Ultrasound is a safe and non-invasive method that allows evaluation of the thyroid gland and any associated cervical lymphadenopathy (Figure 3). It is useful in documenting the extent of any malignant thyroid lesion, which may have an impact on clinical management decisions. Ultrasound can detect cystic lesion as small as 1 mm and solid lesions as small as 3 mm. It cannot distinguish malignant from benign nodules. However, when used in combination with fine needle aspiration cytology (FNAC), it can improve the accuracy of cytological diagnosis by identifying the dominant nodule in a multinodular goitre or allowing any solid component of cystic lesions to be biopsied. Although most thyroid malignancies are solid, in a review of 15 articles, a malignancy rate of 21% for solid lesions, 12% in mixed lesions and 7% in purely cystic thyroid lesion was reported.
Further imaging is not usually required. However, when malignant extracapsular spread or retrosternal extension of the tumour is present, the use of computerised tomography (CT) or magnetic resonance imaging (MRI) may be helpful in defining the extent of the tumour as well as distant metastasis. If CT with iodine contrast is used for further evaluation of disease extent, it should be remembered that the iodine contrast media used will block iodine uptake by thyroid tissue for up to 6 months. This would reduce the benefit of future radioiodine therapy and iodine diagnostic scans. As a consequence, MRI is the preferred imaging modality.
A plain chest X-ray may demonstrate tracheal deviation, mediastinal thyroid extension or pulmonary metastasis (Figure 4). However, respiratory flow-loop studies are more accurate than plain chest X-rays or thoracic inlet views in demonstrating tracheal compression if this is suspected.[9,20]
Int J Clin Pract. 2005;59(11):1340-1344. © 2005 Blackwell Publishing
Cite this: Thyroid Cancer Review 1: Presentation and Investigation of Thyroid Cancer - Medscape - Nov 01, 2005.