Imaging for the diagnosis of thyroid cancer

There has been considerable difference in the mode of the imaging procedure and approach for the workup and post-surgery surveillance of thyroid cancer. Determination of serum thyroglobulin is recommended in the follow-up for monitoring the patients with differentiated thyroid carcinoma. Herein, the precise clinical role of individual imaging modalities is discussed, including ultrasound, computerized tomography (CT), magnetic resonance imaging (MRI) and scintigraphic procedures for the diagnosis of recurrent or metastatic thyroid cancer.

A review is presented of the scientific papers published in the literature between 1982 and 2007. Relevant articles for this review were identified by searching PubMed using the following search terms: thyroid cancer, ultrasound, computerized tomography, magnetic resonance imaging and scintigraphy. The papers were analyzed and categorized in tabular form by date, subject, author and the type of scientific paper (e.g., randomized controlled trial, meta-analysis, clinical cases and review articles).

Sonographic features of malignancy include microcalcifications, solid mass, absence of halo and internal blood flow, and these are helpful to predict thyroid malignancy in a nodule. Ultrasound is used for guiding fine needle aspiration to improve the accuracy of cytological analysis. However, biopsy is often necessary for a definitive diagnosis. This modality is also useful for postoperative neck evaluation of patients with elevated serum thyroglobulin levels to search for local recurrence or regional lymph node metastasis, which are the most common sites of recurrence. Tumor extension to the neighboring musculature, trachea, larynx and retropharyngeal, parapharyngeal and retrotracheal nodes are better defined by other anatomical imaging methods, such as CT or MRI. Anatomical imaging procedures are highly sensitive but not specific for postoperative evaluation of these patients and have few implications for deciding on subsequent I-131 therapy in patients with differentiated thyroid carcinoma. In addition to radioiodine scan, which has been the cornerstone of managing patients with differentiated thyroid cancer, nuclear imaging (scintigraphy) with technetium-99m sestamibi and tetrofosmin have all been used for determination of recurrent or metastatic differentiated thyroid cancer. Meta-iodo-benzylguanidine labeled either with I-123 or with I-131, 99mTc sestamibi and tetrofosmin and In-111 labeled somatostatin receptor analogues have been used for determination of recurrent or metastatic disease of medullary thyroid cancer. Over the last decade, positron emission tomography using 18-F-fluorodeoxyglucose has emerged as a useful tool in detecting non-iodine avid dedifferentiated and/or poorly differentiated thyroid cancer and plays a principal role in such settings.