key: cord-0036906-9pl1v2v7
authors: Al-Tubaikh, Jarrah Ali
title: Alveolar Lung Diseases
date: 2010
journal: Internal Medicine
DOI: 10.1007/978-3-642-03709-2_19
sha: a8876b1ff94071fa03b34a15a4da34c8f68349bc
doc_id: 36906
cord_uid: 9pl1v2v7

Alveolar lung diseases (ALD) are group of disorders characterized by pathological insult involving mainly the alveoli. The alveoli can be imagined as an empty cup, and alveolar diseases are classified according to the content of this cup. Alveolar diseases are characterized by filling of the alveoli with materials that impede its normal physiological function (ventilation). Alveolar diseases can be localized (focal) or diffuse. Names of the conditions depend upon the content of the material filling the alveoli.

¼ calcium : alveolar microlithiasis.

The alveoli are the main units for respiratory-blood ventilation and oxygenation and normally are full of air on inspiration. You can think of the alveoli as an empty cup, and any pathological condition that fi lls this cup will form a pathological condition according to the cup content. Pulmonary edema arises due to alveolar fi lling with serous fl uid (water).

Pulmonary edema can be either due to cardiac disease (cardiogenic), or other conditions (noncardiogenic). Most cases of noncardiogenic pulmonary edema are due to acute respiratory distress syndrome (ARDS).

Cardiogenic pulmonary edema is commonly seen with heart failure. It starts as an interstitial edema before it turns into alveolar edema, because the pulmonary veins lie in the interstitium. As the hydrostatic pressure within the veins rises, they leak into the interstitium fi rst, and then progress to fi ll the alveoli. This process is rapid, and only very early edema can be seen as a pure interstitial linear pattern in chest radiographs.

Noncardiogenic Pulmonary edema has the same radiographic features as the cardiogenic pulmonary edema, but the causes are different: ARDS, chemical pneumonitis, drug-induced pulmonary edema, and transfusion-reaction are the most common causes for noncardiogenic pulmonary edema. ARDS is a situation where an alveolar capillary injury occurs as a result of variety of causes (e.g., sepsis). Chemical pneumonitis is a pulmonary edema that occurs due to inhalation of noxious chemical substance such as ammonia, smoking inhalation, near drowning situations, and gastric acid aspiration. The mechanism of pulmonary edema is the result of one of three mechanisms: irritation of the tracheo-bronchial tree that leads to infl ammation and pulmonary edema formation; absorption of the noxious material from the respiratory tract, which can affect the lungs directly by its metabolites; and asphyxiation due to inhalation of high concentration of the noxious material that will displace oxygen from the blood and cause tissue hypoxia. Drug-induced and transfusion reactions pulmonary edema arise due to anaphylactic lupus-like reaction formation. The radiographic picture cannot be differentiated from ARDS unless you have history of drug ingestion or recent transfusion reaction. Classic examples of drugs causing pulmonary edema are heroin, aspirin, and penicillin. Negative pressure pulmonary edema is a term used to describe noncardiogenic edema that arises due to acute airway obstruction (type 1), or after the relief of chronic airway obstruction (type 2).

There is a centrally-located, bilateral, symmetrical diff use ¼ alveolar opacities emitting from the heilum and spares the periphery (butterfl y or bat-wings sign) ( Fig. 3 Air-bronchogram sign: this is a sign seen when the alveoli are ¼ fi lled with fl uid and the terminal bronchioles and bronchi are devoid of fl uid (fi lled with air). The bronchioles appear as radiolucent lines within whitish radio-opaque opacities ( Fig. 3.2. 3 ). This sign is specifi c for alveolar disease, but nonspecifi c for the cause. Pulmonary edema, pulmonary hemorrhage, pneumonia, and alveolar carcinoma all looks the same on radiographs. All appears as ALD with air-bronchogram. The medical history plays a very important role in diff erentiating these conditions because the radiographic signs can be nonspecifi c. Blood diversion: normally, the upper lobe vessels are not ¼ visualized on radiographs, and the lower lobes vessels are mildly dilated and visible due to the gravity eff ect in upright posteroanterior (PA) radiographs. In cases of cardiac diseases and pulmonary hypertension, the upper lobe vessels will be as wide as the lower lobe vessels in upright radiographs. Note that the upper lobe vessels can be seen dilated normally in supine (lying) chest radiographs (e.g., in intensive care unit radiographs). Silhouette sign: this sign refers to a patchy, ill-defi ned ¼ radio-opaque shadow that obscures part of the normal mediastinal confi guration. 

Pneumonia is a condition characterized by an infectious infl ammation of the lung parenchyma and deposition of pus within the alveoli. Pneumonia can be caused by bacteria (e.g., Methicillin-resistant Staphylococcus aureus (MRSA)), fungi (e.g., pneumocystic cainii ), and viruses (e.g., cytomegalovirus (CMV)). Patients with pneumonia present with dyspnea, purulent sputum, fever, tachycardia, and maybe hemoptysis (e.g., tuberculosis). Complications of pneumonia include lung abscess formation, septicemia, and empyema. Rarely, arthritis and neurological symptoms may be encountered in atypical pneumonias (e.g., Mycoplasma pneumonia).

Pneumonias are divided into "typical pneumonia," which is caused by Streptococcus pneumoniae (pneumococcus) , and "atypical pneumonia," which is caused by any pathogen that is not pneumococcus . Typical pneumonia is clinically dominated by respiratory symptoms, whereas atypical pneumonia clinically is dominated by symptoms of fever and malaise more than the respiratory symptoms.

¼ Air-space pneumonia ( lobar pneumonia ): in this type, the infection is confi ned to a single lobe. There is usually one patch fi lling the whole affected lobe. This type is seen with pneumococcus , Legionella , pseudomonas , and primary tuberculosis infection. Lobar pneumonia is characterized by an "air-bronchogram sign". ¼ Bronchopneumonia : this type is characterized by an infection that starts in the bronchioles and small bronchi walls and then spread to the alveoli. This type is seen with Staphylococcus aureus , Hemophilus infl uenza , and Mycoplasma pneumonias.

¼ Interstitial pneumonia : this type is characterized by an infection that involves the interstitial septa and giving reticular interstitial pattern on chest radiograph. This type can be seen with viral infections like infl uenza virus and Varicella -zoster virus (VZV), and Mycoplasma infections (30% of cases).

MRSA is a serious infection with antibiotic-resistant staphylococci. MRSA is categorized as: communityacquired, nosocomial, and health care-associated infection. MRSA is the leading cause of nosocomial and health care-associated blood stream infection, globally. Also, it is responsible for 30-50% of ventilatorassociated pneumonia. MRSA causes metastatic foci of infections in 30% of cases into the lungs, liver, kidneys, heart valves, and joints. Most community-associated MRSA strains carry the Panton-Valentine Leukocidin (PVL) gene, which is rarely found in the hospitalacquired MRSA or the normal strain of S. aureus . PVL toxin is a potent lethal factor to neutrophils, which causes tissue necrosis and severe necrotizing pneumonia. MRSA pneumonia is more frequently associated with sepsis, high-grade fever, hemoptysis, pleural Viral pneumonias are characterized by several pathologies that include bronchiolitis, tracheobronchitis, and classical pneumonia. Viruses that attack immunocompetent patients include infl uenza viruses, Epstein-Barr virus, and adenoviruses. Viruses that attack immuno-compromised patients include measles virus, VZV, and CMV. Measles virus attack usually children due to immunosuppression or vaccine failure. VZV pneumonia is a common complication of VZV septicemia in children with a mortality rate of 9-50%. Up to 90% of VZV pneumonia cases are seen in patients with lymphoma or immunosuppression. CMV pneumonia is commonly seen in transplant patients and immunocompromised patients. Patients may develop severe necrotizing pneumonia in spite of antiviral therapy.

Hyperimmunoglobulinemia E syndrome ( Job's syndrome ): is a rare condition characterized by marked elevation of serum IgE levels against S. aureus resulting in decreased production of anti-staphylococcus IgG. The patient with this syndrome presents with frequent attacks of S. aureus pneumonia, pustular dermatitis, eczema, and sinusitis. Formation of chronic lung abscesses is a common feature on radiographs. 

Radio-opaque patches with an air-bronchogram sign (Fig. 3.2 

Bulging -fi ssure sign: some infections will increase the volume ¼ of the lobe involved causing the adjacent fi ssure to bulge (commonly the transverse fi ssure) (Fig. 3.2.4 ). This sign is classically seen in Klebsella pneumonia. Bronchopneumonia: there is multiple patchy infi ltration of the ¼ lung with or without segmental lobe atelectasis (if the bronchus is totally obstructed). (Fig. 3.2. 3 ) Interstitial Pneumonia: shows nonspecifi c linear or reticular ¼ interstitial lung pattern. Correlation with history and laboratory fi ndings is essential to establish the diagnosis. Viral pneumonias can appear as poorly-defi ned nodules (4-10 ¼ mm in diameter), with lung hyperinfl ation due to bronciolitis. Measles pneumonia show mix pattern of reticular interstitial ¼ pattern with patchy pneumonia (Fig. 3. 2.5 ). Hilar lymphadenopathy may be associated. VZV pneumonia appears as multiple, ill-defi ned micro-¼ nodules (5-10 mm) (Fig. 3.2.6 ). The lesions may calcify persisting as well-defi ned, randomly scattered, dense pulmonary calcifi cation. CMV pneumonia is commonly seen as a mixed nodular ¼ interstitial pattern with ill-defi ned patchy lung infi ltration. The patchy fi lling is caused pathologically by hemorrhage, neutrophilic and fi brinous exudates, and hyaline memebrane formation (Fig. 3.2.7 ) . Chronic pneumonia can lead to fi brosis, traction bronchiecta-¼ sis, and paracicatricial emphysema (Fig. 3.2.8 ).

In MRSA necrotizing pneumonia , a pneumonic patch or a ¼ pulmonary mass with central cavitary lesion can be found. The lesion can be single, or multi-focal. The same manifestations are observed in HRCT. Diff erential diagnoses of cavitary lung infi ltrations include lung abscess, metastases, pulmonary lymphoma, and Wegner's granulomatosis. 

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Acute pulmonary edema associated with transfusion of packed red blood cells

Negative pressure pulmonary edema: report of three cases and review of the literature

Viral pneumonias in adults: radiologic and pathologic fi ndings

Methicillin-resistant staphylococcus aureus bacteremia and pneumonia

Pathogenesis of MRSA infection

Necrotizing pneumonia caused by community-acquired methicillin-resistant Staphylococcus aureus: an increasing cause of "mayhem in the lung

Bronchial artery aneurysm in hyperimmunoglobulinemia E syndrome