Monday, May 12, 2008
I read a couple of weeks ago about the Arizona Diamondbacks pitcher, Doug Davis, who was diagnosed with thyroid cancer and underwent a thyroidectomy on April 10th. Last week I performed a partial thyroidectomy on a young woman who had an equivocal needle biopsy of a thyroid mass but the frozen section pathology on the right lobe fortunately was benign. So I decided the time had come for a post about thyroid cancer....my mind works in a simple fashion.
The thyroid gland sits atop our trachea like a shield. It is an endocrine organ that synthesizes and maintains our supply of thyroid hormone. (It also helps with calcium homeostasis, but that is perhaps a little too indepth.) About 37,000 new cases of thyroid cancer are diagnosed a year. Risk factors include goiter, Graves disease, family history, and female gender. But the biggest risk factor is a history of radiation exposure during childhood. Believe it or not, kids used to be radiated as a treatment for such conditions as acne, thymus enlargement, and tonsil/adenoid problems. Good thing Clearisil was invented. Nuclear fallout exposure is another biggie. People exposed to fallout from the Chernobyl accident have a significantly higher risk of developing thyroid cancer (something to keep in mind when your patient is a relatively recent immigrant from Russia or the former Soviet Republics).
Thyroid cancer usually presents as a painless, hard mass in the neck. Most people are euthyroid. Things to ask about include voice changes, trouble swallowing, and a sense of not being able to get enough air when the arms are stretched high above the head.
All suspicious thyroid masses get a Fine Needle Aspiration (FNA) on the initial office visit. I also like to ultrasound the gland myself. Other tests that an endocrinologist might order would be CT scans and nuclear medicine scintigraphy.
There are two major determinants of the course and prognosis of thyroid cancer. One is the degree of differentiation of the tumor. The other is the age of the patient.
Well differentiated = good
Poorly differentiated = bad
Patient <45 years old = good
Patient >45 years old = bad
Well differentiated cancers are reasonable cancers. These are the follicular and papillary cancers. The cells are malignant but they follow the rules to some extent. They spread in a fairly predictable fashion. They don't replicate like rabbits in heat. They're like an incorrigible child who gets in trouble at school, gets detentions, C student, but he's not going to embarass the family name. He's a good kid, just a little misguided. Poorly differentiated cancers, conversely, are the kids who torture animals in the basement. The kid who runs a drug ring out of his black wall-papered bedroom. They don't follow the rules. Poorly differentiated cancers are aggressive and fast growing and outcomes are much worse.
Age, interestingly, is also a big prognostic factor. If you're less than 45 years old, you can't be any worse than Stage II. Even with distant metastases, there is no such thing as Stage III or IV cancer for young patients with well differentiated thyroid cancers. Getting the disease at an older age protends worse outcomes.
Overall, however, well differentiated thyroid cancer is one of the best cancers to get. Ten year survival of early stage disease is over 90%. Unusual subtypes such as medullary thyroid cancer and anaplastic tumors have poorer survival rates.
Definitive treatment of well differentiated thyroid cancer is surgical. Specifically, total thyroidectomy (removing the entire gland) is curative and allows one to monitor for recurrence. Several weeks post op, one can perform a "thyroid scan" in nuclear medicine to see if there is any residual thyroid tissue. Then you can specifically eradicate it with radioactive iodine (I-131), with is taken up solely by thyroid-like cells. Patients are kept on synthetic thyroid hormone (Synthroid) for the rest of their lives, with the dose titrated to such a level that Thyroid Stimulating Hormone (TSH) is down regulated (high TSH levels will stimulate growth of any residual cancerous cells).
This is a fun operation. Generally, it's well tolerated and patients go home the next day. The procedure is pretty standardized, by the book. Incision in a skin line in the neck. Raise the platysmal flaps. Open the strap muscles in the midline. Note the gland, red like cranberry sauce, veins and arteries splayed across its surface and pulsating. Free the gland from the undersurface of the strap muscles. I go for the superior pedicle first. This is a branch of the external carotid artery that I always tie. Most of the rest of the vessels can be coagulated with the small, hand held Ligasure device. Two main structures to tighten your anus over. Have to preserve the parathyroid glands (control the body's calcium levels), especially if a total thyroidectomy is done. They look like carmelized little lima beans residing posterior to the thyroid. Sometimes they're hard to find, because embryology can take them in weird places. The other thing to ALWAYS find is the recurrent laryngeal nerve. Cutting one leaves the patient with a raspy, hoarse voice, usually for the rest of their lives. Cutting both sides will paralyze the vocal cords in the midline of the trachea, leading to respiratory compromise and often, an emergent tracheostomy. Never Bovie or cut or Ligasure anything near the trachea until you find it. It looks like a piece of vermicelli cut in half travelling deep in the neck, along the posterior aspect of the trachea.
Post operatively, you have to worry about bleeding. You end up tying off or Ligasuring a ton of vessels and any bleeding in the resultant closed space will collect and press on the trachea. I actually had to do an emergent neck exploration and tracheostomy on the floor on a post op thyroidectomy when I was a resident (the night before the rehearsal dinner of my wedding).
Special side note on medullary cancer. These tumors only comprise 3-8% of all thyroid malignancies. Although 80% are sporadic, a good proportion are associated with the inherited endocrine cancer syndrome of MEN (multiple endocrine neoplasia syndrome). It's important to rule out the concommitant presence of things like pancreatic tumors and pheochromocytomas prior to definitive treatment of the medullary tumor. Outcomes are worse compared to well differeniated cancers, mainly because they are not susceptible to treatment with I-131. Furthermore, central compartment and sometimes modified radical neck dissections are indicated, in addition to total thyroidectomy, depending on presence or absence of local spread to regional lymphatic basins.
Anyway, I read the other day that Doug Davis has started throwing again, and may be due back to the team in a month or so.