LINGUAL THYROID

A Complete 50-Mark Answer for RGUHS ENT Examination

DEFINITION

• Cummings Otolaryngology Head and Neck Surgery, p. 1641
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2, p. 516

EMBRYOLOGY AND PATHOGENESIS

Normal Thyroid Development

Pathogenesis of Lingual Thyroid

1. Defects in TSH receptor signalling
2. Mutations in thyroid transcription factor genes (TTF-1/NKX2.1, TTF-2/FOXE1, PAX8)
3. Hormonal factors - the condition is more common in females (3:1 to 7:1 female predominance), suggesting a hormonal influence

INCIDENCE AND EPIDEMIOLOGY

• Scott-Brown's Vol. 2, p. 516; Cummings, p. 1642; Schwartz's Principles of Surgery, p. 1654

ANATOMY OF LINGUAL THYROID

• Located in the midline at the base of tongue, at or posterior to the circumvallate papillae, near or at the foramen caecum
• Appears as a smooth, reddish-brown, lobulated mass
• Ranges from a few mm to several centimetres
• Covered by normal lingual mucosa
• Has a good blood supply from branches of the lingual artery
• May be the sole functioning thyroid tissue in 70-80% of cases - hence, surgery MUST be preceded by imaging to confirm absence of cervical thyroid

CLASSIFICATION

1. Lingual - at/near foramen caecum (most common)
2. Sublingual - below the foramen caecum, above hyoid
3. Ectopic cervical - along the thyroglossal duct path

• Type 1: Lingual (most superior)
• Type 2: Sublingual
• Type 3: Prelaryngeal (most inferior, pre-tracheal)

CLINICAL FEATURES

Presentation

Symptoms (ABCDE - mnemonic)

• Dysphonia / change in voice (muffled "hot potato" voice)
• Obstructive sleep apnea
• Cough
• Sensation of a lump in the throat

Aggravating Factors (Periods of Increased TSH Demand)

1. Puberty
2. Pregnancy
3. Menopause
4. Periods of increased metabolic demand

• Cummings, p. 1642; K J Lee's Essential Otolaryngology, p. 521

Signs on Examination

• Smooth, red/bluish-red, midline mass at the base of tongue near the foramen caecum
• Surface may be lobulated
• Bleeds easily on probing
• Pulsatile in some cases (vascular supply)

• Absence of thyroid gland in the normal pretracheal position (important!)
• No thyroid palpable in the neck

INVESTIGATIONS

FLOWCHART: Investigation Algorithm

CLINICAL SUSPICION
(Base of tongue mass + absent cervical thyroid)
        |
        ↓
THYROID FUNCTION TESTS
(TSH, Free T3, Free T4)
 - Hypothyroid (30-70%), Euthyroid, rarely Hyperthyroid
        |
        ↓
RADIONUCLIDE SCAN (Tc-99m Pertechnetate or I-123)
 - Confirms functioning thyroid tissue at tongue base
 - Shows NO uptake in normal cervical position
 - GOLD STANDARD for confirming lingual thyroid
        |
        ↓
IMAGING: CT SCAN (unenhanced) / MRI
 - CT: Hyperdense midline tongue base mass (due to iodine content)
 - MRI: Preferred (no radiation); sagittal views most informative
 - Identifies if cervical thyroid is present or absent
        |
        ↓
ULTRASOUND NECK
 - Confirms absence/presence of orthotopic thyroid
 - Can characterize mass
        |
        ↓
FINE NEEDLE ASPIRATION CYTOLOGY (FNAC)
 - Only if malignancy suspected
 - Shows thyroid follicular cells
        |
        ↓
BLOOD TESTS
 - Complete blood count
 - Serum calcium (assess PTH/parathyroid)
        |
        ↓
DEFINITIVE DIAGNOSIS

Details of Each Investigation

1. Thyroid Function Tests (TFTs)

• TSH, Free T3, Free T4
• TSH is elevated in hypothyroidism (most common - up to 70%)
• T3/T4 low in hypothyroidism
• Hyperthyroidism is rare
• Baseline TFTs mandatory before any treatment

2. Radionuclide Thyroid Scintigraphy (MOST IMPORTANT)

• Technetium-99m (Tc-99m) pertechnetate scan is the investigation of choice
• Tc-99m is taken up by metabolically active thyroid tissue
• In lingual thyroid: Uptake at base of tongue, NO uptake in cervical position
• Can also use I-123 or I-131 scanning
• This is the gold standard for:
  • Confirming that the mass is thyroid tissue
  • Establishing whether cervical thyroid tissue exists (critical before surgery)
  • Assessing functional status

3. CT Scan (Computed Tomography)

• Unenhanced CT is preferred - lingual thyroid appears hyperdense compared to surrounding tongue musculature (due to high iodine content)
• Contrast-enhanced CT is an alternative but may obscure density differences
• Sagittal and axial views helpful
• Delineates size, extent, relationship to adjacent structures
• Identifies any cervical thyroid tissue

4. MRI (Magnetic Resonance Imaging)

• Preferred over CT (no ionizing radiation - especially important in children and young women)
• Sagittal views are particularly helpful
• Lingual thyroid: Isointense on T1, high signal on T2 (relative to muscle)
• Better soft tissue detail
• Delineates airway compromise

5. Ultrasonography (USG Neck)

• Confirms absence of thyroid gland in normal cervical position
• Can characterize the mass (echogenicity, vascularity on Doppler)
• Non-invasive, no radiation, widely available
• Less useful than CT/MRI for tongue base, but valuable for neck assessment

6. Fine Needle Aspiration Cytology (FNAC)

• Reserved for cases where malignancy is suspected
• Shows thyroid follicular cells, colloid
• Malignancy reported in ~1% of cases (usually papillary thyroid cancer)
• Must be done cautiously - risk of bleeding given vascularity

7. Laryngoscopy / Nasopharyngoscopy

• Direct visualization of the mass
• Assess airway
• Evaluate degree of obstruction

Summary Table of Investigations

DIFFERENTIAL DIAGNOSIS

MANAGEMENT

FLOWCHART: Management Algorithm

LINGUAL THYROID CONFIRMED
(By Tc-99m scan + TFTs + imaging)
              |
      ┌───────┴───────┐
      |               |
ASYMPTOMATIC      SYMPTOMATIC
 Euthyroid       (Obstructive symptoms /
                  Hypothyroidism /
                  Haemorrhage / 
                  Malignancy suspected)
      |               |
      ↓         ┌─────┴──────────────┐
 OBSERVATION    |                    |
  + TFT         |                    |
 Monitoring   HYPOTHYROID         EUTHYROID
               |                  with Symptoms
               ↓                    |
          LEVOTHYROXINE             ↓
          (TSH Suppression)   Large/Obstructive?
          - Reduces size           |
            over months        ┌───┴──────┐
               |               |          |
         Size reduced?     RADIOIODINE   SURGICAL
               |           ABLATION     EXCISION
            YES: Continue  (I-131)     (See below)
               |            followed   
            NO: Consider     by LT4
          surgical/RAI     replacement
              
SURGICAL EXCISION OPTIONS:
  ├── Transoral routes (preferred for small-moderate):
  │     ├── Transoral coblation-assisted excision (NEW - Recent Advance)
  │     ├── Transoral CO2 laser excision
  │     ├── Transoral robotic surgery (TORS) - Recent Advance
  │     └── Transoral with tongue splitting
  └── External (transcervical) routes (for large lesions):
        ├── Transhyoid pharyngotomy
        ├── Lateral pharyngotomy
        ├── Combined transoral + transcervical
        └── ± Tracheostomy (for massive lesions)

POST-TREATMENT:
  - ALL patients: LIFELONG thyroxine (LT4) replacement
  - TFT monitoring 3-6 monthly
  - Paediatric endocrinology review (children)
  - Annual surveillance imaging if residual tissue

A. CONSERVATIVE MANAGEMENT

1. Observation

• For small, asymptomatic, euthyroid lingual thyroid
• Regular TFT monitoring every 6 months
• Annual imaging to assess size change

2. Thyroid Hormone Suppression (TSH Suppression Therapy)

• Levothyroxine (LT4) - the mainstay of medical management
• Mechanism: Exogenous T4 suppresses pituitary TSH secretion; reduced TSH drive leads to regression/non-growth of the lingual thyroid
• Indication: Small asymptomatic lingual thyroid with or without hypothyroidism
• Reduction in size is often slow; dramatic results should not be expected
• Also corrects hypothyroidism
• Paediatric endocrinology input is essential for children
• Dose: 1.6-2 mcg/kg/day, adjusted to keep TSH in low-normal or suppressed range
• Scott-Brown's Vol. 2; Cummings, p. 1642

B. RADIOIODINE ABLATION (I-131)

• Indication: Symptomatic lingual thyroid in adult patients unfit for surgery, or when surgery is refused
• Mechanism: I-131 is selectively taken up by thyroid tissue and destroys follicular cells by beta radiation
• Advantage: Non-surgical, effective at reducing mass size
• Disadvantage:
  • Destroys the ONLY functioning thyroid tissue in 70-80% of patients - patient becomes permanently hypothyroid
  • Requires lifelong LT4 supplementation post-ablation
  • Generally avoided in children (risk of radiation-induced malignancy)
  • Multiple doses may be needed
• Pre-treatment: Confirm no cervical thyroid on scan
• Post-treatment: Mandatory lifelong thyroxine replacement

C. SURGICAL MANAGEMENT

Indications for Surgery

1. Significant obstructive symptoms (dysphagia, airway obstruction, dysphonia)
2. Recurrent or severe haemorrhage
3. Failed conservative/medical therapy
4. Suspected or confirmed malignancy
5. Cystic degeneration
6. Patient preference

Pre-operative Preparation

• TFT optimization (correct hypothyroidism)
• Crossmatch blood (highly vascular)
• Nasotracheal intubation
• Consent for tracheostomy if indicated
• Endocrinology consultation

Surgical Approaches

I. TRANSORAL APPROACHES (Preferred for small to moderate lesions)

• Puxeddu et al. first described this for lingual thyroid
• Excellent haemostasis, precise cutting
• Shorter hospital stay
• Suitable for moderate-sized lesions

• Da Vinci robotic system used
• Excellent visualization of tongue base
• Magnified, three-dimensional view
• Good haemostasis
• Reduced postoperative pain
• No external scar
• Gaining popularity as preferred approach (D'Andrea et al., 2022, PMID: 33843266)
• Recent Advance: TORS is now considered by many as the best surgical approach for lingual thyroid

• Coblation = Controlled Ablation using radiofrequency energy in a saline medium
• Operates at low temperatures (40-70°C) unlike monopolar cautery (>400°C)
• Advantages:
  • Minimal bleeding (excellent haemostasis)
  • No external incision
  • Less postoperative pain
  • Shorter hospital stay
  • No need for tracheostomy in most cases
  • Quick recovery
• A prospective study of 12 cases from Government ENT Hospital, Hyderabad (2016-2023) showed excellent results with coblation-assisted transoral excision
• Disadvantage: Difficult exposure for very large lesions
• (PMC 10909054 - Indian J Otolaryngol Head Neck Surg, 2024)

• Useful for larger transoral access
• Associated with longer recovery

II. EXTERNAL (TRANSCERVICAL) APPROACHES (For large/deep lesions)

• Access through the hyothyroid membrane
• Good exposure for large tongue base lesions
• Risk: damage to hypoglossal nerve, superior laryngeal nerve

• Access through lateral pharynx
• Less common; for laterally placed lesions

• For very large lesions requiring maximum exposure
• Usually requires tracheostomy

• Mandatory for large masses where post-operative swelling/bleeding could obstruct the airway
• Also required when nasotracheal intubation is not possible

Surgical Complications

1. Haemorrhage (primary/reactionary/secondary) - most feared
2. Airway compromise/oedema
3. Hypothyroidism (if only tissue; permanent)
4. Infection
5. Dysphonia (if nerve injury)
6. Dysphagia (temporary/permanent)

Post-operative Care

• Lifelong levothyroxine supplementation (mandatory, as lingual thyroid is ONLY tissue in 70-80%)
• Regular TFT monitoring
• Nasogastric feeding if significant swelling
• Tracheostomy care if performed

SPECIAL SITUATIONS

Lingual Thyroid in Pregnancy

• Lingual thyroid can enlarge significantly during pregnancy due to elevated TSH demand
• May cause acute airway obstruction
• Management: Careful airway monitoring; LT4 supplementation to suppress TSH
• Surgery if acute airway obstruction; planned caesarean if large mass

Lingual Thyroid in Children

• Presents at puberty with TSH demand
• Radioiodine generally avoided (radiation risk)
• Preferred treatment: LT4 suppression + surgical excision if indicated
• Paediatric endocrinology essential

Malignant Lingual Thyroid

• Risk approximately 1% (same as orthotopic thyroid)
• Usually papillary thyroid carcinoma
• FNAC confirms
• Treatment: Surgical excision + radioiodine + lifelong LT4

TRANSPOSITION PROCEDURE

RECENT ADVANCES

PROGNOSIS

• With appropriate management, prognosis is generally good
• Lifelong thyroxine supplementation is required in most patients post-surgery/radioiodine
• Malignancy is rare but must be excluded
• Surveillance is lifelong

SUMMARY CHART: Lingual Thyroid at a Glance

┌────────────────────────────────────────────────────────────┐
│                    LINGUAL THYROID                         │
├────────────────┬───────────────────────────────────────────┤
│ Definition     │ Ectopic thyroid at base of tongue         │
│ Embryology     │ Failure of descent from foramen caecum    │
│ Prevalence     │ 1:100,000; F:M = 3-7:1                   │
│ Only tissue    │ 70-80% of cases                          │
│ Presentation   │ Dysphagia, dyspnea, hypothyroidism       │
│ Key Inv.       │ Tc-99m scan (Gold Standard) + TFTs       │
│ Imaging        │ Unenhanced CT / MRI (sagittal preferred)  │
│ Medical Rx     │ Levothyroxine (TSH suppression)          │
│ Surgical Rx    │ Transoral (TORS/Coblation/CO2 laser)     │
│ Radioiodine    │ Adults; NOT in children                  │
│ Post-treatment │ LIFELONG LT4 + TFT monitoring            │
└────────────────┴───────────────────────────────────────────┘

REFERENCES

1. Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2 (9781138094634) - Chapter 41: LINGUAL THYROID, pp. 515-516
2. Cummings Otolaryngology Head and Neck Surgery (9780323612173) - Chapter 90: Lingual Thyroid, p. 1641-1642
3. Schwartz's Principles of Surgery, 11th Edition (9781259835346) - Developmental Abnormalities: Lingual Thyroid, p. 1654
4. Sabiston Textbook of Surgery, 21st Edition (9780443124341) - Chapter 73: Ectopic Thyroid Tissue, p. 1485-1486
5. K J Lee's Essential Otolaryngology (9781260122237) - Normal Variants Mimicking Disease, p. 521
6. Dhingra's Diseases of Ear, Nose and Throat - Ectopic Thyroid, Chapter on Neck Swellings
7. Hazarika's Textbook of ENT and Head & Neck Surgery - Lingual Thyroid
8. Zakir Hussain's Manual of ENT - Lingual Thyroid
9. Stell and Maran's Head and Neck Surgery - Ectopic Thyroid
10. D'Andrea G, Vairel B, Vandersteen C. Is Transoral Robotic Surgery the Best Surgical Treatment for Lingual Thyroid? A Case-Report and Literature Review. Ann Otol Rhinol Laryngol. 2022 Jan. [PMID: 33843266]
11. Aldawas G, Ragab S. A Review of Thyroid Rests: From Embryology to Clinical Management. Cureus. 2025 Oct. [PMID: 41127496]
12. Nisa L, Morrison S, Levi E. Airway management in patients with lingual thyroid: a case report and review of the literature. Eur Arch Otorhinolaryngol. 2022 Jul. [PMID: 35201391]
13. Coblation study: Advances in Lingual Thyroid Management Using Coblation Technology: A Case Series Study. Indian J Otolaryngol Head Neck Surg. 2024;76(1):938-43. [PMC 10909054] - Government ENT Hospital, Hyderabad

RGUHS Exam Tip: For a 50-mark answer, the key areas examiners look for are:

1. Embryology (5 marks)
2. Clinical features (5 marks)
3. Investigations with emphasis on Tc-99m scan (10 marks)
4. Management - Medical, Radioiodine, Surgical approaches (20 marks)
5. Recent advances - TORS, Coblation (5 marks)
6. Diagrams and flowcharts (5 marks)