Well I am going to take a stab at this (get it??) OK.......not funny .
I believe a nodule can be classified as cystic ( soft ) or solid as (hard) The structure of that nodule if it is soft (cystic) - or hard ( solid) will determine many things for the person dealing with it - Like having a biopsy or not for example.
Now I think other cysts can form also that do not fall under a classification as a "nodule".
With a Nuclear Medicine scan, the radioactive iodine acts like non-radioactive iodine and is absorbed by the thyroid gland to be used in the production of thyroid hormones. Therefore, functioning thyroid tissue will become radioactive by the absorbtion of the radioactive iodine. Areas of the thyroid which are overly functioning will pick up more radioactive iodine than normal tissue and are referred to as being "hot". Areas of the thyroid that are functioning less than normal or not at all will pick up less or none of the radioactive iodine. These areas are referred to as being "cold". With the use of special "cameras" the radioactive iodine is detected in the thyroid gland and a picture is formed. The "hot" areas will show up darker than normal tissue and the "cold" areas will show up as lighter than normal tissue or as completely blank areas.
The "hot" nodules are overly functioning thyroid tissue, very often palpable from the outer surface of the skin, and are sometimes cancerous tissue. The "cold" nodules are also sometimes palpable from the outer skin surface. These non-functioning areas can be scar tissue, cysts or a variety of non thyroid tissue infiltrating the thyroid gland.
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