Imaging of Intensive Care Patients after
Thoracic Surgery 3
Lung resections vary in their extent from wedge resections of peripheral lesions to complete pneumonectomy. The excision may be extended to include portions of the chest wall, pericardium, diaphragm, or great vessels, depending on the extent of disease.
Pneumonectomy
M. Fuchsjaeger and C. Schaefer-Prokop
A pneumonectomy is performed under standard conditions through a posterolateral thoracotomy.
The most common operation is an intrapleural pneumonectomy, which includes removal of the lung and visceral pleura. It involves opening the pericardium and dissecting the great vessels.
An extrapleural pneumonectomy involves an en-bloc resection of the lung including the parietal and mediastinal pleura, pericardium, and diaphragm.
The mortality rate of pneumonectomy is ca. 5%. Most deaths result from pneumonia, respiratory failure, pulmonary embolism, myocardial infarction, bronchopleural fistula, or pleural empyema.
Normal Postoperative Findings
The volume of the operated hemithorax is reduced after pneumonectomy. The ribs are spaced closer together and are directed at a steeper angle. The contralateral, nonoperated hemithorax often shows increased volume due to compensatory hyperinflation, especially in younger patients, while also showing signs of increased perfusion (Fig. 3.1).
Postoperative chest radiographs or computed tomography (CT) scans usually show pronounced anatomical changes. The radiologist should be aware of previous surgical interventions to understand the changes and interpret them correctly.
The radiologist should be aware of previous surgical interventions when interpreting postoperative chest radiographs and CT scans.
Air–fluid level. The pleural space on the operated side fills increasingly with serous fluid, which appears on radiographs as a homogeneous opacity with an air–fluid level (Fig. 3.2). The air–fluid level may persist for months. A double air–fluid level is caused by fibrinous septa. Multiple fluid levels occur in up to 25% of patients with a normal postoperative course and require differentiation from pleural empyema (see under Pneumonia in Chapter 2, p. 49). Once fluid has completely filled the pneumonectomy cavity, it is gradually reabsorbed. This is accompanied by a reduction of hemithoracic volume due to organization of the residual fluid and increasing fibrosis.
Ordinarily the pneumonectomy cavity shows a continuous decrease in air accompanied by a rising fluid level. Any sudden increase in the air volume (sudden fall of the fluid level) is suspicious for a complication such as bronchopleural fistula or a bronchial anastomotic leak.
A continuous decrease of air and increase of fluid is normal after pneumonectomy. A sudden increase in air volume is suspicious for a complication.
Mediastinal shift. The mediastinum is shifted from the midline toward the operated side, accompanied by a shift of the trachea. The clamped main bronchus generally does not show a reduction in its diameter.
Fig. 3.1 a, b Increased perfusion of the remaining lung.
Pneumonectomy is followed initially by increased perfusion of the remaining lung, which should not be interpreted as “engorgement.” Compare the pulmonary vessels on postoperative day 1 (a) and postoperative day 7 (b).
Fig. 3.2 a–d Normal progression of findings after pneumonectomy.
The pneumonectomy cavity is increasingly filled with fluid.
a Postoperative day 1.
b Postoperative day 2.
c Postoperative day 5.
d Postoperative day 10.
Specific Postoperative Complications
Postpneumonectomy Edema
Postoperative edema has an incidence of up to 5% after pneumonectomy (right > left) and less than 1% after lobectomy, typically occurring ca. 2–3 days after the resection. It is marked clinically by rapid progression of dyspnea and hypoxia. The prognosis with treatment is good. The pathophysiology of postpneumonectomy edema may relate to a fluid overload in the remaining lung, left heart failure, a disturbance of capillary membrane permeability due to sepsis or prolonged ventilation, or a surgically induced disruption of lymphatic drainage.
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Early complications
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Late complications
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Empyema
Cardiac herniation
Pulmonary edema (hydrostatic, permeability edema)
Chylothorax
Hemothorax
Bronchopleural fistula
Wound infection
Esophagopleural fistula
Postpneumonectomy syndrome
Tumor recurrence
Esophagopleural fistula
Fig. 3.3 a, b Hemothorax.
A rapidly progressive pleural effusion after surgery (12 hours passed between a and b) is suspicious for a hemothorax in patients with corresponding clinical symptoms.
Radiography. Interstitial edema is visible on chest radiographs and may spread to form patchy areas of alveolar consolidation.
Hemothorax
A hemothorax is usually the result of persistent bleeding from a bronchial artery or a vessel in the chest wall. The bleeding rarely originates from a central pulmonary vessel. The mortality rate is less than 0.1%. Hemothorax is diagnosed clinically in patients who have a chest tube in place.
Radiography. Hemothorax appears radiographically as a rapidly increasing pleural effusion (possibly accompanied by typical clinical signs such as tachycardia, hypotension, and a fall of hematocrit) with an associated mass effect based on its size (Fig. 3.3a, b).
Computed tomography. CT demonstrates a pleural fluid collection, frequently lobulated (loculated), of variable density. The effusion often has biconvex margins and produces a mass effect based upon its size and typical rapid enlargement.
The attenuation values of a hemothorax range from 15 HU to more than 40 HU, depending on the age of the hemorrhage. It is common to find layering effects within the pleural effusion. As the hemorrhage becomes more organized, the effusion may acquire a tumorlike aspect. It is distinguished from a tumor by noting its high attenuation values on plain scans and its lack of enhancement after IV contrast administration.
The attenuation values of a hemothorax range from 15 to 40 HU, depending on the age of the hemorrhage.
Chylothorax
A chylothorax results from injury to the thoracic duct or one of its tributaries. Sites of predilection are the left inferior paravertebral hemithorax following extrapulmonary pneumonectomy, the aortopulmonary window region following lymphadenectomy, and the region of the pulmonary ligament on both sides.
Radiography. Like a hemothorax, chylothorax appears radiographically as a rapidly increasing pleural effusion (Fig. 3.4).
Computed tomography. Negative, fat-equivalent CT attenuation values confirm the diagnosis of chylothorax. Negative attenuation values are not always present, however, due to the protein content of the collection.
Negative, fat-equivalent CT densities confirm a chylothorax but are not always present.
Pleural Empyema
Extensive infections of the pleural cavity occur in up to 5% of cases, depending on the patient subgroup. A pleural empyema may develop as an early (weeks) or late complication (months to years). The main causative organisms are staphylococci, Pseudomonas, streptococci, and Aerobacter aerogenes.
An empyema occurring in the early postoperative period usually results from the intraoperative spread of infectious organisms or a bronchial leak. The main cause of a late infection is bronchopleural fistulation.
The following factors predispose to the development of a (late) postpneumonectomy empyema:
secondary pneumonectomy after an initial lobectomy
preoperative radiation
sepsis
mediastinal lymphadenectomy
prolonged mechanical ventilation
The drainage of an empyema is described under Pneumonia in Chapter 2 (complications, empyema, p. 67).
Radiography. The following signs are noted, depending on the timing of the infection:
Unusually rapid filling of the hemithorax with fluid
Shift of the mediastinum toward the healthy side (mass effect from the pleural fluid) (Fig. 3.5).
Sudden drop of the air–fluid level in the operated hemithorax via a communication with the main bronchus or a fistula in the pleural wall
Reappearance of air in a completely opaque hemithorax due to a bronchopleural fistula or gas-forming bacteria
Fig. 3.4 a, b Basal chylopneumothorax after lobectomy.
Note extension of the air–fluid level along the full sagittal thoracic diameter (unlike an abscess) (a) and the anterior loculated pneumoserothorax, which also contains an air–fluid level (b).
Fig. 3.5 a, b Pyoserothorax with mass effect.
The collection has caused a contralateral shift of the mediastinum.
Appearance of multiple air–fluid levels at various locations (caution: multiple air–fluid levels are a normal finding in up to 25% of patients; they are suspicious when multiple new air–fluid levels appear after initial homogeneous fluid filling of the hemithorax) (Fig. 3.6).
Fig. 3.6 a, b Postoperative pleural empyema in two different patients.
The pleura is thickened and shows increased contrast enhancement. Multiple air inclusions are seen at different levels.
Ultrasonography. Ultrasound scanning can detect septations earlier and with greater clarity than CT. Echogenicity that is increased or variable due to septations and reverberations from air inclusions are typical sonographic features of a “complicated” effusion (see Fig. 2.91).
Computed tomography. CT signs of pleural empyema are a thickened pleura showing increased contrast enhancement and dense exudate with attenuation values greater than 20 HU. CT is better than radiographs for revealing associated mass effects (Fig. 3.6).
Bronchopleural Fistula
Small air leaks in the main bronchus are not uncommon and will generally heal spontaneously with conservative therapy. Large or persistent leaks give rise to bronchopleural fistulas (BPFs). The origin of the fistula is usually located in the bronchial stump. Generally the diagnosis is confirmed by bronchoscopy.
BPFs rarely occur in the early postoperative period. They more commonly develop as a delayed complication after a bronchial stump infection, bronchial ischemia, extensive lymphadenectomy, tumor recurrence, or in cases where the bronchial stump has been ligated at a tooproximal level. Predisposing factors are preoperative radiation and preoperative pleuropulmonary infection.
BPF is the leading cause of pleural empyema.
Radiography. The following radiographic signs may be noted at varying intervals after a pneumonectomy:
Persistent or increasing pneumothorax with a chest tube in place
Increasing subcutaneous or mediastinal emphysema
More than a 2-cm drop in the air–fluid level with a mediastinal shift toward the healthy side
Sudden onset of pneumoserothorax with a preexisting serothorax (Fig. 3.7)
Consolidated areas in the contralateral lung caused by fluid overflow from the pneumonectomy cavity or by direct communication through a BPF
Computed tomography. In up to 50% of cases, thin-slice CT can directly visualize a BPF between the airway (bronchial stump) and pleural space, or between the lung parenchyma and pleural space (Fig. 3.8).
When the detection of pus confirms a pleural empyema, a bronchopleural fistula should be excluded.
If the fistula cannot be directly visualized, persistent air and fluid collections in the mediastinum or pleural space may suggest the correct diagnosis.
Thin-slice CT can directly visualize a bronchopleural fistula in up to 50% of cases.
Esophagopleural Fistula
This rare complication (< 1%) occurs most commonly after a right pneumonectomy (direct contact between the esophagus and right pleura).
An esophagopleural fistula (EPF) of early onset (within 2 weeks) may be caused by direct esophageal injury or decreased blood flow to the lower esophagus. Later occurrence of the fistula (from 2–6 weeks postoperatively) may result from an empyema, extensive lymphadenectomy, or BPF. An EPF caused by tumor recurrence may develop more than 2 years after the operation.
Fig. 3.7 a–c Anastomotic leak after pneumonectomy.
The pneumonectomy cavity is completely filled with fluid (a). This is followed by secondary air inclusions with air–fluid levels (b), which continue to increase during follow-up (c).
Patients typically present with fever, chest pain, and significant dysphagia. The presence of food constituents in the drained pleural fluid provides direct evidence of an EPF.
Cardiac herniation toward the left side leads to shock symptoms with tachycardia and hypotension due to strangulation of the left ventricle in the pericardial defect.
Radiography and CT. Direct visualization of the fistula (e. g., after oral contrast administration) may be difficult. Visualization is aided by moving the patient to a lateral decubitus position with the operated side down (Fig. 3.9). Imaging can be done by conventional esophagography or by CT after the oral administration of water-soluble contrast medium.
Cardiac Herniation
The heart may herniate through the pericardial defect created by an intrapericardial pneumonectomy. This complication occurs within the first few hours after an intrapericardial pneumonectomy and is extremely rare in cases where the pericardial defect has been closed. Cardiac herniation may occur through a pericardial defect of any size.
A right-sided herniation is manifested clinically by obstructed venous return leading to a rise of central venous pressure (due to counterclockwise rotation of the heart about the superior vena cava). A left-sided herniation leads to shock symptoms with hypotension and tachycardia (caused by strangulation of the left ventricle in the pericardial defect).
Radiography. The cardiac silhouette is markedly displaced toward the side of the pneumonectomy, with the cardiac apex touching the lateral chest wall. An empty, air-filled pericardial space may also be seen.
