologic specimens. Results were interpreted using updated 2013 ASCO/CAP guidelines. RESULTS: 54 women with HER2 FISH results on both cytologic and histologic specimens were identified. HER2 FISH was performed on 26 formalin-fixed thrombin clot cell blocks, 6 Cellient (Hologic, Inc., Bedford, MA) cell blocks and 22 ThinPrep slides, and was negative in 43 (87%), positive in 8 (15%), and equivocal in 3 (5%) cases. Of 43 negative cytology cases, the histologic specimen was also negative in 40 (93%). Of 8 positive cytology cases, the histologic specimen was positive in 5 (63%). Overall, 48 of 54 cases (89%) had a concordant result. In patients with a discordant result, the average interval between HER2 FISH testing was 7 years. Three of 6 discordant cases showed HER2 genetic heterogeneity. Five patients received adjuvant chemotherapy, 2 received endocrine therapy, and 1 received trastuzumab. CONCLUSIONS: FISH is reliable for determining HER2 status in cytopathology specimens. Discordant results between cytologic and surgical specimens are uncommon; possible explanations include genetic heterogeneity or inherent molecular changes associated with disease progression and therapies that occur between testing of the primary carcinoma and the metastasis.

Diagnosis of trichomoniasis in men by urine cytology.

BACKGROUND: Trichomonas vaginalis is a rare finding in urine cytology specimens, especially those from men; only 2 case reports have been described in the literature. The authors of the current report sought to determine the incidence and clinical significance of this finding in urine cytology in males. METHODS: The authors' cytopathology archives were queried for urine cytology specimens that contained Trichomonas over a 30-year period. Clinical information from men with Trichomonas-positive urines was reviewed retrospectively. Slides were reviewed, and the morphologic characteristics of the organisms were recorded. RESULTS: Trichomonas was detected in 73 of 60,000 urine cytology specimens (0.1%). The patients included 45 women and 28 men. Men with Trichomonas in their urine ranged in age from 28 to 87 years (mean age, 67 years; median, 71 years). Trichomonas organisms were round to oval, with eccentric nuclei and cytoplasmic granules. Acute inflammation was observed in 6 of 7 cases. Clinical history was available in 13 of 28 men. Lower urinary tract symptoms were reported in 10 of 13 men, most commonly hematuria; and urethral strictures were identified by cystoscopy in 3 of 13 men. Clinical follow-up was available for 10 of 13 patients; of these, 8 (80%) had received treatment with metronidazole based on urine cytology results. CONCLUSIONS: This study is the largest series of Trichomonas infection in men diagnosed by urine cytology in the literature. Most men had no prior diagnosis of trichomoniasis and received specific antibiotic therapy based on their urine cytology results. Urine cytology may represent the initial diagnostic test for Trichomonas in men, and accurate cytologic diagnosis may prevent undesired adverse outcomes for them and their partners. Cancer Cytopathol 2017;125:55-59. © 2016 American Cancer Society.

Knowledge of the HPV status biases cytotechnologists' interpretation of Pap tests originally diagnosed as negative for intraepithelial lesion or malignancy.

BACKGROUND: Because of cervical cancer screening recommendations and forthcoming first-line human papillomavirus (HPV) screening, many Papanicolaou (Pap) tests will be performed in patients with known concurrent HPV results. This study was designed to evaluate whether knowledge of the HPV status affects cytotechnologists' interpretation of Pap tests. METHODS: A retrospective search of cervical screening Pap tests with known concurrent HPV results provided 250 ThinPrep Pap tests, which were chosen to reflect an atypical rate similar to the rate of the Cleveland Clinic's normal practice. Fifty percent of negative for intraepithelial lesion or malignancy (NILM) and atypical squamous cells of undetermined significance (ASCUS) cases were from patients with positive HPV results. Slides were re-evaluated twice by 8 cytotechnologists blinded to the diagnosis and study purpose. The HPV status was provided for 50% of the cases in the first phase; after a washout period, knowledge of the HPV status for each case was reversed in the second phase. Follow-up information was collected from the medical record. RESULTS: In both phases, there was a significant bias for HPV-positive NILM cases to be upgraded to ASCUS or worse when the HPV-positive status was provided (P < .001). When the HPV status was withheld, there was no difference in upgrading NILM cases (phase 1, P = .69; phase 2, P = .066). A combined analysis showed a significant bias in referral to the pathologist when the HPV-positive status was provided rather than withheld (P < .001). Follow-up data revealed no significant effect of bias when the HPV-positive status was provided between patient groups with benign, low-grade, or high-grade follow-up. CONCLUSIONS: A known HPV-positive status biases cytotechnologists' interpretation of Pap tests, and this results in a higher rate of upgrading to ASCUS or worse; however, it does not improve sensitivity for disease detection. Cancer Cytopathol 2017;125:60-69. © 2016 American Cancer Society.

Solitary lung metastasis from intracranial hemangiopericytoma 18 years after initial resection.

We report a 29-year-old woman who presented with severe headache, nausea and vomiting. A lesion was found in the left petrous ridge and near-total resection was performed. Pathologic examination showed anaplastic hemangiopericytoma (World Health Organization Grade III). Hemangiopericytoma is an uncommon mesenchymal tumor that rarely occurs in an intracranial location. Prior studies have reported a surprisingly high rate of late recurrence and extracranial metastases from intracranial hemangiopericytomas, including metastases to the lungs. Resection was followed by external beam radiation. The tumor recurred intracranially 6 and 13 years later and was treated with gamma knife stereotactic radiosurgery. At year 14, she noticed a lump in her neck and underwent parotidectomy for a mucoepidermoid carcinoma. This new diagnosis prompted a staging chest CT scan which showed a 4mm right upper lobe lung nodule along with additional < 5 mm indeterminate nodules. Over the next 3 years, the nodule increased to 8mm. Wedge biopsy of the lung nodule showed metastatic hemangiopericytoma, histologically similar to the intracranial hemangiopericytoma. Both the primary and the lung metastasis were positive for CD34 and STAT-6. To the best of our knowledge, this is the longest reported interval between a resected intracranial hemangiopericytoma and a histologically confirmed solitary metastasis to the lung.

Visibility of Histoplasma within histiocytes on hematoxylin and eosin distinguishes disseminated histoplasmosis from other forms of pulmonary histoplasmosis.

The visibility of Histoplasma within histiocytes on hematoxylin and eosin is a well-known feature of disseminated histoplasmosis. However, it is unclear whether this finding can be used to differentiate disseminated histoplasmosis involving the lung from other forms of pulmonary histoplasmosis. The aim of this study was to determine whether the visibility of Histoplasma within histiocytes on hematoxylin and eosin in lung biopsies suggests disseminated disease. Lung biopsies in which Histoplasma was identified were re-examined to determine whether organisms were visible within histiocytes on hematoxylin and eosin. Clinical findings were reviewed retrospectively to determine the type of histoplasmosis. Histoplasma was visible within histiocytes on hematoxylin and eosin in lung biopsies from 4 patients (2 men, 2 women, 50-74 years) who presented with pulmonary manifestations without definite evidence of disseminated disease at the time of biopsy. Subsequently, all 4 manifested clinical and/or microbiologic features of disseminated disease (positive extrapulmonary cultures and fatal outcome in 2, positive extrapulmonary cultures in 1, and multiorgan failure and fatal outcome in 1). In contrast, organisms were identified on silver stains but could not be visualized on hematoxylin and eosin in 42 patients, none of whom showed clinical or microbiologic evidence of disseminated disease (pulmonary histoplasmoma, 38; acute pulmonary histoplasmosis, 4). In lung biopsies, the visibility of Histoplasma within histiocytes on hematoxylin and eosin suggests disseminated disease. Recognition of the significance of this finding is helpful in diagnosing disseminated disease in patients who present primarily with pulmonary manifestations without definite clinical evidence of dissemination at the time of biopsy.