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While the use of ultrasound has more than doubled the reported incidence of thyroid nodules over the past 30 years, the incidence of deaths from thyroid cancer remains stable.

"Should we be searching for nonpalpable thyroid nodules with ultrasound and what are we accomplishing by doing so?"

This is the question posed by US radiologist Dr John J. Cronan MD, of Rhode Island Hospital, in this month’s issue of Radiology [1].

The use of ultrasound technology has more than doubled the reported incidence of thyroid nodules over the past 30 years. However, despite this "exponential increase" in detection, Dr Cronan said, "the incidence of thyroid deaths has been stable."

With continual advances in imaging technology, this is not the first time concerns have been raised surrounding improved diagnosis that is not accompanied by the expected therapeutic benefit.

In March, Medicexchange reported on a study that showed increased use of CT for detection of pulmonary emboli had almost doubled diagnoses over ten years in New York, and yet mortality remained unchanged [2].

The identification of thyroid nodules is further complicated by an overlap between benign and malignant characteristics on ultrasound.

In the same issue of Radiology, a group of researchers assessed the diagnostic value of these characteristics using tissue diagnosis as the standard of reference in 831 patients with thyroid nodules [3].

They reported that ultrasound had a sensitivity of 83.3 per cent and specificity of 74 per cent for malignant nodules when one or more malignant feature was present, for example, marked hypoechogenicity and calcification. However, inter-reviewer reliability was "relatively low" and ultrasound features varied according to nodule size.

Dr Cronan questioned whether we should be searching for subpalpable nodules in the asymptomatic patient at all, particularly considering their marked prevalence: "Up to 67 per cent of the population evaluated with ultrasound will have an incidental thyroid nodule." He warned: "Left unchecked, this tsunami of thyroid nodules will overwhelm the health care system and have little beneficial outcome.

"Realising the outcome of screening the thyroid, it well might be better to turn off the ultrasound machines."

[1] Thyroid Nodules: Is it time to turn off the US machines?
Radiology 2008;247:602-604
[2] Increased diagnosis of pulmonary embolism without a corresponding decline in mortality during the CT era
Clin Radiol 2008;63:381-386
[3] Benign and malignant thyroid nodules: US differentiation - multicenter retrospective study
Radiology 2008;247:762-770