A focal marked hypoechogenicity within an isoechoic thyroid nodule: is it a focal malignancy or not?

Background: A marked hypoechogenicity is a reliable criterion for a malignant nodule, whereas isoechogenicity is considered to be a benign ultrasonographic (US) finding. However, there have been no reports to demonstrate whether a focal marked hypoechogenicity within an isoechoic nodule is a focal malignancy. Purpose: To evaluate whether a focal marked hypoechogenicity within an isoechoic nodule on US examination is a focal malignancy and to correlate US histologic findings using surgical or core needle biopsy (CNB) specimens. Material and Methods: From January 2010 to August 2011, 28 consecutive patients (25 women, 3 men; mean age, 52.2 years) with 29 thyroid nodules, which showed a focal marked hypoechogenicity within an isoechoic nodule on US, underwent US-guided CNB for a suspicion of a focal malignancy. All nodules were confirmed by surgery (n = 6) or more than two consecutive US-guided biopsies (n = 23). We evaluated the risk of malignancy, and analyzed histological components which correlated with a focal marked hypoechogenic area within an isoechoic nodule on US. Statistical analysis was performed using the Mann-Whitney U test and Fisher's exact test. Results: Of the 29 nodules, 25 were benign (86.2%) and four were malignant (13.8%). The peripheral location of focal marked hypoechogenicity within an isoechoic nodule was the only significant US finding that suggested malignancy (P = 0.03). All benign focal marked hypoechogenicities were histologically composed of severe fibrosis with a few follicular cells with varying frequencies of hemosiderin, calcification, infarction, and granulation tissue. Conclusion: Although a focal marked hypoechogenicity within an isoechoic nodule is usually benign, the peripheral location of a focal marked hypoechogenicity may be a malignancy. The histologic information obtained by CNB specimen may reduce the needs for repetitive fine needle aspirations or diagnostic surgery.