Differentials for Thyroglossal Duct Cyst

1. Dermoid / Epidermoid Cyst

• Most important differential to exclude
• Also midline, can appear anywhere from submental to suprasternal regions
• Does not move on tongue protrusion - this is the key distinguishing feature
• Doughy in consistency; contains sebaceous material, hair follicles
• Typically at the submental region or along embryonic fusion lines
• USS shows a heterogeneous echogenic mass (not the typical anechoic appearance of TDC)

2. Ectopic / Lingual Thyroid

• Failure of normal caudal migration of the thyroid gland
• Presents as a midline swelling at the base of tongue (foramen caecum) or anywhere along the thyroglossal duct tract
• Critical point: if this is the only functioning thyroid tissue, excision will cause hypothyroidism
• Radionuclide scan or USS should confirm normal thyroid in the neck before surgery
• Sabiston notes: "Failure of normal caudal migration of the thyroid gland results in a lingual thyroid, in which no other thyroid tissue is present in the neck" - Sabiston Textbook of Surgery, p. 1343

3. Subhyoid Bursitis

• Located at or just below the hyoid bone, exactly the most common site for TDC
• Clinically very difficult to distinguish from TDC preoperatively
• Moves with swallowing but not with tongue protrusion
• Thin-walled, fluid-filled structure on USS

4. Enlarged Submental / Submandibular Lymph Nodes

• Can be midline or near-midline in the submental region (level IA nodes)
• Reactive, tuberculous, or metastatic
• Firm or hard consistency; does not move with tongue protrusion
• Multiple nodes may be palpable; associated systemic features (fever, weight loss) in tuberculous or lymphomatous disease

5. Sebaceous / Pilar Cyst

• Intradermal; attached to skin and moves with it
• No movement on swallowing or tongue protrusion
• Punctum (central pore) often visible
• Soft, smooth, fluctuant; may have a cheesy discharge

6. Lipoma

• Soft, lobulated, non-fluctuant, non-transilluminant
• Typically in the submental/suprasternal space or posterior triangle
• Does not move with swallowing or tongue protrusion
• No skin attachment

7. Branchial Cleft Cyst

• Usually lateral neck mass (anterior to sternocleidomastoid at the angle of the mandible)
• Occasionally presents near the midline and may cause confusion
• Contains thick creamy fluid with cholesterol crystals on aspiration
• Does not move with tongue protrusion

8. Cystic Hygroma (Lymphatic Malformation)

• Typically a soft, brilliantly transilluminant multilocular swelling
• More common in infants and children, often at the root of the neck
• Can extend into the mediastinum (shows impulse on coughing)
• Fluid can be shifted between locules on compression
• Lacks movement with tongue protrusion

9. Laryngocoele

• Air-containing diverticulum herniating through the thyrohyoid membrane
• Resonant on percussion - distinct from all cystic swellings
• Enlarges on Valsalva (blowing the nose, straining)
• More common in trumpet players, glassblowers, or those with chronic cough

10. Carcinoma within a TDC (Thyroglossal Duct Carcinoma)

• 1% incidence of malignancy (almost always papillary thyroid carcinoma) within a TDC
• Suggested by solid components, rapid growth, fixation, or cervical lymphadenopathy
• Cummings Otolaryngology notes that solid material within the cyst on imaging warrants suspicion - Cummings Otolaryngology Head and Neck Surgery

Key Distinguishing Features at a Glance