Final answer:
Medullary thyroid carcinoma is a type of thyroid cancer that cannot be diagnosed by fine needle aspiration due to its characteristics. Instead, blood tests and genetic testing are used. Radioactive iodine and other radioisotopes can also play a role in diagnosing and treating thyroid conditions.
Step-by-step explanation:
One type of thyroid cancer that cannot be diagnosed by fine needle aspiration (FNA) is medullary thyroid carcinoma (MTC). This is because MTC does not shed cells easily and FNA may not capture enough cells for a definite diagnosis. Additional tests, like blood tests for calcitonin and genetic testing, are often required to diagnose MTC.
For diagnosing thyroid disorders, such as hypothyroidism or hyperthyroidism, other diagnostic methods such as radioactive iodine uptake tests, where isotopes like I-131 are used, can help. These tests measure how much iodine the thyroid absorbs, which is indicative of its function. If not much iodine is absorbed, it suggests hypothyroidism, and if an excessive amount is absorbed, it implies hyperthyroidism. The use of radioisotopes, like gallium-67 in cancer imaging, enables detection of rapid cell growth associated with tumors.
Radioactive iodine is also employed in both the imaging and treatment of thyroid cancer, as it can destroy excess thyroid tissue as well as cancerous cells. However, some types of thyroid cancers might be better visualized with other techniques such as MRI or CT scans, especially in cases where FNA biopsies are inconclusive.