Adult polyglucosan body disease: an acute presentation leading to unmasking of this rare disorder.

INTRODUCTION: Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy caused by abnormal intracellular accumulation of glycogen byproducts. This disorder is linked to a deficiency in glycogen branching enzyme-1 (GBE-1). Neurologic manifestations include upper and lower motor neuron signs, dementia, and peripheral neuropathy. APBD is typically a progressive disease. In this report, we discuss a novel case of APBD in a patient who had a sudden onset of spastic quadriparesis preceded by gradual difficulty with gait. Genetic and postmortem analysis confirmed the diagnosis of APBD. CASE REPORT: A 65-year-old man was evaluated for a new-onset of spastic quadriparesis, right-gaze preference, and left-sided beat nystagmus. Magnetic resonance imaging (MRI) of the brain revealed areas of white matter hyperintensities most prominent in the brainstem and periventricular regions. MRI of the cervical spine showed marked cord atrophy. Laboratory workup and cerebrospinal fluid analysis were unremarkable. Genetic testing supported the diagnosis of APBD due to GBE-1 deficiency. Postmortem analysis showed multiple white matter abnormalities suggestive of a leukodystrophy syndrome, and histopathologic testing revealed abnormal accumulation of polyglucosan bodies in samples from the patient's central nervous system supporting the diagnosis of APBD. CONCLUSION: APBD is a rare disorder that can affect the nervous system. The diagnosis can be confirmed with a combination of genetic testing and pathologic analysis of affected brain tissue.

The resident macrophages in murine pancreatic islets are constantly probing their local environment, capturing beta cell granules and blood particles.

AIMS/HYPOTHESIS: We studied here the interactions between the resident macrophages of pancreatic islets with beta cells and the blood vasculature. We also examined the immunological consequences of such interactions. METHODS: Islets were isolated from C57BL/6 mice expressing CX3C motif chemokine receptor 1-green fluorescent protein (CX3CR-GFP) and examined live by two-photon microscopy. Islets were also examined by electron microscopy to study the relationship of the intra-islet macrophages with the beta cells. In NOD.Rag1-/- mice and young (non-diabetic) male mice, the acquisition of beta cell granules was tested functionally by probing with CD4+ T cells directed against insulin epitopes. RESULTS: Two-photon microscopy showed that the islet resident macrophages were in close contact with blood vessels and had extensive filopodial activity. Some filopodia had direct access to the vessel lumen and captured microparticles. Addition of glucose at high concentration reduced the degree of filopodia sampling of islets. This finding applied to in vivo injection of glucose or to in vitro cultures. Ultrastructural examination showed the close contacts of macrophages with beta cells. Such macrophages contained intact dense core granules. Functional studies in NOD mice indicated that the macrophages presented insulin peptides to insulin-reactive T cells. Presentation was increased after glucose challenge either ex vivo or after an in vivo pulse. In agreement with the morphological findings, presentation was not affected by insulin receptor blockade. CONCLUSIONS/INTERPRETATION: Islet resident macrophages are highly active, sampling large areas of the islets and blood contents and capturing beta cell granules. After such interactions, macrophages present immunogenic insulin to specific autoreactive T cells.

Opposing Roles of Dendritic Cell Subsets in Experimental GN.

Dendritic cells (DCs) are thought to form a dendritic network across barrier surfaces and throughout organs, including the kidney, to perform an important sentinel function. However, previous studies of DC function used markers, such as CD11c or CX3CR1, that are not unique to DCs. Here, we evaluated the role of DCs in renal inflammation using a CD11c reporter mouse line and two mouse lines with DC-specific reporters, Zbtb46-GFP and Snx22-GFP. Multiphoton microscopy of kidney sections confirmed that most of the dendritically shaped CD11c+ cells forming a network throughout the renal interstitium expressed macrophage-specific markers. In contrast, DCs marked by Zbtb46-GFP or Snx22-GFP were less abundant, concentrated around blood vessels, and round in shape. We confirmed this pattern of localization using imaging mass cytometry. Motility measurements showed that resident macrophages were sessile, whereas DCs were motile before and after inflammation. Although uninflamed glomeruli rarely contained DCs, injury with nephrotoxic antibodies resulted in accumulation of ZBTB46 + cells in the periglomerular region. ZBTB46 identifies all classic DCs, which can be categorized into two functional subsets that express either CD103 or CD11b. Depletion of ZBTB46 + cells attenuated the antibody-induced kidney injury, whereas deficiency of the CD103+ subset accelerated injury through a mechanism that involved increased neutrophil infiltration. RNA sequencing 7 days after nephrotoxic antibody injection showed that CD11b+ DCs expressed the neutrophil-attracting cytokine CXCL2, whereas CD103+ DCs expressed high levels of several anti-inflammatory genes. These results provide new insights into the distinct functions of the two major DC subsets in glomerular inflammation.

Thermoneutrality but Not UCP1 Deficiency Suppresses Monocyte Mobilization Into Blood.

RATIONALE: Ambient temperature is a risk factor for cardiovascular disease. Cold weather increases cardiovascular events, but paradoxically, cold exposure is metabolically protective because of UCP1 (uncoupling protein 1)-dependent thermogenesis. OBJECTIVE: We sought to determine the differential effects of ambient environmental temperature challenge and UCP1 activation in relation to cardiovascular disease progression. METHODS AND RESULTS: Using mouse models of atherosclerosis housed at 3 different ambient temperatures, we observed that cold temperature enhanced, whereas thermoneutral housing temperature inhibited atherosclerotic plaque growth, as did deficiency in UCP1. However, whereas UCP1 deficiency promoted poor glucose tolerance, thermoneutral housing enhanced glucose tolerance, and this effect held even in the context of UCP1 deficiency. In conditions of thermoneutrality, but not UCP1 deficiency, circulating monocyte counts were reduced, likely accounting for fewer monocytes entering plaques. Reductions in circulating blood monocytes were also found in a large human cohort in correlation with environmental temperature. By contrast, reduced plaque growth in mice lacking UCP1 was linked to lower cholesterol. Through application of a positron emission tomographic tracer to track CCR2+ cell localization and intravital 2-photon imaging of bone marrow, we associated thermoneutrality with an increased monocyte retention in bone marrow. Pharmacological activation of ß3-adrenergic receptors applied to mice housed at thermoneutrality induced UCP1 in beige fat pads but failed to promote monocyte egress from the marrow. CONCLUSIONS: Warm ambient temperature is, like UCP1 deficiency, atheroprotective, but the mechanisms of action differ. Thermoneutrality associates with reduced monocyte egress from the bone marrow in a UCP1-dependent manner in mice and likewise may also suppress blood monocyte counts in man.

Lymphoid Aggregates Remodel Lymphatic Collecting Vessels that Serve Mesenteric Lymph Nodes in Crohn Disease.

Early pathological descriptions of Crohn disease (CD) argued for a potential defect in lymph transport; however, this concept has not been thoroughly investigated. In mice, poor healing in response to infection-induced tissue damage can cause hyperpermeable lymphatic collecting vessels in mesenteric adipose tissue that impair antigen and immune cell access to mesenteric lymph nodes (LNs), which normally sustain appropriate immunity. To investigate whether analogous changes might occur in human intestinal disease, we established a three-dimensional imaging approach to characterize the lymphatic vasculature in mesenteric tissue from controls or patients with CD. In CD specimens, B-cell-rich aggregates resembling tertiary lymphoid organs (TLOs) impinged on lymphatic collecting vessels that enter and exit LNs. In areas of creeping fat, which characterizes inflammation-affected areas of the bowel in CD, we observed B cells and apparent innate lymphoid cells that had invaded the lymphatic vessel wall, suggesting these cells may be mediators of lymphatic remodeling. Although TLOs have been described in many chronic inflammatory states, their anatomical relationship to preestablished LNs has never been revealed. Our data indicate that, at least in the CD-affected mesentery, TLOs are positioned along collecting lymphatic vessels in a manner expected to affect delivery of lymph to LNs.

CCR7 and IRF4-dependent dendritic cells regulate lymphatic collecting vessel permeability.

Lymphatic collecting vessels direct lymph into and from lymph nodes (LNs) and can become hyperpermeable as the result of a previous infection. Enhanced permeability has been implicated in compromised immunity due to reduced flow of lymph and immune cells to LNs, which are the primary site of antigen presentation to T cells. Presently, very little is known about the molecular signals that affect lymphatic collecting vessel permeability. Here, we have shown that lymphatic collecting vessel permeability is controlled by CCR7 and that the chronic hyperpermeability of collecting vessels observed in Ccr7-/- mice is followed by vessel fibrosis. Reexpression of CCR7 in DCs, however, was sufficient to reverse the development of such fibrosis. IFN regulatory factor 4-positive (IRF4+) DCs constitutively interacted with collecting lymphatics, and selective ablation of this DC subset in Cd11c-Cre Irf4fl/fl mice also rendered lymphatic collecting vessels hyperpermeable and fibrotic. Together, our data reveal that CCR7 plays multifaceted roles in regulating collecting vessel permeability and fibrosis, with one of the key players being IRF4-dependent DCs.

An improved method for calibrating time-of-flight Laue single-crystal neutron diffractometers.

A robust and comprehensive method for determining the orientation matrix of a single-crystal sample using the neutron Laue time-of-flight (TOF) technique is described. The new method enables the measurement of the unit-cell parameters with an uncertainty in the range 0.015-0.06%, depending upon the crystal symmetry and the number of reflections measured. The improved technique also facilitates the location and integration of weak reflections, which are often more difficult to discern amongst the increased background at higher energies. The technique uses a mathematical model of the relative positions of all the detector pixels of the instrument, together with a methodology that establishes a reproducible reference frame and a method for determining the parameters of the instrument detector model. Since all neutron TOF instruments require precise detector calibration for their effective use, it is possible that the method described here may be of use on other instruments where the detector calibration cannot be determined by other means.

Additive-mediated electrochemical synthesis of platelike copper crystals for methanol electrooxidation.

A room-temperature electrochemical approach to synthesizing anisotropic platelike copper microcrystals and nanocrystals in the presence of potassium bromide is presented. Morphological and elemental characterization was performed using SEM, TEM, and XRD to confirm the anisotropic morphology and crystal structure of the synthesized copper particles. A possible mechanism for explaining the anisotropic crystal growth is proposed on the basis of the preferential adsorption of bromide ions to selective crystal faces. The shape-dependent electrocatalytic property of copper particles is demonstrated by its enhanced catalytic activity for methanol oxidation. Further development of such anisotropic copper particles localized on an electrode surface will lead us to find a suitable alternative for noble metal-based electrocatalysts for the methanol oxidation reaction relevant to fuel cells.

Solid pseudopapillary neoplasm, pancreas type, presenting as a primary ovarian neoplasm.

Solid pseudopapillary neoplasm has historically been associated with the pancreas, categorized as a tumor of low malignancy. Recently, solid pseudopapillary neoplasm was reported to arise as a primary ovarian tumor in 3 women. We report a fourth case identified in a 48 year-old woman with an 8-cm left ovarian mass. A left salpingo-oophorectomy was performed. Microscopic examination demonstrated a predominately cystic neoplasm comprised of solid nests of cells with an epithelioid to plasmacytoid appearance, associated with blood vessels, hemorrhage, and degenerative changes, that is, pseudopapillary structures. The tumor cells stained focally for pancytokeratin, progesterone receptor, and CD57 with diffuse nuclear expression of ß-catenin. Ki-67 was 5% to 10%. Synaptophysin, inhibin, and E-cadherin stains were negative. Clinical and radiologic follow-up of our patient demonstrated no pancreatic lesions. This is a rare report of a primary ovarian solid pseudopapillary neoplasm. Prolonged follow-up is needed to determine how this case will fare clinically.

Axonal injury in young pediatric head trauma: a comparison study of ß-amyloid precursor protein (ß-APP) immunohistochemical staining in traumatic and nontraumatic deaths.

We tested the independent utility of ß-amyloid precursor protein (ß-APP) immunohistochemical staining as evidence of brain trauma in the deaths of young children. Blinded reviewers retrospectively reviewed immunostained brain tissues from homicidal deaths, age-matched control cases without evidence of trauma, as well as cases of sudden infant death syndrome (SIDS). The reviewers correctly identified five of the seven cases with documented inflicted head trauma. However, one of seven age-matched control cases and one of 10 SIDS/sudden unexplained death in infancy (SUDI) cases demonstrated staining patterns similar to those seen in cases of inflicted trauma. We discuss these cases and the circumstances surrounding them with the intent to explain the difficulties associated with immunohistological interpretation of axonal injury. Although the utility of ß-APP is quite powerful if not confounded by global hypoxic-ischemic injury, ultimately, ß-APP studies should be only one piece of information in the determination of cause and manner of death.

Glioblastoma multiforme in the Muir-Torre syndrome.

Muir-Torre syndrome (MTS) is an autosomal dominant subtype of nonpolyposis colorectal carcinoma (HNPCC) characterized by the development of sebaceous gland tumors and visceral malignancies. The most common subtype of MTS is characterized by germline mutations in mismatch repair (MMR) genes leading to microsatellite instability (MSI). Central nervous system tumors have only rarely been associated with MTS. In this report, we describe the development of a glioblastoma multiforme (GBM) in a patient with MTS. Immunohistochemical analysis of the patient's colon carcinoma and his GBM both revealed loss of the mismatch repair proteins mutS homolog 2 (MSH2) and mutS homolog 6 (MSH6).

Acute myeloid leukemia with myelodysplasia-related changes with erythroid differentiation involving pleural fluid: a case report and brief cytopathologic review.

The vast majority of malignant pleural effusions are caused by metastatic adenocarcinoma, most frequently from breast or lung primaries. However, a minority of cases show evidence of involvement by a hematopoietic neoplasm such as lymphoma or leukemia. We report a rare case of a 54-year-old male with a prior diagnosis of acute myeloid leukemia with myelodysplastic-related changes (AML-MDS) with erythroid differentiation having new onset pleural effusions containing leukemic blasts. The pleural specimen was comprised of blast forms having large round nuclei with finely dispersed chromatin and prominent nucleoli, with scattered binucleate forms. The blasts expressed CD45 and CD34 and were negative for epithelial and mesothelial markers. Previous bone marrow biopsies had shown that the blasts exhibited strong staining for hemoglobin and lacked expression of Factor VIII and myeloperoxidase, consistent with erythroid differentiation. Although rare, this case indicates the need for consideration of unusual disease states presenting within a pleural fluid and highlights the differential diagnosis and immunohistochemical profile of AMLs with erythroid differentiation.

High-grade prostatic sarcoma seen in a catheterized urine specimen: case report and differential diagnosis.

Urine cytology has been effectively used in the diagnosis and management of epithelial bladder tumors, particularly high-grade urothelial carcinoma. Indeed it is the gold standard for bladder cancer screening. Although urothelial carcinoma is the most frequently identified bladder tumor by urine cytology, metastatic carcinomas from the kidney, colon, and a variety of other regional organs have been detected. Stromal lesions such as inflammatory myofibroblastic tumor, gastrointestinal stromal tumor, and leiomyosarcoma are other much rarer entities occurring within the bladder. Few to no case reports exist documenting their identification within urine cytology specimens. Herein we report the detection of a high-grade prostatic sarcoma within a catheterized urine specimen of a young male having a diffusely enlarged prostate. The specimen consisted of numerous fragments of relatively uniform spindle cells having ovoid nuclei with rounded ends and finely dispersed chromatin. Cytoplasmic borders were indistinct. No mitoses or significant atypia was present. The background consisted of numerous red blood cells, cellular debris, and a few clusters of unremarkable urothelial cells. Followup surgical biopsy of the patient's prostate revealed a high-grade spindle-cell sarcoma. Further immunohistochemical and molecular delineation of the tumor was not informative for a more definitive diagnosis. Although rare, sarcomas and other mesenchymal tumors involving the bladder are unique entities with a broad differential diagnosis.

Papillary tissue fragments in cervicovaginal (Pap) smears: cytomorphologic characteristics and clinicopathologic significance.

Papillary epithelial fragments (PEFs) are a rarely described architectural feature in cervicovaginal (Pap) smears. Morphologically, PEFs often consist of small, finely branching glandular tissue fragments with varying cytomorphology. This study identified 21 Pap smears (1978-2009) containing PEFs to determine the clinicopathologic significance of such findings. Patients ranged in age from 36 to 81 years (mean, 54 years). The Pap smear diagnoses consisted of 48% overt malignant neoplasms, 24% atypical fragments, and 28% benign entities. The papillary fragments featured a range of cytomorphologies consisting of benign features, mild to marked atypia, and overt malignancy. PEFs were more commonly found (57%) in specimens from patients with significant pathologic outcomes. Hence, the presence of PEFs in a Pap smear should raise concern for a neoplastic process. In smears displaying atypical to malignant cytomorphologic features recommendations for further clinical work-up and/or tissue studies should be made.

Spectrum of pilomyxoid astrocytomas: intermediate pilomyxoid tumors.

To define the spectrum of pilomyxoid morphology and to characterize the association between pilomyxoid astrocytoma (PMA) and pilocytic astrocytoma (PA), 84 cases of pediatric astrocytomas with pilomyxoid features were reviewed. Forty-two of these tumors had coexistent features of PMA and PA ("intermediate"). With the accumulation of more cytoplasm, fibrillar background, microcysts, and thickened blood vessels, these intermediate tumors were more PA-like and less like classic PMA. In the recurrent specimens, PMAs and intermediate tumors sometimes showed more prominent PA features. Both PMA and intermediate tumors involved sites outside the hypothalamus, optic chiasm, and the third ventricle. Both the existence of intermediate tumors and the finding that some PMAs and intermediate tumors mature into PA-like neoplasms over time, provided strong support for a biological relationship between PMA and PA. Additional evidence for a "maturational effect" was the finding that intermediate tumors occurred in patients with a median age of 36 months compared with the median age of 21 months for those with PMAs (P=0.017). Features that were often assumed to be poor prognostic indicators in gliomas, that is, necrosis, mitotic figures, and vascular proliferation, were not uncommon in typical PMAs and intermediate lesions. Further follow-up is needed to more accurately determine the prognosis of intermediate tumors.

Lipoglioblastoma: a lipidized glioma radiologically and histologically mimicking adipose tissue.

BACKGROUND: We report the case of a man with glioblastoma containing a component radiologically and histologically mimicking adipose tissue. CASE DESCRIPTION: A 48-year-old man recently complaining of headaches and difficulty with speech presented with a cystic peripherally enhancing left temporoparietal mass with focal intrinsically (precontrast) bright nodules in fluid attenuated inversion recovery and T1-weighted images similar to adipose tissue. Histologically, the enhancing component was classic glioblastoma, whereas the bright nodules comprised tumor cells that in aggregate closely resembled adipose tissue. CONCLUSIONS: The case illustrates the extent to which lipidized central nervous system tumors of glial origin, or components thereof, can radiologically and histologically resemble adipose tissue. However, immunohistochemical staining and electron microscopy can eliminate diagnostic confusion.

The utility of napsin-A in the identification of primary and metastatic lung adenocarcinoma among cytologically poorly differentiated carcinomas.

BACKGROUND: New developments in the treatment of lung cancer have necessitated the further histologic and cytologic subtyping of nonsmall cell lung carcinomas. Thyroid transcription factor-1 (TTF-1) long has served as the predominant marker for demonstrating lung origin. However, it is also expressed in a variety of other tumors, particularly neuroendocrine neoplasms and, to a much lesser degree, squamous cell carcinoma of the lung. Napsin-A, which is expressed in lung tissue, is a relatively new marker for lung adenocarcinoma. In this study, the authors examined the utility of napsin-A compared with TTF-1 in cytologic specimens of primary and metastatic, poorly differentiated lung adenocarcinomas. METHODS: The archives of the Department of Pathology at The Johns Hopkins Hospital were searched for cytologic cases of poorly differentiated lung adenocarcinoma that were histologically confirmed. In total, 75 patients (cases) along with 95 controls were included, each of whom had adequate cell block material for TTF-1 and napsin-A staining. Tissue microarrays of lung adenocarcinoma also were examined. RESULTS: TTF-1 and napsin-A were detected in 61 of 75 cases (81.3%) and in 49 of 75 cases (65.3%), respectively. The sensitivity and specificity of TTF-1 were 81% each; and napsin-A had a greater specificity of 96%, and sensitivity of 65%. Napsin-A was not detected in small cell carcinomas or in other carcinomas of nonlung origin except for renal cell carcinoma. CONCLUSIONS: Although TTF-1 had a higher sensitivity, napsin-A was useful as a surrogate marker when encountering a poorly differentiated lung adenocarcinoma or an unknown primary tumor, particularly in cytologic specimens and difficult cases. The current results indicate that the dual use of both markers may be necessary to improve diagnostic accuracy.

Rapid malignant transformation of low-grade astrocytomas: report of 2 cases and review of the literature.

BACKGROUND: Low-grade gliomas have been documented to undergo transformation into high-grade astrocytomas, and the time interval of this transformation has been reported to generally occur within 5 years in about 50% of patients harboring these low-grade lesions. Several studies have investigated the evolution of low-grade gliomas into malignant gliomas by CT and MRI characteristics, but many have not documented the timing of these transformation processes. CASE DESCRIPTION: The authors discuss the cases of 2 patients with histopathologically confirmed grade II astrocytomas after craniotomies that underwent rapid evolution into malignant gliomas within 13 weeks. Interestingly, both low-grade astrocytomas were positive with immunostaining for the epidermal growth factor receptor, in which its amplification has been implicated as a molecular marker of malignant gliomas. In addition, the grade II astrocytomas were negative for p53 in both patients but were found to be positive upon transformation into malignant gliomas. CONCLUSIONS: To our knowledge, this is the first report of rapid malignant transformation of low-grade gliomas, which were proven by histology, within 13 weeks. There may be patients with a subtype of low-grade astrocytomas that may warrant molecular characterization to determine if aggressive adjuvant therapy would be of benefit.

Cytologic diagnosis and differential diagnosis of lung carcinoid tumors a retrospective study of 63 cases with histologic correlation.

BACKGROUND:: Neuroendocrine (NE) neoplasms of the lung are a spectrum of tumors including typical carcinoid (TC), atypical carcinoid tumor (ACT), small cell lung carcinoma (SCLC), and large cell NE carcinoma (LCNEC). Given the overlapping features within these tumors, misclassification is a known risk, with significant treatment consequences. METHODS:: A search of the pathology archives from The Johns Hopkins Hospital yielded 390 cases of TC diagnosed over 20 years. Sixty-three cytology cases with corresponding surgical material were identified. The cytology specimens were comprised of 49 cases of lung fine-needle aspiriation specimens and 14 cases of lung brushings/washings. RESULTS:: Among 63 paired cases, 32 cases (51%) demonstrated concordant and 31 cases (49%) demonstrated discordant diagnoses. Among discordant cases, the most notable findings included overdiagnosis of TC as SCLC (4 cases; 6%), ACT (4 cases; 6%), and poorly differentiated carcinoma with NE features (5 cases; 8%) as well as misdiagnosis of other lesions as TC (4 cases; 6%) on cytology. CONCLUSIONS:: The significant morphologic factors for distinguishing low-grade TC from ACT, SCLC, or carcinoma remain the critical evaluation of nuclear features, chromatin patterns, and assessment of nucleoli. Nuclear molding and crowding are not discernible features because they may be found on smears with increased cellularity. Crush artifact can occur in both low-grade and high-grade NE neoplasms and may cause a misinterpretation of SCLC. Other artifacts resulting from delayed fixation or poor processing and sampling error are potential causes of incorrect interpretations. Ki-67 staining may be useful in difficult cases. Cancer (Cancer Cytopathol) 2010. © 2010 American Cancer Society.

Cytologic diagnosis and differential diagnosis of lung carcinoid tumors a retrospective study of 63 Cases with histologic correlation.

BACKGROUND: Neuroendocrine (NE) neoplasms of the lung are a spectrum of tumors including typicalcarcinoid (TC), atypical carcinoid tumor (ACT), small cell lung carcinoma (SCLC), and large cell NEcarcinoma (LCNEC). Given the overlapping features within these tumors, misclassification is a known risk, with significant treatment consequences. METHODS: A search of the pathology archives from The Johns Hopkins Hospital yielded 390 cases of TC diagnosed over 20 years. Sixty-three cytology cases with corresponding surgical material were identified. The cytology specimens were comprised of 49 cases of lung fine-needle aspiriation specimens and 14 cases of lung brushings/washings. RESULTS: Among 63 paired cases, 32 cases (51%) demonstrated concordant and 31 cases (49%) demonstrated discordant diagnoses. Among discordant cases, the most notable findings included overdiagnosis of TC as SCLC (4 cases; 6%), ACT (4 cases; 6%), and poorly differentiated carcinoma with NE features (5 cases; 8%) as well as misdiagnosis of other lesions as TC (4 cases; 6%) on cytology. CONCLUSIONS: The significant morphologic factors for distinguishing low-grade TC from ACT, SCLC, or carcinoma remain the critical evaluation of nuclear features, chromatin patterns, and assessment of nucleoli. Nuclear molding and crowding are not discernible features because they may be found on smears with increased cellularity. Crush artifact can occur in both low-grade and high-grade NE neoplasms and may cause a misinterpretation of SCLC. Other artifacts resulting from delayed fixation or poor processing and sampling error are potential causes of incorrect interpretations. Ki-67 staining may be useful in difficult cases.