Hyalinizing trabecular adenoma of the thyroid gland

Hyalinizing Trabecular Tumor and Warthin Like Variant Coexisting with an Oncocytic Variant of Papillary Carcinoma: Two Case Reports of Rare Thyroid Cancer Types

We present two rare thyroid cancer cases, Hyalinizing trabecular tumor (HTT) and Warthin-like papillary thyroid carcinoma (WL-PTC) coexisting with an oncocytic PTC variant. A 64-year-old female patient presented with a 26 × 11.1 mm isoechoic thyroid nodule on ultrasound. Fine needle aspiration (FNA) cytology showed atypia of undetermined significance (TBS III). Three years later, new FNA cytology showed ''suspicious of malignancy (TBS V)''. The patient was thyroidectomized and pathology revealed HTT. The second patient, a 54-year-old woman presented with a 13 mm ultrasound thyroid nodule with irregular borders and microcalcifications. FNA cytology showed PTC, possibly a tall cell variant (TBS VI). The patient underwent thyroidectomy and pathology revealed WL-PTC coexisting with an oncocytic PTC variant. After radioiodine ablation the patient began levothyroxine therapy.

Hyalinizing trabecular tumor of the thyroid: A case report

A hyalinizing trabecular tumor (HTT), characterized by a trabecular growth pattern and notable hyalinization within the trabeculae, occurs at a rate of ~1%. As patients with HTT may be asymptomatic, accurate diagnosis is a challenge. Due to its resemblance to other tumors, such as papillary thyroid carcinoma and medullary thyroid carcinoma, a precise diagnosis necessitates both pathological and molecular examinations. Additionally, HTT is potentially malignant. The present study described the clinicopathological diagnosis of a patient with HTT; highlighting how an understanding of the clinical and pathological features of HTT is needed to provide an accurate differential diagnosis and thus tailor the treatment approach in order to effectively manage the disease.

Metastasis of clear cell renal cell carcinoma to hyalinizing trabecular tumor of the thyroid: A case report

Renal cell carcinoma (RCC) is the most common malignancy that metastasizes to the thyroid; however, metastasis of RCC to a primary tumor of the thyroid is rare. The present study reports the case of RCC that had metastasized to the primary thyroid tumor; namely, a hyalinizing trabecular tumor (HTT). Notably, the RCC was resected 2 years prior. A 60-year-old female patient was referred to Ningbo Beilun District People's Hospital with radiographic findings indicating thyroid nodules. The patient's previous medical history included a left nephrectomy for the treatment of clear cell (cc)RCC in February 2021. No other distant metastases were identified as of the latest follow-up in April 2023. No abnormalities were observed during thyroid function tests prior to thyroid surgery. The surgical specimen appeared as a multinodular goiter with a solid nodule measuring 55×41×33 mm on the left lobe of the thyroid. Microscopic examination revealed a gray-yellow area inside the capsule of the largest nodule of the left lobe, which was composed of clear cells arranged in a solid pattern. Notably, tumor cells in other areas exhibited trabecular, nested and island patterns. Results of an immunohistochemical examination revealed that the clear cell lesion was negative for thyroid transcription factor-1 and calcitonin, and strongly positive for carbonic anhydrase IX, common acute lymphoblastic leukemia antigen and vimentin. To the best of our knowledge, the present study is the first to report a case of ccRCC that had metastasized to a HTT. A preliminary analysis of the potential mechanisms underlying ccRCC metastasis was performed. Following total thyroidectomy, the patient was treated with levothyroxine, underwent anti-programmed death-1 monoclonal antibody immunotherapy and small molecule tyrosine kinase inhibitor targeted therapy. An enhanced computed tomography scan revealed no evidence of metastatic disease to other organs. As of the latest follow-up, the patient was in a good condition with no sign of metastasis or recurrence.

Comparison of MIB-1-Specific Membrane Staining in Hyalinising Trabecular Tumor Using Mainstream Automated Immunohistochemical Staining Platforms

BACKGROUND

MIB-1, a monoclonal antibody against Ki-67, exhibits specific membrane staining in the immunohistochemistry of hyalinising trabecular tumor (HTT). This specific staining pattern is crucial in diagnosing HTT. Although manual immunohistochemical staining remains the established method for MIB-1 staining, this process is complicated, inconsistent, and prone to false negatives.

METHODS

This study aimed to explore whether the classical reaction pattern can be replicated by utilizing the current mainstream automated immunohistochemical staining platforms. Furthermore, we examined the effect of different conditions on staining efficiency and their value in clinical diagnosis assistance.

RESULTS

Specimens obtained from eight and six cases of HTT and non-HTT, respectively, from a single center were stained using the manual staining method and the Dako Autostainer Link 48 (AS48), Dako Omnis, Ventana BenchMark ULTRA, and Leica BOND-III automated immunohistochemical staining platforms. The Autostainer Link 48 was found to be the most stable staining platform, while the BenchMark ULTRA with primary antibody incubation at room temperature (RT) and the Omnis platform with antigen retrieval at pH 9.0 were able to reproduce membrane-positive staining for MIB-1 in the HTT specimens.

CONCLUSIONS

Our results offer crucial reference value for clinical diagnostic assistance.

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

A case of hyalinizing trabecular tumor of the thyroid: diagnostic significance of PAX8-GLIS3 fusion

BACKGROUND

Hyalinizing trabecular tumor (HTT) is an uncommon follicular cell-derived thyroid tumor classified as a low-risk neoplasm by the World Health Organization Classification of Tumors of Endocrine Organs, 5th edition. The PAX8-GLIS3 gene fusion is reportedly a pathognomonic genetic alteration of HTT.

CASE PRESENTATION

A 43-year-old Japanese female was incidentally discovered to have an 8-mm, well-defined, hypoechoic mass in the left lobe of the thyroid gland by ultrasound examination. Contrast-enhanced computed tomography scan revealed a solid mass exhibiting slight homogeneous enhancement in the lower pole of the thyroid gland. The mass was diagnosed as atypia of undetermined significance by fine-needle aspiration cytology. The patient underwent left hemithyroidectomy with routine central compartment dissection. Histologic findings revealed tumor cells with elongated nuclei and intranuclear pseudoinclusions arranged with trabeculae architecture or small nests in hyalinized stroma. Weak membranous and cytoplasmic staining was found by MIB1 (Ki-67) immunostaining. The final diagnosis was HTT of the thyroid gland. Next-generation sequencing genetic analysis of a surgical specimen revealed no pathologic mutations, including BRAF, H/K/NRAS, or RET-PTC fusions. The PAX8-GLIS3 fusion was detected by RT-PCR.

CONCLUSIONS

A rare case of HTT was demonstrated through imaging, cytologic, histologic and molecular investigations. PAX8-GLIS3 fusion detected by RT-PCR and Sanger sequencing was confirmed to be a genetic hallmark of HTT.

Molecular Pathology of Thyroid Tumors: Essential Points to Comprehend Regarding the Latest WHO Classification

In 2022, the new WHO Classification of Endocrine and Neuroendocrine Tumors, Fifth Edition (beta version) (WHO 5th), was published. Large-scale genomic analyses such as The Cancer Genome Atlas (TCGA) have revealed the importance of understanding the molecular genetics of thyroid tumors. Consequently, the WHO 5th was fundamentally revised, resulting in a systematic classification based on the cell of origin of tumors and their clinical risk. This paper outlines the following critical points of the WHO 5th. 1. Genetic mutations in follicular cell-derived neoplasms (FDNs) highlight the role of mutations in the MAP kinase pathway, including RET, RAS, and BRAF, as drivers of carcinogenesis. Differentiated thyroid cancers such as follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma (PTC) have specific genetic alterations that correlate with morphological classifications: RAS-like tumors (RLTs) and BRAF p.V600E-like tumors (BLTs), respectively. 2. The framework for benign lesions has been revised. The WHO 5th introduces a new category: "developmental abnormalities". Benign FDNs comprise "thyroid follicular nodular disease", follicular thyroid adenoma (FTA), FTA with papillary architecture, and oncocytic adenoma (OA). "Hürthle cell adenoma/carcinoma" is renamed oncocytic adenoma/carcinoma of the thyroid (OA/OCA), which can be distinguished from FTA/FTC by its unique genetic background. 3. Low-risk tumors include NIFTP, TT-UMP, and HTT, and they have an extremely low malignant potential or an uncertain malignant potential. 4. PTC histological variants are reclassified as "subtypes" in the WHO 5th. 5. The concept of high-grade carcinomas is introduced, encompassing poorly differentiated thyroid carcinoma (PDTC), differentiated high-grade thyroid carcinoma (DHGTC), and high-grade medullary thyroid carcinoma (MTC). 6. Squamous cell carcinoma is included in anaplastic thyroid carcinoma (ATC) in the WHO 5th due to their shared genetic and prognostic features. 7. Other miscellaneous tumors are categorized as salivary-gland-type carcinomas of the thyroid, thyroid tumors of uncertain histogenesis, thymic tumors within the thyroid, and embryonal thyroid neoplasms. The WHO 5th thus emphasizes the importance of classifying tumors based on both genetic abnormalities and histomorphology. This approach aids in achieving accurate pathological diagnosis and facilitates the early selection of appropriate treatment options, including molecular targeted therapies.

Understanding and Overcoming the Pitfalls in Cytopathological Diagnosis of Hyalinizing Trabecular Tumor of Thyroid

Hyalinizing trabecular tumor (HTT), a rare low-malignant-potential thyroid neoplasm, is usually treated with conservative surgery. However, cytomorphological diagnosis of HTT is challenging due to the significant overlap of nuclear features with more common malignancies such as papillary thyroid carcinoma (PTC), which usually requires more radical surgical intervention. To avoid unnecessary overtreatment, a precise diagnosis of HTT is therefore essential. Advances in molecular diagnostics provide the opportunity to overcome the limitations of cytological analysis. We present a case of HTT in a 71-year-old male who was initially suspected to be PTC based on cytopathology. However, further molecular analysis revealed PAX8::GLIS3 gene fusion, classifying the lesion as HTT and preventing surgical overtreatment. We discuss the diagnostic pitfall of cytopathology in HTT and suggest using emerging molecular genetic tools to avoid it.

Cytomorphological traits of fine-needle aspirates of hyalinizing trabecular tumor of the thyroid gland: A brief report

Background

The incidence of thyroid tumor is increasing, and preoperative diagnosis of hyalinizing trabecular tumor (HTT) is difficult.

Aim

To investigate the cytological features of HTT of the thyroid gland.

Settings and Design

A retrospective observational study.

Materials and Methods

Ultrasonography, preoperative needle aspiration cytology, postoperative histopathology, immunohistochemistry, and BRAF V600E gene test were performed in five patients with HTT to analyze the pathological characteristics of the patients and review the relevant literature.

Results

Four female and one male patients with HTT were recruited. Fine-needle aspiration cytology (FNAC) showed bloodstained background tumor cells with multiple morphologies. The tumor cells exhibited ovoid nuclei, abundant cytoplasm, fine chromatin, nuclear crowding and overlapping, and small nucleoli. Focal nuclear pseudoinclusions and grooves were present. No papillary structures or psammoma bodies were observed. In all cases, tumor cells were radially distributed around the eosinophilic extracellular matrix. In 40% (2 in 5) of cases, trabecular patterns of elongated tumor cells were present, with their nuclei staggered along the longitudinal axis of tumor cells in the trabeculae. FNAC suggested two cases of HTT and three cases of papillary thyroid cancer. Post-operational biopsy indicated they were HTT cases.

Conclusion

HTT is a rare thyroid tumor with non-specific clinical manifestations. It can be misinterpreted as papillary thyroid carcinoma by FNAC. However, its cytomorphological traits are helpful in the diagnosis. In combination with FNAC, immunohistochemistry, and molecular testing, HTT can be accurately diagnosed.

Diagnostic clues for hyalinizing trabecular tumor on fine needle aspiration cytology

OBJECTIVES

The hyalinizing trabecular tumor (HTT) is a rare benign neoplasm of the thyroid gland. This neoplasm has overlapping cytological features with Papillary Thyroid Carcinoma, Medullary Carcinoma and Follicular Neoplasm with Nuclear Features of Papillary Carcinoma. This can lead to misdiagnosis of malignancy in fine needle aspiration (FNA) cytology specimens with unnecessary total thyroidectomy. The aim of this study is to determine if there are some cytological features that could help us to suspect HTT on FNA specimens and avoid radical surgery.

MATERIAL AND METHODS

With this purpose we have collected 6 cases diagnosed of HTT in Hospital Clínico San Carlos of Madrid (Spain) in the last 10 years and reviewed the cytological specimens.

RESULT

We conclude that the presence of hyaline material in FNA specimens of HTT is a constant feature being a diagnostic clue. We must be cautious not to confuse it with dense colloid or amyloid material, the latter seen in Medullary Carcinoma. Papillary architecture and fibrovascular cores are not present in a HTT. Special stains as ki-67, calcitonin and Congo Red staining could help us in achieving the correct diagnosis.

CONCLUSION

We feel the cytopathologists must be aware of the distinguishing features of this lesion, mainly the typical hyaline material to achieve a proper diagnosis and be able to reduce unnecessary aggressive management of these patients.

Hyalinizing Trabecular Tumor of the Thyroid Gland: A Case Report and Literature Review

A hyalinizing trabecular tumor (HTT) of the thyroid gland is a very rare type of tumor. It is usually diagnosed incidentally during the examination for thyroid gland diseases that need thyroidectomy. Here we report a case of HTT in a 60-year-old male patient who presented with anterior neck swelling and underwent total thyroidectomy for a Bethesda category V nodule. The final histologic diagnosis of the left lobe was consistent with a hyalinized trabecular adenoma of the thyroid gland, or paraganglioma-like adenoma. We discuss the clinical picture and diagnostic approach, including the role of fine needle aspiration biopsy, and the pathologic features of HTT, with particular reference to the possible differential diagnosis.

Top 10 Nested Pattern Head and Neck Lesions to Notice

BACKGROUND

Nested is defined as "cellular clusters arranged in small groupings with intervening vascular or stromal networks, lacking lumens or glandular formation." Using this definition, multiple neoplastic and non-neoplastic lesions of the head and neck come into the differential. We have broadly organized the differential diagnosis of "nested" tumors into entities with neuroendocrine differentiation, squamous differentiation, thyroid follicular cell differentiation, and other lesions.

METHODS

Review.

RESULTS

Many different entities have a nested appearance and the morphologic, immunohistochemical, clinical, and radiographic features contribute to the differential diagnosis. The different tumors covered in this review include neuroendocrine neoplasms, paraganglioma, middle ear neuroendocrine tumor (formerly known as middle ear adenoma), medullary thyroid carcinoma, poorly differentiated thyroid carcinoma, olfactory neuroblastoma, ectopic pituitary neuroendocrine tumor, hyalinizing trabecular tumor, solid subtype of papillary thyroid carcinoma, solid cell nests/C-cell hyperplasia, necrotizing sialometaplasia, and meningioma.

CONCLUSION

In this review, we discuss the morphologic and immunohistochemical features of the covered entities as a guide to differential diagnosis when nested-patterned head and neck lesions are encountered.

Psammomatous calcifications in thyroid oncocytic (Hürthle cell) follicular tumors

Concentric calcifications, also known as psammoma bodies, are a relatively frequent finding in certain types of tumors, particularly papillary thyroid carcinoma (PTC). In the thyroid, they have been assigned a significant role in the diagnosis of PTC and in distinguishing between these tumors and other types of thyroid neoplasms. Concentric calcifications have also less commonly been noted in other processes in the thyroid, such as in tumors characterized by cells containing abundant oxyphilic cytoplasm (i.e., Hürthle cells). We have studied 12 patients with oncocytic thyroid follicular tumors that contained scattered psammomatous calcifications that led to difficulties in diagnosis. The patients were 9 women and 3 men, aged 34 to 63 years. 10 cases corresponded to benign, non-invasive oncocytic tumors and 2 cases were minimally invasive follicular carcinomas of oncocytic (so called Hürthle cell) type. The psammomatous calcifications were randomly scattered throughout the lesions and were present as a focal, incidental finding in 8 cases and were diffuse in 4 cases. They were composed of concentrically laminated deposits of dense basophilic material closely resembling psammoma bodies, often associated with more homogeneous deposits of lightly eosinophilic material without concentric lamination that were interpreted as precipitated thyroglobulin. Seven patients with clinical follow-up, including one with minimally invasive carcinoma, were alive and well between 5 and 12 years after diagnosis. Concentric laminated calcifications may be encountered in oncocytic (Hürthle cell) follicular tumors and should not be interpreted as indicative of PTC in the context of oncocytic neoplasms of the thyroid.

Diagnosis and management of hyalinizing trabecular tumor of the thyroid: a single-institution experience

Hyalinizing trabecular tumor (HTT) of the thyroid is a mostly benign disease. Its cytological and pathological diagnosis is often difficult, because HTT cells and papillary thyroid carcinoma (PTC) cells share similar features (e.g., intranuclear cytoplasmic inclusions and nuclear grooves). At our institution, 38 patients were diagnosed as or highly suspected of having HTT without the possibility of PTC, based on cytology: 19 of these patients underwent immediate surgery (surgery group) and the remaining 19 underwent active surveillance without surgery (AS group). The surgery-group patients' tumor sizes were significantly larger (p < 0.0001) than those in the AS group. During AS (median 38 months), only one patient (5%) showed tumor enlargement by ≥3 mm; the AS was continued. Of the 34 patients pathologically diagnosed with HTT, 22 (65%) were cytologically diagnosed or highly suspected as having HTT without the possibility of PTC. Of the nine patients who were suspected to have HTT but PTC was possible and surgery was performed, two (22%) and seven (78%) were pathologically diagnosed as having PTC and HTT, respectively. Five patients were cytologically diagnosed with PTC, but pathologically diagnosed as having HTT. No patients showed HTT recurrence during postoperative follow-up (median 60 months). These findings suggest that (1) active surveillance can be a valid strategy for managing tumors that are cytologically diagnosed as HTT with no possibility of PTC; (2) surgery is recommended for tumors suspected of being HTT but may be PTC, and (3) the prognosis of HTT in both the AS and surgery groups was excellent.

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

Thyroid hyalinizing trabecular adenoma with a high thyroglobulin level: a case report

Thyroid hyalinizing trabecular adenoma (HTA) is a rare and borderline tumor of follicular origin. It is characterized by a trabecular growth pattern and marked intratrabecular hyalinization. Excessively elevated thyroglobulin levels have not been reported previously in cases without bilateral lung metastases. Here, we present a case of a 54-year-old woman with chronic thyroiditis with a 50-mm tumor in the left lobe of the thyroid gland, which was observed on ultrasonography. Her thyroglobulin level was found to be elevated at 684 ng/ml. Since fine needle aspiration cytology could not exclude possible malignancy, she underwent thyroid lobectomy; the final diagnosis was thyroid HTA. Two weeks after resection, her thyroglobulin level showed negative conversion. To our knowledge, this is the first report of a patient with a thyroid HTA exhibiting a thyroglobulin level as high as that for a patient with hyalinizing trabecular carcinoma.

Hyalinizing trabecular tumor: Cytologic, histologic and molecular features and diagnostic considerations

Hyalinizing trabecular tumors are a follicular origin neoplasm of the thyroid that usually present as an asymptomatic, well circumscribed, solitary mass. However, diagnosis of a hyalinizing trabecular tumor may be challenging especially on fine needle aspiration cytology and requires careful examination of the specimen to rule out potential mimickers such as papillary thyroid carcinoma, medullary thyroid carcinoma, paraganglioma, other follicular patterned neoplasms, intrathyroidal parathyroid tissue, and metastatic disease. We will review the cytologic, histologic and molecular features of hyalinizing trabecular tumors that aid in distinction from these mimickers with overlapping morphologic features and help ensure proper diagnosis for appropriate management.

Neuroendocrine Tumors of the Thyroid and Their Mimics

This paper will review neuroendocrine lesions of the thyroid and the differential diagnosis with the most significant such tumor of the thyroid, that is, medullary thyroid carcinoma. A brief overview of the understanding of this tumor's identification as a lesion of C cells and its familial and syndromic associations will be presented. Then, a discussion of the various mimics of medullary carcinoma will be given with an approach to the types of tests that can be done to arrive at a correct diagnostic conclusion. This review will focus on practical "tips" for the practicing pathologist.

The Diagnosis of Hyalinizing Trabecular Tumor: A Difficult and Controversial Thyroid Entity

Hyalinizing trabecular tumor (HTT) is a benign, follicular-derived neoplasm composed of thick trabeculae with round or elongated cells having irregular and clear nuclei, and containing intra-trabecular hyaline material. The cytological features of HTT resemble those of papillary carcinoma, which helps explain why these lesions are usually classified as indeterminate/suspicious according to the Bethesda system for reporting thyroid cytology. A review of the literature indicates that reaching the correct preoperative cytologic diagnosis of HTT remains elusive, as the correct interpretation was achieved in only 8% of cases. In contrast, the correct diagnosis posed a less significant diagnostic challenge in the majority of histological series, despite the reported controversy on the relationship of this tumor with papillary and medullary thyroid carcinomas. The aim of this review is to highlight the cytological and histological clues in the diagnosis of HTT, as well as its molecular profile.

PAX8-GLIS3 gene fusion is a pathognomonic genetic alteration of hyalinizing trabecular tumors of the thyroid

The hyalinizing trabecular adenoma/tumor is a rare and poorly characterized follicular-derived thyroid neoplasm recently shown to harbor recurrent PAX8-GLIS1 or PAX8-GLIS3 gene fusions. Here we sought to define the repertoire of genetic alterations of hyalinizing trabecular tumors, and whether PAX8-GLIS3 fusions are pathognomonic for hyalinizing trabecular tumors. A discovery series of eight hyalinizing trabecular tumors was subjected to RNA-sequencing (n = 8), whole-exome sequencing (n = 3) or targeted massively parallel sequencing (n = 5). No recurrent somatic mutations or copy number alterations were identified in hyalinizing trabecular tumor, whereas RNA-sequencing revealed the presence of a recurrent genetic rearrangement involving PAX8 (2q14.1) and GLIS3 (9p24.2) genes in all cases. In this in-frame fusion gene, which comprised exons 1-2 of PAX8 and exons 3-11 of GLIS3, GLIS3 is likely placed under the regulation of PAX8. Reverse transcription RT-PCR and/or fluorescence in situ hybridization analyses of a validation series of 26 hyalinizing trabecular tumors revealed that the PAX8-GLIS3 gene fusion was present in all hyalinizing trabecular tumors (100%). No GLIS1 rearrangements were identified. Conversely, no PAX8-GLIS3 gene fusions were detected in a cohort of 237 control thyroid neoplasms, including 15 trabecular thyroid lesions highly resembling hyalinizing trabecular tumor from a morphological standpoint, as well as trabecular/solid follicular adenomas, solid/trabecular variants of papillary carcinoma, and Hurthle cell adenomas or carcinomas. Our data provide evidence to suggest that the PAX8-GLIS3 fusion is pathognomonic for hyalinizing trabecular tumors, and that the presence of the PAX8-GLIS3 fusion in thyroid neoplasms may be used as an ancillary marker for the diagnosis of hyalinizing trabecular tumor, thereby avoiding overtreatment in case of misdiagnoses with apparently similar malignant tumors.

GLIS rearrangements in thyroid nodules: A key to preoperative diagnosis of hyalinizing trabecular tumor

Hyalinizing trabecular tumor (HTT) is a rare thyroid neoplasm with peculiar morphologic features that overlap with those of papillary thyroid carcinoma (PTC). Specifically, the presence of enlarged oval nuclei, nuclear grooves, and intranuclear pseudoinclusions makes precise cytopathologic diagnosis challenging. If the cytopathologic diagnosis is suspicious for malignancy (Bethesda V) or is malignant (Bethesda VI), a total thyroidectomy, which would be considered an overtreatment, may follow. The recent discovery of the strong association between GLIS fusions and HTT sheds light on its pathogenesis and offers a pathway for its presurgical identification. Although the number of cases analyzed is limited, the recent landmark study shows that GLIS fusions are highly specific for HTT and that lobectomy is the likely appropriate surgical treatment, because these neoplasms, which lack invasion, are benign. For overall success, cytopathologic recognition of the subtle features is important to avoid false-positive diagnoses and directing potential HTT cases toward indeterminate cytopathologic diagnoses, which would trigger further molecular testing. Additional studies are needed to determine whether a malignant counterpart of GLIS fusion-positive HTT exists and if more conservative approaches may be taken.

GLIS Rearrangement is a Genomic Hallmark of Hyalinizing Trabecular Tumor of the Thyroid Gland

BACKGROUND

Hyalinizing trabecular tumor (HTT) is a rare thyroid neoplasm with a characteristic trabecular growth pattern and hyalinization. This lesion has been the subject of long-term controversy surrounding its genetic mechanisms, relationship to papillary thyroid carcinoma (PTC), and malignant potential. Due to the presence of nuclear features shared with PTC, HTT frequently contributes to a false-positive cytology, which hampers patient management. The goal of this study was to apply genome-wide sequencing analyses to elucidate the genetic mechanisms of HTT and its relationship to PTC.

METHODS

Whole-exome, RNA-Seq, and targeted next-generation sequencing analyses were performed to discover and characterize driver mutations in HTT. RNA-Seq results were used for pathway analysis. Tissue expression of GLIS3 and other proteins was detected by immunohistochemistry. The prevalence of GLIS fusions was studied in 17 tumors initially diagnosed as HTT, 220 PTC, and 10,165 thyroid fine-needle aspiration samples.

RESULTS

Using whole-exome and RNA-Seq analyses of the initial three HTT, no known thyroid tumor mutations were identified, while in-frame gene fusion between PAX8 exon 2 and GLIS3 exon 3 was detected in all tumors. Further analysis identified PAX8-GLIS3 in 13/14 (93%) and PAX8-GLIS1 in 1/14 (7%) of HTT confirmed after blind pathology review. The fusions were validated by Sanger sequencing and FISH. The fusions resulted in overexpression of the 3'-portion of GLIS3 and GLIS1 mRNA containing intact DNA-binding domains of these transcription factors and upregulation of extracellular matrix genes including collagen IV. Immunohistochemistry confirmed upregulation and deposition of collagen IV and pan-collagen in HTT. The analysis of 220 PTC revealed no PAX8-GLIS3 and one PAX8-GLIS1 fusion. PAX8-GLIS3 was prospectively identified in 8/10,165 (0.1%) indeterminate cytology fine-needle aspiration samples; 5/5 resected fusion-positive nodules were HTT on surgical pathology.

CONCLUSIONS

This study demonstrates that GLIS rearrangements, particularly PAX8-GLIS3, are highly prevalent in HTT but not in PTC. The fusions lead to overexpression of GLIS, upregulation of extracellular matrix genes, and deposition of collagens, which is a characteristic histopathologic feature of HTT. Due to unique genetic mechanisms and an indolent behavior, it is proposed to rename this tumor as "GLIS-rearranged hyalinizing trabecular adenoma."

Applications of Immunohistochemistry to Endocrine Pathology

The role of immunohistochemistry (IHC) in endocrine pathology is similar to that in other organ systems in that it can aid in the subclassification of tumors within an organ, confirm site of primary in metastatic disease, provide prognostic information, identify underlying genetic alterations, and predict response to treatment. Although most endocrine tumors do not require IHC to render a diagnosis, there are certain scenarios in which IHC can be extremely helpful. For example, in thyroid, IHC can be used to support tumor dedifferentiation, in the adrenal it can aid in the diagnosis of low-grade adrenocortical carcinomas, and in paragangliomas it can help identify tumors arising as part of an inherited tumor syndrome. This review will focus on the applications of IHC in tumors of the thyroid, parathyroids, adrenals, and paraganglia in adults.

Hyalinizing trabecular tumor of the thyroid gland

Hyalinizing trabecular tumor was first described by Carney et al. (1) in 1987 and is a rare benign tumor of the thyroid gland that shares some of the microscopic features of medullary and papillary thyroid carcinoma. Hyalinizing trabecular tumor derives from follicular cells, and it is characterized by an apparent trabecular pattern and intratrabecular hyalinization. In this study, we present the case of a 40-year-old female patient with thyroid gland nodules, whose ultrasound results, clinical behavior, and fine-needle aspiration biopsy results were suspicious; the pathology after thyroidectomy indicated hyalinizing trabecular tumor. We aimed to show the role of clinical behavior, radiology, fine-needle aspiration, and histological and immunohistochemical analysis in the differential diagnosis of hyalinizing trabecular tumor. Hyalinizing trabecular tumor which can be confused with papillary and medullar carcinoma of the thyroid gland, is mostly benign but some malignant and metastatic cases have been reported. Therefore, diagnosis, treatment, and follow-up steps of Hyalinizing trabecular tumor should be planned in consideration of a malignant potential.

Recent Advances in the Classification of Low-grade Papillary-like Thyroid Neoplasms and Aggressive Papillary Thyroid Carcinomas: Evolution of Diagnostic Criteria

Papillary thyroid carcinomas account for ∼80% of well-differentiated thyroid tumors. During the past decade, several new variants of papillary-like thyroid neoplasms and papillary thyroid carcinomas have been recognized. Some of these neoplasms that were previously classified as malignant have been reclassified as low-grade neoplasms, as the diagnostic criteria have evolved. Similarly, some of the papillary thyroid carcinomas that were previously classified as conventional or classic papillary thyroid carcinomas have now been recognized as more aggressive variants of papillary thyroid carcinomas. Recognizing these differences becomes more important for the proper medical, surgical, and radiotherapeutic management of patients with these neoplasms.

Hyalinizing Trabecular Tumor of the Thyroid Gland, a Diagnostic Challenge in Fine-Needle Aspiration Cytology: Case Report

Hyalinizing trabecular tumor (HTT) is a rare thyroid tumor with low to minimal malignant potential. HTT is often misinterpreted as other thyroid tumors, including papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC), on fine-needle aspiration (FNA) cytology, because of its overlapping cytologic features, such as nuclear grooves and intranulcear pseudoinclusions. Although cytopathologists cannot definitely conclude HTT by FNA cytology, suspicion of HTT is necessary to avoid misdiagnosing HTT as PTC or MTC and to avoid unnecessary aggressive treatment. Here, we report a case of HTT with novel cytologic features in CellPrep liquid based cytology that was diagnosed as suspicious for papillary carcinoma by FNA and finally diagnosed as HTT in the surgical specimen.

Hyalinizing Trabecular Adenoma of the Thyroid. Report of two Cases, with Cytologic, Immunohistochemical and Ultrastructural Studies

The cytologic, histologic, immunocytochemical and ultra-structural features of 2 cases of hyalinizing trabecular adenoma (HTA) of the thyroid are described. The difficulty of a cytologic diagnosis and the need for an immunohistochemical profile of the lesions for a final histologic diagnosis are emphasized.

Re-evaluation of MIB-1 immunostaining for diagnosing hyalinizing trabecular tumour of the thyroid: semi-automated techniques with manual antigen retrieval are more accurate than fully automated techniques

Hyalinizing trabecular tumour (HTT) immunohistochemically shows cell membranous immunoreactivity for MIB-1. This aberrant immunoreactivity is an important factor for the diagnosis of HTT. However, fully automated stainers frequently fail to confirm the immunoreactivity. The aim of this study is to investigate the cause of false negative cell membranous immunoreactivity for MIB-1 in HTT using fully automated stainers, to determine potential reasons for the problem, and to establish methods confirming cell membranous immunoreactivity for MIB-1 in HTT. Six participating institutions examined immunoreactivity for MIB-1 in 10 HTT cases using two approaches: fully automated and semi-automated methods. In the latter, antigen retrieval was carried out using manual methods adopted for routine assays at each institute. The autostainers used included the BOND-MAX, BOND-III, Benchmark XT, and Omnis systems. Using fully automated methods, institute E showed cell membranous MIB-1 positivity in all HTT cases. In contrast, at institute D, all HTT cases were negative. The positive rates of the remaining four institutes ranged from 10% to 20%. The incidence of positive cases using semi-automated methods was 100%, 90%, 90%, 30%, 80%, and 100% at institutes A, B, C, D, E, and F, respectively. We assert that antigen retrieval should be conducted manually for diagnosis of HTT; furthermore, definitively diagnosed HTT should be prepared as the external positive control.

Stromal tiny black dots, like "sugar-coated", of von Kossa stain is a diagnostic clue to hyalinizing trabecular tumor of the thyroid gland

Hyalinizing trabecular tumor (HTT) is a rare low-grade tumor, and a prominent feature is the basement membranous stroma. We assume that such characteristic stromal findings of HTT are related to calcium deposition, and examined HTT samples by von Kossa special staining. There has been no report describing von Kossa special staining for such stroma. We collected 12 cases of HTT and 30 cases of papillary thyroid carcinoma (PTC) that had matched age, gender, tumor size, and surgical procedure characteristics as a control group. We compared the staining pattern and degree of von Kossa positivity between HTT and PTC, and a grading system of von Kossa stain was adopted to highlight differences between them. On von Kossa staining, all HTT revealed many tiny black dots around vessels in the hyalinized stroma, like "sugar-coated", and a high degree of calcium deposition in most cases, whereas PTC showed sparse stromal calcification in some cases. The degree of von Kossa staining was significantly different between the two groups. This is the first report describing abundant tiny black dots, like a "sugar-coated" appearance, of von Kossa stain in HTT. Here, we propose this finding can be a useful diagnostic clue to HTT.

Hyalinizing trabecular tumour of the thyroid: fine-needle aspiration cytological diagnosis and correlation with histology

Hyalinizing trabecular tumour (HTT) is a rare thyroid neoplasm of follicular cell origin characterised by a trabecular growth pattern and prominent intratrabecular and intertrabecular hyalinisation. These peculiar histological features allow the prompt recognition of this neoplasm in surgical specimens. However, cytological diagnosis of HTT remains elusive and misleading because of overlapping characteristics with other thyroid tumours, particularly papillary thyroid carcinoma (PTC), medullary thyroid carcinoma (MTC) and the newly described non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Nevertheless, the proper recognition of this neoplasm on preoperative cytological preparations is important to avoid unnecessary overtreatment of this indolent lesion. A thorough review of the literature has revealed that the correct diagnosis of HTT in cytological smears is achieved in only 8% of cases. In a further 6% of cases, diagnostic doubt has been indicated. Sixty percent of published cases of HTT have been misdiagnosed as suggestive, suspicious or positive for PTC. These findings underline the difficulties of a cytological-based diagnosis of such entity. In this article we review the cytomorphological features of HTT and their correlation to histological features to provide the reader with the tools to improve diagnostic performance in the identification of HTT on preoperative cytology.

Hemangiopericytoma of the Thyroid

A 52-year-old woman presented with a painless right thyroid mass of 4 months dura tion, with a recent increase in size in the last few weeks. The neoplasm was character ized by bland spindle cells with a low mitotic rate arranged around vascular elements of variable shape and caliber. Multiple immunohistochemical stains failed to show evi dence of epithelial, neuroendocrine, or specific mesenchymal differentiation. Electron microscopic studies revealed spindle cells with micropinocytotic vesicles, surrounded by variable but sometimes abundant basement lamina-like material. To the authors' knowledge, this is the first report of a typical hemangiopericytoma of the thyroid gland. This lesion must be distinguished from epithelial and neuroendocrine tumors with spindle cells and from other mesenchymal neoplasms that may occur in the thyroid. Int J Surg Pathol 2(4):311-318, 1995

Hyalinizing trabecular tumor of the thyroid: diagnosis of a rare tumor using ultrasonography, cytology, and intraoperative frozen sections

Purpose:

The goal of this study was to evaluate the clinicopathological and imaging features of thyroid nodules surgically diagnosed as hyaline trabecular tumor (HTT), and to assess the role of cytology and frozen sections (FS) in the diagnosis of HTT.

Methods:

This study included 21 thyroid nodules in 21 patients treated from August 2005 to March 2015 (mean age, 53.3 years) who were either diagnosed as HTT or had HTT suggested as a possible diagnosis based on cytology, FS, or the final pathology report. Patients’ medical records were retrospectively reviewed for cytopathologic results and outcomes during the course of follow-up. Sonograms were reviewed and categorized.

Results:

Twelve nodules from 12 patients were surgically confirmed as HTT. Ultrasonography (US)-guided fine needle aspiration (FNA) was performed on 11 nodules, of which six (54.5%) were papillary thyroid carcinoma (PTC) or suspicious for PTC and three (27.3%) were HTT or suspicious for HTT. Intraoperative FS suggested the possibility of HTT in seven nodules, of which four (57.1%) were confirmed as HTT. US-FNA suggested the diagnosis of HTT in 10 nodules, of which three (30.0%) were confirmed as HTT. Common US features of the 12 pathologically confirmed cases of HTT were hypoechogenicity or marked hypoechogenicity (83.4%), absence of calcifications (91.7%), parallel shape (100.0%), presence of vascularity (75.0%), and probable benignity (58.3%).

Conclusion:

HTT should be included in the differential diagnosis of solid tumors with hypoechogenicity or marked hypoechogenicity and otherwise benign US features that have been diagnosed as PTC through cytology.

The ultrasonography features of hyalinizing trabecular tumor of the thyroid gland and the role of fine needle aspiration cytology and core needle biopsy in its diagnosis

BACKGROUND

Hyalinizing trabecular tumor (HTT) of the thyroid gland is a rare, benign neoplasm of follicular cell origin. Misdiagnosis of HTT as either papillary or medullary thyroid carcinoma after fine-needle aspiration (FNA) may lead to unnecessary surgery.

PURPOSE

To evaluate the ultrasonography (US) findings of HTT of the thyroid gland and the role of FNA cytology and core needle biopsy (CNB) in its diagnosis.

MATERIAL AND METHODS

Data from 24 patients with a histopathological diagnosis of HTT between January 2000 and May 2013 were retrospectively analyzed. US findings were categorized according to shape, margin, orientation, echogenicity, composition, calcification, and vascularity. Cytologic and histologic results of FNA, CNB, and surgery were reviewed.

RESULTS

US revealed the following tumor features: oval-to-round (24/24), solid (22/24), smooth margin (21/24), hypoechoic or marked hypoechogenicity (18/24), and peri- and/or intranodular vascularity (17/17). Malignant US features such as marked hypoechogenicity (n = 7) and a spiculated margin (n = 3) were also observed. Final confirmation was by surgery in 22 patients and by CNB in two patients. All 19 patients who underwent FNA were initially misdiagnosed, including 12 with malignancies and five with atypia of undetermined significance. All four patients who underwent CNB were correctly diagnosed with HTT. The histology of CNB specimens suggested HTT, which was confirmed by immunostaining of MIB-1.

CONCLUSION

HTT should be suspected when the cytological diagnosis of papillary thyroid carcinoma is made after FNA without malignant US findings. CNB could prevent unnecessary surgery for HTT.

Pathologic diagnosis of papillary thyroid carcinoma: today and tomorrow

Papillary thyroid carcinoma is the most common malignancy of the thyroid. It is a well-differentiated tumor and the majority behaves in an indolent fashion. The pathologic diagnosis of papillary carcinoma in both cytology and histologic specimens is based upon demonstration of typical nuclear morphology. Using these morphologic criteria, most papillary cancers can be diagnosed with ease, except cases in which there is a paucity of diagnostic nuclear features. Despite advances in the treatment of thyroid cancer, disease recurrences and metastasis can be observed in 20% of cases. Recently, many advances have been made in the pathogenesis of papillary thyroid carcinoma. The notable genetic events include Ret/PTC rearrangements, Ras and BRAF gene mutations. The identification of these has also led to their use in diagnosis and predicting prognosis of papillary thyroid carcinoma. In addition, these involved genes may also serve as targets for cancer chemotherapy in patients where standard thyroid cancer treatment is not effective.

Unusual thyroid tumors: a review of pathologic and molecular diagnosis

The most common thyroid neoplasms are either follicular derived (papillary, follicular and Hürthle cell lesions) or C-cell derived (medullary carcinoma). The diagnosis of these tumors can usually be made at the histologic level, with immunohistochemical stains necessary in some circumstances. Specific molecular mutations have been described that can be diagnostically useful or explain, in part, their pathogenesis, including the well-known Ret/PTC and PPARgamma-PAX8 translocations, point mutations in the Ret, Ras and BRAF genes, and loss of heterozygosity of multiple different tumor suppressor genes. Some unusual tumors of the thyroid gland are more difficult to diagnose. In examining these lesions, the pathologist may use the hematoxylin and eosin-stained morphology, coupled with an analysis of the immunohistochemical staining profiles and possibly analysis of the underlying molecular mutational patterns. These less common thyroid tumors include tall cell and cribriform-morular variants of papillary carcinoma, hyalinizing trabecular tumor, mucoepidermoid and sclerosing mucoepidermoid carcinoma with eosinophilia, poorly differentiated (insular) carcinoma, and undifferentiated (anaplastic) carcinoma. The diagnostic features of these rare tumors, including the histology, immunohistochemical expression profiles and the known molecular mutational profiles of each, are reviewed.

HBME-1 expression in hyalinizing trabecular tumours of the thyroid gland

AIMS

Hyalinizing trabecular tumour (HTT) is a rare thyroid neoplasm with a trabecular growth pattern, marked intratrabecular hyalinization and nuclear features of papillary thyroid carcinoma (PTC). Immunohistochemical HBME-1 expression was reported recently in PTC, but not in HTT. To clarify further the value of HBME-1 expression as a tool in differential diagnosis, we investigated the immunophenotype of HTT.

METHODS AND RESULTS

Eight HTT diagnosed from 1997 to 2012 were reviewed on H&E-stained tissue sections and analysed for HBME-1, galectin-3, CK19 and Ki67 expression by immunohistochemistry. Three of eight HTTs (37.5%) were HBME-1 positive, with staining of tumour cells as well as of intratrabecular hyaline matrix material. All cases were CK19 negative. Galectin-3 was expressed weakly in four of eight cases (50%). Five of eight cases (62.5%) showed weak-to-moderate cytoplasmic Ki67 positivity.

CONCLUSIONS

Immunohistochemical HBME-1 expression is present in HTT and may not serve as a reliable marker in differentiating HTT from PTC. The HBME-1 positivity of the hyaline matrix suggests that this material is partly of cytoplasmic origin.

[MicroRNA profiles in fine needle biopsy of the thyroid]

MicroRNAs (miRNAs) are small (20-24 nucleotides), non-coding ribonucleid acids, which regulate gene expression on the post-transcriptional level, thus influencing physiological processes including cellular growth, differentiation and apoptosis. Several miRNAs (e. g. miRNAs 146b, 221 and 222) have been shown to be consistently over-expressed in papillary thyroid carcinoma. The present overview describes and discusses the utilization and problems of miRNA analysis in material from thyroid nodules obtained by fine needle biopsy. Particularly the analysis of defined sets of miRNAs should improve the diagnostic value of this procedure and contribute to a better management of patients with cold thyroid nodules.

[Hyalinizing trabecular tumor of the thyroid. An overcautious designation of a benign thyroid tumour?]

Hyalinizing trabecular tumours of the thyroid represent a rare entity of follicular cell derived tumours and are characterized by a marked intratrabecular hyalinisation. These tumours share architectural similarities with medullary thyroid carcinomas and exhibit nuclear features such as nuclear pseudoinclusions resembling papillary thyroid carcinoma. However, the clinical behaviour remains unclear. On the basis of their inconspicuous appearance and absence of invasion or recurrence during follow-up, the tumour was initially classified as an adenoma. Subsequently, molecular findings such as the detection of RET / PTC rearrangements in some hyalinizing trabecular tumours favoured the designation as a variant of papillary thyroid carcinoma. However, miRNA profiling of hyalinizing trabecular tumours compared with benign thyroid lesions and papillary thyroid carcinoma failed to demonstrate the characteristic up-regulation found in papillary thyroid carcinoma. This article summarizes conventional diagnostic criteria with supplementary information regarding molecular pathogenesis of hyalinizing trabecular tumours of the thyroid.

Hyalinizing trabecular tumor of the thyroid: Case report and review of the literature

In 1987, Carney et al described a rare thyroid tumor termed hyalinizing trabecular adenoma presenting characteristics consisting of a trabecular growth pattern and hyalinizing stroma. In subsequent reports, the observed nuclear features and RET alterations led this tumor to be linked to papillary carcinoma. Subsequent reports concerning hyalinizing trabecular carcinoma further complicated its classification. To avoid uncertainties, the definition of hyalinizing trabecular tumor (HTT) is more widely used. Herein, a case of HTT is reported in detail, and the circumstances are also discussed. HTT is thought to be particularly differentiated from papillary carcinoma despite the identical high frequency of nuclear grooves and cytoplasmic inclusions, and MIB-1-positive staining is one of the most accurate diagnostic methods due to the distinct membrane-positive pattern noted in HTT. It is believed that most HTTs are benign and lobectomy is the standard treatment. Pathologists should offer surgeons information concerning diagnosis overlapping with effective treatment.

Hyalinizing trabecular tumor of the thyroid: a case report

Hyalinizing trabecular tumor (HTT) of the thyroid is a rare neoplasm that was first described by Carney in 1987. It is a tumor of follicular derivation with peculiar nuclear, architectural, histochemical, and immunohistochemical features. We report a case of HTT in a 69-year-old woman with a mutinodular goiter. Since the clinical and ultrasonographic features were nonspecific, fine needle aspiration biopsy (FNAB) of the left lobe-dominant node was performed that resulted in an indeterminate cytologic diagnosis (category THY-3). The patient underwent total thyroidectomy, with a histologic diagnosis of HTT. We discuss the clinical and diagnostic approach, including the role of FNAB, and the pathologic features of HTT with special reference to the possible differential diagnosis. Total thyroidectomy or hemithyroidectomy represent adequate treatments, while radioiodine ablation is not standard. Although rare cases of malignant HTT have been documented, this tumor should be considered a benign neoplasm or, at most, a neoplasm of extremely low malignant potential. As a consequence, once this diagnosis is rendered, clinical management should be conservative, which may include a precautionary annual follow-up in order to exclude the very rare possibility of recurrence, as exceptionally reported.

Hyalinizing trabecular tumor of the thyroid gland

Hyalinizing trabecular tumor (HTT) is an unusual and controversial lesion of the thyroid gland. Some have considered it a unique entity, some have considered it a variant of papillary carcinoma, and still others have considered it a nonspecific pattern that may be seen with a variety of thyroid lesions. The histological and ultrastructural characteristics of this thyroid neoplasm are well documented; however, its cytological diagnosis by fine needle aspiration cytology (FNAC) remains challenging. The cytomorphological features of this entity overlap with both papillary and medullary carcinoma to a varying extent. We report a case of HTT with cytological evaluation by FNAC in a 28-year-old male.

Immunohistochemical subclassification of thyroid tumors with a prominent hyalinizing trabecular pattern

The purpose of this study was to evaluate the immunohistochemical characteristics of thyroid tumors with a prominent hyalinizing trabecular pattern (TTHTP). Immunohistochemical stains for thyroid transcription factor 1 (TTF-1), thyroglobulin, CD56, cytokeratin (CK) 19, galectin-3, and Ki-67 were performed on 16 cases of TTHTP. All TTHTPs were positive for TTF-1 and thyroglobulin, and nine cases expressed CD56 and Ki-67. Of these nine cases, seven satisfied the strict criteria of Carney, and four cases were positive for CK19 or/and galectin-3 and negative for Ki-67 and CD56. The remaining three cases had no Ki-67, CD56, CK19 or galectin-3 expression. All TTHTPs meeting the criteria of Carney were hyalinizing trabecular tumors (HTT), and TTHTPs which did not satisfy the criteria of Carney were subclassified according to the immunohistochemical results as the HTT type [Ki-67 (+) and CD56 (+)], papillary thyroid carcinoma (PTC) type [CK19 or galectin-3 (+)/Ki-67 (-) and CD56 (-)], or null type [Ki-67 (-), CD56 (-), CK19 (-) and galectin-3 (-)]. TTHTPs with typical histologic features and/or with typical immunohistochemical manifestations can be categorized as HTT, and the remaining TTHTPs should be categorized as the PTC or null type.

Diagnostic dilemmas of hyalinizing trabecular tumours on fine needle aspiration cytology: a study of seven cases with BRAF mutation analysis

OBJECTIVE

Hyalinizing trabecular tumours (HTTs) are rare follicular-derived neoplasms that behave in an almost benign manner. HTT is frequently misdiagnosed as papillary carcinoma by fine needle aspiration (FNA) cytology or as papillary or medullary carcinoma on surgical resection.

METHODS

The authors examined FNA material from seven cases of histologically verified HTT. Cytological findings were reviewed and correlated with ultrasonographic and histological features. In addition, MIB-1 and calcitonin immunostaining was performed on surgical specimens, and BRAF mutation analysis on three pre-operative FNA specimens and seven histology specimens.

RESULTS

The original cytological diagnosis was either suspicious or positive for papillary carcinoma in all patients. The FNA-based differential diagnoses included HTT, papillary carcinoma or, less likely, medullary carcinoma in two patients. Aspirates showed oval to spindle-shaped cells with frequent intranuclear inclusions, isolated in loosely cohesive groups with a trabecular or syncytial pattern in a bloody background. Radiating arrangements of tumour cells surrounding hyaline stroma with serrated calcifications and a lack of papillary or sheet-like fragments may suggest HTT on FNA. Spherical calcified bodies and possible psammoma bodies were frequently found in three cases. Retrospectively, six of the seven cases showed membranous immunoreactivity for MIB-1, but none of the seven possessed the BRAF (V600E) mutation or showed calcitonin reactivity.

CONCLUSIONS

Although the recognition of HTT on FNA cytology is difficult, because of its morphological similarities to papillary and medullary carcinoma, its characteristic cytological features along with ultrasonographic findings may suggest the diagnosis preoperatively and avoid surgical over-treatment.