Thorax and Abdomen
1 Chest
Anatomy & Pathology
Thoracic Cavity Overview
The thoracic cavity extends from the thoracic inlet to the diaphragm and is divided into three compartments: two pleural cavities (each containing a lung) and the mediastinum (central compartment containing the heart and great vessels).
Respiratory System
- Pharynx – Musculomembranous passage behind the nasal and oral cavities; conducts air to the larynx.
- Larynx (voice box) – Cartilaginous structure at the level of C3–C6; includes the thyroid cartilage (“Adam’s apple”) and cricoid cartilage; serves as the entrance to the trachea.
- Trachea (windpipe) – Airway extending from the larynx to the carina (≈ T4–T5); composed of C-shaped cartilage rings; bifurcates into the right and left mainstem bronchi.
- Carina – Ridge at the bifurcation of the trachea; important landmark for endotracheal tube placement (ETT should terminate 1–2 inches above).
- Bronchi –
- Right mainstem bronchus – Wider, shorter, and more vertical (common site for aspirated objects).
- Left mainstem bronchus – Longer and more horizontal, passing inferior to the aortic arch.
- Bronchioles and Alveoli – Terminal airways and microscopic air sacs responsible for gas exchange with pulmonary capillaries.
Lungs and Pleura
- Lungs – Cone-shaped organs composed of spongy parenchyma.
- Apex – Superior tip extending above clavicle.
- Base – Rests on the diaphragm.
- Lobes – Right lung (3 lobes: superior, middle, inferior); left lung (2 lobes: superior, inferior).
- Fissures – Oblique (both lungs) and horizontal (right only) separate lobes.
- Pleura – Double-walled serous membrane surrounding each lung.
- Visceral pleura – Covers the lung surface.
- Parietal pleura – Lines thoracic cavity.
- Pleural cavity – Potential space between layers; may contain air (pneumothorax) or fluid (pleural effusion).
- Costophrenic angles – Inferolateral recesses of the pleural cavity where diaphragm meets ribs.
- Cardiophrenic angles – Medial recesses where heart and diaphragm meet; blunting indicates pathology.
Mediastinum
The mediastinum lies between the lungs and contains vital thoracic structures:
- Heart – Located obliquely, 2/3 left of midline.
- Great vessels – Include the aortic arch, ascending aorta, pulmonary arteries, and superior/inferior vena cava.
- Thymus gland – Prominent in infants and children; shrinks after puberty.
- Esophagus and trachea – Pass vertically through posterior mediastinum.
- Hila (roots of lungs) – Regions where bronchi, pulmonary vessels, lymphatics, and nerves enter and exit each lung.
Bony Thorax
Serves as a protective framework and provides attachment for respiratory muscles.
- Sternum – Consists of the manubrium, body, and xiphoid process.
- Clavicles – Articulate with manubrium at sternoclavicular joints; visible on PA chest as upper boundaries.
- Ribs (12 pairs) – Curve around thorax, articulating with thoracic vertebrae posteriorly and costal cartilage anteriorly.
- Thoracic vertebrae (T1–T12) – Form posterior boundary of thorax; T7 corresponds to the level of the inferior angle of the scapula (central ray for PA chest).
- Scapulae – Posterior shoulder blades; rolled forward to clear lung fields on PA projection.
Surface and Positional Landmarks
- Jugular notch (suprasternal notch) – At superior border of manubrium, level of T2–T3.
- Vertebra prominens (C7) – Palpable landmark for locating T1.
- Xiphoid process – Inferior tip of sternum, level of T9–T10.
- Inferior angle of scapula – Level of T7 (used for centering PA chest).
Common Pathologies
- Atelectasis – Partial or complete collapse of lung tissue caused by obstruction or hypoventilation. Appears as increased density and possible tracheal deviation toward the affected side.
Exposure adjustment: Increase mAs or kVp slightly to penetrate denser lung regions. - Pleural Effusion – Accumulation of fluid in the pleural cavity. Demonstrated by blunting of costophrenic and cardiophrenic angles or a meniscus sign on upright or decubitus views.
Exposure adjustment: Increase mAs or kVp moderately to compensate for increased fluid density. - Pneumothorax – Air in the pleural space causing lung collapse and mediastinal shift away from the affected side. Appears as absence of lung markings with sharp lung edge visible.
Exposure adjustment: Decrease mAs slightly because air increases overall radiolucency. - Pneumonia – Inflammation and consolidation of lung parenchyma due to infection. Appears as patchy or lobar opacity with air bronchograms.
Exposure adjustment: Increase mAs moderately to penetrate dense consolidation. - Emphysema – Chronic overdistention of alveoli leading to loss of elasticity and hyperinflation. Lungs appear radiolucent with flattened diaphragms and elongated lung fields.
Exposure adjustment: Decrease mAs to avoid overexposure due to excess air. - Congestive Heart Failure (CHF) – Cardiac enlargement and pulmonary congestion from impaired circulation. Radiographic signs include an enlarged cardiac silhouette and perihilar “bat-wing” opacities.
Exposure adjustment: Increase mAs moderately for fluid-filled lungs. - Chronic Obstructive Pulmonary Disease (COPD) – Group of disorders (including emphysema and chronic bronchitis) causing airflow limitation and air trapping. Radiographs show hyperinflated lungs with flattened diaphragms.
Exposure adjustment: Decrease mAs slightly because of hyperaeration. - Aspiration – Inhalation of foreign material into airways, most often the right main bronchus. Appears as localized opacity corresponding to aspirated contents.
Exposure adjustment: No routine change, unless large areas of consolidation are present. - Pulmonary Embolism (PE) – Blockage of pulmonary artery by thrombus or embolus. May appear normal radiographically but requires clinical correlation or CT angiography.
Exposure adjustment: No change (density unaffected). - Lung Cancer (Bronchogenic Carcinoma) – Malignant growth arising from lung tissue or bronchi. Appears as solitary or multiple nodules or masses; may cause atelectasis or obstructive pneumonia.
Exposure adjustment: No routine change, unless large mass increases local density.
Routine Projections
PA Chest (Upright)
CR Location & Positioning
- SID: 72 inches (reduces heart magnification)
- Patient position: Upright, facing IR, MSP centered
- Adjustments: Chin raised, shoulders rolled forward and down to move scapulae out of lung fields; hands on hips or handles
- CR: Perpendicular to IR at level of T7 (7–8 inches below vertebra prominens or at inferior angle of scapula)
- Patient instructions: Take a deep breath in, hold it
- Exposure: On full inspiration (two inspirations preferred)
Evaluation Criteria
- Coverage: Entire lungs from apices to costophrenic angles
- Rotation checks: Sternoclavicular joints equidistant from spine
- Motion checks: Sharp vascular markings, visible spine through heart shadow
- Technique checks: Adequate contrast with 10 posterior ribs above diaphragm
- Clinical aim: Evaluate lung fields, heart size, and mediastinal structures
AP Chest (Upright or Semi-Erect)
CR Location & Positioning
- SID: 72 inches
- Patient position: Upright or semi-erect, back against IR
- Adjustments: Chin raised, shoulders relaxed, arms at sides
- CR: Angled caudad ~5° to be perpendicular to long axis of sternum, centered at T7
- Patient instructions: Deep inspiration, hold it
- Exposure: On full inspiration
Evaluation Criteria
- Coverage: Both lungs from apices to costophrenic angles
- Rotation checks: Sternoclavicular joints symmetric
- Motion checks: Sharp lung markings, clear diaphragm outline
- Technique checks: Clavicles projected just below apices, adequate contrast for vascular markings
- Clinical aim: Evaluate lungs when PA projection is not possible (bedside, trauma, immobile patients)
Lateral Chest (Upright)
CR Location & Positioning
- SID: 72 inches
- Patient position: Upright, left side against IR (to minimize heart magnification)
- Adjustments: MSP parallel to IR; arms raised above head or holding bar; chin elevated
- CR: Perpendicular at level of T7 (3–4 inches below jugular notch)
- Patient instructions: Deep inspiration, hold it
- Exposure: On full inspiration
Evaluation Criteria
- Coverage: Entire lungs from apices to costophrenic angles
- Rotation checks: Posterior ribs superimposed, sternum in lateral profile
- Motion checks: Sharp lung and diaphragm borders
- Technique checks: Adequate density to visualize retrocardiac lung field
- Clinical aim: Evaluate depth of pathology, heart size, and retrosternal/retrocardiac regions
AP Supine (Bedside Chest)
CR Location & Positioning
- SID: 40–48 inches (mobile)
- Patient position: Supine, MSP centered, arms at sides
- Adjustments: Chin raised, shoulders relaxed
- CR: Angled caudad ~5° to be perpendicular to sternum, centered at T7 (3–4 inches below jugular notch)
- Patient instructions: Deep inspiration, hold it
- Exposure: On full inspiration
Evaluation Criteria
- Coverage: Both lungs included; apices through costophrenic angles
- Rotation checks: SC joints symmetric
- Technique checks: 8–9 posterior ribs above diaphragm (less inspiration expected)
- Clinical aim: Portable evaluation of lungs and pleura in trauma or critically ill patients
Supplementary Projections
AP Lordotic (Apical Lordotic Projection)
CR Location & Positioning
- SID: 72 inches
- Patient position: Upright, 1 foot from IR, leaning back so shoulders rest on IR
- Adjustments: Hands on hips, shoulders rolled forward
- CR: Perpendicular to midsternum (3–4 inches below jugular notch)
- Patient instructions: Deep inspiration, hold it
Evaluation Criteria
- Coverage: Lung apices free of superimposition
- Rotation checks: SC joints symmetric
- Technique checks: Clavicles nearly horizontal and projected above apices
- Clinical aim: Demonstrates apical pathology (tuberculosis, neoplasm)
Lateral Decubitus (Horizontal Beam)
CR Location & Positioning
- SID: 72 inches
- Patient position: Lateral recumbent, side of interest against IR
- Adjustments: Arms above head, chin raised
- CR: Horizontal beam to level of T7 (3–4 inches below jugular notch), centered to MSP
- Patient instructions: Deep inspiration, hold it
Evaluation Criteria
- Coverage: Entire lung field on dependent side
- Rotation checks: SC joints symmetric
- Clinical aim: Detect air-fluid levels or free intrapleural air (fluid side down, air side up)
Chest Pathology and Exposure Adjustment Summary
| Pathology | Radiographic Appearance | Exposure Adjustment | Key Considerations |
|---|---|---|---|
| Atelectasis | Increased density; possible tracheal deviation toward affected side | ↑ mAs or kVp slightly | Collapsed lung increases tissue density |
| Pleural Effusion | Fluid level with meniscus sign; blunted costophrenic angles | ↑ mAs or kVp moderately | Fluid absorbs more radiation — use upright or decubitus |
| Pneumonia | Patchy or lobar consolidation | ↑ mAs moderately | Fluid-filled alveoli reduce beam transmission |
| Pulmonary Edema / CHF | Enlarged heart; “bat-wing” perihilar pattern | ↑ mAs moderately | Fluid overload and venous congestion |
| Emphysema | Hyperinflated, radiolucent lungs; flattened diaphragm | ↓ mAs | Excess air increases radiolucency |
| COPD (Chronic Bronchitis / Emphysema) | Hyperaeration, flattened diaphragm, elongated lungs | ↓ mAs slightly | Reduced attenuation due to chronic air trapping |
| Pneumothorax | Absence of lung markings; lung edge visible | ↓ mAs slightly | Air increases radiolucency; use upright/expiration |
Hows & Whys of Chest Radiography
Anatomy
- How many lobes does each lung have, and why does this matter?
The right lung has three lobes; the left has two to accommodate the heart. Knowing lobe divisions helps localize pathology. - How do the right and left mainstem bronchi differ?
The right mainstem bronchus is shorter, wider, and more vertical than the left, making it a common site for aspirated foreign bodies. - Which lung will foreign bodies most often localize in?
The right lung, because the right main bronchus is larger and more vertical than the left. - How do the costophrenic and cardiophrenic angles help in diagnosis?
Blunting of these angles indicates pleural effusion or cardiomegaly. - How can the carina help evaluate endotracheal tube placement?
The carina is the bifurcation of the trachea; correct tube placement ends 1–2 inches above it. - How does the mediastinum change with patient position?
In supine position, mediastinal structures appear widened due to projection and fluid redistribution. - Which way does the diaphragm move on inspiration? On expiration?
Down on inspiration; up on expiration. - Why?
The diaphragm is a dome-shaped muscle. When it contracts, it flattens and moves downward, creating negative pressure in the thoracic cavity so air flows into the lungs.
When it relaxes, it returns to its dome shape, compressing the lungs and forcing air out.
Positioning
- Why should chest radiographs be performed upright?
To allow full lung expansion and to demonstrate air-fluid levels and pleural effusions accurately. - Why is 72-inch SID used?
It minimizes heart magnification and improves spatial resolution of lung detail. - Why is a PA projection preferred over an AP?
It reduces heart magnification, provides better spatial resolution, and lowers breast dose. - Why are shoulders rolled forward on the PA view?
To move the scapulae laterally, clearing the lung fields. - Why is the chin elevated for PA and lateral views?
To prevent superimposition of the chin on lung apices. - Why is a left lateral preferred?
It places the heart closer to the IR, reducing magnification. - Why angle the CR caudad for AP projections?
To project the clavicles below the apices and avoid obscuring them. - Why are decubitus projections used?
To demonstrate air-fluid levels with a horizontal beam when the patient cannot stand.
Technique & Image Evaluation
- How do you know the patient took a full inspiration?
Ten posterior ribs should be visible above the diaphragm. - How do you check for rotation on PA chest?
Sternoclavicular joints are equidistant from the spine. - How do you detect motion on a chest radiograph?
Vascular markings and diaphragm borders should be sharp with no blurring. If they are blurred, motion has occurred. - How do you check for rotation on a lateral?
Posterior ribs are superimposed and sternum appears in profile. - How do you know exposure is appropriate?
The thoracic spine should be faintly visible through the heart shadow, indicating sufficient penetration without overexposure. - What happens if exposure time is too long?
Motion blur obscures vascular markings and diaphragm borders. - How do you identify under-inspiration?
Less than ten posterior ribs visible, diaphragm appears high, and heart looks enlarged. - How do you confirm correct positioning for a decubitus chest?
No rotation (SC joints symmetric) and horizontal beam clearly showing air or fluid shift.
Clinical Applications
- Why are chest x-rays often the first imaging exam performed?
They provide rapid, low-dose assessment of lungs, heart, and thoracic structures. - When would expiration be used for chest imaging?
When we need to identify possible pneumothorax. - How can pleural effusion be demonstrated best?
With an upright or side-down decubitus projection (fluid rises when side up, layers when side down). - How can pneumothorax be demonstrated best?
With an upright or side-up decubitus projection, often on expiration to accentuate trapped air. - Why are decubitus views ordered for trauma or post-surgical patients?
They demonstrate free air or fluid when upright imaging isn’t possible. - How does COPD or emphysema affect exposure technique?
Decrease mAs slightly — the lungs are hyperinflated and radiolucent. - How does pneumonia or pleural effusion affect exposure technique?
Increase mAs moderately to compensate for denser, fluid-filled lung tissue. - Why is repeatability important in chest imaging?
Comparing current and prior studies allows monitoring of disease progression or resolution.
