1.1 CHEST OVERVIEW
Ultrasound (US) is a noninvasive, relatively inexpensive and most rewarding imaging modality, carries no radiation burden, but not much exploited for evaluation of chest disease because of basic (inherent) properties of US waves not to pass through bony cage and air-filled lungs. However, over a couple of years, US has emerged as a useful tool in evaluating wide range of perplexing clinical problems of chest due to presence of fluid in pleural space, consolidating or atelectatic lung or even tumor, provide window for US to penetrate and this has helped in diagnosis of certain conditions or limit the differential diagnosis (DD) of conditions under consideration.
- Chest wall (Fig. 1.1.1): It has helped in diagnosing soft tissue abscesses, masses, osteomyelitis, rib tumors and even fracture where plain X-ray gives only soft tissue swelling or obliteration of costophrenic angle (may be due to pleural fluid or sometimes by rib tumor) and also where rib erosion is due to underlying carcinoma. Sometimes, when clinically mass is suspected with fractures, US can be used as a first modality particularly in children to avoid radiation by getting an X-ray chest.
- Mediastinum: Anterior mediastinum can be very well-evaluated by US through suprasternal route by elevating shoulders and extending the neck. This will avoid structures particularly thymus in children. Even paratracheal and hilar adenopathy can be diagnosed especially in tubercular patients where it is not only helpful in diagnosis but also in follow-up when child is on antitubercular therapy, thus avoiding unnecessary radiation and getting repeated X-rays.
- Lung parenchyma: It is also helpful in differentiating cystic lesions of the lung parenchyma like hydatid cyst (Fig. 1.1.2) consolidation (Figs. 1.1.3 to 1.1.5), collapse and tumor of lung. Also differentiates a tumor and pleural fluid/consolidation above the diaphragm from (subpulmonic effusion) below the diaphragm.
- Fig. 1.1.2: Lung hydatid seen as anechoic cystic lesion in transverse scan of lung. (SOL: space occupying lesion; RT: right)Fig. 1.1.3: Consolidation—seen as a homogeneous hypoechoic lesion with air bronchogram in right lower lobe of lung.Figs. 1.1.5A and B: US scans show lobar consolidation with presence of color flow on color Doppler flow imaging (CDFI). (M: mass)It is also helpful in diagnosing minimal amount of fluid in pleural cavity, even 5–10 mL of fluid, thus avoiding need of lateral decubitus film/lateral chest film.
- It also gives the etiology of pleural fluid due to its appearance as anechoic, hypoechoic, echogenic, presence of debris, nodules and types of septa.
- Anechoic—all transudates are anechoic, however, all anechoic collections are not transudates. About one-third of exudative collection tends to be anechoic in the beginning.
- Hypoechoic—Usually exudative effusions, empyema and later stages of hemothorax.
- Echogenic—Hemothorax or empyema.
- Debris—Represents settled down pus cell, blood cells, etc.
- Septations—Usually represent process of loculation and fibrosis occurring in pleural effusion. Thin clean septa with no or very minimal debris—tubercular pleural effusion. However, thick, shaggy irregular septations with debris—pyogenic effusion.
- Pleural nodule/masses (Figs. 1.1.6A to C), represent meso-thelioma, metastatic nodule and tuberculomata. In addition to characteristics septations the thickness of parietal pleura and combined (parietal + visceral) also give etiological diagnosis. As tubercular pleural effusion-parietal pleural thickness varies 2–8 mm and combined pleural varies from 4–10 mm. In pyogenic pleural effusion, parietal pleural thickness varies from 5–22 mm and combined 8–27 mm. In hemothoraces (post-traumatic) thick irregular mantle of pleura around hypoechoic pleural collection is seen, pleural thickness varies from 12–18 mm.Pleural effusion v/s ascites: Bare area sign—if fluid interface is abutting the bare area of liver than it is pleural effusion and if it is not than it is ascites.Diaphragmatic crus sign—pleural effusion is posterolateral and superior to crus of diaphragm while ascites is anteromedial and inferior to crus of diaphragm.
- Intervention: US is very helpful in fine needle aspiration biopsy, pleural tapping, guided pleural aspiration and tube placement.
- ICU: US is very helpful in critically ill-patients that is trauma and ICU-needs serial X-rays to see day-to-day changes in lesions like consolidation and lung abscess (Fig. 1.1.7), particularly when there is inability to position the patient as required and usually substandard quality of X-rays.
Figs. 1.1.6A to C: US scans show pulmonary mass with color flow associated with mild pleural effusion causing compression atelectasis of underlying parenchyma and hepatic metastases. (M: mass)
- Limited information about mediastinum, hilar and proximal airways
- Limited information of the underlying lung parenchyma in the setting of complex pleural and lung parenchymal disease.
- No preferred for complicated interventional procedures, such as empyema drainage with a pigtail catheter or biopsy of pleural masses.
- Restricted field of view
- Familiarity of clinician
- Operator dependent.
- Lower cost
- Increase flexibility
- No radiation
- Good guidance tool
- Repeated evaluation with no radiation cost
- Portability in ICU settings
- Better in differentiating pleural effusion from pleural thickening
- More sensitive than X-ray in differentiating pleural fluid from consolidation
- Ultrasound guidance is associated with a reduced risk of pneumothorax during thoracentesis.
Ability to detect abdominal lesions associated with causative of chest lesion as liver abscesses leading to pleural effusion.
1.2 PLEURAL EFFUSION
Pleural effusion can be transudative or exudative.
Signs of pleural fluid on USG:
Transudative effusion: Pleural (fluid) that changes shape with respiration.
- Fluid with floating echodensities
- Septations—thick and shaggy (Figs. 1.2.1A to C)
- Fibrin strands
- May be anechoic fluid
- Echogenic fluid (Fig. 1.2.2)
- Pleural nodules
- Thickened pleura.
Causes of Transudative Pleural Effusion
- Increased hydrostatic pressure
- Congestive heart failure
- Superior vena cava (SVC) obstruction
- Constrictive pericarditis.
- Decreased osmotic pressure
- Cirrhosis with ascites
- Peritoneal dialysis
- Acute glomerulonephritis
- Nephrotic syndrome
- Figs. 1.2.1A to C: (A) Pleural effusion superior to the diaphragm; (B) Pleural effusion and ascites outlining the diaphragm; (C) Ascites only. Irregular outline of the gut is seen due to ascites. (L: liver)Fig. 1.2.2: Longitudinal intercostal view in a patient with pleural effusion showing echogenic surface of visceral and parietal pleura.
- Parapneumonic effusion
- Empyema (see Fig. 1.1.7)
- Fungi (nocardia, actinomycosis).
- Pleural metastasis
- Pleural mesothelioma
- Bronchogenic carcinoma
- Lymphoma.Fig. 1.2.5: Multiseptated fluid collection seen in right pleural cavity in the case of infected pleural effusion.Fig. 1.2.8: US scans show hydropneumothorax with compression atelectasis of underlying pulmonary parenchyma. (PLS: pleural lung scan)Fig. 1.2.9: US scan shows tuberculous pleural effusion with pleural thickening. (PLE: pleural effusion)
- Pulmonary emboli.
- Collagen vascular disease
- Systemic lupus erythematosus (SLE)
- Rheumatoid arthritis.
- Abdominal disease
- Subphrenic abscess
- Drug induced effusion
- Acute respiratory distress syndrome (ARDS).
1.3 PLEURAL PLAQUE
Common causes of pleural plaque includes:
- Asbestos exposure
- Pulmonary infarction
- Chemical pleurodesis
- Drug-related pleural disease.
Plaques resulting from asbestos exposure are usually confined to the parietal pleura. Ultrasound demonstrates pleural plaques as smooth, elliptical, hypoechoic pleural thickening.
Visceral pleural plaques are differentiated from parietal pleura by observing the ‘gliding sign’ during respiration.
Calcified pleural plaques are irregular, echogenic and produce acoustic shadowing and comet tail artifact.
Differential diagnosis to be considered while diagnosing pleural plaques:
- Diffuse pleural thickening
- Extrapleural fat
- Pleural tumors
- Pleural pseudotumors
- Rib fracture.
1.4 PLEURAL MASSES
- Loculated pleural effusion
- Malignant mesothelioma
- Pleural fibroma
- Fibrin balls.
Loculated Pleural Effusion
Anechoic collection seen within the pleural cavity.
- Malignant cell implantation on the pleura (common causes: lung, breast and GIT cancers)
- Obstruction of pleura or pulmonary lymphatics (common causes: lymphoma, breast cancer)
- Obstruction of pulmonary veins usually by lung cancers
- Malignant cells shed freely into pleural space
- Obstruction of thoracic ducts, resulting in chylous effusion (usually due to lymphoma).
Sonographic findings favoring malignant etiology.
- Solid nodules in the pleural space
- Circumferential pleural thickening
- Nodular pleural thickening or >1 cm pleural thickening
- Pleural thickening involving the mediastinal pleura.
Malignant mesothelioma is a rare and usually fatal pleural tumors associated with asbestos exposure.
Diffuse pleural thickening, often nodular and irregular (86%).
- Calcification in pleura (74%)
- Focal pleural mass (25%).
Rib destruction occurs with advanced disease.
Pleural Fibroma (Local Benign Mesothelioma)
A smooth lobular mass, 2–15 cm diameter arising more frequently from the visceral pleura.
- Pedunculated mass changes shape with respiration (30–50%)
- Forms an obtuse angle with the chest wall.
These develop in serofibrinous pleural effusion and become visible following absorption of fluid.
- Small and tend to be situated near the lung base.
- May disappear spontaneously or remain unchanged for many years.
1.5 MEDIASTINAL LYMPHADENOPATHY
Right paratracheal and tracheobronchial nodes are most commonly involved
Bilateral hilar with or without right paratracheal, aortopulmonary window lymphadenopathy
Superior mediastinum most common site with or without unilateral or bilateral hilar nodes
In non-Hodgkin lymphoma (NHL) involvement of other nodal groups (cardiophrenic, posterior media stinal) also seen more commonly
Mild homogeneous enhancement to rim enhancement
Homogeneous mild to moderate enhancement
Mild homogeneous enhancement
May show calcification
May show rim calcification
Calcification unusual without treatment
More likely to be confluent
May be confluent with large nodal masses
1.6 VASCULAR LESIONS OF MEDIASTINUM
Ultrasound is an excellent, noninvasive method of diagnosing masses of vascular origin in the mediastinum.
Vascular nature of a suspected mass can be confirmed by ultrasound using imaging supplemented by color flow and spectral Doppler effect:
- Tortuous brachiocephalic artery
- Aneurysm of the aorta
- Aneurysm of the sinus of Valsalva
- Right-sided aortic arch
- Double aortic arch
- Dilated superior vena cava.
1.7 CYSTIC MASSES OF MEDIASTINUM
- Congenital cyst (Benign)
- Bronchogenic cyst
- Pericardial cyst
- Esophageal duplication cyst
- Neuroenteric cyst
- Thymic cyst.
- Mature cystic teratoma
- Meningocele (Lateral)
- Cystic degeneration
- Hodgkin's disease
- Metastasis to lymph nodes
- Nerve root tumors
- Mediastinal abscess
- Pancreatic pseudocyst.
Ultrasonography can be useful in evaluating a mass adjacent to pleural surface or cardiophrenic angle. At US, the benign cysts typically appear as anechoic thin-walled masses with increased through transmission.
- Ultrasound is used to characterize wall thickness, septations, vascularity, appearance of internal fluid, location and relationship to adjacent structures.
Pericardial cyst-results from aberrations in the formation of celomic cavities. Pericardial cysts are invariably connected to the pericardium but only a few cases unable to show communication with the pericardial sac. Thus ultrasound can help in detecting the pericardial involvement.
The majority of pericardial cysts arise in anterior cardiophrenic, more commonly on the right side. Occasionally cysts are pedunculated.
Mature Cystic Teratoma
These are cystic tumors composed of well-differentiated derivations from at least two of the three germ layers.
Majority of dermoid cysts are in the anterior mediastinum.
Most cystic teratoma are multilocular but unilocular cystic lesions also occur.
They may contain four types of tissues-including fluid, fat, soft tissues, calcium but fluid containing cystic component are usually prominent.
A fat fluid level within the mass is highly specific finding but is seen less frequently.
Many tumors and lymph nodes can undergo cystic degeneration and demonstrate mixed solid and cystic elements. If degeneration is extensive, the appearance of the lesion is indistinguishable from those of a congenital cyst. Cystic degeneration of a solid mass is more likely to occur after radiation therapy or chemotherapy but may be seen prior to treatment.
- A mediastinal abscess or pancreatic pseudocyst appears as a fluid containing mediastinal cystic mass, but clinical features usually permit differentiation from true cysts or neoplasms.
Bilateral diaphragmatic elevation
- Abdominal cause (USG useful by showing fluid, fetus or an abdominal mass as the cause)
- Any large abdominal mass.
- Pulmonary causes—USG little use
- Chext X-ray/CT required making the diagnosis.
- Neuromuscular disorders
- Myasthenia gravis—chest CT may show thymoma.
- Amyotropic lateral sclerosis—USG is of little use.
- MRI required for diagnosis.
Unilateral Diaphragmatic Elevation
Subpulmonic Pleural Effusion
- Ultrasound confirmatory
- Shows the presence of fluid is pleural cavity with normal relative position of both domes of diaphragm.
- Chest X-ray/CT will confirm the cause for diaphragmatic elevation and relation to diaphragm with other structures.
Phrenic Nerve Paralysis (Diaphragmatic Paralysis)
- May occur due to:
- Primary lung tumor
- Malignant mediastinal
- Diagnosis is made on USG by observing the absent or paradoxical movement on the affected side with usual or exaggerated excursion on the opposite side. Paradoxical movement can be elicited by the coughing or sniffing tests.
Fig. 1.8.1: Liver in transverse scan—right lobe of liver. (Ao: aorta; IVC: inferior vena cava; PV: portal vein)
Fig. 1.8.2: Longitudinal image showing the various relation along the anteroposterior extent of the diaphragm on right side.
- Subphrenic abscesses
- In appropriate clinical setting usually history of surgery
- USG shows—elevated hemidiaphragm
- Reduced or absent movement of the ipsilateral diaphragm
- Usually ipsilateral pleural effusion present
- Liver mass: Tumor, echinococcal cyst, abscess
- Distended stomach or colon
- Interposition of colon.
Diaphragmatic Hernia (Fig. 1.8.3)
- USG may show the discontinuity of the dome of diaphragm
- Bowel, spleen, kidney may be visualized inside thorax above dome of diaphragm
- Contralateral displacement of heart is visualized
- In congenital diaphragmatic hernia, polyhydramnios may be associated after 25 weeks.
Eventration of Diaphragm
- Complete—more commonly on left
- Partial—more commonly on right
- Complete eventration of diaphragm can be diagnosed by ultrasound
- Traumatic—blunt or penetrating trauma
- Infection—ruptured amebic liver abscess
- In post-traumatic rupture in large, usually over 10 cm, defects ultrasound may detect—disruption of diaphragmatic echoes. Herniation of abdominal viscera into thorax-associated pleural effusion. Sometimes, small diaphragmatic rents may be difficult to detect, but due to availability of high frequency transducers, it is now possible to detect small disruption of diaphragmatic contour.
Fig. 1.8.3: Diaphragmatic hiatus for inferior vena cava (IVC), esophagus and aorta. (PE: pleural effusion)
- Very rarely diaphragmatic neoplasms
- Primary—various types of sarcomasFig. 1.8.4: Amebic liver abscess—a hypoechoic space-occupying lesion (SOL) is seen in the posterosuperior aspect of liver with evidence of posterior enhancement. It is extending into subdiaphragmatic space.Fig. 1.8.5: Subdiaphragmatic collection—fluid collections with multiple internal septae is seen below the diaphragm.
- Secondary—local invasion by adjacent pleural, peritoneal, thoracic and abdominal wall malignancies
- Distant metastasis from bronchogenic or ovarian carcinoma
- Wilms’ tumor and osteogenic sarcoma are less
- More common on left side, due to protective effect of liver on right side
- Part of diaphragm or entire diaphragm may be affected
- May show little or asynchronous motion with respiration.
Fig. 1.8.8: Transverse view—a large pleural effusion inverting the diaphragm can look like a large cyst. (L: liver; K: kidney)
Fig. 1.8.9: Free-fluid seen in right pleural cavity with collapsed lung inside—note the inverted diaphragm.
Ultrasound should be the primary imaging modality to see for the cause of elevated diaphragm. In helps to give an etiology at many instances and could narrow down the differential diagnosis in others.