A 4-year-old girl is brought by her mother to the pediatrician for neck drainage. The mother reports that the child has always had a small pinpoint opening on the front of her neck, though the opening has never been symptomatic. The child developed a minor cold approximately 10 days ago which resolved after a week. However, over the past 2 days, the mother has noticed clear thick drainage from the opening on the child’s neck. The child is otherwise healthy. She had an uncomplicated birth and is currently in the 45th and 40th percentiles for height and weight, respectively. On examination, there is a small opening along the skin at the anterior border of the right sternocleidomastoid at the junction of the middle and lower thirds of the neck. There is some slight clear thick discharge from the opening. Palpation around the opening elicits a cough from the child. This patient’s condition is caused by tissue that also forms which of the following?

Epithelial lining of the Eustachian tube

A child is born by routine delivery and quickly develops respiratory distress. He is noted to have epicanthal folds, low-set ears that are pressed against his head, widely set eyes, a broad, flat nose, clubbed feet, and a receding chin. The mother had one prenatal visit, at which time the routine ultrasound revealed an amniotic fluid index of 3 cm. What is the most likely underlying cause of this patient's condition?

Autosomal recessive polycystic kidney disease (ARPKD)

A microdeletion in chromosome 22

A 25-year-old man presents to the clinic with a midline swelling in his neck. He is unsure about when it appeared. He denies any difficulty with swallowing or hoarseness. His past medical history is insignificant. On physical examination, there is a 1 cm x 2 cm firm mildly tender nodule on the anterior midline aspect of the neck which moves with deglutition and elevates with protrusion of the tongue. Which of the following is the most likely embryologic origin of the nodule in this patient?

Midline endoderm of the pharynx

A 25-year-old woman gives birth to a male child at 30 weeks of gestation. Pregnancy was complicated by polyhydramnios diagnosed on ultrasonography at 26 weeks of gestation. The baby is born vaginally weighing 1.2 kg (2.64 lb). Because he does not cry immediately after birth, endotracheal intubation is attempted to secure the airway. However, the vocal cords cannot be visualized because there is only a single opening corresponding to the esophagus. He is transferred to the NICU under bag and mask ventilation, where intubation is attempted once again by passing the endotracheal tube in the visualized opening, after which his oxygen saturation begins to improve. His temperature is 37.0ºC (98.6°F), pulse is 120/min, and respiratory rate is 42/min. On physical examination, no abnormalities are noted. Chest radiography is suggestive of respiratory distress syndrome. Which of the following most likely failed to develop in this patient?

Fourth and sixth branchial arches

A 29-year-old mother brings in her 2-week-old baby boy to a pediatrician because he has been having difficulty feeding. The mother reveals that she had no prenatal care during her pregnancy and gave birth at home without complications. She says that her son seems to be having difficulty sucking, and she occasionally sees breast milk coming out of the infant’s nose. Physical exam reveals that this patient has a gap between his oral and nasal cavities behind the incisive foramen. He is therefore prescribed specialized bottles and his mom is taught positional techniques to ensure better feeding. Failure to fuse which of the following structures is most likely responsible for this patient's disorder?

Palatine shelves with nasal septum

Maxillary and medial nasal prominences

Nasal septum with primary plates

Maxillary and lateral nasal prominences

Palatine shelves with primary plates

A six year-old female presents for evaluation of dry skin, fatigue, sensitivity to cold and constipation. The patient’s mother recalls that the patient had surgery to remove a “benign mass” at the base of her tongue 3 months ago because of trouble swallowing. What was the likely cause of the surgically removed mass?

Failed caudal migration of the thyroid gland

Failed fusion of the palatine shelves with the nasal septum

Clinical correlations of pharyngeal development for USMLE Step 1: High-Yield Anatomy Lessons

Arch Development Defects - When Blueprints Go Wrong

Clinical features of Treacher Collins Syndrome

1st Arch Syndromes: Result from insufficient neural crest cell migration into the first arch.
- Treacher Collins Syndrome: Autosomal dominant defect of the TCOF1 gene. Presents with mandibulofacial dysostosis: hypoplastic mandible and zygomatic bones, down-slanting palpebral fissures, coloboma, and malformed external ears leading to conductive hearing loss.
- Pierre Robin Sequence: Characterized by a triad: micrognathia (small mandible), glossoptosis (posteriorly displaced tongue), and a U-shaped cleft palate causing airway obstruction.
DiGeorge Syndrome (22q11.2 Deletion): Faulty development of the 3rd and 4th pharyngeal pouches, affecting arch-derived structures.

⭐ 📌 CATCH-22: Cardiac defects (conotruncal), Abnormal facies, Thymic aplasia (impaired T-cell immunity), Cleft palate, Hypocalcemia/Hypoparathyroidism.
Goldenhar Syndrome (Oculo-auriculo-vertebral spectrum): A sporadic defect involving 1st and 2nd arch derivatives. Features include unilateral facial hypoplasia, microtia (small ear), epibulbar dermoids, and vertebral anomalies.

Pouch & Cleft Anomalies - Pockets of Trouble

Pharyngeal Cleft Cysts (Branchial Cysts)
- Pathophysiology: Incomplete obliteration of pharyngeal clefts (usually 2nd-4th).
- Presentation: Soft, painless lateral neck mass, anterior to the sternocleidomastoid muscle. Can become infected.
- Fistula: A tract may connect the cyst to the skin or pharynx.
Pharyngeal Pouch Anomalies
- DiGeorge Syndrome (22q11.2 deletion): Failure of 3rd & 4th pouch development.
  - Presentation: 📌 CATCH-22: Cardiac defects (Truncus Arteriosus), Abnormal facies, Thymic aplasia (T-cell deficiency), Cleft palate, Hypocalcemia/Hypoparathyroidism.

⭐ Exam Favorite: A branchial cleft cyst is a lateral neck mass. A thyroglossal duct cyst is typically midline.

Neck cysts and masses

Key Syndromes - Rogues' Gallery

Treacher Collins Syndrome (1st Arch)
- Cause: Autosomal dominant; TCOF1 gene mutation → defective neural crest migration.
- Features: Mandibular hypoplasia, down-slanting eyes, absent/abnormal ossicles (conductive hearing loss), zygomatic bone hypoplasia.
- 📌 Mnemonic: Treacher Collins = Treble Chance of 1st arch defects.
Pierre Robin Sequence (1st Arch)
- Pathogenesis: Micrognathia → Glossoptosis (posterior tongue) → Airway obstruction & U-shaped cleft palate.
- Key Issue: Neonatal respiratory distress.
DiGeorge Syndrome (3rd & 4th Arches/Pouches)
- Cause: 22q11.2 microdeletion; TBX1 gene haploinsufficiency.
- Features: Thymic & parathyroid hypoplasia/aplasia (→ T-cell deficiency, hypocalcemia), conotruncal cardiac defects, abnormal facies.
- 📌 Mnemonic: CATCH-22

⭐ High-Yield: DiGeorge syndrome results from failure of the 3rd pouch (absent thymus, inferior parathyroids) and 4th pouch (absent superior parathyroids).

Goldenhar Syndrome (1st & 2nd Arches)
- Features: Oculo-Auriculo-Vertebral (OAV) spectrum. Unilateral facial hypoplasia, epibulbar dermoids, preauricular skin tags, and vertebral anomalies.

Treacher Collins vs. DiGeorge syndrome facial features

Treacher Collins syndrome: 1st arch neural crest failure leads to mandibular hypoplasia and facial abnormalities.

Pierre Robin sequence: 1st arch defect causing micrognathia, glossoptosis, and cleft palate.

DiGeorge syndrome (22q11 deletion): 3rd/4th pouch failure causes thymic/parathyroid aplasia and cardiac defects.

Branchial cleft cyst: Persistent 2nd-4th clefts forming a lateral neck mass.

Cleft lip: Failure of maxillary and medial nasal processes to fuse.

Cleft palate: Failure of palatal shelves to fuse.

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