Ultrasound (US), along with a clinical follow-up, could be a diagnostic alternative to detect thyroid nodule malignancy instead of repeating a biopsy following non-diagnostic fine-needle aspiration (FNA), according to a study published in the September issue of Radiology.

Although current guidelines recommend a second FNA after a first FNA comes back with a non-diagnostic result, researchers found that this diagnosed very few malignancies (two out of 336, or 0.6 percent). “Therefore, clinical and US follow-up may be more appropriate than repeat FNA following non-diagnostic biopsy results,” wrote lead researcher Thomas J. T. Anderson, MD, of Rhode Island Hospital, in Providence, and colleagues.

While thyroid nodules are common and typically benign, approximately five percent to 15 percent are malignant, but US cannot reliably differentiate cancers from benign nodules, the authors noted. As a result, clinical guidelines recommend FNA of nodules with a maximal diameter greater than 1–1.5 cm and of nodules that are smaller with US features of concern, they said.

Although the first diagnostic FNA performed has a reported diagnostic yield of 85 percent, studies have shown that the second FNA’s rate for detecting malignancy may be substantially lower, they wrote.

“The purpose of this study was to identify demographic and US features of thyroid nodules that may be predictive of malignancy after initially non-diagnostic FNA results to help clarify the role of repeat FNA, surgical excision, or serial US in these nodules,” the authors wrote.

Anderson and colleagues retrospectively examined 393 single nodules that had non-diagnostic FNA results but adequate cytologic, surgical, or US follow-up. These were selected from more than 5,000 thyroid nodules that underwent US-guided FNA at the authors' institution from 2004 to 2012.

Nine malignancies (2.3 percent) of the 393 nodules were subsequently diagnosed with repeat FNA or with surgical pathologic examination; 330 (84 percent) were benign, and 54 (13.7 percent) were stable or decreased in size at serial US.

The mean follow-up period was three years; the median follow-up was at 2.5 years after the initial FSA, according to the study.

Patients with malignancies were significantly older, with a mean age of 62.7 years and a median age of 64 years. The odds of malignancy were 4.2 times greater for men than for women. The odds also increased significantly for each 1-cm increase in anteroposterior, minimum, and mean nodule diameter (odds ratios of 1.78, 2.10, and 1.96, respectively), the authors wrote.

The false-positive rate of repeat FNA following non-diagnostic FNA results was 4.9 percent.

Subsequent FNA allowed the diagnosis of 245 of 336 nodules (72.9 percent) as benign; 167 of 336 (49.7 percent) were diagnosed on the first repeat FNA, while the rest (78 of 336, or 23.2 percent) were diagnosed as benign at subsequent FNA, the authors wrote.

Of the remaining 73 nodules, 49 (14.6 percent) were surgically excised, yielding four papillary cancers and one follicular cancer, and 24 (7.1 percent) were followed up with serial US examinations. they said.

Among patients who did not undergo repeat FNA, 47.4 percent (27 of 57) underwent surgical excision, which led to the diagnosis of one papillary and one follicular cancer, the authors wrote.