You are in: eMedicine Specialties > Thoracic Surgery > Infection Lung Abscess, Surgical PerspectiveArticle Last Updated: Apr 19, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Shabir Bhimji, MD, PhD, Locum Cardiothoracic and Vascular Surgeon, Saudi Arabia and Middle East Hospitals Shabir Bhimji is a member of the following medical societies: American Cancer Society, American College of Chest Physicians, American Lung Association, and Texas Medical Association Editors: Jeffrey C Milliken, MD, Chief, Division of Cardiothoracic Surgery, University of California at Irvine Medical Center; Clinical Professor, Department of Surgery, University of California at Irvine School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Shreekanth V Karwande, MBBS, Chair, Professor, Department of Surgery, Division of Cardiothoracic Surgery, University of Utah School of Medicine and Medical Center; Rajalaxmi McKenna, MD, FACP, Consulting Staff, Department of Medicine, Southwest Medical Consultants, SC, Good Samaritan Hospital, Advocate Health Systems; Mary C Mancini, MD, PhD, Director of Cardiothoracic Transplantation, Professor, Department of Surgery, Louisiana State University Health Sciences Center Author and Editor Disclosure Synonyms and related keywords: lung abscess, aspiration, pneumonia, anaerobic bacteria, antibiotic therapy, percutaneous drainage, bronchoscopy, empyema, alcoholism, seizures, poor oral hygiene, bronchogenic neoplasm, infected lung, pyogenic lung abscess, lung abscesses, oral surgery, dysphagia, achalasia, dental infection, gingival disease, gum disease, bad oral hygiene, gingivodental disease, lung necrosis, necrotic lung tissue, anaerobic necrotizing pneumonia, pulmonary gangrene, amebiasis, amoebiasis, amebic lung abscess, amoebic lung abscess INTRODUCTIONSection 2 of 10
  A lung abscess is a subacute infection that destroys lung parenchyma. Further, chest radiographs reveal one or more cavities, often with an air-fluid level. Because the development of a cavity requires some amount of prior tissue damage and necrosis, presumably, lung abscesses usually begin as a localized pneumonia. Before the availability of antibiotics, the etiology of a typical abscess was complications after oral surgical procedures (ie, tonsillectomy), resulting in aspiration of infected material into the lungs. In the absence of satisfactory antibiotic treatment, this event usually led to a lung abscess or to a necrotizing pneumonia with or without pleural empyema. Prior to the availability of antibiotics, the clinical course of a patient with a lung abscess would gradually worsen. Fifty years ago, the mortality rate was greater than 50%, and many patients were left with significant residual symptomatic disease. Most patients underwent surgery during the latter stages of the disease, and the results were discouraging. The availability of effective antibiotic therapy for primary lung abscess has drastically modified the natural history of the disease and diminished the role of surgery. Operative indications are less frequent in current practice, and these procedures are undertaken electively for chronic illnesses only after medical therapy has been unsuccessful. In addition to antibiotics, pulmonary care has advanced and now includes postural drainage. Currently, bronchoscopy is occasionally used as an adjunct to expedite drainage and to identify underlying occult lesions such as foreign bodies and malignancies. In the last 2 decades, the increasing use of corticosteroids, immunosuppressive drugs, and chemotherapeutic agents has changed the natural milieu of the oropharyngeal cavity and contributed to the mounting frequency of opportunistic lung abscesses. For excellent patient education resources, visit eMedicine's Infections Center, Lung and Airway Center, Pneumonia Center, and Procedures Center. Also, see eMedicine's patient education articles Bacterial Pneumonia, Abscess, Antibiotics, and Bronchoscopy. CLASSIFICATION, ETIOLOGY, AND PATHOPHYSIOLOGYSection 3 of 10
Classification Lung abscesses are considered acute or chronic depending on the duration of symptoms at the time of patient presentation. The arbitrary dividing time is 4-6 weeks. Primary lung abscess are commonly observed in patients who are predisposed to aspiration or in otherwise healthy individuals, whereas secondary lung abscesses represent complications of a preexisting local lesion such as a bronchogenic carcinoma or a systemic disease (eg, HIV infection) that compromises immune function. Etiology Lung abscesses have numerous infectious causes. Anaerobic bacteria continue to be accountable for most cases. These bacteria predominate in the upper respiratory tract and are heavily concentrated in areas of oral-gingival disease. Other bacteria involved in lung abscesses are gram-positive and gram-negative organisms. However, lung cavities may not always be due to an underlying infection. Factors contributing to lung abscess
Pathogenesis Aspiration of infectious material is the most frequent etiologic mechanism in the development of pyogenic lung abscess. Aspiration due to dysphagia (eg, achalasia) or to compromised consciousness (eg, alcoholism, seizure, cerebrovascular accident, head trauma) appears to be a predisposing factor. Poor oral hygiene, dental infections, and gingival disease are also common in these patients. Although lung abscesses can occur in edentulous patients, an occult carcinoma should be considered. Edentulous patients very seldom, if ever, develop a putrefied abscess because they lack periodontal flora. Patients with alcoholism and those with chronic illnesses frequently have oropharyngeal colonization with gram-negative bacteria, especially when they undergo prolonged endotracheal intubation and are administered agents that neutralize gastric acidity. A pyogenic lung abscess can also develop from aspiration of infectious material from the oropharynx into the lung when the cough reflex is suppressed in a patient with gingivodental disease. Pathology Abscesses generally develop in the right lung and involve the posterior segment of the right upper lobe, the superior segment of the lower lobe, or both. This is due to gravitation of the infectious material from the oropharynx into these dependent areas. Initially, the aspirated material settles in the distal bronchial system and develops into a localized pneumonitis. Within 24-48 hours, a large area of inflammation results, consisting of exudate, blood, and necrotic lung tissue. The abscess frequently connects with a bronchus and partially empties. After pyogenic pneumonitis develops in response to the aspirated infected material, liquefactive necrosis can occur secondary to bacterial proliferation and an inflammatory reaction to produce an acute abscess. As the liquefied necrotic material empties through the draining bronchus, a necrotic cavity containing an air-fluid level is created. The infection may extend into the pleural space and produce an empyema without rupture of the abscess cavity. The infectious process can also extend to the hilar and mediastinal lymph nodes, and these too may become purulent. Bacteriology of lung abscess
CLINICAL FEATURESSection 4 of 10
Generally, most of the patients admitted to the hospital with a diagnosis of lung abscess have had symptoms for at least 2 weeks. These patients typically have an intermittent febrile course, productive cough, weight loss, general malaise, and night sweats. Initially, foul sputum is not observed in the course of the infection; however, after cavitation occurs, putrid expectorations are quite prevalent. The odor of the breath and sputum of a patient with an anaerobic lung abscess is often quite pronounced and noxious and may provide a clue to the diagnosis. Hemoptysis may occasionally follow the expectoration of putrid sputum. Primary lung abscesses that occur following staphylococcal suppurative pneumonia in infants and children lack the typical indolent recurrent course of the more common postaspiration infections. Their onset tends to be abrupt and more threatening, producing chills, fever, tachycardia, tachypnea, and unremitting production of putrid sputum. The sputum is rarely without odor because an anaerobic infection has no indolent course. The physical findings are similar to those of pneumonia, with or without a pleural effusion. Auscultation may reveal coarse rhonchi and absent breath sounds. Clubbing of the fingers is sometimes noted. CLINICAL TYPESSection 5 of 10
Anaerobic necrotizing pneumonia Usually, anaerobic necrotizing pneumonia is chiefly restricted to one pulmonary segment or lobe, although it may progress to encompass an entire lung or both lungs. This type of anaerobic lung infection is the most serious. The inflammatory process often spreads quickly and causes destruction characterized by greenish staining of the lung and a huge amount of putrid tissue, resulting in pulmonary gangrene. These patients are gravely ill with a progressive septic course. Leukocytosis is obvious, and the sputum is putrid. Secondary lung abscess In cases of secondary lung abscess, the fundamental process (eg, bacteremia, endocarditis, septic thrombophlebitis, subphrenic infection) is generally apparent along with the pulmonary pathology. Infections below the diaphragm may extend to the lung or pleural space by way of the lymphatics, either directly through the diaphragm or via defects in it. The most typical hematogenous lung abscesses are observed in persons with staphylococcal bacteremia, especially in children. These abscesses are multiple and are located in the periphery of the lung. Infections may arise in or posterior to an obstruction (eg, an enlarged mediastinal lymph node) and migrate to the lungs. Septic emboli from bacterial endocarditis or emboli from deep pelvic veins may result in metastatic lung abscess. Septic emboli are suggested when multiple lesions appear over an extended period. Fewer than 5% of bland pulmonary infarcts become secondarily infected. Secondary infection of infarcts is suggested if fever and leukocytosis are present. Abscess formation may also occur within a necrotic pulmonary tumor. Amebic lung abscess Patients who develop an amebic lung abscess often have symptoms associated with a liver abscess. These may include right upper quadrant pain and fever. After perforation of the liver abscess into the lung, the individual may develop a cough and expectorate a chocolate or anchovy paste–like sputum that has no odor. The patient may give a history of diarrhea and travel outside the country. DIAGNOSIS AND WORKUPSection 6 of 10
Diagnosis The diagnosis of a typical lung abscess can usually be confirmed based on history and physical examination findings. Approximately 10-20% of patients with anaerobic lung abscess have no obvious oral cavity disease or predisposition to aspiration, which are the 2 most important factors in the development of anaerobic lung infection. Evaluation of expectorated sputum is the first step in the diagnosis of a patient with a lung abscess. Perform a Gram stain and culture for both gram-positive and gram-negative organisms and special staining for acid-fast bacteria and fungi. Generally, in patients with a typical anaerobic lung abscess, sputum analysis is not useful, but the analysis is helpful to exclude other causes of lung abscess (eg, tuberculosis, aerobic bacteria). The sputum Gram stain in patients with anaerobic lung abscesses often shows numerous polymorphonuclear leukocytes along with a mixture of bacteria, some of which are contaminants of oral flora. Because of the presence of anaerobes in the oral cavity, cultures of these microorganisms are not worthwhile. Regular aerobic culture of expectorated sputum should always be performed. When a single predominant organism is cultured, it is accepted to be the pathogen. Empyema fluid, if accessible, provides an excellent medium. Occasionally, particularly with metastatic lung abscesses, blood culture findings may be positive. Most patients never have appropriate specimens obtained for culture; most are treated empirically and do well despite the lack of exact microbiologic culture results. Chest radiographs The chest radiograph of a lung abscess is not pathognomic in the early stages, ie, before communication is achieved between the abscess cavity and draining bronchus. An area of thick pneumonic consolidation precedes the emergence of the typical cavitary air-fluid form. The distinctive characteristic of lung abscess, the air-fluid level, can only be observed on a chest x-ray film taken with the patient upright or in the lateral decubitus position. In the presence of associated pleural thickening, atelectasis, or pneumothorax, the air-fluid level may be obscured. When better anatomic interpretation is required, CT scans have proven very useful. Opportunistic lung abscesses are more difficult to diagnose. They occur in patients at the extremes of age and in patients with multiple medical problems. Under these conditions, multiple abscesses often evolve, and most of these are nosocomial. Typically, the microbial flora in these patients is gram-negative. Similar to aspiration-induced lung abscess, cavitation is generally apparent on chest radiographs 2 weeks after the onset of cough, fever, and pleuritic chest pain. Chest CT scan images are valuable for demonstrating cavitation within an area of consolidation, for evaluating the thickness and regularity of the abscess wall, and for determining the exact position of the abscess with regard to the chest wall and bronchus. CT scan images can also aid in evaluating the extent of bronchial involvement proximal or distal to the abscess. Invasive diagnostic procedures Invasive diagnostic techniques occasionally recommended to diagnose lung abscesses include transtracheal aspirates, transthoracic aspirates, and fiberoptic bronchoscopy. These procedures must be performed prior to the institution of antibiotic therapy in order to acquire dependable microbiological data. The indications and comparative benefits of such procedures are controversial and depend to a great extent on operator ability. Most pulmonologists believe that these diagnostic procedures should not be performed routinely in patients with possible anaerobic lung abscesses; they should be reserved for patients with atypical presentations. Fiberoptic bronchoscopy is a useful adjunct in the diagnostic evaluation of patients with lung abscess. Secretions obtained from the lower respiratory tract via either lavage or brush can be submitted for culture and sensitivity. Rigid, sterile, and aseptic technique is crucial (eg, use of lidocaine without preservatives, minimal use of topical anesthetic, specimen transport under anaerobic conditions, avoidance of delays in processing), although prior or concurrent antibiotic therapy can cause confusing results. Thus, in patients who have a classic history and radiological presentation of anaerobic lung abscess, the medically sound decision may be to start with empirical antibiotic therapy without prior bronchoscopy. However, for patients with atypical presentations or unclear diagnoses, bronchoscopy should be considered. Bronchoscopy may also be used to exclude the presence of a foreign body or neoplasm. If no specimens are available for analysis and diagnosis, percutaneous transtracheal aspiration is an easy, safe, and dependable way of establishing the specific cause of a lung abscess. This procedure should be avoided in patients with coagulation disorders or bleeding tendencies and in those for whom it is difficult to provide adequate oxygenation. For patients with amebic liver abscess, Entamoeba histolytica may be recovered from the sputum. The vast majority of patients with extraintestinal amebiasis have high titers of hemoagglutinin in the serum. Differential diagnosis Cavitary lesions in the lung parenchyma have several causes, but a patient with an acute presentation of an illness with air-fluid levels should elicit consideration of a lung abscess. Lung parenchymal cystic lesions and secondarily infected bullae can occasionally confuse the picture. The prior existence of these lesions, as documented by old radiographs and the segmental location, are not typical of lung abscess. Patients with squamous cell bronchial carcinomas can also present with cavitary lesions that are sometimes difficult to differentiate from lung abscesses. Realizing that the wall of the carcinomatous abscess is usually thicker and more irregular than that of the primary abscess is helpful. Further, foul sputum, no response to antibiotics, and the absence of fever may help distinguish the 2 entities. Because an abscess distal to bronchial obstruction usually occurs in an area of lobar pneumonitis and atelectasis—but otherwise appears as a primary abscess—early bronchoscopy is recommended in all cases. Differential diagnoses of a cavitary lung lesion
MEDICAL TREATMENTSection 7 of 10
The current management of anaerobic lung abscesses includes prolonged antibiotic therapy. Because effective broad-spectrum antibiotics are available, primary or nonspecific abscesses can frequently be arrested in the early stage of suppurative pneumonitis. Whereas penicillin has always been the antibiotic of choice, recent trials show clindamycin to be superior. Intravenous therapy is appropriate for adults until an initial clinical response is observed, after this time, oral therapy is safe. Although the overall efficacy of penicillin seems to diminish with time, it presently remains a practical drug for most patients, especially if clindamycin is contraindicated. Tetracycline is considered inadequate therapy because most anaerobes are resistant to it. Similarly, metronidazole is ineffective in approximately 50% of patients, presumably because of the contribution of aerobic bacteria. Therefore, if this agent is to be used, combine it with either a penicillin derivative or a cephalosporin. After initial antibiotic therapy, the clinical and radiographic response is gradual. The fever generally subsides in 4-7 days, but normalization of the chest radiograph may require 2 months. Antibiotics in lung abscess
Drainage Most lung abscesses communicate with the tracheobronchial tree early in the course of the infection and drain spontaneously during the course of therapy. Dependent drainage (with appropriate positions based on the pulmonary segment) is commonly advocated using chest physical therapy and sometimes bronchoscopy. Bronchoscopy can also facilitate abscess drainage by aspiration of the appropriate bronchus through the bronchoscope. Transbronchial drainage by catheterization of the appropriate bronchus under fluoroscopy has been successful. Generally, augmenting this passive drainage with invasive procedures is unnecessary. In fact, attempts at therapeutic bronchoscopy may sometimes produce adverse consequences. Reports have been received of bronchoscopy-induced release of large amounts of purulent material from the involved lung segment into other parts of the lung, occasionally inducing acute respiratory failure, acute respiratory distress syndrome (ARDS), or both. Course of treatment If treatment is started in the acute stage of the disease and is continued for 4-6 weeks, approximately 85-95% of patients with anaerobic lung abscesses respond to medical management alone. Successful medical therapy resolves symptoms with no radiographic evidence or only a residual thin-walled cystic cavity (<2 cm after 4-6 wk of antibiotic therapy). The success of medical therapy is dependent on the duration of symptoms and the size of the cavity before the initiation of therapy. Antibiotic therapy is rarely successful if symptoms are present for longer than 12 weeks before the initiation of antibiotic therapy or if the original diameter of the cavity is more than 4 cm. When patients with lung abscesses do not respond to proper medical therapy, consider the probability of an underlying malignancy. SURGICAL TREATMENTSection 8 of 10
Contraindications to surgery Several important factors must be considered prior to undertaking surgery. Because of the high risk of spillage of the abscess into the contralateral lung, it is almost essential that a double-lumen tube be used to protect the airway. If this is not available, surgery poses a very high risk of abscess in the other lung and a risk of ARDS. In such cases, postponing the surgery is a wise decision. Another, less-satisfactory method to deal with this problem includes positioning the patient in the prone position. The surgeon must be skilled in resecting the abscess and in rapid clamping of the bronchus to prevent spillage into the trachea. These factors are extremely important when dealing with the surgical aspects of treating a lung abscess. If doubt persists, postponing the surgery is best. Surgical treatment is now rarely necessary and is almost never the initial choice in the treatment of lung abscesses. In current practice, fewer than 15% of patients need surgical intervention for the unchecked disease and for complications that occur in both the acute and chronic stages of the disease. Surgical management is reserved for specific indications such as little or no response to medical treatment, inability to eliminate a carcinoma as a cause, critical hemoptysis, and complications of lung abscess (eg, empyema, bronchopleural fistula). In addition, if after 4-6 weeks of medical treatment a notable residual cavity remains and the patient is symptomatic, surgical resection is advocated. The results of surgery are difficult to assess because of the varying patient population and the tremendous increase in illicit drug abuse, alcoholism, AIDS, and infections by gram-negative and opportunistic organisms. These factors have increased the incidence of lung abscess and the associated morbidity. A great deal of caution is needed during anesthesia when patients with lung abscess undergo surgery because spillage of the abscess material into the uninvolved lung can occur. Therefore, a double-lumen endotracheal tube is used in all cases. Indications for surgery
Percutaneous drainage Percutaneous drainage of a complicated abscess (ie, one associated with fever and signs of sepsis) is beneficial in selected patients who do not respond to adequate medical therapy. These are ventilator-dependent patients who are not candidates for extensive thoracic procedures. Other indications for drainage include ongoing sepsis despite adequate antimicrobial therapy, progressively enlarging lung abscess in imminent danger of rupture, failure to wean from mechanical ventilation, and contamination of the opposite lung. In current practice, most of these lung abscesses are drained under CT guidance. Results achieved with percutaneous drainage show it to be safe and effective compared to surgery. Percutaneous drainage is rarely complicated by empyema, hemorrhage, or bronchopleural fistula. Although a few patients who undergo percutaneous drainage develop bronchopleural fistulas, most of these fistulas close spontaneously with resolution of the abscess cavity. Percutaneous drainage may be used to stabilize and prepare critically ill patients for surgery. Abscess from gram-negative and opportunistic bacteria Hospital-acquired gram-negative infections are usually due to nosocomial organisms (eg, Pseudomonas, Enterobacter, Proteus). Patients with these infections are often elderly, debilitated with numerous major medical disorders, or have sustained multiple trauma. These patients are typically treated in a critical care unit. The infection is usually with a resistant organism originating from a single source. The lung abscess appears rapidly as an area of pneumonitis with associated pleural involvement. These patients often require percutaneous drainage as an emergency procedure. Unfortunately, the infection is systemic and often out of control, and the pulmonary pathology represents only one aspect of a multiorgan involvement with a rapidly deteriorating course. Among fungal infections, Candida albicans has become a major organism in lung abscesses. Fungal infections are difficult to treat, and amphotericin/fluconazole and surgical drainage remain the only modalities of treatment; however, at best, they have had only limited success. COMPLICATIONS AND PROGNOSISSection 9 of 10
Complications Approximately one third of lung abscesses are complicated by empyema. This may be observed with or without bronchopleural fistulas. Hemoptysis is a common complication of a lung abscess and can be treated with bronchial artery embolization. Occasionally, the hemoptysis can be massive, thus requiring urgent surgery. Brain abscess may also be a complication in patients who receive inadequate treatment. Prognosis The prognosis of patients with lung abscesses depends on the underlying or predisposing pathologic event and the speed with which appropriate therapy is established. Negative prognostic factors include a large cavity (>6 cm), necrotizing pneumonia, multiple abscesses, immunocompromise, age extremes, associated bronchial obstruction, and aerobic bacterial pneumonia. The mortality rate associated with an anaerobic lung abscess is less than 15%, although it is slightly higher in patients with necrotizing anaerobic pneumonia and pneumonia caused by gram-negative bacteria. The prognosis associated with amebic lung abscess is good when treatment is prompt. REFERENCESSection 10 of 10
Lung Abscess, Surgical Perspective excerpt Article Last Updated: Apr 19, 2006 |
