• The filling and obstruction of segmental or subsegmental bronchi by thickened, tenacious secretions or other aspirated material.
• On CT, this appears as hyperattenuating material within the airways, which may be completely occluded.

• In the context of trauma and difficult nasogastric tube placement, airway inspissation in the basilar segments is highly suggestive of an aspiration event.
• The dependent location is characteristic for a patient in a recumbent or semi-recumbent position.
• This finding represents obstruction of the airways by the aspirated contents.

Chandola S, et al. J Thorac Imaging. 2025.

• Small (1-3 mm), well- or poorly-defined nodular opacities located in the center of the secondary pulmonary lobule, often with a branching or “tree-in-bud” appearance on high-resolution CT.
• These represent material filling or impacting the terminal and respiratory bronchioles.

• This finding is a common manifestation of aspiration, reflecting cellular bronchiolitis and peribronchiolar inflammation caused by the aspirated material.
• The tree-in-bud pattern is produced by impacted centrilobular bronchioles.
• Its presence in the dependent lung zones, such as the basilar segments, further supports aspiration as the etiology, especially in a patient with known risk factors.

Franquet T, et al. RadioGraphics. 2004.
Cardasis JJ, et al. Ann Am Thorac Soc. 2014.

• A CT pattern defined by the Fleischner Society as a “patchwork of regions of differing attenuation seen on CT of the lungs”.
• This heterogeneous pattern can be caused by diseases of the small airways, pulmonary vasculature, or lung parenchyma (alveoli and interstitium).

• In the context of aspiration, mosaic attenuation is typically due to small airway disease, where bronchiolar obstruction leads to air trapping.
• This results in hypoattenuated  lung regions adjacent to more normally ventilated, hyperattenuated regions.
• The pattern may be subtle on inspiratory images and is often accentuated on expiratory CT scans.

Kligerman SJ, et al. RadioGraphics. 2015.

• Aspiration is the inhalation of oropharyngeal or gastric contents into the larynx and lower respiratory tract.
• This can result in a spectrum of pulmonary syndromes, including airway obstruction, chemical pneumonitis (due to acidic or other toxic substances), and infectious pneumonia (caused by aspirated bacteria).

• The primary cause is a failure of the protective mechanisms that normally prevent entry of contents into the lower airways.
• In this case, the patient’s history of trauma, hypoxia, and difficult nasogastric tube placement are significant risk factors.
• Other major predisposing factors include depressed level of consciousness (e.g., from trauma, sedation, anesthesia, or intoxication), dysphagia from neurologic disorders (like stroke), and gastroesophageal reflux.

• The pathophysiology depends on the nature and volume of the aspirated material.
• Aspiration can lead to three main consequences:
• 1. Airway Obstruction: Particulate matter can mechanically block airways, leading to sudden hypoxemia and atelectasis.
• 2. Chemical Pneumonitis (Mendelson’s Syndrome): Aspiration of sterile gastric acid (pH < 2.5) causes direct toxic injury to the respiratory epithelium, leading to an intense inflammatory response, cytokine release, neutrophil infiltration, and interstitial pulmonary edema, which can progress to ARDS.
• 3. Bacterial Pneumonia: Inhalation of oropharyngeal secretions colonized with bacteria leads to a pulmonary infection. This is often due to microaspirations over time, which overwhelm the mucociliary clearance mechanisms and macrophage-dependent defenses, allowing an infection to establish. The resulting inflammation is characterized by patchy consolidation and, in some cases, abscess formation.

• At a macroscopic level, aspiration results in inflammation and consolidation in gravity-dependent segments of the lungs.
• In a recumbent patient, this typically involves the posterior segments of the upper lobes and the superior segments of the lower lobes.
• In an upright patient, the basilar segments of the lower lobes are most affected.
• Histologically, findings can include airway mucosal desquamation, diffuse alveolar damage, and an inflammatory infiltrate.
• Chronic or recurrent aspiration may lead to the formation of foreign-body granulomas, organizing pneumonia, bronchial wall thickening, bronchiectasis, and fibrosis.
• Complications can include necrotizing pneumonia, lung abscesses, and empyema.

• The functional consequences range from asymptomatic to severe respiratory failure.
• Acute effects include hypoxemia due to V/Q mismatch from airway obstruction and edema-filled alveoli.
• Increased work of breathing and decreased lung compliance are common.
• The inflammatory cascade from chemical pneumonitis can rapidly lead to acute respiratory distress syndrome (ARDS).
• Aspiration can also trigger a systemic inflammatory response, potentially leading to extrapulmonary organ damage, including cardiac and renal dysfunction.

• Chest Radiography: Findings often show infiltrates or consolidation in dependent lung segments.
• Computed Tomography (CT): CT is the most sensitive method for diagnosis and characterization.
• Typical findings include patchy or confluent consolidation, ground-glass opacities, and evidence of bronchiolitis, such as centrilobular nodules and “tree-in-bud” opacities.
• These findings are consistent with the basilar segmental airway inspissation and centrilobular micronodules seen in this case.
• CT is also superior for detecting complications like lung abscesses, which may present as a round, fluid-filled lesion with or without an air-fluid level, and empyema.

• Laboratory evaluation is often non-specific but reflects inflammation and infection.
• An elevated white blood cell count (leukocytosis) is common, though it may be absent in frail or elderly patients.
• Blood cultures may be obtained but are often negative.
• Sputum cultures are prone to contamination and are generally not useful for initial diagnosis, especially for anaerobic organisms.
• Some experts suggest that serum procalcitonin may help differentiate aspiration pneumonia from pneumonitis.
• Arterial blood gas (ABG) analysis is crucial for assessing the degree of hypoxemia and respiratory compromise.

• Management depends on the specific aspiration syndrome.
• Witnessed Aspiration: Immediate oropharyngeal suctioning is critical to clear the airway.
• Aspiration Pneumonitis: Treatment is primarily supportive, including oxygen therapy and mechanical ventilation if ARDS develops. Prophylactic antibiotics are not recommended as the initial injury is chemical, not infectious; however, antibiotics are considered if the patient does not improve within 48 hours or if gastric colonization is suspected (e.g., in bowel obstruction). Corticosteroids have not been shown to be beneficial.
• Aspiration Pneumonia: Antibiotics are the cornerstone of therapy. Empiric treatment should cover likely pathogens based on whether the pneumonia is community- or hospital-acquired. Regimens may include a β-lactam/β-lactamase inhibitor (e.g., ampicillin-sulbactam). Specific anaerobic coverage (e.g., with clindamycin or metronidazole) is typically reserved for cases where a lung abscess or empyema is suspected.

• The prognosis for aspiration pneumonia is highly variable and depends on the volume and nature of the aspirate, the patient’s underlying health status, and the development of complications.
• The overall 30-day mortality rate is approximately 21%, but this increases in healthcare-associated cases.
• Long-term mortality is high, with one-year mortality rates reported at 40%, often due to the patient’s underlying comorbidities rather than the pneumonia itself.
• Factors associated with worse long-term outcomes include male sex, low BMI, hypoalbuminemia, anemia, and the need for mechanical ventilation.
• Complications such as ARDS, sepsis, and lung abscess significantly worsen the prognosis.

• The term aspiration originates from the Latin word “aspirare,” which means “to breathe upon” or “to blow upon.” This is derived from “ad” (to) and “spirare” (to breathe). In a medical context, it describes the pathological process of breathing in foreign substances.
• The term pneumonia has ancient roots, described by Hippocrates around 460 BC as “peripneumonia.” It stems from the Greek “pneumon” (lung) and the suffix -ia (a condition of disease), denoting an inflammatory condition of the lung.
• Inspissation comes from the Latin “inspissare,” meaning “to thicken,” from “in-“ (into) and “spissus” (thick, dense).

• Mendelson’s Syndrome: This term specifically refers to the acute chemical pneumonitis caused by the aspiration of acidic gastric contents. It is named after Curtis Mendelson, who first described it in 1946. It is also known as peptic pneumonia or gastric acid aspiration.
• Café Coronary: A colloquial term coined by Haugen in 1963 for a sudden collapse and death during a meal, initially mistaken for a heart attack (coronary). It is, in fact, an asphyxiation event caused by a food bolus obstructing the airway.
• Aspiration Pneumonitis vs. Aspiration Pneumonia: A crucial distinction is made between pneumonitis, which is a chemical inflammation from sterile gastric acid (Mendelson’s Syndrome), and pneumonia, which is a bacterial infection resulting from the inhalation of colonized oropharyngeal or gastric contents.

• Ancient Recognition: The symptoms of pneumonia were described by the Greek physician Hippocrates (c. 460 BC), who considered it a disease “named by the ancients.” Maimonides in the 12th century also provided a description of its classic symptoms.
• Microbial Discovery: The link between bacteria and pneumonia was not established until the late 19th century. In 1875, German pathologist Edwin Klebs was the first to observe bacteria in the airways of patients who died from pneumonia. This was followed by the independent isolation of Streptococcus pneumoniae in 1881 by Louis Pasteur and George Sternberg.
• The 20th Century and Mendelson’s Contribution: In 1946, American obstetrician and cardiologist Curtis Lester Mendelson published his seminal paper, “The aspiration of stomach contents into the lungs during obstetric anaesthesia.” He studied over 44,000 pregnancies and identified 66 cases of aspiration, distinguishing between airway obstruction from solid food and a distinct “asthma-like” chemical pneumonitis from liquid gastric acid. His work established that the acidity of the aspirate (pH < 2.5) was the key factor in the resulting lung injury. This research was foundational to modern anesthetic practice, particularly the “Nil per os” (NPO) or “nothing by mouth” guidelines for laboring patients to prevent aspiration.

• Anesthetic Practice: Mendelson’s findings directly led to a major shift in anesthetic practice, especially in obstetrics. The practice of keeping patients NPO before surgery and during labor became a standard of care to minimize the volume and acidity of stomach contents, thereby reducing the risk of aspiration pneumonitis. The widespread adoption of regional anesthesia over general anesthesia for childbirth has also dramatically reduced the incidence of Mendelson’s Syndrome in this population.
• Demographics and Risk: Historically and culturally, certain populations are recognized as being at higher risk. This includes individuals who consume excessive alcohol, which suppresses the gag reflex, and those with poor dentition, which impairs proper mastication, leading to the “Café Coronary” phenomenon. In contemporary medicine, there is a significant focus on aspiration in the elderly, particularly in nursing homes and in aging societies like Japan, where it accounts for a very high percentage of pneumonia cases.
• Diagnostic Evolution: The understanding of aspiration microbiology has evolved. While historically considered an infection caused by anaerobes from the oral cavity, it is now recognized that in many settings, especially hospitals, aerobic and nosocomial bacteria are common culprits. This has influenced antibiotic selection over time.

• Hippocrates (c. 460-370 BC): First to formally describe the clinical symptoms of pneumonia.
• Edwin Klebs (1834-1913): A German pathologist who, in 1875, was the first to visualize bacteria in the airways of patients who had died from pneumonia, laying the groundwork for the germ theory of the disease.
• Louis Pasteur (1822-1895) & George Sternberg (1838-1915): Independently isolated the pneumococcus bacterium (Streptococcus pneumoniae) in 1881, identifying a primary causative agent of pneumonia.
• Curtis Lester Mendelson (1913-2002): An American obstetrician and cardiologist whose 1946 study definitively characterized chemical pneumonitis from gastric acid aspiration. His experimental work on rabbits differentiated the effects of acidic versus neutral aspirates and solid versus liquid material, leading to his eponymous syndrome and revolutionizing anesthetic safety protocols.

• “Not all that enters the lung is infection.” This line distinguishes chemical pneumonitis from infectious pneumonia.
• “The stomach is a dangerous neighbor to the lungs.” A classic teaching line emphasizing the peril of aspiration.
• “Aspiration may be silent, but its consequences scream.” This refers to the phenomenon of silent aspiration, where no overt choking or coughing occurs, yet can lead to severe pneumonia, often diagnosed days or weeks later.
• “In 1946, Mendelson revealed that hydrochloric acid is the culprit… The acid produces a bronchiolar spasm and a peri-bronchiolar congestive and exudative reaction.” – Paraphrased from Mendelson’s original findings, this highlights the core pathophysiology of chemical pneumonitis.