A 3-year-old girl is brought to the emergency department by her parents with sudden onset shortness of breath. They tell the emergency physician that their daughter was lying on the bed watching television when she suddenly began gasping for air. They observed a bowl of peanuts lying next to her when they grabbed her up and brought her to the emergency department. Her respirations are 25/min, the pulse is 100/min and the blood pressure is 90/65 mm Hg. The physical findings as of now are apparently normal. She is started on oxygen and is sent in for a chest X-ray. Based on her history and physical exam findings, the cause of her current symptoms would be seen on the X-ray at which of the following sites?

The posterior segment of the right lower lobe

The superior segment of the right lower lobe

The lingula of the left upper lobe

The apical segment of the right upper lobe

The apical segment of the left upper lobe

A 16-year-old boy comes to the physician because of a 1-week history of difficulty swallowing, a foreign body sensation at the back of his throat, and trouble breathing at night. He has just recovered from an upper respiratory tract infection that began 5 days ago. On questioning, he reports that he has had similar symptoms in the past each time he has had an upper respiratory tract infection. Physical examination shows a 3 x 2-cm, nontender, rubbery midline mass at the base of the tongue. His skin is dry and cool. An image of his technetium-99m pertechnetate scan is shown. Which of the following is the most likely underlying cause of this patient’s condition?

Arrested endodermal migration from pharyngeal floor

Chronic infection of the palatine and lingual tonsils

Ductal obstruction of the sublingual salivary glands

Persistent epithelial tract between the foramen cecum and thyroid isthmus

Failure of obliteration of the second branchial cleft

A 26-year-old G1P0 woman at 40 weeks estimated gestational age presents after experiencing labor pains. Pregnancy has been uncomplicated so far. Rupture of membranes occurs, and a transvaginal delivery is performed under epidural anesthesia, and the baby is delivered alive and healthy. The patient voids a few hours after the delivery and complains of mild irritation at the injection site on her back. On the second day, she complains of a severe headache over the back of her head. The headache is associated with pain and stiffness in the neck. Her headache is aggravated by sitting up or standing and relieved by lying down. The pain is relieved slightly by acetaminophen and ibuprofen. The patient is afebrile. Her vital signs include: pulse 100/min, respiratory rate 18/min, and blood pressure 128/84 mm Hg. Which of the following statements is the most accurate regarding this patient’s condition?

This patient’s condition can resolve on its own

A blockage of CSF is the cause of this patient’s headache

An infection is present at the epidural injection site

Excessive bed rest will worsen this patient’s condition

Immediate intervention is required

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 27-year-old woman comes to the physician because of a 3-day history of a sore throat and fever. Her temperature is 38.5°C (101.3°F). Examination shows edematous oropharyngeal mucosa and enlarged tonsils with purulent exudate. There is tender cervical lymphadenopathy. If left untreated, which of the following conditions is most likely to occur in this patient?

Post-streptococcal glomerulonephritis

A 42-year-old woman comes to the physician because of increasing pain in the right hip for 2 months. The pain is intermittent, presenting at the lateral side of the hip and radiating towards the thigh. It is aggravated while climbing stairs or lying on the right side. Two weeks ago, the patient was treated with a course of oral prednisone for exacerbation of asthma. Her current medications include formoterol-budesonide and albuterol inhalers. Vital signs are within normal limits. Examination shows tenderness to palpation over the upper lateral part of the right thigh. There is no swelling. The patient is placed in the left lateral decubitus position. Abducting the extended right leg against the physician's resistance reproduces the pain. The remainder of the examination shows no abnormalities. An x-ray of the pelvis shows no abnormalities. Which of the following is the most likely diagnosis?

Greater trochanteric pain syndrome

Head and neck fascial spaces for USMLE Step 3: High-Yield Anatomy Lessons

Cervical Fascia Layers - Neck's Nifty Napkins

Cross-section of cervical fascia layers

Superficial Cervical Fascia:
- Contains platysma muscle, cutaneous nerves, blood vessels, and lymphatics.
Deep Cervical Fascia (3 Layers):
- Investing Layer: Surrounds the entire neck; splits to enclose sternocleidomastoid and trapezius muscles.
- Pretracheal Layer: Encloses thyroid gland, trachea, and esophagus.
- Prevertebral Layer: Surrounds the vertebral column and associated muscles.
Carotid Sheath:
- A unique fascial column receiving contributions from all three deep layers.
- Contents: Common/Internal Carotid Artery, Internal Jugular Vein, Vagus Nerve (CN X).

⭐ Infections in the "danger space" (retropharyngeal space) can readily spread inferiorly into the posterior mediastinum.

Key Fascial Spaces - Corridors of Concern

Retropharyngeal Space
- Location: Between buccopharyngeal fascia (anteriorly) and alar fascia (posteriorly).
- Clinical Significance: Pathway for infection from pharynx/esophagus to spread inferiorly into the superior mediastinum.
"Danger Space" (Alar Space)
- Location: Between alar fascia (anteriorly) and prevertebral fascia (posteriorly).
- Clinical Significance: Most dangerous route for infection spread.
⭐ Infections in the "danger space" can travel from the base of the skull directly to the diaphragm and posterior mediastinum, leading to severe complications like acute mediastinitis.
Prevertebral Space
- Location: Posterior to the danger space, anterior to vertebral bodies.
- Clinical Significance: Infection can erode into vertebral bodies, causing osteomyelitis.
Submandibular & Masticator Spaces
- Source: Most commonly from dental infections (e.g., abscessed mandibular molar).
- 💡 Ludwig's Angina: Rapidly spreading cellulitis of the submandibular space, potentially causing fatal airway compromise from tongue elevation and glottic edema.

Deep neck fascial spaces: sagittal and axial views

Infection Spread - Pathways to Peril

Deep neck fascial spaces: sagittal and axial views

Odontogenic, pharyngeal, or tonsillar infections can erode through fascial layers, spreading rapidly along paths of least resistance.

Retropharyngeal Space: Between buccopharyngeal & alar fascia. Drains into the superior mediastinum.
"Danger Space": Between alar & prevertebral fascia. This space provides a direct, rapid conduit from the skull base to the diaphragm.
Ludwig's Angina: Aggressive, bilateral cellulitis of the submandibular space; can cause fatal airway obstruction.

⭐ Infections in the "danger space" are the most feared, as they can descend directly into the posterior mediastinum, leading to necrotizing mediastinitis with a mortality rate approaching 50%.

High-Yield Points - ⚡ Biggest Takeaways

The danger space, between the alar and prevertebral fascia, is the most critical route for infection spread to the posterior mediastinum.

Infections in the retropharyngeal space can travel down to the superior mediastinum.

Ludwig's angina is a rapidly spreading cellulitis of the submandibular space that can cause acute airway obstruction.

The pretracheal space offers a direct path for infection to the anterior mediastinum.

Cavernous sinus thrombosis can arise from infections in the danger triangle of the face.

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