Management of Persistent or Recurrent Structural Neck Disease in Differentiated Thyroid Carcinoma: Point and Counterpoint.

The optimal management of structurally identified neck disease after initial surgery for thyroid carcinoma is nuanced and must be individually tailored to thepatient andhis or her disease. As such, it is ideally evaluated and managed with the patient from an experienced interdisciplinary program perspective. Proficiency and focused expertise in diagnostic imaging (ultrasound, cross-sectional, and nuclear), pathology, surgery, endocrinology, radiation oncology, and systemic therapy are integral components of such a program.Athoroughunderstandingof the risksof thediseaseandtreatmentoptions, includingmanagementof complications, is required. While no single algorithm is available, several large series, systematic reviews, andguidelineshavebeenpublished, fromwhich some generalities can be gleaned.1-8 The likelihood of persistent or recurrent structural disease can be predicted by tumor type, TNM stage, and American Thyroid Association (ATA) risk of recurrence. A structurally incomplete response to initial therapy implies disease that can be identified with imaging and is biopsy proven or highly likely to be malignant. For well-differentiated papillary and follicular thyroid carcinoma, this occurrence is observed in approximately 5% of ATA low-risk patients, 25% of ATA intermediate-risk patients, and 70% of ATA high-risk patients. The disease-specific mortality rate of patients with biochemically incomplete response but without structurally identifiable disease is essentially zero but increases to approximately 10% in patients with locoregional structural disease and approximately 60% in patients with distant disease. The histologic type of thyroid carcinoma significantly affects both prognosis and local, regional, or distant disease. Classic papillary thyroid carcinomahas a highpredilection for nodalmetastasis, whereas follicular carcinomas, including Hurthle and insular variants, have a higher likelihood of hematogenous and lymphatic spread, especially when vascular invasion is present, which in the neck often manifests as soft-tissue and local recurrence. Local invasion ismuchmorecommon insoft-tissue recurrence, althoughextranodal extension of regional metastatic disease can also be invasive. The morbidity of untreated invasive disease is inherently greater, arguing formore aggressivemanagement, but the surgical morbidity is also greater. The likelihood of surgical cure of persistent structural disease isolated to the neck is greatest for initially understaged and undertreated nodal disease, for which a compartment-oriented neck dissection has a 70% to 90% chance of complete eradication of structurally detectable disease.3 Biochemical resolution of disease is less likely, approximately 25% to 50% based on stimulated thyroglobulin levels.3 The structural burden of disease inversely correlates with the likelihood of surgical cure, with patients having multiple detectable lesions in multiple levels less likely curable than those with one or a few isolated lesions. The biochemical burden of disease also inversely correlates, such that patients with higher biochemical markers are much less likely to be cured surgically. The small subset of patients with radioiodine-avid, low-volume structural disease have the highest likelihood of biochemical cure (80%) with revision surgery and repeat radioiodine therapy.3 The goal of revision neck surgery is generally resolution of all structurally detectable disease, as well as associated occult microscopic disease, while minimizing the surgical morbidity. However, patients with known distant metastasis may occasionally benefit from revision neck surgery to prevent complications of locally invasive disease, especially involving the aerodigestive tract. A lateral neck dissection for differentiated thyroid cancer is a frequently performed surgery; however, the dissection is not the same as that for aerodigestive tract cancers, and nuances are worth elucidating. Surgery for lateral neck disease should include levels IIa to Vb to minimize risk to the marginal and spinal accessory nerves unless there is disease beyond these levels or bulky disease at the borders. The spinal accessory nerve should be identified and preserved in all lateral neck dissections for thyroid malignancies. The transverse cervical lymphatics, including the infraclavicular nodes, extending into level Vb and lymphatic contents posterior to the carotid artery in levels III and IV are the primary echelon of lateral neck nodal metastases due to the thyroid vasculature originating from the thyrocervical trunk inferiorly and external carotid superiorly. Meticulous dissection in the carotid and vertebral area is required, and control of chylous and lymphatic vessels is a necessary component of the dissection. Last, the lateral neck dissection must fully dissect level IIa anterior to the internal jugular vein in the subdigastric area, identify the hypoglossal nerve, and remove the nodal basins through to the transition to level VI superiorly. In the event of prior lateral neck surgery, more selective revision compartmental surgery may be appropriate to minimize the surgical morbidity.