Solid cell nests of the thyroid. A histologic and immunohistochemical study

Comparative Histology of C Thyrocytes in Four Domestic Animal Species: Dog, Pig, Horse, and Cattle

Simple Summary

In this study we have proved that dogs, pigs, cattle, and horses, species belonging to four distinct families, differ in regard to microscopical characteristics of their C thyrocytes. Although the total number of C thyrocyte profiles and their localization within thyroid lobes were comparable, each of the examined species displayed their unique morphological characteristics and distribution pattern. The differences described in our study, easily recognizable microscopically, can be used as a reference material for further studies focused on C thyrocytes biology in physiological and pathological conditions.

Abstract

The number, morphology, and distribution of C thyrocytes within the thyroid gland vary among species; however, studies in domestic animals are limited. In this study we compared the morphology, distribution pattern, and percentage of C thyrocytes in four domestic species: dogs, pigs, horses, and cattle. Eighty thyroid glands, 20 per species, were examined. C thyrocytes were visualized immunohistochemically with anti-calcitonin rabbit polyclonal antibody alone and combined with the periodic acid Schiff method to simultaneously visualize C thyrocytes with the basement membranes of thyroid follicles. C thyrocyte morphology varied considerably between species, from oval- (dogs) and spindle-shaped (pigs) to polymorphic (cattle and horses). Bovine C thyrocytes demonstrated cytoplasmic protrusion. C thyrocytes were located intrafolliculary (all species), epifollicularly (dogs, horses, cattle), or interfolicularly (cattle). Most porcine and bovine C thyrocytes existed individually whereas canine C thyrocytes usually formed clusters. In horses, they tended to form groups of various shapes and sizes or even rims encompassing whole follicles. In all species, the number of C thyrocyte profiles increased from the periphery to the central area of the thyroid lobe. The mean total fraction of C thyrocytes in the superficial, intermediate, and central areas were as follows: 2.55%, 8.43%, and 12.48% in dogs; 3.81%, 7.66%, and 10.79% in pigs; 1.55%, 7.44%, and 8.87% in horses; and 2.62%, 10.75%, and 12.96% in cattle. No statistical differences in the total number of C thyrocyte profiles were observed among species (8.87% in dogs, 8.58% in cattle, 7.98% in pigs, and 5.83% in horses). Our results indicated that the studied species displayed their own morphological characteristics and distribution pattern of C thyrocytes; however, total numbers of C thyrocyte profiles and their localization within the thyroid lobe are comparable.

Primary mucoepidermoid carcinoma of the intrahepatic bile duct: A case report

Mucoepidermoid carcinoma (MEC) is the most common salivary gland carcinoma; however, hepatobiliary MEC is extremely rare. A 74-year-old patient was diagnosed with hepatobiliary MEC after hepatectomy. We considered its origin could be the peribiliary glands. Its genome profile was similar to salivary MEC rather than standard biliary tract carcinoma.

Follicular cell lineage in persistent ultimobranchial remnants of mammals

It has been a subject of much debate whether thyroid follicular cells originate from the ultimobranchial body, in addition to median thyroid primordium. Ultimobranchial remnants are detected in normal dogs, rats, mice, cattle, bison and humans and also in mutant mice such as Eya1 homozygotes, Hox3 paralogs homozygotes, Nkx2.1 heterozygotes and FRS2α^2F/2F. Besides C cells, follicular cell lineages immunoreactive for thyroglobulin are located within these ultimobranchial remnants. In dogs, the C cell complexes, i.e., large cell clusters consisting of C cells and undifferentiated cells, are present together with parathyroid IV and thymus IV in or close to the thyroid lobe. In addition, follicular cells in various stages of differentiation, including follicular cell groups and primitive and minute follicles storing colloid, are intermingled with C cells in some complexes. This review elaborates the transcription factors and signaling molecules involved in folliculogenesis and it is supposed why the follicular cells in the ultimobranchial remnants are sustained in immature stages. Pax8, a transcription factor crucial for the development of follicular cells, is expressed in the fourth pharyngeal pouch and the ultimobranchial body in human embryos. Pax8 expression is also detected in the ultimobranchial remnants of Eya1 and Hes1 null mutant mice. To determine whether the C cells and follicular cells in the ultimobranchial remnants consist of dual lineage cells or are derived from the common precursor, the changes of undifferentiated cells in dog C cell complexes are examined after chronically induced hypercalcemia or antithyroid drug treatment.

Derivation of thyroid lymphoepithelial cysts from follicular cells

The pathogenesis of thyroid lymphoepithelial cysts is controversial, and two hypotheses have been proposed, namely derivation from branchial-derived remnants or from squamous metaplasia of the follicular cells. The aim of this study was to clarify the pathogenesis of thyroid lymphoepithelial cysts. We performed pathological and immunohistochemical examination of 21 thyroid lymphoepithelial cysts, 13 non-neoplastic squamous metaplasia samples without thyroid carcinoma, 13 solid cell nests, and 14 lateral cervical cysts. On ultrasound, half of thyroid lymphoepithelial cysts were interpreted as calcified nodules regardless of no calcification. Thyroid lymphoepithelial cysts and squamous metaplasia tended to be located in the central and lower portions of the thyroid, while solid cell nests were located in the upper and central portions (p < 0.05). In 95.2% of patients with thyroid lymphoepithelial cysts and all patients with squamous metaplasia, lesions were histologically associated with chronic thyroiditis forming lymph follicles. Hashimoto's disease was serologically confirmed in 18 patients with lymphoepithelial cysts (85.7%) and 10 patients with squamous metaplasia (76.9%). Immunohistochemically, lymphoepithelial cysts showed nuclear positivity for PAX8, thyroid transcription factor 1, and p63. One lateral cervical cyst (7.1%) showed positive staining for PAX8, while solid cell nests were PAX8-negative. In three (14.3%) cases of thyroid lymphoepithelial cysts, squamous cells located on the superficial layer were focally and weakly positive for CEA. We concluded that thyroid lymphoepithelial cysts originate from follicular cells and are unrelated to solid cell nests and lateral cervical cysts arising from branchial-derived remnants.

Immunohistochemical profiling of the ultimobranchial remnants in the rat postnatal thyroid gland

Ultimobranchial (UB) remnants are a constant presence in the thyroid throughout rat postnatal life; however, the difficulty in identifying the most immature forms from the surrounding thyroid tissue prompted us to search for a specific marker. With that objective, we applied a panel of antibodies reported to be specific for their human counterpart, solid cell nests (SCNs), using double immunohistochemistry and immunofluorescence. Our results demonstrated that cytokeratin 34βE12 and p63 are highly sensitive markers for the immunohistologic screening of UB-remnants, independently of their maturity or size. Furthermore, rat UB-follicles (UBFs) coincided with human SCNs in the immunohistochemical pattern exhibited by both antigens. In contrast, the pattern displayed for calcitonin and thyroglobulin differs considerably but confirm the hypothesis that rat UB-cells can differentiate into both types of thyroid endocrine cells. This hypothesis agrees with recent findings that thyroid C-cells share an endodermic origin with follicular cells in rodents. We suggest that the persistence of p63-positive undifferentiated cells in UB-remnants may constitute a reservoir of basal/stem cells that persist beyond embryogenesis from which, in certain unknown conditions, differentiated thyroid cells or even unusual tumors may arise.

Branchial cleft-like cysts in Hashimoto's thyroiditis: A case report and literature review

We report an extremely rare case of branchial cleft-like cysts in Hashimoto's thyroiditis. The patient was a 77-year-old man with a growing mass in the anterior neck. Ultrasonography and computed tomography revealed a cystic lesion with septum in the left thyroid and multiple small cystic lesions in the right thyroid. Lymph node swelling of the cervical region, supraclavicular fossa and submandibular region was also observed. Left thyroidectomy and lymph node dissection were performed. Histologically, cysts were lined by stratified squamous epithelium and dense lymphoid tissue having conspicuous follicle formation surrounded the epithelial lining. Solid cell nest (SCN)-like aggregations were seen in the thyroid parenchyma adjacent to the cyst walls and a small number of thyroid follicles were observed in the fibrous wall. Immunohistochemically, it is suggested that both the cyst lining and SCN-like aggregations are originally from thyroid follicles. Although, the exact histogenesis of branchial cleft-like cysts remains unclear, there are probably two different processes for its development, one is of branchial cleft origin and the other is mere squamous metaplasia, while in our case the latter is suggested. Herein, we report our new case and update information about branchial cleft-like cysts that appears in the literature.

Postnatal fate of the ultimobranchial remnants in the rat thyroid gland

The ultimobranchial follicles (UBFs) are considered embryonic remnants from the ultimobranchial body (UBB). They are follicular structures that vary in size and appearance depending on the age of the rat. The main objective of this article was to study the progressive changes in shape, size, and frequency of the UBFs in the postnatal rat, from birth to old-age. To accomplish that objective, a systematic morphometric and incidental study of the UBF has been carried out in 110 Wistar rats of different ages and both sexes, divided into three groups: 1) young rats (5-90-day-old); 2) adult rats (6-15-month-old), and 3) old rats (18-24-month-old). The glands were serially sectioned and immunostained for calcitonin at five equidistant levels. According to our results, UBFs were observed in all thyroid glands but a more exhaustive sampling was occasionally necessary in male rats. In young rats, immature UBFs predominantly appeared whereas in adult rats, mature UBFs with cystic appearance and variable luminal content prevailed. We frequently found spontaneous anomalous UBFs in old rats, which we have termed as "ultimobranchial cystadenomata." Additionally, in young rats, UBF areas significantly increased with age and they were larger when compared to that of normal thyroid follicles. Likewise, in adult rats, UBFs were significantly larger than normal thyroid follicles but only in female rats. In general, UBFs in females were also significantly larger than those found in male rats. Finally, all these differences related to UBFs together with a higher incidence in females of UB cystadenomata suggest a sexual dimorphism in regard to the destiny of these embryonic remnants during postnatal thyroid development.

Absence of the BRAF and the GRIM-19 mutations in oncocytic (Hürthle cell) solid cell nests of the thyroid

We report the first case of oncocytic solid cell nests (SCNs), found in the right lobe of the thyroid of a 70-year-old man. Conventional SCNs and 1 papillary microcarcinoma (mPTC) were also found in the left lobe. In the oncocytic SCNs, 80% of the main cells showed oncocytic cytoplasm immunoreactive for porin and proteins of the SDHB and SDHA genes. Positivity for cytokeratin 19, p63, galectin-3, and HBME-1 and negativity for thyroglobulin, thyroperoxidase, vimentin, Oct-4, and α-fetoprotein were found in oncocytic and conventional SCNs. An inverse correlation was found between oncocytic metaplasia and p63. Association with C cells was confirmed at protein and messenger RNA levels in both types of SCNs. No germinal mutation of GRIM-19 was detected. No somatic BRAF mutation was found in any of the SCNs nor in the mPTC. We conclude that SCNs may acquire mitochondrial alterations similar to those seen in follicular and C cells, as well as in their respective tumors.

Clinical and pathological implications of concurrent autoimmune thyroid disorders and papillary thyroid cancer

Cooccurrences of chronic lymphocytic thyroiditis (CLT) and thyroid cancer (DTC) have been repeatedly reported. Both CLT and DTC, mainly papillary thyroid carcinoma (PTC), share some epidemiological and molecular features. In fact, thyroid lymphocytic inflammatory reaction has been observed in association with PTC at variable frequency, although the precise relationship between the two diseases is still debated. It also remains a matter of debate whether the association with a CLT or even an autoimmune disorder could influence the prognosis of PTC. A better understanding about clinical implications of autoimmunity in concurrent thyroid cancer could raise new insights of thyroid cancer immunotherapy. In addition, elucidating the molecular mechanisms involved in autoimmune disease and concurrent cancer allowed us to identify new therapeutic strategies against thyroid cancer. The objective of this article was to review recent literature on the association of these disorders and its potential significance.

Solid cell nests in Hashimoto's thyroiditis sharing features with papillary thyroid microcarcinoma

Solid cell nests (SCN) associated with Hashimoto's thyroiditis may show some atypical nuclear features including prominent nuclear grooves, enlarged overlapping nuclei and nuclear clearing. These features are sometimes mistaken for papillary thyroid microcarcinomas especially when the SCN are numerous. We reviewed SCN associated with Hashimoto's thyroiditis in 12 patients selected from 1,420 archival routinely processed formalin-fixed, paraffin-embedded thyroid specimens of Hashimoto's thyroiditis in which there was more than ten SCN per slide. In addition to the atypical nuclear features, there was a distinct eosinophilic basement membrane surrounding the SCN. Immunohistochemical analysis showed that the SCN were strongly positive for p63, stained weakly for TTF-1 and were negative for thyroglobulin, HBME-1, and calcitonin. This was compared to papillary thyroid microcarcinomas which were strongly positive for thyroglobulin, TTF-1, HBME-1, and variably positive for p63, while calcitonin and chromogranin were negative. These histological and immunophenotypic features can be used to distinguish SCN from papillary thyroid microcarcinomas associated with Hashimoto's thyroiditis.

[Mucoepidermoid carcinoma of the thyroid: a case report and literature review]

The mucoepidermoid carcinoma is a neoplasia that usually occurs at salivary glands, breast, pancreas and gastrointestinal tract. The primary occurrence on thyroid gland is rare and only 33 cases were previously published. Although the majority of cases of mucoepidermoid carcinoma of the thyroid (MECT) show a benign evolution, this paper describes a patient with an aggressive tumor. A literature review over clinical, histopathological, immunohistochemical features and histogenetic origin was discussed.

Immunohistochemical detection of p53 homolog p63 in solid cell nests, papillary thyroid carcinoma, and hashimoto's thyroiditis: A stem cell hypothesis of papillary carcinoma oncogenesis

Most models suggest that the cell of origin of papillary carcinoma is the mature thyroid follicular epithelial cell. In a recent study, p63 was detected in papillary carcinoma, Hashimoto's thyroiditis, and in squamoid aggregates and solid cell nests (SCNs), embryonic remnants found sporadically in the fully developed thyroid. In the present study, the relationship between solid cell nests and papillary carcinoma was investigated further. Four-micrometer sections from 88 routinely fixed and processed archival thyroidectomy specimens were pretreated with citric acid pH 6.0 for antigen retrieval, then incubated overnight with anti-p63 monoclonal antibody 4A4. Slides were stained with a streptavidin-biotin kit and diaminobenzidine as chromogen and were counterstained with hematoxylin. Squamoid aggregates or SCNs were noted in 21 specimens. Several morphologic variants of SCNs were found, all of which displayed p63 positivity. These included undifferentiated SCNs and those displaying commitment toward squamoid and ciliated glandular differentiation. Small, morphologically inconspicuous aggregates of p63-positive cells were commonly found in Hashimoto's thyroiditis. Commitment of p63-positive undifferentiated cells toward thyroid follicular epithelial differentiation was occasionally noted. One SCN variant, also associated with Hashimoto's thyroiditis, was a floretlike arrangement of p63-positive cells with fusiform nuclei. p63 staining was strong and uniform in some SCNs, but in other SCNs it was compartmentalized and homologous to stem cell-staining patterns in normal squamous or bronchial epithelia. Stem cell-like staining, associated with compartmentalized p63 staining or p63-positive undifferentiated cells, was noted in 7 of 27 papillary carcinomas. p63 immunostaining is a highly sensitive means of detecting SCNs. p63 expression patterns in SCNs and a subset of papillary carcinomas are closely homologous to stem cell-associated p63 staining patterns that have been described elsewhere in squamous and bronchial epithelia. We propose a stem-cell-associated model of papillary carcinoma oncogenesis that suggests that (1) p63-positive embryonal remnants rather than mature follicular cells are the cells of origin of a subset of papillary carcinomas; (2) these p63-positive cells are pluripotent and may stay undifferentiated or undergo benign squamoid or glandular maturation, may undergo thyroid follicular epithelial differentiation, may undergo oncogenic change leading to papillary carcinoma, or may trigger an immune reaction, resulting in lymphoid infiltration and Hashimoto's thyroiditis; and (3) Hashimoto's thyroiditis and papillary carcinoma may therefore be linked etiologically, because both disorders may be initiated by the same population of pluripotent p63-positive embryonal stem cell remnants.

p63 expression in solid cell nests of the thyroid: further evidence for a stem cell origin

Solid cell nests of the thyroid are embryonic remnants of endodermal origin that may be difficult to distinguish from squamous metaplasia, metastatic squamous carcinoma, papillary microcarcinoma, medullary carcinoma, and C-cell hyperplasia. These embryonic structures are composed of main cells and C-cells; cystic structures and mixed follicles are sometimes observed intermingled with solid cell nests. Recently, p63, a p53 homologue that is consistently expressed in basal/stem cells of stratified epithelia and plays a major role in triggering the differentiation of some specific cell lineages, has been characterized. We evaluated the immunohistochemical expression of p63, cytokeratins (CAM 5.2, AE1/AE3, 34betaE12, 7, and 20), carcinoembryonic antigen, thyroid transcription factor 1 (TTF-1), thyroglobulin, and calcitonin using the streptavidin-biotin-peroxidase complex technique in 6 bona fide solid cell nests. We observed that main cells of solid cell nests are strongly decorated by p63, while C-cells and all other thyroid structures were consistently negative. Moreover, main cells expressed carcinoembryonic antigen and all cytokeratins but cytokeratin 20 and lacked TTF-1, thyroglobulin and calcitonin. In contrast to this, C-cells of solid cell nests were immunoreactive for calcitonin, CAM 5.2, AE1/AE3, and cytokeratin 7; focal immunoreactivity for TTF-1 was also observed in some C-cells. We conclude that main cells of the solid cell nests display a basal/stem cell phenotype (p63 and basal cytokeratin positivity), whereas C-cells show features of parafollicular differentiation. We conclude, furthermore, that p63 antibodies may help in distinguishing solid cell nests from their mimics.

Immunocytochemical study of parafollicular cells of the thyroid and ultimobranchial remnants of the European bison

The aim of the present study was to compare parafollicular cells in the bison thyroid and its ultimobranchial remnants. The thyroid of 26 European bisons was fixed in Bouin's fluid, 5 microns thick paraffin sections were stained with hematoxylin and eosin. Azan or silver Grimelius methods. For immunocytochemical analysis specific rabbit antisera were used against human calcitonin (CT), human calcitonin gene-related peptide (CGRP), bovine (b) or rat (r) neuron-specific enolase (NSE), human synthetic somatostatin (ST), and porcine chromogranin. Strongly positive reactions in the majority of parafollicular cells were observed after application of antisera against CT, CGRP, bNSE and rNSE only. ST-immunopositive cells were found in small numbers. Immunopositive parafollicular cells were also present outside typical structures of the thyroid within persistent ultimobranchial remnants. In persistent ultimobranchial bodies, parafollicular cells were frequently observed in groups between ultimobranchial follicles in form of solid cell nests. Many of these cells did not react with any of the antisera used and showed features of immature cells. It is concluded that histomorphologic analysis and immunocytochemical examination reveals a heterogeneous population of parafollicular cells in the bison thyroid, and this heterogeneity was particularly clear in persistent ultimobranchial bodies.

Primary mucoepidermoid carcinoma of the thyroid gland: a report of six cases and a review of the literature of a follicular epithelial-derived tumor

Primary mucoepidermoid carcinomas of the thyroid gland are uncommon tumors of low-grade malignant potential. We report six cases of thyroid mucoepidermoid carcinoma, four occurred in women and two in men with an age range of 29 to 57 (median, 46 years). The clinical presentation was that of a painless mass. Radiographic studies showed a single, solid, "cold" nodule in either the right or left lobe, or isolated to the isthmus. There was no history of a mucoepidermoid carcinoma developing in more typical locations (eg, salivary gland) in any of the patients. Histologically, the tumors were characterized by an intimate admixture of squamoid/epidermoid cells and mucocytes. The tumors were delineated but not encapsulated with prominent cyst formation and a variable amount of associated fibrosis. The squamoid component showed horny pearl formation, individual cell keratinization and/or the presence of intercellular bridges. Intracytoplasmic and luminal epithelial mucin was observed in all cases. In three of the cases a prominent eosinophilic cellular infiltrate was intimately identified within the neoplastic proliferation. One other case was noteworthy for the presence of ciliated epithelium. In all of the cases the uninvolved thyroid tissue showed the presence of lymphocytic thyroiditis. Rare foci of squamous metaplasia were observed in two of the cases. A microscopic focus of thyroid papillary carcinoma was observed adjacent to the mucoepidermoid carcinoma in one case. Immunohistochemical evaluation of the mucoepidermoid carcinoma showed the following antigenic profile: cytokeratin (five of five), CAM 5.2 (four of four), thyroglobulin (five of six), calcitonin (none of six), chromogranin (none of six), polyclonal carcinoembryonic antigen (four of four), and monoclonal carcinoembryonic antigen (none of five). Surgical excision was the treatment of choice. All of the patients reported are alive without disease (recurrence or metastasis) over periods ranging from 1 to 15 years. Based on our findings, we believe that these tumors are of low-grade malignant potential and originate from thyroid follicular epithelial cells rather than from solid cell nests of the ultimobranchial body.