Journal of Cancer Research and Therapeutics Medknow Publications on behalf of the Association of Radiation Oncologists of India (AROI) ISSN: 0973-1482 EISSN: 1998-4138 Vol. 7, Num. 1, 2011, pp. 3-10

Journal of Cancer Research and Therapeutics, Vol. 7, No. 1, January-March, 2011, pp. 3-10

Review Article

Imaging in postpneumonectomy complications: A pictorial review

SH Chandrashekhara¹, AS Bhalla¹, R Sharma¹, AK Gupta¹, A Kumar², R Arora¹

¹ Department of Radio-diagnosis, All India Institute of Medical Sciences, New Delhi, India
² Department of Surgery, All India Institute of Medical Sciences, New Delhi, India

Correspondence Address: A S Bhalla, Department of Radiology, All India Institute of Medical Sciences, New Delhi - 110 029, India, ashubhalla1@yahoo.com

Code Number: cr11002

PMID: 21546734

DOI: 10.4103/0973-1482.80426

Abstract

Keywords: Chest radiograph, computed tomography, postpneumonectomy complications

Introduction

Pneumonectomy is done in patients with operable bronchogenic cancer and intractable end-stage lung diseases such as tuberculosis and bronchiectasis, but it is often followed by postoperative complications with an incidence of 20-60% percent of patient factors. Complications following pulmonary resection differ according to the type of surgery and the time elapsed since surgery was performed. The mortality rate is three times higher after right pneumonectomy than that done on the left side. The combined mortality and morbidity after pneumonectomy is 30%, whereas after lobectomy it is 20%. ^[1],[2] Depending on the underlying disease, three types of pneumonectomy techniques are used with each having different complications. The first is intrapleural pneumonectomy performed in patients with bronchogenic carcinoma without pericardial or chest wall invasion. Second is intrapericardial pneumonectomy performed in patients with lung cancer with pericardial invasion or where the ligation of pulmonary veins becomes necessary. The third type is extra-pleural pneumonectomy where the plane of dissection is between parietal pleura and endothoracic fascia and is performed in patients with operable malignant mesothelioma. ^[1] Many of postpneumonectomy complications are potentially fatal and require appropriate immediate management. ^[1],[2] Therefore, the knowledge of the diverse radiologic appearances of these complications as well as familiarity with the clinical settings in which specific complications are likely to occur are vital for prompt and effective treatment. ^[3] Serial chest radiographs and computed tomography (CT) play an important role in the evaluation of these complications.

Normal Postpneumonectomy Changes

In the immediate postoperative period, the postpneumonectomy space (PPS) contains air and fluid. Mediastinum is in the midline and the remaining lung is mildly plethoric. After almost 1 week, fluid starts accumulating in the PPS by bleeding, from lymphatics and passive exudation, at a rate of approximately 2 intercostal spaces per day. As there is resorption of gas from the surgical site, there is ipsilateral shifting of the mediastinum, elevation of hemidiaphragm, and hyperinflation of the remaining lung. This process may take 3 weeks to 7 months. In some patients, a small amount of gas persists indefinitely. After that in two-thirds of patients, CT shows the PPS filled with fluid with thick fibrous margins, and in the remaining one-third the PPS is filled with fibrous tissue or normal mediastinal structures [Figure - 1] and [Figure - 2]. Because of constant volume in the PPS and exhalation in the contralateral lung on expiration, a contralateral mediastinal shift of up to 3.5 cm on expiration is considered normal. Familiarity with the normal postoperative chest is important for early recognition of the complications. Unexpected early and rapid accumulation of fluid suggests hemorrhage, infection, or chylothorax, whereas a rapid contralateral mediastinal shift suggests atelectasis of the remaining lung or an abnormal accumulation of air or fluid in the PPS (due to bronchopleural fistula [BPF], hemorrhage, or empyema). ^[4]

Early Postoperative Complications

Pulmonary complications

Pulmonary edema

Postpneumonectomy pulmonary edema is a life-threatening complication that develops 2-3 days after the procedure, with a reported prevalence of 2.5-5% and a mortality rate of 80-100%. Histopathology within 5 days shows lost endothelial integrity with extravasation of fluid, protein, and inflammatory cells into alveolar spaces along with a marked proliferation of fibroblasts and type 2 pneumocytes. After 10 days, there is interstitial and intra-alveolar fibrosis with thrombotic and obliterative changes. ^[5],[6] Various predisposing factors include an excess perioperative fluid load, transfusion of fresh frozen plasma (FFP), arrhythmia, marked postsurgical diuresis, and low serum colloidal osmotic pressure leading to increased hydrostatic pressure and altered permeability of capillaries. ^[5],[7] Patients who undergo right pneumonectomy are at a higher risk because a large amount of fluid in the right PPS results in an increased pulmonary blood flow through the left lung. The left lung normally receives only 15% of the total pulmonary blood flow and contains approximately 45% of the total lymphatic capacity of the lungs. ^[5] Other causes like aspiration pneumonia, bacterial pneumonia, heart failure thromboembolism, BPF, or other causes of acute respiratory distress syndrome (ARDS) must be excluded before a diagnosis of postpneumonectomy pulmonary edema is made. ^[6] Severe pulmonary edema appears as extensive airspace opacities identical to those seen in ARDS. Commonly observed findings include Kerley lines, peribronchial cuffing, and haziness of the vessel outlines. ^[5],[7]

Bronchopleural fistula

Although the incidence of BPF has reduced in the recent years, it is still a potentially fatal complication with an incidence of 0-9% and a mortality rate of 16-23%. ^[8],[9] BPF is more common after right pneumonectomy than after left. This is due to a larger size, greater tendency to spring open, and having less mediastinal coverage than the left as well as greater vulnerability to ischemia, with blood supplied via a single bronchial artery. ^[8] Other predisposing factors are uncontrolled pleuropulmonary infection, trauma, preoperative radiation therapy, postoperative positive ventilation, and a faulty closure of the bronchial stump. ^[8],[9],[10] BPF is the main cause of postpneumonectomy empyema. In the immediate postoperative period, BPF is rare and is usually due to a faulty closure of the bronchus. Radiologic findings in BPF consist of failure of the PPS to fill, persistent or progressive pneumothorax despite adequate tube drainage, subcutaneous or mediastinal emphysema, a more than 2-cm drop in the air-fluid level with contralateral mediastinal shift, consolidation in the remaining lung because of the transbronchial spill, and a sudden pneumothorax or reappearance of air in a previously opaque PPS [Figure - 3]. A decrease in the height of the fluid level by 2 cm or more is indicative of a fistula. ^[9] A minor degree should be ignored unless accompanied by a medistinal shift away from the PPS because it can be due to a difference in the posture or in degree of inspiration. ^[9] The most common cause of death associated with this condition is aspiration pneumonia with subsequent ARDS. ^[3] An adequately long stump, a disease-free margin, and maintenance of bronchial vascularity by preserving the bronchial artery or peribronchial tissue have been strongly suggested as means of avoiding avascular necrosis of the stump. ^[10]

ARDS and acute lung injury

Both ARDS and acute lung injury (ALI) are fatal complications of pneumonectomy with an incidence of approximately 5% and a mortality rate of about 80%. These are thought to represent a spectrum of the same disease characterized by the acute onset of hypoxemia with radiographic infiltrates consistent with pulmonary edema that occur in the absence of evidence of other identifiable causes, and without elevations in the pulmonary capillary wedge pressure. Various risk factors are age more than 60 years, male gender, chronic suppurative lung disease, reduced diffusion capacity of the lung for carbon monoxide (CO), predicted postoperative lung perfusion less than 55% of the total lung perfusion, prior radiation or chemotherapy and concurrent cardiac disease. Increased postoperative blood flow through the remaining lung disrupting the capillary endothelial cell alveoli barrier is the postulated mechanism of ARDS/ALI. The observation of the characteristic pulmonary opacities on chest radiography diffusely and a pulmonary artery wedge pressure of less than 18 mmHg are the basis for the diagnosis. CT shows the ground glass opacity, increased visibility of the interlobular septa, and an anteroposterior opacity gradient. ^{[11],[12],[13]}

Pneumonia

The incidence and mortality rates of pneumonia following pneumonectomy are 2-15% and 25%, respectively. ^[14] Various predisposing factors are prolonged ventilatory support and difficulty in clearing tracheobronchial secretions. ^[15] The aspiration of gastric secretions and bacterial colonization of the atelectatic lobe most often lead to pneumonia. ^[9] Aspiration via BPF is another possible cause. There is often a time lag between clinical presentation and radiographic manifestation. Various species of Gram-negative bacilli are often the causative pathogens with a patchy bronchopneumonic pattern on chest radiographs. The lobar consolidation pattern is much less common. ^[16] CT has an advantage of demonstrating BPF in patients of aspiration pneumonia caused by the transbronchial spill [Figure - 4].

Pleural complications

Empyema

Empyema remains a potentially fatal complication though its incidence has greatly decreased over the years, with most reports citing an incidence of less than 5% due to advanced surgical techniques and use of potent antibiotics. ^[17],[18] Mortality rates range from 16% to 71%. ^[10] Empyema most often occurs after completion of pneumonectomy (performed after a previous lobectomy), right pneumonectomy, preoperative radiation, gross contamination of the pleura, surgery-related sepsis, mediastinal lymph node dissection, postoperative mechanical ventilation, and with longer bronchial stumps than the shorter ones. ^[19] In the early postoperative period, empyema occurs due to intraoperative contamination or residual infection in the pleural cavity. ^[15] Empyema may also occur secondary to BPF or esophagopleural fistula where it is associated with high mortality. Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcal species, and Aerobacter aerogenes are the most commonly cultured organisms in most reported series. ^[15] Presentation is usually with features of systemic toxicity and a raised white cell count. Various radiographic features of empyema are rapid filling of the PPS with fluid; contralateral mediastinal shift; a decrease in the air-fluid level in the PPS accompanied by communication with the outside via the bronchus or through the skin; and a new air-fluid level in a previously opacified PPS indicative of BPF or a gas-forming organism. ^[18] CT shows the volume expanding process in the PPS better than the chest radiography, along with an irregularly increased thickening of the residual parietal pleura and BPF or esophagopleural fistula which may either cause or coexist with empyema ^[20] [Figure - 5].

Other early complications

Other early complications include hemothorax, chylothorax, wound infection or disruption, atelectasis, cardiac herniation , cardiac arrhythmia, and pulmonary embolism. It is not possible to differentiate hemothorax, chylothorax, and empyema radiologically and they are differentiated according to their time of development after surgery and rate of accumulation of secretions. Rapid accumulation just after surgery suggests hemorrhage. Chylothorax usually develops with a delay of almost 10 days after surgery and empyema may occur weeks to months after surgery though it can occur in the early post operative period, where patients present with features of systemic toxicity and a raised white cell count. ^[17]

Late postoperative complications

Postpneumonectomy syndrome

Postpneumonectomy syndrome which consists of intrathoracic major airway compression is more likely to occur in infants and young children within a year after surgery. It occurs due to stretching of the intrathoracic airways of the remaining lung against fixed mediastinal structures. The increased incidence in infants, young children, and women is believed to be due to increased elasticity and compliance of their lungs and mediastinum compared with those of older patients and men. Right pneumonectomy is more likely to result in postpneumonectomy syndrome because of several anatomic factors. The right lung volume is more than the left one, so right pneumonectomy results in a greater mediastinal shift toward the right side with the heart being displaced into the right hemithorax with increased chances of compression between the mediastinal structures. The left main bronchus is also more prone to compression as it is stretched and pushed down by the left aortic arch and is then compressed inferiorly between the left pulmonary artery and the descending aorta. Chest radiograph shows displacement of the heart and trachea toward the right side and posteriorly. CT shows the exact site of bronchial obstruction along with the status of the PPS and position of mediastinal blood vessels, bronchi, and thoracic spine [Figure - 6]. Early diagnosis and treatment is important to prevent tracheobronchomalacia. Treatment is by surgical repositioning of the mediastinum and filling of the PPS with a nonabsorbable material like saline solution-filled prosthesis/silicone breast implants and anterior pericardiorrhaphy. ^[21],[22]

Esophagopleural fistula

Esophagopleural fistula is an uncommon complication after pneumonectomy with an incidence of 0.2-1%. Such fistulas can develop during the early/late postoperative periods. In the early period, it is due to surgical injury or compromised blood supply to lower esophagus during surgery. In the late postoperative period, either recurrent tumor or chronic inflammation in the esophagus, bronchial stump, or surrounding tissues may be the causal mechanism. ^[3],[23] When the fistula is large, food particles appear in the drainage fluid and the diagnosis is straightforward. Smaller leaks tend to cause chronic empyema and are difficult to detect. ^[23],[24] Diagnosis is confirmed with various investigations like chest radiograph, CT, esophagoscopy, and bronchoscopy. Chest radiographs show a decrease in the air-fluid level or reappearance of an air-fluid level in a previously opacified PPS. Barium swallow can demonstrate the fistula but a tiny fistulous tract can be missed on esophagography especially in the upright position. CT is useful in demonstrating the fistula and other findings such as recurrent tumor, inflammatory lymph nodes, empyema, and aspiration pneumonia in the contralateral lung. Treatment is by keeping the patients nil orally along with the drainage of the pleural cavity and surgical closure of the fistula. ^[24]

Late-onset BPF

Delayed BPF is much more common than the early form and occurs due to infection or recurrent tumor in the bronchial stump. ^[10] Radiologic findings are the same as those in BPF in the early period [Figure - 7].

Late-onset empyema

Late-onset empyema occurs months to years after surgery and may elicit only mild symptoms. It is either due to the hematogenous spread or delayed onset bronchial/esophageal fistula which is more likely due to recurrent carcinoma. It is seen as multiple air-fluid levels in the PPS on chest radiographs. A sudden bulge in the postpneumonectomy space with a contralateral mediastinal shift also suggests empyema. CT is especially useful to diagnose empyema in the absence of BPF when there are minimal changes on chest radiographs ^[15],[19] [Figure - 8].

Pneumonia of the contralateral lung

Late-onset pneumonia is usually community acquired and seen as newly developed opacity in the contralateral lung. It is diagnosed in the appropriate clinical settings with the exclusion of radiation- and chemotherapy-induced changes or recurrence of primary diseases such as primary or secondary malignancy or tuberculosis [Figure - 9].

Complications Due to Radiation Therapy

Pneumonitis

It is a well-recognized clinicopathological syndrome which is generally confined to the radiation field. Its severity correlates with the extent of lung volume incorporated within the field of radiation. It usually occurs approximately 1-3 months after the completion of radiotherapy. Fibrous changes take 6-24 months to evolve but usually remain stable after 2 years. CT scans show ground glass opacity or consolidation in the acute phase and traction bronchiectasis, volume loss, and consolidation in the later phase ^{[25],[26],[27]} [Figure - 10].

Pericarditis

Pericardial damage is one of the consequences of radiation that may lead to chronic pericarditis and or tamponade. Radiation-induced pericarditis usually occurs 6-9 months following therapy. ^[25] It is seen as a symmetric enlargement of cardiac silhouette on chest radiographs. CT and MR have the advantage of demonstrating pericardial effusion and thickening [Figure - 11]. It should be differentiated from malignant pericardial effusion in which there is eccentric pericardial thickening with associated adjacent lymph nodes or mass. ^{[28],[29],[30]}

Pleurits

It usually develops within 6 months of the completion of therapy. It may occur because of the decreased pulmonary venous return due to radiation-induced constrictive pericarditis. ^[31] It is difficult to differentiate it from malignant pleural effusion radiologically, as well as by cytological analysis.

Local tumor recurrence

In addition to the recurrence at the bronchial stump, local tumor recurrence (LTR) includes ipsilateral mediastinal node metastasis, and recurrence in the chest wall or parietal pleura. ^[32] It usually occurs within 2 years after surgery. A chest radiograph is insensitive in detecting bronchial stump recurrence and a lateral shift in the position of the mediastinum is often the only finding. CT offers an advantage by demonstrating a recurrent soft tissue mass at or near the bronchial stump, pleural seeding, and mediastinal lymphadenopathy. In cases where differentiation from postsurgical fibrosis is difficult, a correlation with bronchoscopic, PET, and follow-up CT findings are helpful to evaluate the growth of the mass [Figure - 12]. Usually, these patients are treated with radiation therapy and CT is further helpful for assessing tumor regression after radiation therapy. ^[32],[33]

Chronic infections and tuberculosis

Pneumonectomy may be done as a curative treatment in the massive destruction of the lung tissue, significant hemoptysis in tuberculosis or chronic infections, and in multidrug-resistant infection. The incidence of recurrent TB after pneumonectomy is infrequent. On chest radiographs, findings of reactivation TB may mimic BPF/empyema. CT is superior for showing the findings of reactivation TB like lymph node necrosis and their complications ^[34] [Figure - 13].

Other late complications

Rarely, cor pulmonale from increased vascular resistance in the remaining lung can occur as a late complication. With the resection of the ipsilateral diaphragmatic leaflet in extrapleural pneumonectomy, transdiaphragmatic herniation of the abdominal viscera can also occur. In cases of left pneumonectomy associated with the effacement of the cardiac incisura, gastroesophageal reflux can be a source of concern. Rarely scoliosis and lordosis may occur ^[17] [Figure - 14].

Summary

Major causes of death after pneumonectomy are pneumonia, pulmonary edema, empyema, and BPF. Serial chest radiographs should be done in the early postoperative period following pneumonectomy to screen for complications, and CT should be used as the problem-solving modality when the findings are subtle or equivocal. CT is also useful for detecting delayed complications in the late postoperative period. Familiarity with the clinical features and various imaging findings of the various postpneumonectomy complications is important for their early recognition, as many of them are fatal and with appropriate timely management, associated morbidity and mortality can be significantly decreased.

References

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