lunedì 11 agosto 2008
Transverse (Figure 1) and sagittal (Figure 2 and Figure 3) ultrasound images of the left thyroid lobe demonstrate a nodule with multiple punctuate echogenic foci and associated comet-tail artifact. These represent colloid crystals and are a reliable ultrasonographic feature indicating a benign nodule. The comet-tail artifact distinguishes these echogenic foci from microcalcifications.
Diagnosis: Benign hyperplastic adenomatoid nodule of thyroid
Ultrasound is of great benefit in the management of thyroid nodules in that it is a noninvasive test, can identify suspicious features, determines the presence of other coexisting nodules in the gland, helps demonstrate lymphatic spread and can be used as a guide for percutaneous biopsy. There is considerable overlap in US features of benign and malignant thyroid nodules and no one sonographic finding is absolutely 100% specific or sensitive for malignancy. However, certain sonographic characteristics have been described as more suggestive of malignancy or benignity, and become especially helpful when multiple signs suspicious for malignancy are present.
Size, number and slight interval growth detected only on ultrasound are generally unreliable signs in deciding whether a nodule is malignant or benign.
US features suggestive of malignancy
1.Thyroid microcalcifications, or psammoma bodies, are one of the most specific findings for thyroid malignancy, and if present in a hypoechoic nodule are highly predictive of papillary carcinoma.
2.Large, coarse dystrophic calcifications from tissue necrosis are also associated with a high malignancy rate.
3.An ill-defined and irregular margin may hint at malignant infiltration into adjacent thyroid parenchyma, but this finding has a wide range of sensitivity and specificity.
4.A solid nodule that is taller than it is wide (greater AP to transverse dimension) may be potentially malignant, although this sign has not been widely described.
5.Intrinsic hypervascularity is seen in a majority of malignant nodules, but is not a very specific sign.
6.Malignant nodules typically have a solid and hypoechoic appearance, but again around half of benign nodules may have a similar appearance. Marked hypoechogenicity less than that of the strap muscles is more specific.
US features suggestive of benignity
1.The presence of inspissated colloid is a reliable sign of benignity and should be distinguished from microcalcifications using high frequency probes to demonstrate its characteristic reverberation artifact.
2.A thin, uniform hypoechoic halo is produced by a pseudocapsule of fibrous tissue and compressed thyroid parenchyma. Its presence is highly suggestive that a nodule is benign, however it is also seen in a small percentage of malignant nodules.
3.A predominantly cystic nodule is more likely to be benign. A cystic variant of papillary carcinoma has been described, but it is rare and close US examination will demonstrate malignant signs such as solid hypervascular component or microcalcifications.
4.Small subcentimeter cystic nodules represent benign colloid-filled cysts.
5.Peripheral calcifications are usually seen in benign multinodular thyroid, but may also be present in malignancy.
One must keep in mind that in the approach to a thyroid nodule, the decision to biopsy should be based not only on the sonographic characteristics of the nodule, but the findings need to be taken in context with physical exam findings, laboratory tests, and patient history. The age and sex of the patient, personal or family history of thyroid cancer, and prior history of neck irradiation are important considerations in a patient’s history that would lower the threshold for biopsy. Likewise a firm and fixed nodule, the concomitant symptoms of dysphagia or hoarseness, a rapidly growing nodule, and the presence of lymphadenopathy raise the likelihood a nodule may be malignant.