Central Compartment Neck Dissection

Introduction

The central compartment contains the first nodal basin for cancer originating in the thyroid and parathyroid and can be involved in cancers of the laryngotracheal complex. This space encompasses the prelaryngeal, pretracheal, and paratracheal lymph nodes, also known as the level VI lymph nodes, although superior mediastinal nodes and retro-esophageal nodes are often included and represent level VII. In cases of squamous cell cancer involving the central compartment viscera or parathyroid carcinoma, comprehensive central compartment lymph node dissection is routinely employed, often in combination with ipsilateral thyroidectomy. However, the central compartment lymph nodes are most commonly affected by the regional spread of thyroid cancers. Well-differentiated thyroid cancer (WDTC) will prove to have metastases in the central compartment in 20% to 50% of cases. In these cases, central compartment neck dissection is unquestionably indicated, given the strong relationship between loco-regional control and treatment of clinically positive central compartment disease. Subclinical micrometastases have been shown to be present in up to 90% of cases of thyroid cancer, presumably with less defined clinical significance when compared with macrometastases. There has been no survival benefit associated with prophylactic treatment of the central neck, with equivocal data on local control. Patients with known metastasis in the central compartment are more likely to experience recurrence than their counterparts. Prophylactic central compartment dissection with total thyroidectomy has shown increased rates of postoperative hypocalcemia when compared with total thyroidectomy alone. However, the use of prophylactic central compartment neck dissection results in improved local control and decreases the potential risk of morbidity of reoperative surgery. Additionally, the pathologic assessment of the central compartment lymph nodes may help in risk stratification for additional adjuvant treatment such as radioactive iodine (RAI).

The literature fails to offer definitive evidence advocating prophylactic treatment of the central compartment in the management of well-differentiated thyroid cancer (WDTC). The role of prophylactic central compartment neck dissection remains controversial, largely due to the lack of a large randomized prospective trial—the feasibility of which is questionable given the prohibitively large sample size it would require. Ultimately, comprehensive preoperative evaluation and appropriate risk assessment and anatomic knowledge are imperative for successful surgical treatment of the central neck. The presence of medullary thyroid carcinoma, with or without evidence of nodal involvement, is an indication for dissection of the lymph nodes in the central compartment.

Key Operative Learning Points

1.
Central compartment dissection is often a reoperative surgery and may require a different surgical strategy (lateral to medial).
2.
Identification and continued observation of the recurrent laryngeal nerve (RLN) is the best way to avoid injury to the nerve.
3.
Identify and lateralize the superior parathyroid glands with their blood supply.
4.
A low threshold for auto-transplantation of inferior parathyroid glands after pathologic verification
5.
Complications are more common with paratracheal dissection, especially hypocalcemia, vocal fold paralysis, and injury to the esophagus.

Preoperative Period

History

1.
History of present illness
- a.
  Determine if this is primary or secondary disease. Central compartment dissection is often employed in the case of a loco-regional recurrence of thyroid cancer.
  - 1)
    Obtain operative and pathology reports from previous surgeries.
- b.
  Evaluate for pre-existing morbidity.
  - 1)
    chronic obstructive pulmonary disease (COPD) or cardiovascular disease
  - 2)
    History of gastric bypass or gastrointestinal absorption abnormality
    - a)
      May require calcium challenge if parathyroid hormone (PTH) is elevated to ensure gastric absorption
- c.
  Invasive symptoms: hemoptysis, skin fixation, or voice changes from vocal cord paralysis
  - 1)
    Fiberoptic laryngoscopy
  - 2)
    Advanced imaging
2.
Risk factors for severe morbidity
- a.
  Pre-existing vocal fold paralysis
  - 1)
    Contralateral deficit may result in tracheostomy
- b.
  History of previous neck surgery or radiation
- c.
  Hemoptysis or cough
  - 1)
    May signify invasive component
  - 2)
    Require cross-sectional imaging
3.
Past medical history
- a.
  Well-differentiated thyroid cancer (WDTC)
- b.
  Medullary thyroid carcinoma, multiple endocrine neoplasia (MEN)

Physical Examination

1.
Complete examination of the head and neck
- a.
  Palpate thyroid bed and paratracheal regions.
  - 1)
    Note location of masses with, relation to swallowing, fixation to skin, or underlying structures.
- b.
  Palpate lateral neck for lymphadenopathy.
- c.
  Listen for hoarseness, stridor.
- d.
  Determine location of native anatomy.
  - 1)
    Low-lying larynx/cricoid
2.
Direct or indirect laryngoscopy
- a.
  Essential in detecting vocal cord paralysis
- b.
  The voice may be normal despite a paralyzed vocal cord.

Diagnostic Studies

Laboratory Studies

1.
Thyroid stimulating hormone (TSH)
- a.
  Verify that the patient is euthyroid.
2.
Thyroglobulin (Tg)/thyroglobulin antibody (Tg Ab)
- a.
  Determine relative burden of disease, especially in reoperative cases.
3.
Calcitonin
- a.
  Patient with a family history of medullary thyroid carcinoma or MEN-2, or biopsy shows medullary thyroid carcinoma
4.
Parathyroid hormone

Imaging

1.
High-resolution ultrasound (US)
- a.
  Microcalcifications are associated with markedly increased risk of malignancy, while cystic and spongiform appearance may be associated with benign lesions.
- b.
  Low-cost, no radiation, and reliable when performed by experienced clinicians
- c.
  Low sensitivity of detecting lymphadenopathy in the central neck due to shadowing effect of the thyroid gland
2.
Computed tomography (CT) and magnetic resonance imaging (MRI)
- a.
  Helpful for:
  - 1)
    Substernal extension
  - 2)
    Cervical and mediastinal lymphadenopathy
  - 3)
    Invasion of surrounding structures such as trachea and esophagus
  - 4)
    Metastasis to distant sites
- b.
  High sensitivity and specificity in detecting cervical lymphadenopathy, and less operator dependence, offers visualization of adjacent structures
- c.
  Expensive, radiation exposure, and use of iodinated contrast may preclude the use of RAI for 1 to 3 months
3.
Radionuclide scanning
- a.
  Useful for rising Tg with negative imaging
4.
positron emission topography (PET) imaging
- a.
  Useful for RAI negative, Tg positive patients

Fine-Needle Aspiration

1.
Essential for reoperative surgery
- a.
  Minimally invasive, safe, and cost-effective
- b.
  Sensitivity 65% to 98%, specificity 72% to 100%
- c.
  US guidance increases accuracy and success of fine needle aspiration (FNA).
2.
Suspicious cervical lymph nodes or masses should undergo FNA.
3.
When multiple nodules are present, the largest and/or most sonographically suspicious should be biopsied preferentially.
- a.
  Multiple nodules may need to be biopsied to increase diagnostic yield.
- b.
  Biopsies should direct surgical planning.

Molecular Biomarkers

1.
Newer studies introduced to increase accuracy of FNA and better characterize the risk of malignancy, especially in indeterminate cytology, Atypia of Undetermined Significance (AUS), and Follicular Lesion of Undetermined Significance (FLUS). These markers may:
- a.
  Reduce unnecessary surgery for benign lesions
- b.
  Reduce completion thyroidectomy by guiding initial use of total thyroidectomy
- c.
  Provide prognostic information such as:
2.
BRAF, RAS, TIMP1, RET/PTC, Pax8-PPARγ, galectin-3, cytokeratin, microRNA, gene sequencing
3.
Uncertain evidence regarding efficacy and utility

Indications

1.
Differentiated thyroid cancer
- a.
  Initial surgery
  - 1)
    BRAF positive disease
  - 2)
    Gross extrathyroidal extension
  - 3)
    Presence of suspicious paratracheal lymph node (LN)
    - a)
      Microcalcifications
  - 4)
    Initial presentation of well-differentiated thyroid carcinoma (WDTC) with lateral neck metastasis
- b.
  Contralateral thyroid nodule or distant metastasis
- c.
  Multinodular goiter with radiation exposure to the head and neck
- d.
  First-degree family members with thyroid cancer
2.
Medullary thyroid carcinoma
- a.
  May require concomitant lateral neck dissection
3.
Parathyroid cancer
- a.
  Ipsilateral thyroid lobectomy

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