Congenital neck masses are developmental anomalies that can manifest either at birth or later in life, usually following a respiratory infection. The most common congenital neck masses are thyroglossal duct cysts, branchial cleft cysts, and cystic hygromas. These malformations manifest as painless neck masses that, as they grow, can cause dysphagia, respiratory distress, and neck pain by compressing surrounding structures. The location of the mass depends on the embryological structure the cyst arises from. Diagnosis is based on clinical findings and imaging results (ultrasound, CT, MRI), which also help in surgical planning. Treatment consists of complete surgical resection to prevent recurrence and complications such as infection or abscess formation.
Thyroglossal duct cyst
- Definition: a remnant of the thyroglossal duct, which forms during the embryonic development of the thyroid gland and normally regresses before birth
- Incidence: ∼ 7% of the population
- Second most common neck abnormality after lymphadenopathy
- The thyroid gland originates from the foramen cecum at the base of the tongue and descends caudally into the neck, forming the thyroglossal duct.
- If the thyroglossal duct fails to obliterate, midline neck cysts or ectopic thyroid tissue can develop anywhere along its path.
Clinical features: The cyst is present from birth and is usually detected during early childhood.
- Painless, firm, midline neck mass that elevates with swallowing and tongue protrusion
- Usually located near the hyoid bone
- May cause dysphagia or neck/throat pain if the cyst enlarges
- Neck and thyroid examination
Ultrasound of the neck to evaluate the cyst and confirm the location of the thyroid
- Patients with thyroglossal duct cysts can have an ectopic thyroid gland. 
- In the absence of ectopy, it is important to assess the anatomical relation of the cyst to the thyroid for preoperative planning.
Contrast-enhanced CT of the neck: preferred imaging modality
- Thyroglossal duct cysts are demonstrated as well-defined lesions with homogenous fluid attenuation and surrounding rim enhancement, typically close to the hyoid bone.
- Allows for assessment of anatomical location, relation, and extent of the cyst as well as its relation to normal orthotopic thyroid tissue.
- TSH levels
- If an infection is suspected, fine needle aspiration should be performed for Gram stain and culture (including AFB and mycobacterial culture).
- Elective surgical excision (Sistrunk procedure) to prevent infection: includes removal of the cyst, a portion of the hyoid bone, and excision of tissue comprising the path of descent from the foramen cecum
- Treatment of any active infection with antibiotics before surgery
- Complications 
Thyroglossal duct cysts manifest as a painless, firm, midline neck mass that moves with swallowing and tongue movement.
Branchial cleft cyst
- Definition: remnants of the embryological second branchial cleft or cervical sinus, which normally regresses before birth
- Accounts for ∼ 20% of pediatric neck masses
- ∼ 95% of all branchial cleft malformations are anomalies of the second branchial cleft.
- Pathophysiology: : formed due to incomplete obliteration of branchial clefts and pouches
Clinical features: usually diagnosed in late childhood or in adulthood after a previously undiagnosed cyst becomes infected 
- History of upper respiratory infection
Painless, firm mass
- Located lateral to the midline, usually anterior to the sternocleidomastoid muscle
- Does not move with swallowing
- There may be a small draining opening if a fistula is present.
- Neck examination
- CT or MRI to further assess anatomical structures for surgical planning
- Treatment: : complete surgical excision of both the cyst and any associated tracts 
- Complications: : infection of the cyst, tract, or sinus, with possible abscess formation
Branchial cleft cysts manifest as a painless, firm neck mass lateral to the midline.
- Definition: a congenital lymphatic cyst (macrocystic lymphangioma) in the posterior triangle of the neck caused by malformation and obstruction of the fetal lymphatic system 
- ∼ 1:6,000 live births 
- Strongly associated with fetal aneuploidy; (e.g., Turner syndrome, trisomy 21) and congenital malformations (e.g., congenital heart defects)
- Present at birth as a soft, compressible, painless, posterior triangle neck mass
- Can cause dysphagia or airway compromise
- Positive transillumination test
- Prenatal ultrasound : fluid-filled neck mass with or without septations 
- Ultrasound to identify mass in infancy
- CT or MRI may be used to further assess anatomical structures for surgical planning
- Treatment: : Small masses may regress spontaneously, but surgical excision is usually indicated to prevent infection or airway compromise, as well as for cosmesis. 
- Prognosis: Recurrence is common following surgical excision of extensive hygromas.
- Unilateral cervical lymphadenopathy
- Cervical teratoma
- Dermoid cysts
- Midline cervical cleft cyst
The differential diagnoses listed here are not exhaustive.