Clinical and Radiologic Findings
Recurrent aspiration of gastric contents, or chronic occult aspiration, is a common, often silent, process that especially affects infants with feeding problems, adults with neurologic deficits, and patients with decreased gastroesophageal motility and acid reflux. Recurrent aspiration is known to cause lung disease and recurrent pneumonia and may also be a contributing factor in exacerbating chronic lung diseases, such as idiopathic pulmonary fibrosis (IPF), chronic obstructive lung disease, chronic rejection in lung transplant patients, and cystic fibrosis.
In a series of patients with lung infiltrates and pulmonary symptoms that could not be explained by routine evaluation, almost half showed pulmonary aspiration by overnight scintigraphy, which correlated positively with obstructive sleep apnea and recurrent pneumonias.1
Gastroesophageal reflux disease (GERD) is a proven risk factor for recurrent microaspiration, which may cause lung injury. Unfortunately, there are no reliable widely used diagnostic tests for microaspiration. Proximal esophageal acid detection by pH monitoring is widely available but lacks sensitivity. Impedance monitoring measures both acid and nonacid reflux episodes and is therefore more sensitive.2
In fact, experimental studies have shown that microaspiration is a fairly common phenomenon and can be seen in up to 40% of normal individuals and in up to 70% of people with neurologic alterations or obstructive sleep apnea. However, normal people tend to clear such aspirations without sequelae.3,4
Aspiration pneumonia generally results from a single large event and is a common autopsy finding in debilitated patients with neurologic defects or other predisposing factors.
Common presenting symptoms of aspiration-induced lung disease include dyspnea, fever, and cough. There is a history of recurrent pneumonia in about 25% of patients. In addition to reflux and neurologic disease, drug use is an additional predisposing factor.5
The most common clinical settings for aspiration are presented in Table 25.1
Chest radiograph shows bilateral infiltrates or nodules in about half, with unilateral findings in the other half. Areas most prone to aspiration are the right middle and lower lobes, due to the anatomic configuration of the bronchi. However, these vary depending on the patient’s position at the time of aspiration (e.g., sleep patterns). In some cases, nodules may be solitary and raise a clinical concern for malignancy. Computed tomography (CT) in patients with prominent small airway involvement typically shows centrilobular nodules in dependent portions of the lung. In aspiration pneumonia, imaging often demonstrates airspace disease (ground glass or consolidation), reticular densities, and nodules.
Gross and Histologic Findings
Aspiration pneumonia is characterized by patchy areas of consolidation (Fig. 25.1
). Abscess formation is not uncommon.
The histologic findings of aspiration depend on the type and amount of aspirated material. Aspiration of a large bolus of acid gastric content causes diffuse alveolar damage (Chapter 4). Aspiration of recurrent small amount of food or pills usually causes acute and organizing pneumonia with multinucleated foreign body giant cell reaction and suppurative granulomas. Chronic bronchiolitis may be the predominant histologic finding secondary to chronic occult aspiration.9
A definitive diagnosis rests on the identification of foreign material within the giant cells or suppurative granulomas (Figs. 25.2
The most common vegetable matter seen in chronic aspiration is the starch grain or granule, found in legumes, including peas, beans, and lentils. The starch granule is about 100 µ in length (Fig. 25.3
), is eosinophilic and well demarcated and oval, and eventually degenerates as macrophages engulf the material (Fig. 25.4
). Other foreign materials that may be seen in aspiration include cellulose (Fig. 25.5
), crospovidone (Fig. 25.6
), Kayexalate (Fig. 25.7
and talc (Fig. 25.8
), each with characteristic histologic features. If foreign material is not present,
a histologic diagnosis of aspiration pneumonia cannot be made, although can be surmised with clinical documentation of aspiration and exclusion of other causes of lung disease.11
TABLE 25.1 Most Common Aspiration Material and ClinicoPathologic Findings
Gastric acid aspiration
Major cause of diffuse alveolar damage in patients with neurologic impairment
May lead to lung abscess
Chronic airway disease
Interstitial fibrosis associated with foci of organizing pneumonia
Especially common in children, it produces rapid symptoms: congestion, hemorrhage, edema, and hyaline membrane formation
Most commonly vegetable matter (seeds), skeletal muscle, fat tissue, or fragments of bone
Acute exudative response in <24 h
Chronic changes include foreign body giant cell reaction and organizing pneumonia.
Fibrosis and calcification can occur at later stages.
Recurrent aspiration can lead to diffuse bronchiolitis in a miliary form.
Tablet components (cellulose, crospovidone, talc, etc.) may be found alone or in association with food material.
Some of the components may be birefringent on polarization.
Kayexalate has a distinctive histologic appearance—large dark PAS-positive basophilic glassy particles.
Oil (exogenous lipid)
Mineral, vegetable, and animal oil can all be aspirated into the lung.
Mineral oil used in drugs is the most common agent in exogenous lipid pneumonia.
Microscopically, the droplets are usually dissolved by tissue processing, and one can see as circular negative images within the tissue and commonly associated with giant cells.
FIGURE 25.1 ▲ Aspiration pneumonia, autopsy. Gross findings are patchy areas of consolidation, especially in dependent portions of the lung.
FIGURE 25.2 ▲ Aspiration pneumonia. There is organizing pneumonia with scattered multinucleated giant cells. Even if no foreign material is found, the finding is suggestive of aspiration.
FIGURE 25.3 ▲ Aspirated starch granule. The starch is about 100 µ in length and has elicited an acute inflammatory reaction.
FIGURE 25.4 ▲ Aspirated foreign material. There is a multinucleated giant cell reaction to acellular debris, which by size and shape may represent degenerated starch grains.
FIGURE 25.5 ▲ Aspirated cellulose. A. Microcrystalline cellulose aspiration of ground pills forming gray rod-like sheet material. B. Typical longitudinal central groove of microcrystalline cellulose under polarized light.
FIGURE 25.6 ▲ Polyvinylpyrrolidone (PVP). PVP and related compounds are found in adhesives and toothpaste and is the most widely used excipient in pharmaceuticals. The material forms hematoxylinophilic irregular deposits in this case surrounded by macrophage giant cells (arrows).
FIGURE 25.7 ▲ Kayexalate aspiration. There are crystals within an airway. There is autolysis of the mucosa secondary to autopsy artifact.
FIGURE 25.8 ▲ Talc granulomas, transbronchial biopsy. A. High magnification photomicrograph demonstrates nonnecrotizing granulomas. B. Viewed under polarized light, talc crystals are readily identified.
Aspiration pneumonia may result in an infectious process due to superinfection by bacteria from the oropharynx or bacteria found in aspirated matter. Histologically, the features are those of an acute bronchopneumonia, often necrotizing, and foreign material may or may not be present.11
Recurrent Aspiration and Idiopathic Pulmonary Fibrosis
Gastroesophageal reflux may play a role in advancing the course of disease as well as causing symptoms in patients with IPF. A high prevalence of reflux has been found among patients with IPF.12,13
The clinical impact of reflux on IPF disease progression is unclear, and the benefits of antireflux surgery have not been entirely substantiated. However, it is believed that a subset of patients with IPF benefit from antireflux therapy.2
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