Describe the general lobar and segmental anatomy of the lungs (diagram).
What does the minor fissure separate? On what view is it seen on plain radiograph?
The major (oblique) fissure is seen on what view on plain radiograph? What does it separate?
What is an azygous fissure and what does it make?
- The minor fissure separates the right upper lobe (RUL) from the right middle lobe (RML) and is seen on both the frontal and lateral views as a fine horizontal line.
- The major (oblique) fissures are seen only on the lateral radiograph as oblique lines.
- On the right, the major fissure separates the RUL and RML from the right lower lobe.
- On the left, the major fissure separates the left upper lobe from the left lower lobe.
- The azygos fissure is an accessory fissure present in less than 1% of patients, seen in the presence of an azygos lobe. An azygos lobe is an anatomic variant where the right upper lobe apical or posterior segments are encased in their own parietal and visceral pleura.
What is atelectasis?
What are the direct signs of atelectasis? What are they from?
What are the indirect signs of atelectasis and what is it due to?
When do you see air bronchograms associated with atelectasis?
What is commonly seen in post surgical patients?
- Atelectasis is loss of lung volume due to decreased aeration. Atelectasis is synonymous with collapse.
- Direct signs of atelectasis are from lobar volume loss and include:
- Displacement of the fissures
- Vascular crowding.
- Indirect signs of atelectasis are due to the effect of volume loss on adjacent structures and include:
- Elevation of the diaphragm.
- Rib crowding on the side with volume loss.
- Mediastinal shift to the side with volume loss.
- Overinflation of adjacent or contralateral lobes.
- Hilar displacement.
- Air bronchograms are not seen in atelectasis when the cause of the atelectasis is central bronchial obstruction, but air bronchograms can be seen in subsegmental atelectasis. Subsegmental atelectasis is caused by obstruction of small peripheral bronchi, usually by secretions.
- Subsegmental atelectasis and mild fever are both commonly encountered in postsurgical patients, although it has been proposed that there is no causative relationship between atelectasis and postoperative fever.
What are the mechanisms of atelectasis?
- Relaxation (passive)
When does obstructive atelectasis occur?
Can obstructive atelectasis cause complete collapse of a lobe?
What does supplemental O2 have to do with the rate of obstructive atelectasis?
In general, is obstructive atelectasis volume negative, neutral, or positive? What about in ICU patients?
What is the most common cause of airway obstruction in children? What is the significance of the ball-valve effect in these kiddoes?
What is subsegmental atelectasis?
- Obstructive atelectasis occurs when alveolar gas is absorbed by blood circulating through alveolar capillaries but is not replaced by inspired air due to bronchial obstruction.
- Obstructive atelectasis can cause lobar atelectasis, which is complete collapse of a lobe.
- Obstructive atelectasis occurs more quickly when the patient is breathing supplemental oxygen since oxygen is absorbed from the alveoli more rapidly than nitrogen.
- In general, obstructive atelectasis is associated with volume loss. In critically ill ICU patients, however, there may be rapid transudation of fluid into the obstructed alveoli, causing superimposed consolidation.
- In children, airway obstruction is most often due to an aspirated foreign object. In contrast to adults, the affected side becomes hyperexpanded in children due to a ball-valve effect.
- Subsegmental atelectasis is a subtype of obstructive atelectasis commonly seen after surgery or general illness, due to mucus obstruction of the small airways.
What causes relaxation (passive) atelectasis?
What are some causes?
- Relaxation (passive) atelectasis is caused by relaxation of lung adjacent to an intrathoracic lesion causing mass effect, such as a pleural effusion, pneumothorax, or pulmonary mass.
What is adhesive atelectasis?
- Adhesive atelectasis is due to surfactant deficiency.
- Adhesive atelectasis is seen most commonly in neonatal respiratory distress syndrome, but can also be seen in acute respiratory distress syndrome (ARDS).
What is cicatricial atelectasis?
- Cicatricial atelectasis is volume loss from architectural distortion of lung parenchyma by fibrosis.
What is lobar atelecatasis usually caused by, which is secondary to what two possible causes?
If lobar atelectasis is acute, what is the most likely cause?
What if it is seen in an outpatient setting?
- Lobar atelectasis is usually caused by central bronchial obstruction (obstructive atelectasis), which may be secondary to mucus plugging or an obstructing neoplasm.
- If the lobar atelectasis occurs acutely, mucus plugging is the most likely cause. If lobar atelectasis is seen in an outpatient, an obstructing central tumor must be ruled out.
Describe the patterns of lobar atelectasis! (diagram)
What sign is indicative of a left upper lobe collapse?
Why is it so important to recognize left upper collapse and not mistake left lung opacity for PNA?
- The luftsichel (air-sickle in german) sign of left upper lobe collapse is a crescent of air seen on the frontal radiograph, which represents the interface between the aorta and the hyperexpanded superior segment of the left lower lobe.
- It is important to recognize left upper lobe collapse and not mistake the left lung opacity for pneumonia, since a mass obstructing the airway may be the cause of the lobar atelectasis.
What radiologic sign is indicative of a right upper lobe collapse 2/2 hilar mass?
Similar to left upper lobe collapse, what should a right upper lobe collapse raise concern for?
What is the juxtaphrenic peak sign?
- The reverse S sign of Golden (aka Golden’s S) is seen in right upper lobe collapse caused by an obstructing mass. The central convex margins of the mass form a reverse S. Similar to left upper lobe collapse, a right upper lobe collapse should raise concern for an underlying malignancy, especially with a golden’s S sign present.
- The juxtaphrenic peak sign is a peridiaphragmatic triangular opacity caused by diaphragmatic traction from an inferior accessory fissure or an inferior pulmonary ligament.
Describe the pattern seen in left lower lobe atelectasis. (diagram)
What is the flast waist sign?
- In left lower lobe collapse, the heart slightly rotates and the left hilum is pulled down.
- The flat waist sign describes the flattening of the left heart border as a result of downward shift of hilar structures and resultant cardiac rotation.
What is the pattern for a right lower lobe collapse? (diagram)
- Right lower lobe atelectasis is the mirror-image of left lower lobe atelectasis.
- The collapsed lower lobe appears as a wedge-shaped retrocardiac opacity.
What are the findings of a right middle lobe collapse?
- The findings of right middle lobe atelectasis can be subtle on the frontal radiograph. Silhoueting of the right heart border by the collapsed medial segment of the middle lobe may be the only clue.
- The lateral radiograph shows a wedge-shaped opacity anteriorly.
What is it?
Where is it more common?
What findings must be present to diagnose this?
What is the comet tail sign?
- Round atelectasis is focal atelectasis with a round morphology that is always associated with an adjacent pleural abnormality (e.g., pleural effusion, pleural thickening or plaque, pleural neoplasm, etc.).
- Round atelectasis is most common in the posterior lower lobes.
- All five of the following findings must be present to diagnose round atelectasis:
- Adjacent pleura must be abnormal.
- Opacity must be peripheral and in contact with the pleura.
- Opacity must be round or elliptical.
- Volume loss must be present in the affected lobe.
- Pulmonary vessels and bronchi leading into the opacity must be curved - this is the comet tail sign.
Overview of Pulmonary Edema
What are the three stages of pulmonary edema progression? What do these correspond to?
What are Kerley A and B lines?
- The radiographic severity of pulmonary edema typically progresses through three stages, corresponding to progressively increased pulmonary venous pressures.
- Vascular redistribution is the first radiographic sign of increased pulmonary venous pressure. Imaging shows increased caliber of the upper lobe vessels compared to the lower lobe vessels.
- Interstitial edema is caused by increased fluid within the pulmonary veins, which surround the periphery of each hexagonal secondary pulmonary lobule. On radiography, there are increased interstitial markings, indistinctness of the pulmonary vasculature, peribronchial cuffing, and Kerley B and A lines.
- Kerley B lines are seen at the peripheral lung and represent thickened interlobular septa.
- Kerley A lines radiate outward from the hila and may represent dilation of lymphatic channels. They are not thought to be clinically relevant.
- Alveolar edema is caused by filling of the alveoli with fluid. On imaging, perihilar (central) opacifications are present. Pleural effusions and cardiomegaly are often present.
What are the CT findings of pulmonary edema?
Describe pattern of intrathoracic vs systemic causes of pulmonary edema.
What is a classic cause of assymetric pulm edema?
What is a complication of aggressive thoracentesis?
- CT findings of pulmonary edema include dependent ground glass opacification and interlobular septal thickening. Intrathoracic causes of pulmonary edema, such as heart failure, generally cause patchy ground glass, while systemic cause of pulmonary edema (e.g., sepsis or low protein states) often cause diffuse ground glass.
- Pulmonary edema is usually symmetric and dependent. A classic cause of asymmetric pulmonary edema is isolated right upper lobe pulmonary edema, caused by acute mitral regurgitation secondary to myocardial infarction and papillary muscle rupture.
- A complication of aggressive thoracentesis is reexpansion pulmonary edema, caused by rapid reexpansion of a lung in a state of collapse for more than three days.
What is the vascular pedicle?
What are the borders?
What is the significance of an interval increase of width of the vascular pedicle width on sequential supone AP ICU-type chest radiographs?
- The vascular pedicle is the transverse width of the upper mediastinum.
- The right border of the vascular pedicle is the interface of the superior vena cava (SVC) and the right mainstem bronchus.
- The left border of the vascular pedicle is the lateral border of the takeoff of the subclavian from the aorta.
- The vascular pedicle width is normally <58 mm.
- An interval increase in vascular pedicle width (both >63 and >70 mm have been proposed as cutoffs) on sequential supine AP ICU-type chest radiographs generally correlates with increased pulmonary capillary wedge pressure (>18 mm Hg) and fluid overload.
How far above the carina should an endotracheal tube tip be?
A tip position closer to the carina can be used in what scenario?
Direct intubation of the right or left mainstrem bronchus is more common? What can happen in these cases?
- The endotracheal tube tip should be approximately 4-6 cm above the carina with the neck in neutral alignment. However, in situations with low pulmonary compliance (e.g., ARDS), a tip position closer to the carina may reduce barotrauma.
- Direct intubation of either the right or left mainstem bronchus (right mainstem bronchus far more common) is an emergent finding that can cause complete atelectasis of the un-intubated lung.
Where should the tip of a central venous catheter, including a PICC, be located?
How often does azygos malposition occur in bedside-placced PICCS? Significance?
Where should a dialysis catheter tip be located?
- The tip of a central venous catheter, including a PICC, should be in lower SVC or the cavoatrial junction. Azygos malposition is seen in approximately 1% of bedside-placed PICCs. Azygos malposition is associated with increased risk of venous perforation and catheter-associated thrombosis, and repositioning is recommended.
- A dialysis catheter should be located in the right atrium.
Where should the tip of a Swan-Ganz catheter be?
What risk is increased if the tip is proximal to the interlobular pulmonary artery?
What other complications are associated with a Swan-Ganz catheter?
- The tip of a Swan-Ganz pulmonary artery catheter should be in either the main, right, or left pulmonary artery.
- If the tip is distal to the proximal interlobar pulmonary artery, there is a risk of pulmonary artery rupture or pseudoaneurysm. Other complications of pulmonary artery catheter placement include intracardiac catheter knot and arrhythmia.