Malignancy risk for solitary and multiple nodules in Hürthle cell–predominant thyroid fine‐needle aspirations: A multi‐institutional study

Abstract

BACKGROUND: Hürthle cell metaplasia is common in hyperplastic nodules, particularly within the setting of lymphocytic thyroiditis (LT). The Bethesda System for Reporting Thyroid Cytopathology indicates that it is acceptable to classify Hürthle cell-predominant fine-needle aspiration (HC FNA) specimens as atypia of undetermined significance (AUS) rather than suspicious for a Hürthle cell neoplasm (HUR) within the setting of multiple nodules or known LT. The goal of the current study was to address whether this approach is justified. METHODS: HC FNA specimens were identified and correlated with ultrasound and surgical pathology reports if available. Multinodularity was determined based on findings on macroscopic examination if imaging results were unavailable. RESULTS: A total of 698 HC FNA specimens were identified, including 576 resected nodules, 455 of which (79%) were benign. The overall risk of malignancy for HUR was 27%, whereas the risk of malignancy for AUS was 10%. The mean size of the benign nodules was 2.1 cm on surgical resection specimens, with multiple nodules noted in 293 cases (64%) and histologic LT noted in 116 cases (25%). The mean size of the malignant nodules was 2.8 cm, with multiple nodules and histologic LT noted in 74 cases (61%) and 22 cases (18%), respectively. The malignancy rate did not differ between solitary or multiple nodules (P = .52) or in the presence or absence of LT (P = .12). However, size did significantly differ between malignant and benign nodules (P < 0.01). CONCLUSIONS: The malignancy rate did not differ significantly in the presence of multiple nodules or LT, although the latter demonstrated a statistical trend. A diagnosis of AUS over HUR based solely on the presence of multinodularity is not warranted.

Hürthle cell lesions of the thyroid: Progress made and challenges remaining

“…63 Very limited data raise the possibility that multiple Hürthle cell nodules may represent a low-risk scenario, but this observation needs further study in a larger case series. 63 Incorporation of clinical findings into cytologic diagnoses should therefore be performed judiciously.…”

“…However, the literature on whether this approach is justified is limited. Although some studies have raised the possibility that LT may have a modest effect on risk of malignancy (ROM) in patients with Hürthle cell–predominant FNA, the differences in ROM did not reach significance 62,63 . Similarly, a difference in ROM was not seen in patients with multiple thyroid nodules compared to those with solitary nodules 63 .…”

“…Although some studies have raised the possibility that LT may have a modest effect on risk of malignancy (ROM) in patients with Hürthle cell–predominant FNA, the differences in ROM did not reach significance 62,63 . Similarly, a difference in ROM was not seen in patients with multiple thyroid nodules compared to those with solitary nodules 63 . Very limited data raise the possibility that multiple Hürthle cell nodules may represent a low‐risk scenario, but this observation needs further study in a larger case series 63 .…”

“…Various studies have demonstrated that the ROM associated with AUS‐C (including cytologic atypia alone or in combination with architectural atypia) is often significantly higher than AUS‐A or AUS‐HC 72‐83 . The ROM for AUS‐HC is variable but appears to be toward the lower end of the spectrum for AUS reported by TBSRTC, with a 0% to approximately 30% ROM (median, 15%) reported in the literature 63,73,74,76,77,81,82,84 . The ROM for nodules diagnosed as HUR also has a wide reported range (14% to 45%; median 23%), 60‐64,69,70,74,79,85‐92 again tending to occur toward the lower bound reported in TBSRTC for follicular neoplasm/suspicious for follicular neoplasm (25% to 40%) 55…”

The dilemma of 18F-FDG PET/CT thyroid incidentaloma: what we should expect from FNA. A systematic review and meta-analysis

“…This study shows that FDG avid nodules show a relative excess of BETHESDA category IV and V FNA (see Table 4 ). Although the published studies included in this meta-analysis do not give specific information on the prevalence of Hurthle cell neoplasms, the finding of relatively higher frequencies of category IV and V FNA in thyroid TI implies that this is due to the underlying higher clinical ROM of PET avid thyroid nodules, in combination with a relative excess of HCN in nodules that are FDG avid which would typically fall in BETHESDA categories III and IV [ 14 , 32 – 34 ].…”