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