Based on the history and appearance, the most likely diagnosis is:

This image shows a midline neck swelling in a child. Based on the history and appearance, the most likely diagnosis is:

Thyroglossal Duct Cyst (TGDC)

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✅ Supporting features:

Age: Common in children and young adults.

Location: Midline neck swelling, typically below the hyoid bone.

Movement with swallowing and tongue protrusion: A key feature (because the cyst is connected to the foramen cecum of the tongue via a tract).

Pain: Suggests possible infection of the cyst.

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Other possible diagnoses to consider:

1. Infected dermoid cyst (if it’s midline but doesn’t move with swallowing).

2. Submental lymphadenitis (but lymph nodes are usually lateral and multiple).

3. Thyroid nodule (but rare at this age).

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Next steps:

🩺 Clinical tests:

Ask the child to stick out the tongue and swallow – if the swelling moves upward, it strongly supports TGDC.

📖 Investigations:

Ultrasound neck: To confirm cystic nature and relationship to surrounding structures.

Thyroid scan: To ensure a normally located thyroid gland before surgery.

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Treatment:

If infected: Start antibiotics and drainage if abscess forms.

Definitive management: Sistrunk procedure (surgical excision of the cyst along with the central part of the hyoid bone and tract to the base of the tongue) to prevent recurrence.

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🔑 Key point:

Midline neck swelling in a child that moves with swallowing or tongue protrusion = Think thyroglossal duct cyst.