CT Detection of Metastatic Lymphadenopathy in Papillary Thyroid Cancer

Overview

Localized thyroid cancer is potentially curable. Before thyroid surgery, an ultrasound test is done to see if cancer has spread to the lymph nodes in the neck. Excellent for evaluation of the thyroid gland, this test has limitations in evaluating larger anatomic areas, like all groups of lymph nodes in the neck. It has a limited area of coverage making it difficult to define an area of interest, depends on the skill level of the person performing it, and is difficult to exactly reproduce on follow-up. For these reasons, CT is often performed in these patients but without intravenous (IV) contrast since iodine-based contrast agents may saturate the thyroid, limiting the usefulness of other iodine-based diagnostic and treatment options. However, contrast-CT can give more detailed information about tumor spread including spread to lymph nodes. We aim to determine if use of IV contrast agent during CT leads to earlier and more accurate detection of lymph node disease from thyroid cancer.

Papillary thyroid cancer represents 75% of all epithelial thyroid malignancies. Imaging not only delineates the primary tumour within the thyroid gland, but also helps assess lymph nodal metastatic disease helping guide the extent of surgical neck dissection. Ultrasonography (US) is the current imaging standard (American Thyroid Association guidelines). However, US is limited by operator skills and lacks specific anatomic references essential to plan surgery. CT is performed to address these issues, often without intravenous (IV) contrast for fear of saturating thyroid tissue with iodine present in it, thus rendering iodine-labeled nuclear testing/treatment ineffective for a finite period of time. But post-contrast nodal enhancement is a predominant morphologic feature of suspicious lymphadenopathy in papillary thyroid cancer, and contrast-CT can facilitate an earlier detection. Iodine-saturation is not a concern in these patients as its concentration will normalize during recovery. In pre-surgical thyroidectomy patients with proven papillary thyroid cancer, the use of intravenous (IV) CT contrast improves the reliability and accuracy of suspicious head and neck lymph node detection, in comparison to CT without IV contrast. This study will help define the accuracy and reliability of intravenous (IV) contrast use in the detection of metastatic neck lymph nodes from papillary thyroid cancer. Improved detection of suspicious metastatic lymphadenopathy in papillary thyroid cancer will directly impact the patient's management since the surgical plan will be based upon the detection of these suspicious lymph nodes. CT imaging provides an anatomically relevant approach to surgery and is consistently reproducible, thus providing direct benefits to the pre-surgical assessment. Ultimately, this will result in decreased nodal recurrences within the neck.