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Total Thyroidectomy - In Detail

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1. SURGICAL ANATOMY

Position and Structure

• The thyroid gland lies anterior to the cricoid cartilage and inferior to the thyroid cartilage
• Two lobes joined at midline by the isthmus
• In 1 in 4 patients, a pyramidal lobe extends superiorly from the isthmus (thyroglossal duct remnant)
• Layers from superficial to deep: skin → dermis → platysma → sternohyoid/omohyoid → sternothyroid → pretracheal fascia → thyroid

Blood Supply

• 2 arteries per lobe: Superior thyroid artery (from external carotid) + Inferior thyroid artery (from thyrocervical trunk)
• 3 veins per lobe: Superior, middle, inferior thyroid veins (inferior usually a plexus, not a single vessel)

Key Nerves - The Two "Critical Nerves"

• Innervates the cricothyroid muscle (controls high-pitch voice projection)
• Travels lateral to the superior thyroid pedicle, crosses it medially to enter the cricothyroid
• Cernea Classification (how close the nerve is to the superior pole):
  • Type 1: Crosses >1 cm above the superior pole (safest)
  • Type 2A: Crosses within 1 cm above the superior pole
  • Type 2B: Crosses below the superior border of the superior pole (most at risk)

• Innervates all intrinsic laryngeal muscles except cricothyroid
• Left RLN: Loops around the aortic arch, ascends in the tracheoesophageal groove
• Right RLN: Loops around the subclavian artery, ascends more laterally and obliquely
• ⚠️ Non-recurrent laryngeal nerve (0.5% prevalence): Occurs when the right subclavian artery originates directly from the aortic arch (aberrant "arteria lusoria") - the nerve then runs nearly horizontal across the field instead of vertically
• 3 most dangerous zones for RLN injury:
  1. Posterior to the inferior pole of the thyroid
  2. At the intersection with the inferior thyroid artery
  3. Behind the Ligament of Berry

Parathyroid Glands

• Classically 4 glands (2 superior, 2 inferior) per patient
• Superior glands: Lie posterior to the RLN plane, within 2-5 mm of the nerve; 80% symmetrically located
• Inferior glands: Lie anterior to the RLN plane, more variable, 7-10 mm from the nerve
• Ectopic glands in 15% of patients - locations include retroesophageal, intrathyroidal, carotid sheath, thyro-thymic ligament, or mediastinum
• ⚠️ Up to 25% of superior glands are supplied by the superior thyroid artery (not inferior) - ligating the superior artery too far from the gland can devascularize them

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2. PATIENT POSITIONING AND EXPOSURE

1. Position: Supine, head raised ~15 degrees, neck extended with posterior shoulder roll. Avoid excessive extension (uncomfortable postoperatively); avoid inadequate extension (crowds field).
2. Incision: Collar (Kocher) incision along Langer's lines or within an existing neck crease, typically 2-3 cm above the clavicular heads. A preoperative ultrasound by the surgeon helps optimize placement.
3. Skin flaps: Carried through platysma; subplatysmal flaps raised inferiorly to the clavicular heads and superiorly to the thyroid cartilage using sharp + blunt dissection.
4. Strap muscles: Lifted off the thyroid capsule at midline and separated posteriorly along avascular planes. The middle thyroid vein is then ligated between the thyroid and internal jugular vein (IJV).
5. For large/firm glands: The sternothyroid muscle may be divided. Always divide it high (near thyroid cartilage insertion) since ansa cervicalis innervation enters inferiorly.

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3. STEP-BY-STEP TECHNIQUE

Step 1 - Isthmus and Pyramidal Lobe

• Begin by isolating the draining veins of the isthmus and pyramidal lobe
• Early isthmus division facilitates mobilization (especially through small <4 cm incisions for lobectomy)

Step 2 - Superior Pole Dissection

• Develop the avascular cricothyroid space (Space of Reeve) between the superior pole and cricothyroid muscle
• Superior thyroid artery is isolated through blunt, closed-tip dissection (excessive spreading causes bleeding)
• Identify the EBSLN (visually or with nerve monitor) before ligating the superior pedicle
• Divide the pedicle as close to the gland as possible to keep the nerve safe

Step 3 - Inferior Pole

• Retract the inferior pole superiorly to expose inferior thyroid vein branches
• Ligate these close to the thyroid gland - straying lateral/deep risks RLN injury and devascularizes the lower parathyroid

Step 4 - Preservation of Parathyroid Glands

• After dividing venous drainage, rotate the thyroid lobe medially
• Expose the tracheoesophageal groove and carotid sheath
• Identify the inferior thyroid artery and RLN posteriorly
• In 80% of cases, both parathyroid glands are supplied by the inferior thyroid artery
• Dissect immediately along the thyroid capsule, dividing the tertiary branches of the inferior thyroid artery individually - this preserves parathyroid blood flow
• If a parathyroid is intrathyroidal, the capsule is entered focally to liberate it (preserves vascular pedicle)
• ⚠️ Truncal ligation of the inferior thyroid artery without first identifying the parathyroids is strongly discouraged

Step 5 - RLN Identification and Protection

• To safely find the nerve: spread perpendicular to the nerve axis through fatty/nodal tissue posterior to the thyroid
• Once found, use a blunt hemostatic clamp (tip upward) to separate the nerve from superficial structures along its course
• The Tubercle of Zuckerkandl (posterior thickened thyroid projection) must be mobilized to expose the nerve coursing within the fissure between it and the remaining gland
• Divide the Ligament of Berry only after full nerve visualization

Step 6 - Intraoperative Neuromonitoring (IONM)

• Receiving electrode on the endotracheal tube senses vocal cord signaling; grounding electrode on skin
• Negative predictive value approaches 100% (loss of signal reliably predicts injury risk)
• Positive predictive value <50% (signal loss does not always mean permanent injury)
• Used to: confirm visual nerve assignment, map branching pattern, ensure signal during retraction at Ligament of Berry, and confirm at the vagus and tracheoesophageal groove at start and end
• Has not been proven to prevent nerve injury, but assists decision-making

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4. CLOSURE

• No routine drainage needed after thyroidectomy
• Valsalva maneuver is used to inspect for bleeding sites
• Strap muscles reapproximated in the midline with absorbable suture, leaving a 1 cm gap inferiorly (prevents blood/fluid from compressing the trachea)
• Platysma closed with absorbable suture; skin closed subcuticularly

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5. COMPLICATIONS

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Radioiodine (RAI / ¹³¹I) Ablation - In Detail

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1. WHAT IS IT AND HOW DOES IT WORK?

• ¹³¹I is an unsealed radionuclide of iodine that is taken up by thyroid tissue (both normal and differentiated thyroid cancer) in the same way as dietary stable iodine
• After a total/near-total thyroidectomy, residual thyroid tissue called the thyroid remnant remains - this remnant preferentially takes up ¹³¹I over cancer tissue
• ¹³¹I destruction of this residual tissue is called Radioiodine Remnant Ablation (RRA)

1. Destroys microscopic foci of cancer in the remnant
2. Allows detection of residual/metastatic disease on whole-body scan (remnant uptake would otherwise mask it)
3. Aids interpretation of serum thyroglobulin (Tg) levels during follow-up - Tg becomes a reliable tumor marker only after all normal thyroid tissue is gone
4. May reduce local recurrence and improve survival (evidence mixed)

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2. INDICATIONS (Risk Stratification)

• Aggressive histology (tall cell, poorly differentiated, diffuse sclerosing PTC)
• Widely invasive follicular thyroid cancer
• Extracapsular invasion
• Multiple involved lymph nodes or high ratio of involved:uninvolved nodes
• Large individual node size

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3. PATIENT PREPARATION - TSH STIMULATION

Method 1 - Thyroid Hormone Withdrawal (THW)

• Patient stops thyroxine (T4) 4-6 weeks before RAI
• Patient becomes hypothyroid → TSH rises naturally
• Drawback: Significant hypothyroid symptoms (fatigue, depression, cognitive impairment, reduced quality of life)

Method 2 - Recombinant Human TSH (rhTSH / Thyrogen™)

• Patient stays on thyroxine throughout
• rhTSH (0.9 mg) injected intramuscularly (deep into buttock) on Days 1 and 2
• ¹³¹I administered on Day 3
• Preferred whenever possible to avoid hypothyroid morbidity

• Hypopituitarism (cannot raise own TSH)
• Functional metastases suppressing TSH
• Severe ischaemic heart disease
• History of psychiatric illness triggered by hypothyroidism
• Advanced disease or frailty

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4. LOW-IODINE DIET AND PREPARATION

• Before ¹³¹I administration, the total body iodine pool must be reduced so that ¹³¹I uptake is maximized
• Low daily iodine intake increases the effective radiation dose delivered by ¹³¹I
• Duration: Usually 1-2 weeks (no universal consensus on duration)
• Eliminate: iodinated IV contrast media, amiodarone, and other iodine-rich sources before treatment

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5. DOSES OF ¹³¹I

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6. PRE-ABLATION SCAN

• Not routinely indicated but may be used to assess remnant size
• If a large remnant is seen: consider further surgery before RAI, or prescribe prophylactic corticosteroids
• Preferred isotopes for pre-ablation scan: ⁹⁹ᵐTc pertechnate or ¹²³I (NOT ¹³¹I)
  • Reason: Using ¹³¹I for the diagnostic scan causes "stunning" - a reduction in uptake of the subsequent therapy dose

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7. POST-TREATMENT WHOLE-BODY SCAN

• Performed 2-10 days after RAI administration
• More sensitive than diagnostic scans (higher activity used)
• SPECT-CT added to planar gamma camera imaging allows precise anatomical localization of iodine uptake
• Physiological ¹³¹I uptake is seen in: salivary glands, genitourinary tract, GI tract, and sinuses (these are normal findings)

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8. SPECIAL CONSIDERATION - HURTHLE CELL TUMORS

• Hurthle cell (oncocytic) lesions are generally poorly responsive to radioiodine
• Distant metastases from Hurthle cell tumors are often resistant to RAI therapy

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9. THYROID HORMONE REPLACEMENT AFTER RAI

• If patient was on THW: Start thyroid hormones 1-3 days after RAI administration
• If patient received rhTSH: Can stay on thyroxine throughout the entire procedure

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10. SIDE EFFECTS AND TOXICITY OF ¹³¹I

Reproductive Considerations

• Females: Amenorrhea/oligomenorrhea for 4-10 months; defer pregnancy for 6 months (BTA) / 6-12 months (ATA) post-treatment; breastfeeding must be stopped at least 8 weeks before RAI (prevents excessive breast tissue uptake)
• Males: Defer fathering a child for 4 months; offer sperm banking as infertility is possible

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11. ISOLATION REQUIREMENTS

• Patients must remain in an isolation ward following RAI
• Must avoid contact with adults and children for 14-25 days after treatment
• This is one of the important inconveniences to counsel patients about beforehand

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SUMMARY COMPARISON

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