Standard treatment for differentiated thyroid cancer is a total thyroidectomy. A lobectomy (hemithyroidectomy) is considered sufficient for certain patients with low risk tumors. Lymph node dissections are performed to varying degrees of extensiveness and are a topic of discussion.
Clear definitions of surgical procedures are important, and the following terms should be used:
- Lobectomy – complete resection of a thyroid lobe including the isthmus and the pyramidal lobe, if present.
- Near total lobectomy – lobectomy where the least possible thyroid tissue remains (< 1 g tissue) if there danger of injury to the recurrence nerve or blood supply to the parathyroid.
- Total thyroidectomy – complete resection of both thyroid lobes, isthmus, and pyramidal lobe.
- Near total thyroidectomy – complete resection of thyroid lobe (lobectomy) on one side with near total lobectomy on the other side.
If a total thyroidectomy is not performed, the extent of the resection of each lobe should be described.
The lymph nodes and pre and paratracheal spaces should be inspected and thoroughly palpated for metastases, to determine whether a therapeutic lymph node dissection should be performed.
Some groups routinely recommend prophylactical central lymph node dissection as standard treatment, but this is somewhat controversial in Norway. Arguments for carrying out this type of dissection are to reduce the necessity of reoperating which significantly increases the risk for injury to the recurrence nerve in the central compartment. The collective assessment is in line with international guidelines, which recommends a prophylactical lymph node dissections as part of the primary surgery, when it can be performed with low risk of complication.
A lymph node dissection in the lateral field of the neck should only be carried out if metastasis is found.
Thorough inspection of the lymph node status with ultrasound is an important part of the preoperative work-up.
Frozen section testing is not very sensitive for papillary thyroid carcinoma, therefore a negative result will not exclude malignancy. For follicular thyroid carcinoma, frozen section should not be performed when the preoperative cytological diagnosis is a follicular tumor, as there is a risk of a false positive cancer diagnosis.
Medullary thyroid carcinoma
Surgery is the only effective treatment for this disease. A total thyroidectomy should be performed with a lymph node dissection, and often up to four field dissections (neck and mediastinum), but preferably in multiple sessions.
In about 10% of patients with a primary tumor ≤ 1 cm, local and regional metastases are found, and for larger tumors, up to 90%. The metastases can be very small. Bilateral dissection of pre and paratracheal areas as well as antero-superior mediastinum should therefore always be performed. If metastases are found, a modified neck dissection should be performed. This should include section III and IV of the involved side, at minimum. If the there are midline metastases, the dissection should be carried out on both sides.
Anaplastic thyroid carcinoma
For anaplastic thyroid carcinoma, a total thyroidectomy should be performed secondary to radiation therapy, if there is no presence of metastasis.