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THYROGLOSSAL DUCT CYST - A Comprehensive Review (20 Marks)

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OUTLINE / SUBHEADINGS (RGUHS 20-mark pattern)

1. Definition & Introduction
2. Embryology & Applied Anatomy
3. Pathology
4. Classification
5. Clinical Features
6. Investigations
7. Differential Diagnosis
8. Treatment - Sistrunk's Operation (with steps)
9. Complications
10. Malignant Change
11. Recent Advances
12. Diagrams & Flowcharts

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1. DEFINITION & INTRODUCTION

• Most common congenital cystic swelling of the neck (70% of all congenital neck masses)
• Incidence: ~7% of the general population have a persistent thyroglossal duct remnant
• Most commonly presents in children (first decade), but may present at any age
• Males = Females (slight male predominance in some series)

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2. EMBRYOLOGY & APPLIED ANATOMY

Thyroid Descent Pathway

EMBRYOLOGICAL PATHWAY OF THYROID DESCENT
─────────────────────────────────────────────────────────────────
Week 3-4 of gestation:
  Thyroid anlage forms at FORAMEN CECUM
  (junction of anterior 2/3 and posterior 1/3 of tongue)
         │
         ▼
  Descends as a bilobed diverticulum
  (= thyroglossal duct / tract)
         │
         ▼
  Passes ANTERIOR to hyoid bone (most common)
  OR through/posterior to hyoid bone
  (bifurcates extensively ABOVE hyoid bone)
         │
         ▼
  Reaches final position:
  Isthmus at C5-C6 vertebral level
         │
         ▼
  Week 5-7: Duct NORMALLY OBLITERATES
         │
         ▼
  Failure of obliteration → THYROGLOSSAL DUCT CYST
─────────────────────────────────────────────────────────────────

• The duct passes through or around the hyoid bone - this is WHY the central hyoid must be excised in Sistrunk's operation
• Extensive branching occurs above the hyoid bone - this explains why simple cystectomy leads to high recurrence
• The remnant tract elevates with tongue protrusion (attached to foramen cecum via muscle)
• Any abnormal cyst may arise anywhere along the tract and may contain thyroid tissue (Scott-Brown Vol 2, p.514)

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3. SITES OF OCCURRENCE (Classification by Position)

SITES OF THYROGLOSSAL DUCT CYST (percentage distribution)
──────────────────────────────────────────────────────────
  Intralingual / Lingual (base of tongue)    — 2%
  Suprahyoid                                 — 25%
  ◄── AT THE LEVEL OF HYOID BONE            — 15%
  INFRAHYOID (most common) ◄────────────     — 65%
      (Subhyoid to suprasternal notch)
  Intratracheal (rare)                       — <1%
──────────────────────────────────────────────────────────
  * 95% occur in MIDLINE; ~10% slightly to left side

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4. PATHOLOGY

• Smooth, rounded, tense cystic swelling
• Usually 1-4 cm in diameter
• Contains mucoid/mucinous fluid (yellow or clear)
• Wall is thin and translucent

• Lined by pseudostratified ciliated columnar epithelium (respiratory type) - most common
• Can also be stratified squamous, or cuboidal epithelium
• Wall contains thyroid follicles (in ~20-45% of cases)
• Chronic inflammation with fibrosis if previously infected

1. Simple thyroglossal cyst
2. Thyroglossal sinus (opens to skin after spontaneous rupture/incision)
3. Thyroglossal fistula (opening at both ends - rare)

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5. CLINICAL FEATURES

Symptoms

• Painless midline neck swelling - most common presentation
• Becomes painful / tender when infected
• Dysphagia (if large or lingual type)
• Dyspnoea (rare, if large)

Signs - The Classic Triad:

CLASSIC SIGNS OF THYROGLOSSAL CYST
┌─────────────────────────────────────────────────────┐
│  1. MIDLINE swelling (95%) / slightly left-sided    │
│     (10%) in neck between hyoid & thyroid           │
│                                                      │
│  2. Moves UPWARD on SWALLOWING                      │
│     (connected to pre-tracheal fascia & thyroid)     │
│                                                      │
│  3. Moves UPWARD on TONGUE PROTRUSION               │
│     ← PATHOGNOMONIC SIGN                            │
│     (tethered to foramen cecum via duct & muscle)   │
└─────────────────────────────────────────────────────┘

• Soft, cystic, non-tender (unless infected)
• Smooth, mobile, transilluminable
• Overlying skin normal (unless fistula present)
• Not attached to overlying skin (unless previously infected/drained)
• Moves superiorly with both swallowing AND tongue protrusion

• Infected cyst - red, tender, fluctuant; may rupture → thyroglossal sinus/fistula
• Lingual TDC - presents as base of tongue mass; dysphagia, snoring
• Infective episode often triggered by URI (upper respiratory tract infection)

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6. INVESTIGATIONS

INVESTIGATION ALGORITHM FOR THYROGLOSSAL CYST
──────────────────────────────────────────────────────────
CLINICAL DIAGNOSIS (midline cyst + tongue protrusion sign)
         │
         ▼
  ULTRASOUND NECK ◄─── FIRST-LINE INVESTIGATION
  • Confirms diagnosis (anechoic/cystic mass, may show septa)
  • Confirms NORMAL THYROID GLAND in orthotopic position
    (Critical: if absent → cyst may be ONLY thyroid tissue!)
  • Differentiates from dermoid (SIST score: septa, irregular
    wall, solid components = TDC > dermoid)
         │
         ▼
  Normal thyroid seen?
  ┌─────YES──────┐         ┌──────NO──────────────┐
  ▼              │         ▼                       │
Proceed to       │  Radionuclide scan (Tc99m scan) │
surgery          │  to confirm ectopic thyroid     │
                 │  or absent thyroid              │
                 └────────────────────────────────►┘
                                    ▼
                         TFTs (T3, T4, TSH)
                         Consider NOT excising
──────────────────────────────────────────────────────────

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7. DIFFERENTIAL DIAGNOSIS

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8. TREATMENT

A. Non-Surgical (temporary)

• For acutely infected cyst: antibiotics (amoxicillin-clavulanate), incision and drainage if needed
• Definitive surgery DEFERRED until infection resolves (6-8 weeks)

B. SISTRUNK'S OPERATION (Definitive Treatment)

STEPS OF SISTRUNK'S OPERATION

SISTRUNK'S OPERATION - STEP BY STEP
═══════════════════════════════════════════════════════════════

PATIENT POSITION: Supine, neck extended, sandbag under shoulders

ANESTHESIA: GA with endotracheal intubation

INCISION: Transverse elliptical incision (Kocher/collar incision)
          centered over the cyst in a skin crease
          │
          ▼
STEP 1: Deepen incision through platysma
        Raise superior and inferior flaps
          │
          ▼
STEP 2: Identify and free the cyst
        Handle gently - avoid rupture (increases recurrence)
          │
          ▼
STEP 3: Trace duct SUPERIORLY toward hyoid bone
        Stay in continuity with all tissue between strap muscles
          │
          ▼
STEP 4: EXCISE CENTRAL PORTION OF HYOID BONE
        ← KEY STEP (rationale: duct passes through or around
          hyoid; branches extensively at this level)
        Divide hyoid on each side of midline
        Preserve greater cornua bilaterally
          │
          ▼
STEP 5: Continue dissection ABOVE hyoid
        Follow core of tissue toward base of tongue
          │
          ▼
STEP 6: Excise core of GENIOGLOSSUS MUSCLE
        extending to FORAMEN CECUM
        (ensures complete removal of all duct remnants)
          │
          ▼
STEP 7: Suture tongue musculature (purse-string/interrupted)
        Close in layers: muscle, platysma, skin
        Suction drain placement (optional)

═══════════════════════════════════════════════════════════════

• Simple excision alone: 46% recurrence
• Sistrunk's operation (modified): 5.8% recurrence (Cummings, p.3879)

C. MODIFIED / EXTENDED SISTRUNK'S OPERATION

• Wider block dissection incorporating the infrahyoid region to thyroid isthmus
• Skin paddle excised if fistula present
• See intraoperative image below (Scott-Brown Fig 41.7)

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9. COMPLICATIONS

Complications of the Disease:

1. Infection - most common complication; may lead to abscess
2. Sinus / Fistula formation - after spontaneous rupture or surgical drainage
3. Malignant transformation - rare (see below)

Complications of Surgery (Sistrunk's):

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10. MALIGNANT CHANGE IN THYROGLOSSAL DUCT CYST

• Rare complication; incidence ~1% of all thyroglossal cysts
• Most common type: Papillary thyroid carcinoma (>85%)
• Also: follicular carcinoma, squamous cell carcinoma (from squamous epithelium)
• Associated 6.6% risk of microcarcinoma in the normal-appearing thyroid gland

1. Normal thyroid tissue in the cyst wall
2. Smooth transition from normal to malignant tissue
3. No similar lesion elsewhere (i.e., not a metastasis to the cyst)

MANAGEMENT ALGORITHM - MALIGNANT THYROGLOSSAL DUCT CYST
─────────────────────────────────────────────────────────────
Diagnosed malignancy in TDC
         │
         ▼
  Sistrunk's operation (adequate local excision)
         │
  ┌──────┴──────────────────────────────────┐
  ▼                                         ▼
PAPILLARY Ca (most common)           FOLLICULAR Ca / SCC
  │                                         │
  ▼                                         ▼
Evaluate normal thyroid               Total thyroidectomy
by USG + FNAC                         + RAI therapy
  │
  ▼
Thyroidectomy NOT automatically
required (Cummings 2023 guidelines)
Monitor thyroid for life
(6.6% microcarcinoma risk in thyroid)
─────────────────────────────────────────────────────────────

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11. RECENT ADVANCES (2020-2026)

A. Sclerotherapy as Alternative to Surgery

• Systematic review (Talmor et al., Otolaryngol Head Neck Surg, 2021, PMID 33755513): Sclerotherapy with agents such as OK-432 (picibanil), bleomycin, or ethanol reported for benign cystic head and neck lesions including TDC
• Reserved for poor surgical candidates or recurrent cysts
• Overall success rates variable; not yet standard of care

B. Endoscopic / Minimally Invasive Approaches

• Endoscopic management of intralingual TDC (Pereira NM et al., Auris Nasus Larynx, 2023, PMID 35659788): Systematic review of case series; transoral endoscopic excision feasible for selected intralingual cysts
• Robotic-assisted and endoscopic remote-access Sistrunk's being explored in adults for better cosmesis (limited evidence)

C. SIST Score - Preoperative USG Scoring

• SIST score: Sonographic scoring system on ultrasound to differentiate TDC from dermoid cyst preoperatively
• Variables: septa, irregular wall, solid components - higher score = more likely TDC
• Guides surgical planning and consent (K.J. Lee, p.9928)

D. Role of Pre-op Imaging

• 2025 systematic review (Taishan W et al., J Med Life 2025, PMID 40757114): Thyroid scan and ultrasound are complementary; USG alone is sufficient in most cases; radionuclide scan reserved for when normal thyroid cannot be confirmed on USG

E. TDC Carcinoma - Updated Guidelines

• Thyroidectomy is NOT mandated for incidental papillary TDC carcinoma (Cummings 7th ed.)
• Active surveillance/monitoring protocol for thyroid gland post-Sistrunk's
• Systematic review (Thimsen 2025, Virchows Arch, PMID 40347268): Retrospective study and review confirms excellent prognosis; low-risk papillary TDC Ca managed by Sistrunk's alone

F. Multiple Thyroglossal Duct Cysts

• Rare entity reported (Bao YY et al., Ear Nose Throat J 2025, PMID 37194164): multiple simultaneous TDCs; may require modified extended Sistrunk's covering entire tract

G. Extended / Modified Sistrunk's - Now Standard

• Extended Sistrunk's (block dissection to thyroid isthmus) previously reserved for recurrent cases is now increasingly used as primary procedure to minimize recurrence
• [Scott-Brown's, p.2370-2375]

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12. SUMMARY FLOWCHART - COMPLETE MANAGEMENT

THYROGLOSSAL CYST - MANAGEMENT FLOWCHART
══════════════════════════════════════════════════════════════

        MIDLINE NECK SWELLING
               │
               ▼
   Moves UP with tongue protrusion?
        YES ────────────────────────► NO → Consider dermoid,
               │                           subhyoid bursa,
               ▼                           enlarged LN
   CLINICAL DIAGNOSIS: TDC
               │
               ▼
   ┌──────── INVESTIGATIONS ─────────┐
   │  USG Neck (FIRST-LINE)          │
   │  → Is normal thyroid present?   │
   │       YES         NO            │
   │        │           │            │
   │        │    Tc99m scan + TFTs   │
   │        │    If only thyroid →   │
   │        │    Do NOT excise       │
   └─────────────────────────────────┘
               │
               ▼
     Currently INFECTED?
        YES ──────────────────────────► Antibiotics ± I&D
               │                         Wait 6-8 weeks
               │ NO (or after resolution)
               ▼
   ┌────────────────────────────────────┐
   │      SISTRUNK'S OPERATION         │
   │  - Elliptical incision over cyst  │
   │  - Dissect cyst en bloc           │
   │  - Excise central hyoid bone      │
   │  - Core of genioglossus muscle    │
   │    up to foramen cecum            │
   │  - ± Extended dissection          │
   └────────────────────────────────────┘
               │
               ▼
         HISTOPATHOLOGY
               │
    ┌──────────┴──────────┐
    │                     │
  BENIGN               MALIGNANT
    │                     │
    ▼                     ▼
  Discharge          Papillary Ca → Monitor thyroid
  + Follow-up        (Sistrunk's sufficient in most)
                     Follicular/SCC → Total thyroidectomy

══════════════════════════════════════════════════════════════

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13. KEY ANATOMICAL DIAGRAM

ANATOMY OF THYROGLOSSAL DUCT - SCHEMATIC
════════════════════════════════════════════════════════

        TONGUE  (dorsum)
         │
    [FORAMEN CECUM] ◄── Origin of thyroglossal duct
         │
         │ Suprahyoid segment
         │ (extensive branching ← reason for wide resection)
         │
    [HYOID BONE] ◄──── Central portion excised in Sistrunk's
         │
         │ Infrahyoid segment
         │ ← MOST COMMON SITE OF CYST FORMATION
         │
    [THYROID ISTHMUS]
         │
    [PYRAMIDAL LOBE] ◄── Remnant of descent in 50%

Sites of cyst formation:  ● = possible location of cyst
   Lingual (rare) ●
   Suprahyoid ●●
   At hyoid ●●●
   Infrahyoid ●●●●●●● (most common)
   Suprasternal (rare) ●

════════════════════════════════════════════════════════

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SOURCES CITED

• Talmor et al. 2021 - Sclerotherapy for cystic head & neck lesions (PMID 33755513)
• Pereira et al. 2023 - Endoscopic management of intralingual TDC (PMID 35659788)
• Taishan et al. 2025 - Thyroid scan and USG in TDC management (PMID 40757114)
• Thimsen et al. 2025 - TDC carcinomas systematic review (PMID 40347268)
• Bao et al. 2025 - Multiple TDCs review (PMID 37194164)

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EXAM TIPS FOR RGUHS 20 MARKS

1. Sistrunk's operation - the central hyoid must be excised and why
2. Recurrence 46% (simple excision) vs 5.8% (Sistrunk's)
3. Tongue protrusion sign is pathognomonic
4. USG must confirm normal thyroid before surgery
5. Most common histology in malignant TDC = papillary carcinoma
6. First described by Sistrunk in 1920 (Mayo Clinic)
7. Most common site = infrahyoid (subhyoid)