INTRODUCTION<\/p>\n
Andrew H. Fischer, M.D<\/em><\/p>\n Note: The cell block images presented here were generated using a manual method during development of the automated instrument.<\/p>\n The Papanicolaou Society of Cytopathology recently proposed a uniform thyroid FNA classification system to minimize ambiguity between pathologists and clinicians [1]<\/sup>. In this chapter, we will use their proposed classification:<\/p>\n Conventional thyroid FNA cytology preparations provide the following diagnostic information:<\/p>\n As described below, nuclear morphology has to be examined in order to diagnose or exclude papillary thyroid carcinoma. Whether a lesion is microfollicular or macrofollicular relates directly to the amount of colloid and the proportion of follicular cells to colloid. In general, follicular type neoplasms are microfollicular with scant dense colloid [2]<\/sup>. Papillary thyroid carcinomas may be either micro or macrofollicular [2]<\/sup>. Benign follicular nodules are generally macrofollicular and very commonly show cystic degeneration [2, 3]<\/sup>. The cystic degeneration in benign follicular nodules appears as though it has a component of venous stasis, and exhibits edematous, watery colloid together with hemosiderin. Papillary thyroid carcinoma also often shows macrophages with hemosiderin [2]<\/sup>. However, such cystic degeneration is reportedly very uncommon in follicular neoplasms [2, 3]<\/sup>, and this has also been our experience. Therefore, once papillary thyroid carcinoma is excluded (based on the absence of the characteristic nuclear features described below), the presence of hemosiderin is very strong evidence in favor of a benign follicular lesion. Lymphocytes, often with plasma cells and fragments of germinal centers, are seen in lymphocytic thyroiditis, but they are rare in follicular neoplasms [2]<\/sup>, even follicular neoplasms arising in the setting of lymphocytic thyroiditis. Lymphocytes and plasma cells are, however, relatively common in papillary thyroid carcinoma. Benign follicular lesions will typically show some variation in the cytologic features from group to group, rather than a monomorphic population.<\/p>\n Cell blocks provide all of the diagnostic information listed above, with the exception of very watery colloid. In our experience, the presence of hemosiderin in a follicular-type lesion is virtually always associated with watery colloid. Solid colloid fragments tend to be more abundant in the cell block than in the corresponding ThinPrep\u00ae<\/sup>.<\/p>\n Core biopsy can be synergistic with FNA for accurate evaluation of thyroid nodules [4, 5]<\/sup>. Likewise, combining cell blocks with FNA has been found to be useful, disclosing diagnostic patterns that may not be evident in monolayers [6, 7]<\/sup>. Kern found that 1\/5 of thyroid FNA’s had diagnostic material only in the cell block sections and not in smears [8]<\/sup>. In the following, the diagnostic synergy between monolayer preparations such as ThinPreps\u00ae<\/sup> and cell blocks are illustrated. ThinPrep will present the smaller fragments that are easy to study without histologic sectioning. The remaining largest fragments are captured in the cell block and enhance the ability to see how cell morphology varies over larger-scale distances, useful for the following diagnostic challenges:<\/p>\n This chapter illustrates some of these advantages. In general, non-neoplastic H\u00fcrthle cell changes, or focal reactive-type nuclear clearing suggestive of papillary thyroid carcinoma, will show a spectrum of changes that blend over the span of a few follicles with normal-appearing follicular cells. In cell blocks, one may have the opportunity to see how the reactive changes are related spatially to areas of lymphocytic destruction of the follicles, or areas in a benign colloid nodule that have become denuded to evoke the reparative reaction resembling papillary thyroid carcinoma. In contrast, neoplastic H\u00fcrthle cells or papillary thyroid carcinoma will show an abrupt (“clonal-appearing”) transition when compared to benign follicular cells, without any apparent relation to a lymphocytic infiltrate.<\/p>\n Cell blocks allow the follicle size to be judged in a manner that complements ThinPrep slides. For a follicle to be considered large, the follicular cells need to be arranged 2-dimensionally over a fairly broad distance; if the follicles are small, the cells will not present in a broad 2-dimensional flat sheet. Surprisingly, it is difficult to find a consensus on the definition of “macrofollicular” [9]<\/sup>. Eight to 10 follicular cell diameters appears to be a reasonable definition for the macrofollicular colloid fragments [9]<\/sup>, or for the diameter of flat, 2-dimensional macrofollicular sheets. In tissue sections that cut perpendicular to a macrofollicular group, macrofollicles will appear as a linear arrangement of at least 8 follicular cells. If the section cuts in the plane of a macrofollicular group, one can occasionally encounter a solid-appearing mass of cells analogous to a tissue section that cuts tangentially right through the ductal cell layer in a breast biopsy. Just as surgical pathologists can recognize such tangential sectioning and distinguish this from ductal hyperplasia, one can recognize tangential sectioning through macrofollicular groups. This is illustrated below. Microfollicles by definition have a high proportion of cells to colloid, and the cells cannot lie within a broad 2-dimensional sheet. In cell block sections, microfollicles will not show long linear arrangements of cells. Renshaw et al., found a significant gray zone among experts in the distinction between microfollicular and macrofollicular groupings on cytology preparations [9]<\/sup>. One of the major gray areas relates to the problem of disaggregated follicular cells artifactually piled on top of each other. This artifactual piling up of cells appears easier to diagnose in tissue sections. Another problem area includes those cases in which there are mixtures of microfollicles and macrofollicles. We and others have noted that benign goiterous nodules tend to show flattened cytoplasm in the cells of the microfollicles. The more robust cells of a follicular neoplasm tend to show mostly cuboidal, or even columnar, follicular cells lining the microfollicles [7]<\/sup>. These features are evident in cell block sections and are illustrated below.<\/p>\n Benign follicular nodules tend to show an admixture of cytologically different types of follicular cells. Follicular neoplasms are more likely to be uniform from follicle to follicle. While the appearance of the follicles in a cytology preparation can be compared from group to group, this approach to judging “clonality” may at times be difficult. For example, it can be impossible to know whether the FNA needle sampled areas outside of a neoplasm. Cell blocks can often allow assessment of the morphologic features of truly adjacent follicles over a span of several hundred microns, as illustrated below.<\/p>\n There are some differences in the appearance of nuclei in direct smears, ThinPreps\u00ae<\/sup>, and cell blocks. One advantage of cell blocks is that they provide a common platform that can be shared with the surgical pathologists who will ultimately diagnose a resection specimen. We illustrate the utility of this approach for trying to classify the FNAs of problematic follicular-patterned lesions with partially developed nuclear features of papillary thyroid carcinoma [3]<\/sup>.<\/p>\n Papillary thyroid carcinoma is an easy diagnosis if the nuclear features are well-developed and the sample is well-preserved. The best diagnostic features of papillary thyroid carcinoma are finely dispersed chromatin, and nuclear envelope irregularity [2]<\/sup>. Interestingly, papillary thyroid carcinoma is the first example of cancer where the diagnostic nuclear features are known to be directly related to the genes that cause it (reviewed in [10]<\/sup>). A spectrum of nuclear envelope irregularity can be present [11]<\/sup>. The chromatin of a papillary thyroid carcinoma is dispersed into very fine particles, and since much of the chromatin is smoothly adherent to the nuclear envelope, even a tiny fold will cause the nuclear envelope-associated chromatin to appear as a linear aggregate or longitudinal groove. Intranuclear cytoplasmic inclusions are particularly characteristic of papillary thyroid carcinoma, but may also be seen in medullary thyroid carcinoma. This intranuclear cytoplasmic inclusion appears as a sharp demarcation which comes from the nuclear envelope-associated heterochromatin, giving it a distinct dark purple border with the cytoplasm. Intranuclear cytoplasmic inclusions are very uncommon in follicular neoplasms [2]<\/sup>.<\/p>\n In contrast to papillary thyroid carcinoma, follicular neoplasms tend to show compact aggregates of heterochromatin. As a rough way of distinguishing the papillary carcinoma nuclei from follicular carcinoma nuclei, we have found it useful to note that papillary thyroid carcinomas tend to show more linear aggregates of chromatin (representing very shallow folds of the nuclear envelope) compared to rounded or clumped aggregates of chromatin. These features are illustrated below.<\/p>\n Finally, cell blocks provide a stable platform for immunohistochemistry. Immunohistochemistry for calcitonin is recommended for confirming medullary thyroid carcinoma [1]<\/sup>. Immunohistochemical distinction of papillary thyroid carcinoma from follicular neoplasms has not been widely successful [12]<\/sup>. In general, it appears that when cells develop papillary thyroid carcinoma-like nuclear changes, the cells will show markers of papillary thyroid carcinoma, including cytokeratin 19 and HBME positive staining [13, 14]<\/sup>. The distinction between papillary thyroid carcinoma and reactive changes in such cases is determined by the larger-scale architectural features that are sometimes evident in cell blocks. The future development of markers that can distinguish the diagnostic categories of follicular lesions on FNA will likely require a stable platform for immunohistochemistry or molecular studies. Paraffin-embedded cell blocks provide such a platform. We illustrate one novel application of CD34 immunostaining that suggested the specific diagnosis of an insular-type of poorly differentiated thyroid carcinoma.<\/p>\n Hyperplastic\/Adenomatoid Nodule<\/p>\n Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Benign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong> Follicular neoplasm, Thyroid FNA, Cell Block.<\/strong>\n
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\nfor an enlarged view.<\/strong><\/p>\n
\n![\"Image](\"\/gallery\/images_large\/slide1721.jpg\" "\\"Click")
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\nMacrofollicular groups are arranged in a flat, two-dimensional sheet. Note the round shape and regular, wide spacing of nuclei. As a rough guide, if the nuclei all lie in the same plane over about 8-10 cell diameters (e.g., between the two arrows), the follicle is macrofollicular (see text).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nMacrofollicular groups are arranged in a flat, two-dimensional sheet. Note the round shape and regular, wide spacing of nuclei. As a rough guide, if the nuclei all lie in the same plane over about 8-10 cell diameters (e.g., between the two arrows), the follicle is macrofollicular (see text).
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\nA macrofollicle with colloid measuring about 10 follicular cells in diameters is present at the left (arrows). A macrofollicular group (broad, flat, 2 dimensional) that has spilled its colloid is present in the upper right (open arrows).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nA macrofollicle with colloid measuring about 10 follicular cells in diameters is present at the left (arrows). A macrofollicular group (broad, flat, 2 dimensional) that has spilled its colloid is present in the upper right (open arrows).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nA macrofollicular group that has spilled its colloid will show a long linear arrangement of 8-10 follicular cells. Note the basal positioning and regular round shape of the nuclei that are features of benign follicular-type epithelium.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nA macrofollicular group that has spilled its colloid will show a long linear arrangement of 8-10 follicular cells. Note the basal positioning and regular round shape of the nuclei that are features of benign follicular-type epithelium.
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\nIt is sometimes difficult to characterize whether follicular groups are macro or microfollicular when the follicles are disrupted and clusters overlap in a monolayer preparation. The finding of hemosiderin in macrophages (arrow) in a follicular-type lesion favors a benign nodule.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nIt is sometimes difficult to characterize whether follicular groups are macro or microfollicular when the follicles are disrupted and clusters overlap in a monolayer preparation. The finding of hemosiderin in macrophages (arrow) in a follicular-type lesion favors a benign nodule.
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\nRarely a macrofollicular group is sectioned parallel to the plane of the nuclei. The clue to the macrofollicular nature of such a group is to recognize the tangential sectioning that leaves only cytoplasm at the edges of the groups (arrows). This particular macrofollicular group shows nuclear overlapping, a feature that should prompt careful examination of the nuclei to rule out papillary thyroid carcinoma (see below).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nRarely a macrofollicular group is sectioned parallel to the plane of the nuclei. The clue to the macrofollicular nature of such a group is to recognize the tangential sectioning that leaves only cytoplasm at the edges of the groups (arrows). This particular macrofollicular group shows nuclear overlapping, a feature that should prompt careful examination of the nuclei to rule out papillary thyroid carcinoma (see below).
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\nThe corollary of large sized follicles is the presence of large pieces of colloid, and an increased proportion of colloid compared to follicular cells.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nThe corollary of large sized follicles is the presence of large pieces of colloid, and an increased proportion of colloid compared to follicular cells.
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\nLarge pieces of colloid that were not deposited on the ThinPrep\u00ae<\/sup> slide from the above case are displayed in the cell block sections.
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\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nLarge pieces of colloid that were not deposited on the ThinPrep\u00ae<\/sup> slide from the above case are displayed in the cell block sections.
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\nSame magnification as Figure 6 shows large pieces of colloid that reflect the macrofollicular architecture of the follicular cells that produced the colloid. Note the linear strips of epithelium (arrow), representing macrofollicular groups.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nSame magnification as Figure 6 shows large pieces of colloid that reflect the macrofollicular architecture of the follicular cells that produced the colloid. Note the linear strips of epithelium (arrow), representing macrofollicular groups.
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\nNote the abundant macrofollicular-sized colloid fragments and macrofollicular strips of follicular epithelium (arrow).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nNote the abundant macrofollicular-sized colloid fragments and macrofollicular strips of follicular epithelium (arrow).
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\nThe mostly large size of the follicles is readily apparent. Note the presence of hemosiderin in macrophages (arrow), a finding that also favors a benign nodule if the nuclear features of papillary thyroid carcinoma are not present (see text).
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nThe mostly large size of the follicles is readily apparent. Note the presence of hemosiderin in macrophages (arrow), a finding that also favors a benign nodule if the nuclear features of papillary thyroid carcinoma are not present (see text).
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\nThe lower right side of the group appears macrofollicular, but the upper and left sides of this fragment could represent microfollicular groups (arrows) because the cells do not lie in a two-dimensional flat sheet. Hemosiderin in a macrophage is helpful in favoring a benign colloid nodule.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nThe lower right side of the group appears macrofollicular, but the upper and left sides of this fragment could represent microfollicular groups (arrows) because the cells do not lie in a two-dimensional flat sheet. Hemosiderin in a macrophage is helpful in favoring a benign colloid nodule.
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\nSome definite microfollicular groups are present (arrows) in this same case shown in Figure 11. Note the macrophages with hemosiderin at the lower left.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, ThinPrep\u00ae<\/sup>.<\/strong>
\nSome definite microfollicular groups are present (arrows) in this same case shown in Figure 11. Note the macrophages with hemosiderin at the lower left.
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\nThe cell block corresponding to Figures 11-12 shows a clear admixture of micro and macrofollicles. Two features favor a benign nodule. The first is that the microfollicles show a flattened cytoplasm compared to the more robust-appearing macrofollicular cells (compare the height of the cytoplasm at the two arrows). A second feature is the variation in the appearance of the colloid from follicle to follicle. Note the edematous colloid in one follicle adjacent to a follicle with dense colloid (open arrows). Benign hyperplastic\/adenomatoid nodules are anticipated to show heterogeneity, while follicular neoplasms are more monotonous.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nThe cell block corresponding to Figures 11-12 shows a clear admixture of micro and macrofollicles. Two features favor a benign nodule. The first is that the microfollicles show a flattened cytoplasm compared to the more robust-appearing macrofollicular cells (compare the height of the cytoplasm at the two arrows). A second feature is the variation in the appearance of the colloid from follicle to follicle. Note the edematous colloid in one follicle adjacent to a follicle with dense colloid (open arrows). Benign hyperplastic\/adenomatoid nodules are anticipated to show heterogeneity, while follicular neoplasms are more monotonous.
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\nNote the flattened cytoplasm in the microfollicles compared to the cuboidal to columnar cytoplasm of the macrofollicular epithelium at the upper left. Note also the watery colloid in one follicle (arrow) compared to the dense colloid in the microfollicles.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nNote the flattened cytoplasm in the microfollicles compared to the cuboidal to columnar cytoplasm of the macrofollicular epithelium at the upper left. Note also the watery colloid in one follicle (arrow) compared to the dense colloid in the microfollicles.
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\nDense fibrous tissue (not actively desmoplastic) containing hemosiderin and markedly atrophic, flattened follicles are seen.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nDense fibrous tissue (not actively desmoplastic) containing hemosiderin and markedly atrophic, flattened follicles are seen.
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\nThin colloid at the lower left compared to the denser colloid in the microfollicles together with a flattened, atrophic appearance of the follicular cells in the microfollicles favor a benign hyperplastic\/adenomatoid nodule.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nThin colloid at the lower left compared to the denser colloid in the microfollicles together with a flattened, atrophic appearance of the follicular cells in the microfollicles favor a benign hyperplastic\/adenomatoid nodule.
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\nThe tissue architecture evident here illustrates the variability in the cytoplasm between neighboring follicles, with the follicles marked with arrows showing varying degrees of H\u00fcrthle cell change compared to the unmarked follicles.
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\n<\/strong>
\nBenign, Hyperplastic\/adenomatoid nodule, Thyroid FNA, Cell Block.<\/strong>
\nThe tissue architecture evident here illustrates the variability in the cytoplasm between neighboring follicles, with the follicles marked with arrows showing varying degrees of H\u00fcrthle cell change compared to the unmarked follicles.
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\nThe uniformity of the cytoplasm, the robust cuboidal epithelial cells, the microfollicular arrangement, the absence of hemosiderin, and the uniformity of the colloid favor a follicular neoplasm in this one field.
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\n<\/strong>
\nFollicular neoplasm, Thyroid FNA, Cell Block.<\/strong>
\nThe uniformity of the cytoplasm, the robust cuboidal epithelial cells, the microfollicular arrangement, the absence of hemosiderin, and the uniformity of the colloid favor a follicular neoplasm in this one field.
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