Radiology:: Respiratory System

The first investigation for mediastinal lesions is a chest X-ray (CXR).

The mnemonic for anterior mediastinal lesions is 4T, which stands for: 1. Thymoma, 2. Teratoma, 3. Terrible lymphoma, 4. Thyroid lesions.

The most common posterior mediastinal lesion is neurogenic tumors.

The most common middle mediastinal mass overall is lymph node mass.

Bronchogenic cysts are the most common mediastinal lesions in children.

Neurogenic tumors are the most common type of posterior mediastinal lesions, typically evaluated using CE-MRI.

The clinical features of pneumomediastinum include:

• History of chest trauma or neck surgery
• Chest discomfort
• Crepitations over the neck or chest wall

The Postero-anterior (PA) view is the most common (m/c) view used in chest X-rays.

The Antero-posterior (AP) view is used for bedside imaging, typically with a portable x-ray unit for patients who are unable to stand.

The tube to film distance for the PA view is 6 feet, or 72 inches, or 180 cm.

In the PA view, the x-ray beam direction is posterior to anterior, while in the AP view, it is anterior to posterior.

The Antero-posterior (AP) view can lead to false cardiomegaly due to diverging x-ray beams.

Low KVP technique uses 60 - 80 KV, while high KVP technique uses 120 - 170 KV.

The low KVP technique provides a high contrast image, which is useful for detecting miliary nodules and lung parenchymal calcifications.

The high KVP technique increases penetration, making it useful for identifying abnormalities in hidden areas of the body and for imaging obese individuals.

1. PA projection
2. Erect position
3. Suspended end-inspiration (Prevents artefacts)

• Pneumothorax
• Foreign body aspiration: Detects air trapping
• Obstructive airway diseases: Chronic bronchitis/emphysema
• Diaphragmatic palsy

Lateral decubitus view is best to detect minimal pleural effusion (15-25 ml).

The right anterior oblique view is best for visualizing the sternum/esophagus during a barium swallow.

The lordotic view is best for detecting middle lobe pathologies.

The apicogram is the best view to visualize the lung apex.

Ultrasound (USG) is used for detecting pleural effusion.

The cardiothoracic ratio is used to assess heart size relative to the thoracic cavity, with a normal PA view ratio being < 0.50 and indicating cardiomegaly if > 0.50.

Normal findings on a chest X-ray include:

1. Retro-sternal lucency
2. Retro-cardiac lucency
3. Increased lucency along the vertebrae from above downwards
4. Posterior costo-phrenic recess, which is the most dependent part of the lung.

Adequate inspiration is indicated by the presence of 6 anterior ends or 10 posterior ends of ribs above the dome of the diaphragm.

Computed Tomography (CT) is used for diagnosing pneumomediastinum.

The key exposure factors to assess in a normal CXR are:

1. kVp (kilovolt peak)
2. mAs (milliampere-seconds)

The anatomical landmarks used for assessing centering and rotation in a chest X-ray include:

• Midline Landmark: Spinous process of upper thoracic vertebrae
• Lateral Landmark: Medial ends of clavicle

Proper centering in a chest X-ray is indicated by:

• The spine being central in the image.
• Equidistant measurements from both ends of the clavicle to the middle, shown as a=b (equidistant).

Signs of an improperly centered X-ray include:

• Non-parallel red dotted lines on each side of the spine.
• Measurements from both ends of the clavicle indicating a<b, suggesting patient rotation.
• Presence of unilateral radiolucency.

• Superior vena cava (SVC)
• Right atrium (RA)
• Inferior vena cava (IVC)

• Aortic Knuckle
• Main pulmonary artery (MPA)
• Left atrial appendage
• Left ventricle (LV)

The normal hilar shape is concave laterally.

A convex lobulated contour of the hilum is seen in conditions such as lymphadenopathy, tuberculosis (TB), or sarcoidosis.

• Normal: Left hilar level is higher or equal to right.
• Abnormal: Right hilar level is higher than left.

• Bronchi: Very little contribution.
• Lower lobe pulmonary veins: None.

• Dextrocardia with situs inversus
• Ciliary dysfunction leading to:
  • Recurrent respiratory infections
  • Bronchiectasis
  • Sinusitis
  • Nasal polyps
  • Infertility

• Pleural effusion: Blunting of costophrenic angle
• Right cardiophrenic angle: Site of Morgagni's hernia

The diaphragmatic level is lower on the left side than on the right due to the weight of the heart.

High KVP technique can visualize hidden areas that are poorly visualized due to bony/soft tissue overlap.

The presence of air below the diaphragm may indicate pneumoperitoneum.

A cervical rib articulates with the transverse process of C₇ and is associated with thoracic outlet syndrome, leading to compression of subclavian vessels and ischemia of the ipsilateral upper limb.

Scoliosis is measured by the Cobb's angle, which quantifies the lateral curvature of the spine.

The absence of a breast shadow on the side of mastectomy indicates the surgical removal of breast tissue, which is a common finding in post-mastectomy chest X-rays.

The silhouette sign indicates the presence of similar radiographic densities at the junction of structures, which can help identify pathologies such as consolidation or pleural effusion.

The order of radiographic densities from least to most dense is:

1. Air
2. Fat
3. Water
4. Bone
5. Metal

The Positive Silhouette Sign indicates that sharp radiographic borders are not visualized due to similar tissue densities of adjacent structures, often suggesting consolidation in the lung.

The right heart border is obscured due to consolidation in the right middle lobe (RML).

Consolidation in the right upper lobe (RUL) obscures the right upper mediastinal border.

Obscuration of the left heart border indicates consolidation in the lingular segment of the left upper lobe (LUL).

Obscuration of the dome of the diaphragm on the right side is due to consolidation in the right lower lobe (RLL).

The Positive Silhouette Sign is significant as it helps identify areas of lung consolidation, which can indicate pneumonia or other pulmonary infections.

The Air Bronchogram Sign indicates air within the bronchi but not in the alveoli, visible as linear branching lucencies on imaging. Common causes include:

• Infective consolidation (most common cause)
• Pulmonary edema
• Interstitial lung disease
• Bronchoalveolar carcinoma
• Pulmonary lymphoma
• Pulmonary infarct
• Pulmonary hemorrhage

In Staphylococcal Pneumonia, the characteristic features on chest X-ray (CXR) include:

• Pneumatoceles: Single or multiple air-filled cysts within the lung.

Clinical features include:

• Fever
• Cough with expectoration
• Breathlessness

Atypical/Mycoplasma Pneumonia presents with:

• Constitutional symptoms: Headache, myalgia
• Decreased LRTI symptoms
• Thickening of alveolar walls

CXR findings include:

• Reticular/nodular opacities

Key imaging findings include:

• Marked increase in density with obscuration of underlying blood vessels
• Presence of air bronchograms
• Consolidation in the affected lung areas

The reverse halo sign (atoll sign) is often associated with COVID-19 pneumonia and indicates areas of ground glass opacity surrounded by consolidation, suggesting an inflammatory process.

Imaging characteristics include:

• NSIP: Peripheral posterior subpleural ground glass opacity
• UIP: Honeycombing due to extensive fibrosis of alveoli

Typical clinical history includes:

• Dry cough
• Breathlessness
• Restrictive lung pattern observed in Pulmonary Function Tests

• Reticular interstitial opacities in the central perihilar regions.
• Subpleural blebs/pneumatoceles.
• Ground glass opacities (GGO) observed on HRCT.

• Cough with expectoration.
• High grade fever.
• History of chronic alcoholism and possible aspiration leading to the abscess.

• Causative agent: Aspergillus fumigatus (most common).
• History: Known case of tuberculosis (K/c/o TB).

• Lung cavity with mobile, dependent contents.
• Air crescent sign indicative of invasive aspergillosis.

• Bilateral multifocal involvement.
• Waterborne transmission via air conditioning systems or water coolers.

• Persistent rhinorrhea
• Nasal congestion
• Acute otitis media

The 'Thumb sign', which indicates a thickened and enlarged epiglottis on CXR.

• Protracted barking cough
• Inspiratory stridor

The 'Steeple sign', characterized by an elongated, narrow subglottic airway on CXR.

Post-primary Tuberculosis is the most common type in adults.

Imaging findings include apical cavitation with surrounding consolidation and the Tree in bud sign, indicating endobronchial spread of disease.

Miliary nodules are diffusely scattered nodules in bilateral lung fields due to hematogenous spread.

Other causes include infections (e.g., healed varicella, histoplasmosis), cardiac conditions (e.g., mitral stenosis), neoplasms (e.g., lymphangitis carcinomatosa), pneumoconiosis (e.g., coal workers pneumoconiosis), and allergic conditions (e.g., Loeffler's syndrome).

Cavitation is not seen in primary tuberculosis due to the absence of hypersensitivity to the tuberculosis antigen.

Ghon's focus is the lung parenchymal evidence of primary TB infection.

Ghon's complex includes Ghon's focus along with lymphatic and hilar lymph node involvement.

Ranke's complex refers to a calcified Ghon's complex.

Simon's focus is an apical nodule resulting from hematogenous spread from an extra-pulmonary primary TB.

Assman's focus is the reactivation of Simon's focus, typically located infraclavicularly.

Puhl's lesion, also known as Aschoff Puhl re-infection, is an isolated chronic pulmonary TB lesion in the lung apex.

Weigert focus is a sub-intimal caseating nodule found in the pulmonary vein.

Rasmussen's aneurysm is a pulmonary artery aneurysm that can lead to hemoptysis.

The best CXR view for detecting pleural effusion is the lateral decubitus view.

The investigation of choice (IOC) for minimal pleural effusion (5 - 10 mL) is ultrasound (USG).

The earliest sign of pleural effusion on a chest X-ray is blunting of the costophrenic angle.

The pleural meniscus sign indicates the presence of fluid in the pleural space.

An opaque hemithorax suggests a significant pleural effusion or white-out lung, indicating a large volume of fluid.

Ellis' S-curve indicates the highest point of a pleural effusion on the lateral half of the hemithorax.

The mediastinum is pushed to the opposite side.

The mediastinum is pulled to the same side as the lung collapse.

There is no shift in the mediastinum with consolidation.

Pleural effusion may appear as an increase in vasculature markings of the lung parenchyma.

A lamellar pleural effusion is characterized by a thin layer of fluid along the lung's edge, often visible on an erect X-ray.

The presentation includes dyspnea on exertion, basal crepitations, and bipedal edema.

A tension pneumothorax is characterized by air trapped at high pressure in the pleural cavity, constituting a medical emergency.

The best CXR view for diagnosing tension pneumothorax is the expiratory CXR.

The initial imaging of choice for tension pneumothorax is a CT scan.

Tension pneumothorax occurs when air enters the pleural cavity, leading to a one-way valve effect. This results in:

• Positive intrapleural pressure
• Mediastinal shift
• Compression of the SVC and IVC, causing decreased venous return and cardiac output, ultimately leading to patient collapse.

The clinical features include:

• Mechanical ventilation
• Hypoxia
• Increased JVP
• Tachycardia
• Hypotension

The treatment involves:

1. Needle thoracocentesis
2. Intercostal drain tube insertion
   • For children: 2nd ICS in mid-clavicular line
   • For adults: 5th ICS in anterior to mid-axillary line

Ultrasound assessment (POCUS) for pneumothorax includes observing the sliding pleural line:

• Normal: Sliding movement of the pleural line with respiration
• Pneumothorax: Absent sliding movement

B-lines are vertical bright lines seen in ultrasound imaging that indicate normal lung conditions.

A-lines are horizontal bright lines in ultrasound imaging that suggest pneumothorax, formed by USG rays being reflected back by air.

The seashore sign indicates normal lung conditions, characterized by a distinct pattern of lines and textures in the ultrasound image.

The stratosphere/barcode sign indicates pneumothorax, characterized by a layered pattern with fine, closely spaced horizontal lines.

The most common anterior mediastinal lesion is thymoma.

The signs of pneumomediastinum visible on a chest X-ray include:

1. Spinnaker sail/angel wing sign: Air outlines the thymus gland.
2. Continuous diaphragm sign: Air between the heart and diaphragm.
3. Naclerio's V sign: 'V' shaped lucency lining the descending thoracic aorta and diaphragm.

A Solitary Pulmonary Nodule (SPN) is defined as being less than 3 cm in size.

The first investigation for a Solitary Pulmonary Nodule (SPN) is a Chest X-ray (CXR).

The investigation of choice (IOC) for a Solitary Pulmonary Nodule (SPN) is Contrast-Enhanced Computed Tomography (CECT).

Common clinical features of a Pancoast tumor include:

1. Cough
2. Hemoptysis
3. Ipsilateral Horner's syndrome (due to cervical sympathetic ganglion involvement):
   • Ptosis
   • Anhydrosis
   • Miosis
4. Pain, paresthesia, weakness in the ipsilateral upper limb (due to brachial plexus nerve root involvement).

The investigation of choice (IOC) for Pancoast tumors is Contrast-Enhanced Magnetic Resonance Imaging (CE-MRI) to visualize neural invasion.

The exception for the investigation of choice for lung tumors is Pancoast tumors, for which the IOC is CE-MRI instead of CECT.

• Cough with hemoptysis
• Recurrent chest infections

HRCT (High-Resolution Computed Tomography) is the investigation of choice for bronchiectasis.

1. Tram-track sign: Parallel enlarged bronchi.
2. String of beads sign: Varicose dilatations in long axis.
3. Signet ring sign: A dilated bronchus adjacent to a smaller artery.
4. Cluster of grapes sign: A cluster of air-filled spaces resembling grapes.

• Mild cough in middle-aged patients.
• Elevated ACE levels.

Bilateral hilar lymphadenopathy: Enlarged densities in the hilar regions of both lungs.

The Lambda sign indicates increased uptake in the paratracheal lymph nodes and bilateral hilar lymph nodes.

The Panda sign indicates increased uptake in the lacrimal gland, nasopharynx, and parotid glands.

The most common aspirated foreign body in children is a peanut, which is not radio-opaque.

The management for peanut aspiration in children is bronchoscopy.

On an X-ray, a coin in the esophagus appears en face.

On an X-ray, a coin in the trachea appears slit-like.

The management for a coin lodged in the esophagus is esophagoscopy.

The management for a coin lodged in the trachea is bronchoscopy.

Immediate esophagoscopy/bronchoscopy is required to manage button battery ingestion.

Complications include:

• Esophageal perforation
• Tracheo-esophageal fistula
• Aortic aneurysm
• Vertebral discitis

The mnemonic SLAB of Calcium stands for:

• Sarcoidosis
• Lymphoma (Post-radiotherapy)
• Amyloidosis
• Blastomycosis
• Silicosis
• Coal worker's pneumoconiosis
• Scleroderma

The split pleura sign indicates pleural wall enhancement, which is a characteristic feature of empyema. It shows:

• Lateral wall: Parietal pleura
• Medial wall: Visceral pleura

1. Loss of aeration -> Change in density.
2. Displacements of interlobar fissures (most reliable).
3. Crowding of blood vessels.

1. Mediastinal shift.
2. Diaphragmatic shift.
3. Hilar shift.
4. Crowding of ribs.
5. Compensatory hyperinflation of opposite lung.

The Golden S sign is observed in the context of a central mass lesion causing Right Upper Lobe (RUL) collapse, characterized by:

• Lateral concavity at the RUL collapse
• Mass in the RUL medial convexity

The Luftsichel sign indicates hyperinflation of the Left Lower Lobe (LLL) with the aortic knuckle lined by the superior segment of the LLL, typically seen in Left Upper Lobe (LUL) collapse.

Chronic RML collapse can lead to bronchiectasis, which is characterized by the abnormal dilation of the bronchi due to recurrent infections and inflammation.

Lady Windermere Syndrome involves RML and lingual involvement, leading to suppression of cough and increased retention of secretions, which results in recurrent infections.

The Superior A Sign indicates left lower lobe (LL) collapse, which can be associated with changes in the mediastinum and heart rotation.

The Juxta phrenic Sign indicates any upper lobe collapse, which is characterized by loss of volume in the upper lobe and a peak in the diaphragmatic contour.

RLL collapse can lead to a rotation of the heart, which may be observed on imaging studies.