PICTORIAL ESSAY
Aspiration-Related Lung Diseases Andrew D. Prather, MD,* Tristan R. Smith, MD,* Dana M. Poletto, MD,* Fabio Tavora, MD,w Jonathan H. Chung, MD,z Leelakrishna Nallamshetty, MD,* Todd R. Hazelton, MD,* and Carlos A. Rojas, MDy
Abstract: Aspiration is a common but underrecognized clinicopathologic entity, with varied radiographic manifestations. Aspiration represents a spectrum of diseases, including diffuse aspiration bronchiolitis, aspiration pneumonitis, airway obstruction by foreign body, exogenous lipoid pneumonia, interstitial fibrosis, and aspiration pneumonia with or without lung abscess formation. Many patients who aspirate do not present with disease, suggesting that pathophysiology is related to a variety of factors, including decreased levels of consciousness, dysphagia, impaired mucociliary clearance, composition of aspirate, and impaired host defenses. In this pictorial essay, we will review the different types of aspiration lung diseases, focusing on their imaging features and differential diagnosis. Key Words: aspiration, diffuse aspiration bronchiolitis, aspiration pneumonia, chronic aspiration, Mendelson syndrome, aspiration pneumonitis, fibrotic lung disease, diffuse pulmonary ossification
(J Thorac Imaging 2014;29:304–309)
A
spiration is defined as, “the inhalation of oropharyngeal or gastric contents into the laryngeal or lower respiratory tract.” Aspiration is an important and underrecognized clinicopathologic entity. Some researchers suggest that as many as 5% to 15% of cases of communityacquired pneumonia are related to aspiration, and approximately half of all healthy adults silently aspirate.1–3 However, most people who aspirate do not develop disease, indicating that pathophysiology is multifactorial. The risk of aspiration is affected by the level of consciousness, neurological status, oropharyngeal motility, cough reflex, and the presence or absence of gastroesophageal reflux disease (GERD).3,4 Aspiration represents a spectrum of diseases, with patterns of lung injury that overlap, both pathologically and radiographically. These patterns are determined by the aspirated content and volume, as well as by host defenses. In this pictorial essay, we will first review the pathologic findings in aspiration-related lung disease. Next, we will review the different types of aspiration lung disease, including diffuse aspiration bronchiolitis (DAB), aspiration pneumonitis and Mendelson syndrome, aspiration pneumonia (with or without abscess formation), From the *Department of Radiology; yDiagnostic Radiology Residency, University of South Florida College of Medicine, Tampa, FL; zDepartment of Radiology, National Jewish Health, Denver, CO; and wArgos Laboratory, Fortaleza, Brazil. The authors declare no conflicts of interest. Correspondence to: Carlos A. Rojas, MD, Diagnostic Radiology Residency, University of South Florida College of Medicine, 2 Tampa General Circle, STC 7035, Tampa, FL 33606 (e-mail: [email protected]). Copyright r 2014 by Lippincott Williams & Wilkins
304 | www.thoracicimaging.com
foreign body aspiration, exogenous lipoid pneumonia, and sequela of chronic aspiration, discussing the etiology and clinical features of each, then focusing on imaging characteristics and differential diagnosis.
PATHOLOGIC FINDINGS IN ASPIRATION PNEUMONIA Aspiration into the respiratory tract causes a wide range of effects that include bronchiolitis, pneumonitis, acute pneumonia, organizing pneumonia (OP), abscess formation, and interstitial fibrosis. These different effects should be recognized as a spectrum of pathology, often coexisting in the same patient. However, several more specific pathologic patterns can be observed. When the contents of the aspirated material cause a chemical pneumonitis, as in aspiration pneumonitis, intraalveolar edema, acute and chronic hemorrhage with hemosiderin-laden macrophages, and diffuse alveolar damage are seen. Chemical pneumonitis resulting from massive aspiration of gastric contents with pH < 2.5 is known as Mendelson syndrome. In this entity, injury occurs in 2 phases. The first phase results from the direct caustic effects of the acidic aspirate, and the second phase results from recruitment of neutrophils.1 Alveolar damage and edema can progress to diffuse alveolar damage, hemorrhage, and pulmonary necrosis.2 In foreign body aspiration, the material may cause large bronchial obstruction, which can lead to distal abscess formation and parenchymal necrosis. However, these changes are nonspecific, and often the pathologist may not be able to reach a more specific diagnosis.5 However, there are 2 more distinct findings that can be seen on transbronchial biopsies. The first involves the aspiration of either seeds, plant material, or meat (Fig. 1). In this setting, the inflammatory reaction surrounding the foreign bodies is composed of either neutrophils in the setting of acute bronchopneumonia or foreign body–type macrophages in the setting of OP. The use of polarization microscopy may be of value in identifying the foreign particles themselves. Even more specifically, aspiration of partially digested vegetable matter such as legumes (peas, lentils, or beans) can cause a form of granulomatous pneumonitis known as lentil aspiration pneumonia. This pattern can begin with microabscess formation and progress to the formation of epithelioid granulomas with central necrosis.6,7 The second more specific pathologic pattern of foreign body aspiration is due to the aspiration of oily material, commonly mineral oil, which leads to lipoid pneumonia. The lung parenchyma in these cases may show fibrosis, as well as a histiocytic reaction involving the accumulation of lipid-laden macrophages.8 Cystic spaces are often seen in J Thorac Imaging
Volume 29, Number 5, September 2014
J Thorac Imaging
Volume 29, Number 5, September 2014
Aspiration Changes in the Lungs
FIGURE 1. A, Hematoxylin and eosin–stained, low-power view of the lung in a patient with chronic aspiration. There are ill-defined and confluent areas of necrosis with abscess and granuloma formation (black arrow) and foreign body giant cell reaction. B, Hematoxylin and eosin–stained, high-power view of the lung of a different patient with a history of chronic aspiration demonstrates granulomatous and giant cell inflammatory infiltrates surrounding amorphous, aspirated material, which forms palisading granulomas (white arrow) in a nodular distribution along alveolar septa (courtesy of Dr Allen Burke, University of Maryland, Baltimore, MD).
close association with these changes, giving the tissue a unique histologic picture. These empty spaces are composed of vacuoles that washed out the lipid during tissue processing. Multinucleated giant cells may be present, and focal tissue necrosis may also be an associated feature.8 In chronic aspiration cases, a pattern of OP may result (Fig. 2).6,7 OP is characterized pathologically by a fibroblastic response, with granulation tissue formation in peripheral alveolar spaces.9 However, this pattern is nonspecific and can be seen in OP secondary to multiple causes, including autoimmune disease. A differentiating factor specific to aspiration-related OP is the presence of multinucleated giant cells and foreign body granulomas.9,10
DAB DAB describes the resultant inflammation of bronchioles secondary to aspiration. Although uncommon, occurring in
Aspiration-Related Lung Diseases Andrew D. Prather, MD,* Tristan R. Smith, MD,* Dana M. Poletto, MD,* Fabio Tavora, MD,w Jonathan H. Chung, MD,z Leelakrishna Nallamshetty, MD,* Todd R. Hazelton, MD,* and Carlos A. Rojas, MDy
Abstract: Aspiration is a common but underrecognized clinicopathologic entity, with varied radiographic manifestations. Aspiration represents a spectrum of diseases, including diffuse aspiration bronchiolitis, aspiration pneumonitis, airway obstruction by foreign body, exogenous lipoid pneumonia, interstitial fibrosis, and aspiration pneumonia with or without lung abscess formation. Many patients who aspirate do not present with disease, suggesting that pathophysiology is related to a variety of factors, including decreased levels of consciousness, dysphagia, impaired mucociliary clearance, composition of aspirate, and impaired host defenses. In this pictorial essay, we will review the different types of aspiration lung diseases, focusing on their imaging features and differential diagnosis. Key Words: aspiration, diffuse aspiration bronchiolitis, aspiration pneumonia, chronic aspiration, Mendelson syndrome, aspiration pneumonitis, fibrotic lung disease, diffuse pulmonary ossification
(J Thorac Imaging 2014;29:304–309)
A
spiration is defined as, “the inhalation of oropharyngeal or gastric contents into the laryngeal or lower respiratory tract.” Aspiration is an important and underrecognized clinicopathologic entity. Some researchers suggest that as many as 5% to 15% of cases of communityacquired pneumonia are related to aspiration, and approximately half of all healthy adults silently aspirate.1–3 However, most people who aspirate do not develop disease, indicating that pathophysiology is multifactorial. The risk of aspiration is affected by the level of consciousness, neurological status, oropharyngeal motility, cough reflex, and the presence or absence of gastroesophageal reflux disease (GERD).3,4 Aspiration represents a spectrum of diseases, with patterns of lung injury that overlap, both pathologically and radiographically. These patterns are determined by the aspirated content and volume, as well as by host defenses. In this pictorial essay, we will first review the pathologic findings in aspiration-related lung disease. Next, we will review the different types of aspiration lung disease, including diffuse aspiration bronchiolitis (DAB), aspiration pneumonitis and Mendelson syndrome, aspiration pneumonia (with or without abscess formation), From the *Department of Radiology; yDiagnostic Radiology Residency, University of South Florida College of Medicine, Tampa, FL; zDepartment of Radiology, National Jewish Health, Denver, CO; and wArgos Laboratory, Fortaleza, Brazil. The authors declare no conflicts of interest. Correspondence to: Carlos A. Rojas, MD, Diagnostic Radiology Residency, University of South Florida College of Medicine, 2 Tampa General Circle, STC 7035, Tampa, FL 33606 (e-mail: [email protected]). Copyright r 2014 by Lippincott Williams & Wilkins
304 | www.thoracicimaging.com
foreign body aspiration, exogenous lipoid pneumonia, and sequela of chronic aspiration, discussing the etiology and clinical features of each, then focusing on imaging characteristics and differential diagnosis.
PATHOLOGIC FINDINGS IN ASPIRATION PNEUMONIA Aspiration into the respiratory tract causes a wide range of effects that include bronchiolitis, pneumonitis, acute pneumonia, organizing pneumonia (OP), abscess formation, and interstitial fibrosis. These different effects should be recognized as a spectrum of pathology, often coexisting in the same patient. However, several more specific pathologic patterns can be observed. When the contents of the aspirated material cause a chemical pneumonitis, as in aspiration pneumonitis, intraalveolar edema, acute and chronic hemorrhage with hemosiderin-laden macrophages, and diffuse alveolar damage are seen. Chemical pneumonitis resulting from massive aspiration of gastric contents with pH < 2.5 is known as Mendelson syndrome. In this entity, injury occurs in 2 phases. The first phase results from the direct caustic effects of the acidic aspirate, and the second phase results from recruitment of neutrophils.1 Alveolar damage and edema can progress to diffuse alveolar damage, hemorrhage, and pulmonary necrosis.2 In foreign body aspiration, the material may cause large bronchial obstruction, which can lead to distal abscess formation and parenchymal necrosis. However, these changes are nonspecific, and often the pathologist may not be able to reach a more specific diagnosis.5 However, there are 2 more distinct findings that can be seen on transbronchial biopsies. The first involves the aspiration of either seeds, plant material, or meat (Fig. 1). In this setting, the inflammatory reaction surrounding the foreign bodies is composed of either neutrophils in the setting of acute bronchopneumonia or foreign body–type macrophages in the setting of OP. The use of polarization microscopy may be of value in identifying the foreign particles themselves. Even more specifically, aspiration of partially digested vegetable matter such as legumes (peas, lentils, or beans) can cause a form of granulomatous pneumonitis known as lentil aspiration pneumonia. This pattern can begin with microabscess formation and progress to the formation of epithelioid granulomas with central necrosis.6,7 The second more specific pathologic pattern of foreign body aspiration is due to the aspiration of oily material, commonly mineral oil, which leads to lipoid pneumonia. The lung parenchyma in these cases may show fibrosis, as well as a histiocytic reaction involving the accumulation of lipid-laden macrophages.8 Cystic spaces are often seen in J Thorac Imaging
Volume 29, Number 5, September 2014
J Thorac Imaging
Volume 29, Number 5, September 2014
Aspiration Changes in the Lungs
FIGURE 1. A, Hematoxylin and eosin–stained, low-power view of the lung in a patient with chronic aspiration. There are ill-defined and confluent areas of necrosis with abscess and granuloma formation (black arrow) and foreign body giant cell reaction. B, Hematoxylin and eosin–stained, high-power view of the lung of a different patient with a history of chronic aspiration demonstrates granulomatous and giant cell inflammatory infiltrates surrounding amorphous, aspirated material, which forms palisading granulomas (white arrow) in a nodular distribution along alveolar septa (courtesy of Dr Allen Burke, University of Maryland, Baltimore, MD).
close association with these changes, giving the tissue a unique histologic picture. These empty spaces are composed of vacuoles that washed out the lipid during tissue processing. Multinucleated giant cells may be present, and focal tissue necrosis may also be an associated feature.8 In chronic aspiration cases, a pattern of OP may result (Fig. 2).6,7 OP is characterized pathologically by a fibroblastic response, with granulation tissue formation in peripheral alveolar spaces.9 However, this pattern is nonspecific and can be seen in OP secondary to multiple causes, including autoimmune disease. A differentiating factor specific to aspiration-related OP is the presence of multinucleated giant cells and foreign body granulomas.9,10
DAB DAB describes the resultant inflammation of bronchioles secondary to aspiration. Although uncommon, occurring in
