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

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.

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.

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.

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.

Comparison of Korean vs. American Thyroid Imaging Reporting and Data System in Malignancy Risk Assessment of Indeterminate Thyroid Nodules

BACKGROUND

The management of cytologically indeterminate thyroid nodules is challenging for clinicians. This study aimed to compare the diagnostic performance of the Korean Thyroid Imaging Reporting and Data Systems (K-TIRADS) with that of the American College of Radiology (ACR)-TIRADS for predicting the malignancy risk of indeterminate thyroid nodules.

METHODS

Thyroid nodules diagnosed by fine-needle aspiration (FNA) followed by surgery or core needle biopsy at a single referral hospital were enrolled.

RESULTS

Among 200 thyroid nodules, 78 (39.0%) nodules were classified as indeterminate by FNA (Bethesda category III, IV, and V), and 114 (57.0%) nodules were finally diagnosed as malignancy by surgery or core needle biopsy. The area under the curve (AUC) was higher for FNA than for either TIRADS system in all nodules, while all three methods showed similar AUCs for indeterminate nodules. However, for Bethesda category III nodules, applying K-TIRADS 5 significantly increased the risk of malignancy compared to a cytological examination alone (50.0% vs. 26.5%, P=0.028), whereas applying ACR-TIRADS did not lead to a change.

CONCLUSION

K-TIRADS and ACR-TIRADS showed similar diagnostic performance in assessing indeterminate thyroid nodules, and K-TIRADS had beneficial effects for malignancy prediction in Bethesda category III nodules.

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.

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.

Oncogenic properties and signaling basis of the PAX8-GLIS3 fusion gene

Hyalinizing trabecular tumors of the thyroid are rare and mostly benign epithelial neoplasms of follicular cell origin, which have recently been shown to be underpinned by the PAX8-GLIS3 fusion gene. In our study, we sought to investigate the potential oncogenic mechanisms of the PAX8-GLIS3 fusion gene. Forced expression of PAX8-GLIS3 was found to increase proliferation, clonogenic potential and migration of human nonmalignant thyroid (Nthy-ori 3-1) and embryonic kidney (HEK-293) cells. Moreover, in xenografts, Nthy-ori 3-1 PAX8-GLIS3 expressing cells generated significantly larger and more proliferative tumors compared to controls. These oncogenic effects were found to be mediated through activation of the Sonic Hedgehog (SHH) pathway. Targeting of smoothened (SMO), a key protein in the SHH pathway, using the small molecule inhibitor Cyclopamine partially reversed the increased proliferation, colony formation and migration in PAX8-GLIS3 expressing cells. Our data demonstrate that the oncogenic effects of the PAX8-GLIS3 fusion gene are, at least in part, due to an increased activation of the SHH pathway.

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."

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 tumor of the thyroid: a clinicopathological analysis of four cases and review of the literature

OBJECTIVE

To explore the clinicopathological features, diagnosis and differential diagnosis of hyalinizing trabecular tumor (HTT) of the thyroid.

METHODS

The four HTT specimens were collected including demographics, clinical information, relevant images, the extent of thyroidectomy, the follow-up and representative pathological data of tumors were available for analysis. In addition, the immumohistochemical staining related to the tumor as well as the BRAF and N-ras mutation analysis were analysed.

RESULTS

The mean age of four patients was 47 years old and the mean size of the tumor was 2.8 cm. Most of the patients were asymptomatic, while detecting incidentally by using neck ultrasound test. Ultrasound imaging of all cases showed demarcated substantial hypoechoic nodules in ipsilateral thyroid lobe. Computed Tomography (CT) showed a clear low density shadow in the affected thyroid lobe. Tumors of three cases were located at the left, but the other one was located at the right thyroid gland with a complete fibrous capsule. The cytological features resembled papillary thyroid carcinoma (PTC). The histological test indicated that the tumors had characteristic of trabecular growth pattern with hyalinizing material. The tumor cells were in shape of polygonal, oval or high columnar with an acidophilic or clear cytoplasm. The nuclei were oval with inconspicuous small nucleoli, prominent grooves and pseudoinclusion body in cell nucleus. Mitosis and psammoma bodies were rare to be observed. Cytoplasmic "yellow bodies" were frequently observed. The hyaline material was prominent, with positive periodic acid-Schiff (PAS) and negative Congo red staining. Immunohistochemically, tumor cells were positive for thyroglobulin (Tg), thyroid transcription factor-1 (TTF-1), CD56 and negative for calcitonin, cytokeratin 19 (CK19), HBME-1, S-100 and synaptophysin (SyN). Chromogranin A (CgA) and galectin-3 were expressed weakly in some cases. Staining with the MIB-1 antibody showed membranous/cytoplasmic immunoreactivity. Whereas, another clone of Ki-67 (SP6) showed a common nuclear pattern with an index of <1%. None of the four cases exhibited the BRAF V600E protein reactivity. Gene mutation analysis demonstrated no BRAF and N-ras mutation. There was no evidence of local recurrence or metastasis after 6 to 36 months of follow-up.

CONCLUSIONS

HTT is an uncommon thyroid tumor with very low malignant potential. It has no particular clinical features, so it's often misdiagnosed in fine needle aspiration cytology (FNAC)/Ultrasonography-guided fine needle aspiration cytology (US-FNAC) and frozen section (FS). Its final diagnosis mainly relies on typical histopathological features and characteristic expression pattern of MIB-1 immunohistochemical staining.

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.

Core Needle Biopsy of the Thyroid: 2016 Consensus Statement and Recommendations from Korean Society of Thyroid Radiology

Core needle biopsy (CNB) has been suggested as a complementary diagnostic method to fine-needle aspiration in patients with thyroid nodules. Many recent CNB studies have suggested a more advanced role for CNB, but there are still no guidelines on its use. Therefore, the Task Force Committee of the Korean Society of Thyroid Radiology has developed the present consensus statement and recommendations for the role of CNB in the diagnosis of thyroid nodules. These recommendations are based on evidence from the current literature and expert consensus.