A large series of hyalinizing trabecular tumors: Cytomorphology and ancillary techniques on fine needle aspiration

Abstract

BACKGROUND:Hyalinizing trabecular tumors (HTTs) are rare, essentially benign, follicular cell-derived thyroid neoplasms characterized by a trabecular growth pattern and nuclear pseudoinclusions. Their cytological findings are misleading, because these tumors are often misinterpreted on fine needle aspirate cytology as malignant lesions, such as papillary thyroid cancer and/or medullary thyroid cancer, leading to unnecessary total thyroidectomy. The aim of this study was to analyze the cytomorphological features and application of ancillary techniques in a series of HTTs. METHODS: Of 26 histological cases of HTT collected from September 2001 to December 2018, 18 cases had concomitant cytopathology. Cytological cases were processed with liquid-based cytology (LBC). Immunocytochemistry for HBME-1 and galectine-3 as well as molecular testing for BRAF V600E mutation were performed on both LBC and histological specimens. RESULTS:The 18 lesions with fine needle aspirate cytology ranged in size from 5 to 45 mm. Cytological diagnoses included: 1 benign lesion favoring goiter (5.5%), 4 atypia of undetermined significance (22.2%), 6 follicular neoplasms (33.3%), 5 suspicious for malignancy favoring papillary thyroid cancer (28%), and 2 malignant (11%). Hence, 89% HTT had a negative concordant immunopanel, and they were 100% wild-type BRAF V600E . CONCLUSION: The majority of our HTTs (83.3%) were diagnosed in the indeterminate Bethesda categories, suggesting that their cytomorphological features pose issues for reaching a conclusive cytological diagnosis. The ancillary test results in our series support the fact that HTT is a benign neoplasm.

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

“…The challenges to solving the problem of presurgical diagnostics are 3‐fold: First, some of the key cytologic features of PTC and medullary thyroid carcinoma, such as enlarged oval nuclei, nuclear grooves, and intranuclear pseudoinclusions, are typically seen in HTT (Fig. ) . Tabulation of the cytology diagnoses standardized into the Bethesda System for Reporting Thyroid Cytopathology showed that 42.1% and 26.4% of HTT cases were diagnosed on FNA as suspicious for malignancy (Bethesda V) and malignant (Bethesda VI), respectively (Table ), which often triggered total thyroidectomy.…”

“…Third, the relative rarity of HTT has limited the opportunity for general cytopathologists to become proficient in recognizing the key cytologic features this entity. Although the exact incidence is not known, the finding that 11 of 26 reports (42%) documenting the cytology of HTT are individual case reports is likely a reflection of its rarity . Therefore, heightened awareness of the subtle cytologic features of HTT and the availability of novel, specific molecular markers are important in the presurgical identification of this neoplasm.…”

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

“…16,30 BRAF and RAS mutations, which are common in PTC and follicular variant of PTC (FVPTC), respectively, have not yet been discovered in HTT. 16 However, Dell’Aquila et al 18 found a wild type BRAF V600E in all of their reported HTT cases.…”

“…2,16 The cytopathological diagnosis of HTT remains challenging as it displays some cellular characteristics similar to PTC. 17 Despite HTT exhibiting several unique cytomorphological traits such cellular aggregates within hyaline matrix, no papillary formations, low nuclear to cytoplasmic ratio, and fine chromatin, 18 both HTT and PTC can exhibit hypercellularity, and cellular atypia including nuclear clearing, grooves, and pseudoinclusions on FNA. 13,19,20 However, the accurate diagnosis of HTT is critical as it guides the course of treatment.…”

“…22 Therefore, although the NCCN guidelines may limit excessive intervention, an inaccurate diagnosis of HTT may still lead to unwarranted overtreatment if the patient has bilateral nodularity. In a large series of HTT cases, Dell'Aquila et al 18 demonstrated that over 80% of HTTs were diagnosed in the indeterminate Bethesda categories, including, 22.2% atypia of undetermined significance, 33.3% suspicious for follicular neoplasm, 28% suspicious for malignancy. Furthermore, Saglietti et al 8 have documented that 60% of published HTT cases were diagnosed as suggestive, suspicious or positive for PTC.…”