Hyalinizing Trabecular Adenoma of the Thyroid Revisited: A Histologic and Immunohistochemical Study of Thyroid Lesions With Prominent Trabecular Architecture and Sclerosis

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.

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.

Comparison of Thyroid Nodule Prevalence by Ultrasound in Childhood Cancer Survivors With and Without Thyroid Radiation Exposure

PURPOSE

Children receiving radiotherapy of the head, neck, or chest as treatment of primary malignancies are at increased risk for secondary thyroid malignancy. We hypothesized that current standards (yearly thyroid physical examination) lead to a substantial number of missed thyroid nodules. Our objectives were: (1) use thyroid ultrasound to assess thyroid nodules in childhood cancer survivors; and (2) compare prevalence of thyroid nodules in thyroid radiation-exposed patients as compared with cancer survivors without radiation exposure.

METHODS

We recruited 60 patients with thyroid radiation and chemotherapy exposure (median age at cancer diagnosis 10.8 y) and 59 patients with chemotherapy exposure alone (median age at diagnosis 4.3 y) from our long-term survivorship clinics. Each patient had a thyroid physical examination and thyroid ultrasound performed.

RESULTS

Thirty-three patients (27.7%) had nodules >0.3 cm of which 2 were palpated (6.1%). We found 22 radiated patients (36.7%) with nodules versus 11 nonradiated patients (18.6%) (P=0.03). Eleven patients were biopsied and 1 diagnosis of secondary papillary thyroid carcinoma was confirmed.

CONCLUSION

Our study supports further examination of incorporating thyroid ultrasounds into long-term survivorship follow-up guidelines in radiation-exposed patients for the detection of thyroid nodules and secondary malignancies.

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.

[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.

Unusual thyroid carcinoma with excessive extracellular hyaline globules: a case of "hyalinizing papillary carcinoma"

We present an unusual case of papillary thyroid carcinoma in a 47-year-old Japanese woman. The tumor, 0.8 cm in diameter, was located in the upper left lobe of the thyroid. Histologically, we observed a microfollicular-like and trabecular arrangement of the tumor cells with marked hyalinized stroma and hyaline globules. Immunohistochemically, tumor cells were positive for thyroglobulin and thyroid transcription factor 1. Hyaline stroma and globular bodies were immunopositive for laminin and type IV collagen. MIB-1 index was approximately 1% without membranous immunoreactivity. Under the electron microscope, hyaline stroma and globules showed electron-dense, complex meshwork structures composed of granular and fibrous elements similar to the structure of the lamina densa. Genetic analysis demonstrated a BRAF(V600E) mutation. Based on these findings, we diagnosed the present tumor as a rare morphological variation of papillary thyroid carcinoma with excessive hyaline globules consisting of basal membrane materials.

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.

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.

Hyalinizing trabecular adenoma of the thyroid gland

Hyalinizing trabecular adenoma (HTA) is a rare primary thyroid neoplasm. Ever since its initial descriptions, controversy has surrounded the lesion, particularly in regard to its malignant potential and most appropriate terminology. HTA shares many features with medullary thyroid carcinoma and particularly papillary thyroid carcinoma, making it an especially treacherous lesion on fine-needle aspiration (FNA). This manuscript reviews the history and pathologic features of HTA, with particular attention to cytologic findings and differential diagnosis.

Immunohistochemical and electron microscopy studies of a case of hyalinizing trabecular tumor of the thyroid gland, with special consideration of the hyalinizing mass associated with it

Hyalinizing trabecular tumor (HTT) of the thyroid gland is rare and benign, and it neither recurs nor metastasizes. In this lesion, tumor cells are arranged in trabeculae, in association with hyalinizing mass in the stroma. The origin and nature of the hyalinizing mass are still controversial. We report here a case of HTT with cytological, immunohistochemical, and ultrastructural findings, focused in particular on the hyalinizing mass. Cytologically, tumor cells exhibiting many intranuclear cytoplasmic inclusions and nuclear grooves were found in association with light green-positive, irregular, fluffy membranous structures on touch smear. Staining with antibody to collagen type IV was positive in these membranous structures. Histopathologically, tumor cells exhibited many intranuclear cytoplasmic inclusions, and were positive for staining with antibodies to S100 protein, neuron-specific enolase, thyroglobulin, and vimentin. The hyalinizing eosinophilic mass, which was positive for PAS reaction, and for staining by antibody to collagen type IV, gradually increased in the areas surrounding tumor cells. This mass then appeared to replace the tumor cells, and exhibited a peculiar filiform pattern. We demonstrated ultrastructurally that this pattern was composed of long, irregular, fine cytoplasmic processes of tumor cells and basal lamina-like substance in the hyalinizing mass. In fact, the homogeneous hyalinizing mass, similar to basal lamina-like substance, contained many degenerated cytoplasmic processes at the ultrastructural level. These results suggested that the key cytological finding in differentiating HTT from papillary carcinoma is the fluffy membranous structure, although nuclear pseudoinclusions are important as well. The filiform pattern noted at light microscopic level consisted of long cytoplasmic processes of tumor cells and hyalinized mass at the ultrastructural level.

Hyalinizing trabecular tumors of the thyroid gland are almost all benign

In 1987, Carney et al reported 11 thyroid tumors with the following features: circumscription or encapsulation, trabecular architecture with intratrabecular hyalin and colloid, polygonal and spindle cells, nuclei with frequent grooves and cytoplasmic inclusions, occasional psammoma bodies, and a low mitotic rate. The neoplasms did not recur or metastasize during a follow-up period that averaged 10 years, and they were titled hyalinizing trabecular adenomas. Subsequently, the nuclear features of the neoplasm led to the introduction of 2 modified titles for it, hyalinizing trabecular tumor and hyalinizing trabecular neoplasm. Later, discovery of RET/PTC mutations in the tumor resulted in it being designated as a type of papillary thyroid carcinoma. We studied 119 neoplasms of the type outlined, collected over a 20-year period, for invasion, recurrence and metastasis, and obtained follow-up in 96% of the cases. One hundred eighteen tumors showed no evidence of aggressive behavior (capsular, vascular, and parenchymal invasion), local recurrence, or metastasis. One tumor showed vascular and capsular invasion, and pulmonary metastasis. We conclude that the overwhelming majority of hyalinizing trabecular tumors of the thyroid behave as benign neoplasms and that, at this time, hyalinizing trabecular adenoma is the most appropriate title for them.

Fine-needle aspiration biopsy of primary osteosarcoma of the thyroid: report of a case and review of the literature

Primary osteosarcoma of the thyroid is an extremely rare tumor, with only 27 well-documented cases reported in the literature, including only one in the cytology literature. We describe here an additional case with fine-needle aspiration biopsy findings. A 60-year-old woman presented with a 1-month history of progressive midline neck swelling. CT and ultrasound demonstrated a large thyroid mass with tracheal compression. Fine-needle aspiration biopsies were performed and showed pleomorphic spindle and epithelioid neoplastic cells, multinucleated giant cells, and scant metachromatic extracellular matrix material. Cell block sections contained minute tissue fragments with neoplastic spindle cells. Immunohistochemical stains showed the tumor cells to be positive for vimentin and negative for cytokeratins, TTF-1, calcitonin, synatophysin, chromogranin, and S-100 protein, suggesting a sarcoma; however, the differential diagnosis also included anaplastic thyroid carcinoma and medullary thyroid carcinoma. Tissue biopsy revealed a high-grade spindle cell neoplasm with osteoid production, consistent with osteosarcoma of the thyroid. The patient developed a large pulmonary embolus and superior vena cava syndrome and no further surgical intervention was performed. She died 5 weeks after the initial diagnosis. Upon retrospective review, the cytologic features resemble osteosarcoma in other areas. Although cytologic features on fine-needle aspiration biopsy may suggest a diagnosis of this rare entity, definitive diagnosis should be deferred to histologic examination.

Hyalinizing trabecular tumors of the thyroid gland: quadruply described but not by the discoverer

Hyalinizing trabecular tumors of the thyroid have been described on 4 occasions, by Carney and colleagues in 1987, by Ward and coworkers in 1982, by Pierre Masson in 1922, and by Rahel Zipkin in 1905. Zipkin credited her chief, Theodor Langhans (of Langhans giant cell fame), with identification of the cases she reported. Unaware of the 3 earlier descriptions, Carney and colleagues described 11 circumscribed or encapsulated thyroid tumors with elongated and polygonal cells arranged in trabeculae that contained a hyaline material resembling amyloid. The nuclei of the tumor cells had cytoplasmic invaginations and grooves similar to those of papillary carcinoma. Carney and colleagues labeled the neoplasms hyalinizing trabecular adenomas because of their microscopic appearance, absence of invasion, and benign natural history. Subsequently, the nuclear features of the tumor and the molecular genetic findings led to the introduction of equivocal designations for it, hyalinizing trabecular tumor and hyalinizing trabecular neoplasm, and later to its designation as a variant of papillary carcinoma. Experience has shown that most circumscribed or encapsulated follicular thyroid tumors with intratrabecular hyalin and nuclear features of papillary carcinoma behave as benign neoplasms. Hyalinizing trabecular carcinoma is a very rare tumor.