Though I no longer perform this surgery, I often get asked for my opinion regarding this surgery. Rationale for why surgery should be done or not, I leave to others as it would literally take a textbook, especially given the controversy regarding when to observe and when to surgically remove. Back when I WAS performing thyroidectomy, I should state my bias was towards removal... and belief that a needle biopsy is not 100% accurate. Indeed, in certain situations, a needle biopsy (FNA) is at best no better than flip of a coin whether cancer is present (it is wrong 50% of the time!).
In any case, there are several risks involved when this surgery is performed. Other than the typical risks common to all surgeries like infection and the ho-hum bleeding, there are several unique risks specific to thyroid surgery. Let's go over each one:
Windpipe
Given the thyroid is located over the windpipe, the surgeon may accidentally (or deliberately if thyroid cancer is invading the windpipe's wall) enter into the airway. Why may this be a problem? Well, it may cause air to leak into the neck causing it to suddenly swell up and potentially lead to a pneumothorax (collapsed lung) if severe enough. The scary thing is that it could potentially occur days after the surgery though if it is going to happen, it usually occurs within hours after surgery.
Bleeding
Bleeding is ALWAYS a risk of surgery causing a hematoma to form. What makes this particular complication especially concerning is that it often occurs DAYS after surgery. Even more worrisome is that it could lead to death as the hematoma formation can cause significant swelling with resulting airway compression (remember that the thyroid is located over the windpipe). This particular complication unfortunately occurs not uncommonly... and often leads the patient to obtain emergency care in the local ER by a local surgeon to drain/remove the hematoma and stop the bleeding even if the surgery was done by surgeon located an hour or more away. A tracheostomy (a hole in the neck to the windpipe) may need to be performed at this time as well.
Recurrent Laryngeal Nerve Damage
The nerve that allows you to talk is called the recurrent laryngeal nerve. This nerve is RIGHT NEXT to your thyroid gland. As such, it can be damaged or cut resulting in a very breathy sounding voice. Oftentimes, it is temporary. Rarely, BOTH nerves can get cut if undergoing total thyroidectomy causing stridor or airway problems mandating a tracheostomy.
In the event that a patient suffers a vocal cord paralysis from recurrent laryngeal nerve damage, it can be corrected surgically resulting in an almost normal sounding voice. If BOTH vocal cords are paralyzed... well... breathing and talking will be a problem and options are quite limited if this unfortunate complication occurs.
Superior Laryngeal Nerve Damage
With this type of nerve damage, you can talk just fine... but you lose your upper range and falsetto.
Parathyroid Gland Loss
Summary
Thyroid surgery has risks and should be performed by a well-qualified surgeon. However, keep in mind that the best person to take care of you should you experience any surgical complication is the surgeon who actually did the surgery (one of many factors to take into consideration when considering having the surgery done far from home).
References:
Mediastinal emphysema and pneumothorax following thyroidectomy. The Journal of Clinical Endocrinology Vol. 9, No. 10 987-998 doi:10.1210/jcem-9-10-987
Complications of Thyroid Surgery. EMedicine
