Hyalinizing trabecular tumor of the thyroid gland and its significant diagnostic issue

Abstract

BackgroundHyalinizing trabecular tumors (HTT) are rare follicular cell-derived tumors of the thyroid gland that are infrequently reported in otolaryngology literature. We present here an interesting case of HTT which provides the basis for review of this entity’s clinical characteristics, criteria useful in making the diagnosis, and any currently available therapeutic modalities.Case presentationA 70-year-old Caucasian female underwent a CT scan of her chest and was incidentally found to have a nodule within the right thyroid lobe. Gross examination of the excised thyroid lobe revealed a circumscribed and encapsulated lesion (tan / gritty in texture), confined to the gland. Histologic sections of the lesion revealed a circumscribed neoplasm with a trabecular and organoid architecture associated with abundant dystrophic calcification. Neoplastic cells showed a spindled morphology with clumped chromatin and ample eosinophilic cytoplasm.ConclusionsHistologically, HTT is a follicular cell-derived tumor composed of neoplastic cells arranged in a trabecular pattern with hyalinization and calcification of extracellular material. Distinguishing features of HTT include minimal cytologic atypia with a low nuclear: cytoplasmic ratio, cellular aggregates around hyalinized material, and nuclei with clumped chromatin and occasional grooves and/or pseudoinclusions. Though debated in the literature, the general consensus is that this tumor is a benign entity. It is our hope that additional clinical research will elicit awareness of these rare tumors.

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

“…The cytological interpretation of HTT is equally difficult. The difficulty in rendering a cytological diagnosis of HTT is caused by the cytomorphological features of nuclear pseudoinclusions, nuclear grooves, and hyaline material that can result in a false‐positive diagnosis of PTC or MTC . Different published series including cytological samples of HTT have documented that up to 60% of cases were diagnosed as positive and/or suspicious for malignancy, despite the fact that the samples had a lack of papillary structures and that lesions exhibited elongated nuclei associated with acellular hyaline stroma .…”

“…Several cytomorphological features have been recognized with HTT including cellular aggregates arranged around hyaline material, cells with a low nuclear/cytoplasmic ratio, fine chromatin (that differs from the optical clear chromatin seen in PTC), abundant nuclear pseudoinclusions and grooves, and samples with a bloody background . Despite the difficulty in diagnosing HTT with FNA due to these overlapping cytomorphological features, Carney et al demonstrated that HTT could be cytologically diagnosed in 72% of their cases …”

“…The latter authors described a lesion with peculiar histological features composed of a trabecular growth pattern with prominent deposition of hyaline material. Following this description, several authors published case reports or small series demonstrating that HTT is essentially a benign neoplasm requiring conservative management, even though it is worth noting that very rare cases of invasive HTT have been described …”

“…The majority of histological series show that reaching the correct diagnosis of this neoplasm does not pose a diagnostic challenge . However, a review of the literature indicates that reaching the correct preoperative diagnosis of HTT is more elusive, as the correct interpretation was achieved in only 8% of cases .…”

“…However, a review of the literature indicates that reaching the correct preoperative diagnosis of HTT is more elusive, as the correct interpretation was achieved in only 8% of cases . More concerning, however, is the fact that the remaining 92% of cases resulted in false‐positive diagnoses . The problem in achieving a correct preoperative diagnosis is largely ascribed to the fact that in cytology samples of HTT, the nuclear features and hyaline material mimic thyroid malignancy.…”