Imaging Modalities
Ultrasound is the cornerstone of imaging thyroid cancer, and plays a role in diagnosis, staging, operative planning, and disease monitoring in pediatric patients.15 The advantages of ultrasound are that it is portable, can be performed quickly, is cost-effective, and requires no patient preparation and no sedation or anesthesia.16 The high spatial resolution and ability to detect microcalcifications as a finding of tumor are additional advantages, and ultrasound is superior to other imaging modalities at characterizing thyroid nodules.17 The primary disadvantage of ultrasound is that it is operator-dependent, and screening for cervical nodal metastatic disease requires experience and meticulous technique.
Computed tomography (CT) may play a role in imaging locoregional metastatic disease as well as pulmonary metastases. However, use of iodinated IV contrast material is discouraged because it interferes with radioactive iodine (RAI) uptake, and if RAI therapy is deemed necessary, treatment must be delayed for weeks to 3 months. CT scanning parameters should be optimized for patient size to minimize radiation exposure. Additionally, sedation or anesthesia may be required to achieve breath-holds necessary to detect miliary pulmonary metastases in patients unable to comply with breath holding instructions.
Magnetic resonance imaging (MRI) in patients with thyroid cancer is primarily used in the evaluation of bulky cervical metastatic disease and extrathyroidal invasion.18 Although the spatial resolution of MRI is lower than both ultrasound and CT, the tissue contrast resolution is higher. However, punctate calcifications relevant to identifying disease are not apparent by MRI. MRI examinations are lengthy, which may require use of sedation or anesthesia to ensure patient immobility.
RAI scintigraphy capitalizes on the physiologic uptake of iodine by most differentiated thyroid cancers and may be used in post-surgical disease staging. 18F-FDG PET/CT is not typically used but may play a role in the evaluation of undifferentiated tumors that are not iodine avid. 68Ga-DOTATATE PET/CT may be useful for medullary thyroid cancer disease evaluation.19