A 52-year-old man presents to a medical clinic to establish care. He has no known chronic illnesses but has not seen a physician in over 20 years. He generally feels well but occasionally has shortness of breath when he jogs and exercises. He smokes 2-5 cigarettes per day and uses IV heroin “now and then.” Physical exam is unremarkable. ECG shows prominent QRS voltage and left axis deviation. Trans-thoracic echocardiogram shows mild concentric left ventricular hypertrophy but is otherwise normal. Which of the following is the most likely etiology of the echocardiogram findings?

Chronic obstructive pulmonary disease

A 42-year-old woman comes to the physician because of 2 episodes of loss of consciousness over the past week. She recovered immediately and was not confused following the episodes. During the past 5 months, she has also had increased shortness of breath and palpitations. She has been unable to carry out her daily activities. She also reports some chest tightness that resolves with rest. She has no history of serious illness and takes no medications. She immigrated with her family from India 10 years ago. Her temperature is 37.3°C (99.1°F), pulse is 115/min and irregular, and blood pressure is 108/70 mm Hg. Examination shows jugular venous distention and pitting edema below the knees. Bilateral crackles are heard at the lung bases. Cardiac examination shows an accentuated and split S2. There is an opening snap followed by a low-pitched diastolic murmur in the fifth left intercostal space at the midclavicular line. An ECG shows atrial fibrillation and right axis deviation. Which of the following is the most likely underlying mechanism of these findings?

Increased left ventricular end diastolic pressure

Increased left to right shunting

Increased systemic arterial resistance

Decreased left ventricular contractility

A tall, slender 32-year-old man comes to the emergency room because of sudden chest pain, cough, and shortness of breath. On physical examination, he has decreased breath sounds on the right. Chest radiography shows translucency on the right side of his chest. His pCO2 is elevated and pO2 is decreased. What is the most likely cause of his symptoms?

Chronic obstructive pulmonary disease

A 64-year-old man presents to the office for an annual physical examination. He has no complaints at this visit. His chart states that he has a history of hypertension, chronic obstructive pulmonary disease (emphysema), Raynaud’s disease, and glaucoma. He is a 30 pack-year smoker. His medications included lisinopril, tiotropium, albuterol, nifedipine, and latanoprost. The blood pressure is 139/96 mm Hg, the pulse is 86/min, the respiration rate is 16/min, and the temperature is 37.2°C (99.1°F). On physical examination, his pupils are equal, round, and reactive to light. The cardiac auscultation reveals an S4 gallop without murmur, and the lungs are clear to auscultation bilaterally. However, the inspection of the chest wall shows an enlarged anterior to posterior diameter. Which of the following is the most appropriate screening test for this patient?

Bronchoalveolar lavage with cytology

A young researcher is responsible for graphing laboratory data involving pulmonary blood flow and ventilation pattern obtained from a healthy volunteer who was standing in an upright position. After plotting the following graph, the researcher realizes he forgot to label the curves and the x-axis (which represents the position in the lung). Which of the following is the appropriate label for each point on the graph?

A: Ventilation B: Blood flow C: Base of the lung D: Apex of the lung

A: Ventilation B: Blood flow C: Mid-portion of the lung D: Apex of the lung

A: Dead Space B: Shunt C: Base of the lung D: Apex of the lung

A: Blood flow B: Ventilation C: Base of the lung D: Lung hilum

A: Blood flow B: Ventilation C: Apex of the lung D: Lung hilum

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 2-year-old child is brought to the emergency department with rapid breathing and a severe cyanotic appearance of his lips, fingers, and toes. He is known to have occasional episodes of mild cyanosis, especially when he is extremely agitated. This is the worst episode of this child’s life, according to his parents. He was born with an APGAR score of 8 via a normal vaginal delivery. His development is considered delayed compared to children of his age. History is significant for frequent squatting after strenuous activity. On auscultation, there is evidence of a systolic ejection murmur at the left sternal border. On examination, his oxygen saturation is 71%, blood pressure is 81/64 mm Hg, respirations are 42/min, pulse is 129/min, and temperature is 36.7°C (98.0°F). Which of the following will most likely be seen on chest x-ray (CXR)?

Increased pulmonary vascular markings

Cardiomegaly with globular heart

A 45-year-old woman comes to the physician because of progressive difficulty swallowing solids and liquids over the past 4 months. She has lost 4 kg (9 lb) during this period. There is no history of serious illness. She emigrated to the US from Panama 7 years ago. She does not smoke cigarettes or drink alcohol. Cardiopulmonary examination shows a systolic murmur and an S3 gallop. A barium radiograph of the chest is shown. Histopathologic examination of the esophageal wall is most likely to show which of the following?

Absence of myenteric plexus neurons

Presence of intranuclear basophilic inclusions

Atrophy of esophageal smooth muscle cells

Infiltration of eosinophils in the epithelium

Presence of metaplastic columnar epithelium

Cardiac radiologic landmarks for USMLE Step 3: High-Yield Anatomy Lessons

Cardiac Silhouette - The Heart's Shadow

Cardiac Anatomy on PA Chest X-ray

PA View Borders: The heart's edges are formed by specific chambers and great vessels.
- Right: Superior Vena Cava (SVC) and the Right Atrium (RA).
- Left: Aortic knob, main Pulmonary Artery, Left Atrial appendage, and the Left Ventricle (LV).
Lateral View Key Spaces:
- Retrosternal Space: Area behind the sternum. Normally clear; opacification suggests Right Ventricle (RV) enlargement.
- Retrocardiac Space: Area behind the heart. Opacification (e.g., by a double density) suggests Left Atrium (LA) enlargement.

⭐ Cardiothoracic Ratio (CTR): On a PA chest X-ray, the transverse cardiac diameter should be less than 50% of the transverse thoracic diameter. A CTR > 0.5 is a key indicator of cardiomegaly.

PA View Landmarks - Borders & Bosses

PA Chest X-ray: Cardiac & Great Vessel Landmarks

The cardiac silhouette on a PA chest X-ray presents distinct borders formed by different chambers and great vessels.

Right Heart Border: Primarily formed by two convexities.
- Superior: Superior Vena Cava (SVC)
- Inferior: Right Atrium (RA)
Left Heart Border: Composed of four "bumps" or convexities.
- Aortic Knob: The arch of the aorta.
- Main Pulmonary Artery (MPA): The "pulmonary bay".
- Left Atrial Appendage (LAA): Not always visible; enlargement suggests mitral stenosis.
- Left Ventricle (LV): Forms the cardiac apex.
- 📌 Mnemonic (Superior to Inferior): All People Love Lunges

⭐ Cardiothoracic Ratio: On a PA film, the maximum horizontal cardiac diameter should be less than 50% of the maximum horizontal thoracic diameter. A ratio >0.5 is a key indicator of cardiomegaly.

Lateral View Landmarks - A Sideways Glance

Labeled lateral chest X-ray of cardiac silhouette anatomy

On a lateral CXR, the heart chambers are viewed from the side, revealing different borders than the PA view. Key landmarks are assessed by their relationship to the retrosternal and retrocardiac clear spaces.

Anterior Border: Formed almost exclusively by the Right Ventricle (RV).
- RV enlargement causes opacification (filling-in) of the normally clear retrosternal space.
Posterior Border: Composed of two chambers.
- Left Atrium (LA): Forms the upper third of the posterior border.
- Left Ventricle (LV): Forms the lower two-thirds.

⭐ Left Atrial Enlargement: The most reliable sign on lateral view is posterior displacement of the esophagus, often visualized with a barium swallow. Severe enlargement can cause dysphagia (dysphagia megalatriensis).

Enlargement Patterns - When Hearts Get Big

Left Atrium (LA): Straightening of the left heart border, a "double density" sign, and splaying of the subcarinal angle to >90°.
Right Atrium (RA): Increased convexity of the right heart border.
Left Ventricle (LV): The cardiac apex is displaced inferiorly and to the left.
Right Ventricle (RV): The cardiac apex is lifted upward, creating a "boot-shaped" heart. On a lateral view, it fills the retrosternal clear space.

Boot-shaped heart in Tetralogy of Fallot on chest X-ray

⭐ A globally enlarged, globular, "water-bottle" shaped heart on CXR strongly suggests a large pericardial effusion, which can mimic cardiomegaly.

The right heart border is formed by the Superior Vena Cava (SVC) and the Right Atrium.

The left heart border comprises the aortic knob, main pulmonary artery, and left ventricle.

A cardiothoracic ratio > 0.5 on a PA film is abnormal and suggests cardiomegaly.

The aortic knob forms the most superior part of the left cardiac silhouette.

The carina typically sits at the T4 vertebral level.

The left hilum is normally higher than the right.

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