A 10-year-old boy comes for a post-operative clinic visit with his ENT surgeon three months after airway reconstruction surgery and placement of a tracheostomy tube. Since the surgery, he says that he has been able to breathe better and is now getting used to tracheostomy care and tracheostomy tube changes. In addition to this surgery, he has had over twenty surgeries to implant hearing aids, reconstruct his cheekbones, and support his jaw to enable him to swallow. He was born with these abnormalities and had difficult breathing, hearing, and eating throughout his childhood. Fortunately, he is now beginning to feel better and is able to attend public school where he is one of the best students in the class. Abnormal development of which of the following structures is most likely responsible for this patient's malformations?

Third and fourth branchial pouches

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 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

A 64-year-old woman presents to an endocrinologist after her second time having a kidney stone in the last year. The patient reports no other symptoms except overall fatigue. On evaluation, the patient’s temperature is 98.4°F (36.9°C), blood pressure is 120/76 mmHg, pulse is 72/min, and respirations are 12/min. The patient has no neck masses and no tenderness to palpation in the abdomen. On laboratory workup, the endocrinologist finds that the patient has elevated parathyroid hormone levels and serum calcium. For surgical planning, the patient undergoes a sestamibi scan, which localizes disease to an area near the superior aspect of the thyroid in the right neck. Which of the following is the embryologic origin of this tissue?

Dorsal wings of the third branchial pouch

Ventral wings of the third branchial pouch

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

Pharyngeal membrane derivatives for USMLE Step 3: High-Yield Anatomy Lessons

Pharyngeal Membranes - From Groove to Eardrum

Formed where the ectoderm of the pharyngeal grooves meets the endoderm of the pharyngeal pouches.
1st Pharyngeal Membrane:
- Develops into the tympanic membrane (eardrum).
- Composed of three layers:
  - Outer ectodermal layer (from 1st pharyngeal groove).
  - Inner endodermal layer (from 1st pharyngeal pouch).
  - Intermediate mesenchyme layer.
2nd, 3rd, & 4th Membranes:
- Temporarily exist but are obliterated when the 2nd arch grows over the 3rd and 4th arches, forming the cervical sinus, which later disappears.

⭐ Clinical Pearl: Failure of the cervical sinus (formed from the 2nd, 3rd, and 4th pharyngeal clefts) to obliterate can result in a branchial cleft cyst in the lateral neck.

High‑Yield Points - ⚡ Biggest Takeaways

The first pharyngeal membrane is the only one to persist, forming the tympanic membrane (eardrum).

It separates the first pharyngeal cleft (future external auditory meatus) from the first pharyngeal pouch (future middle ear).

The tympanic membrane is composed of all three germ layers: ectoderm, mesoderm, and endoderm.

The 2nd, 3rd, and 4th pharyngeal membranes are obliterated by the overgrowth of the second pharyngeal arch.

Incomplete obliteration can result in branchial (cervical) cysts.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play