Keywords: Chapter 12, The Lung

Abscess

Is a localized suppurative process characterized by necrosis of pulmonary parenchyma, most frequently caused by aspiration (especially common in alcoholics, comatose patients and post-anesthesia). Infections are often polymicrobial and usually are due to anaerobes from the oropharynx (especially common in those with poor dentition). However, staphylococcus aureus can cause mono-microbial abscess.
Acute Interstitial Pneumonia (AIP)
(Synonymous with Hamman-Rich Syndrome) is a rapidly progressive acute interstitital pneumonitis that histologically resembles the organizing stage of Diffuse Alveolar Damage (DAD); some individuals view this as a variant of DAD. AIP most frequently affects young adults, who present with a flu-like syndrome, and bilateral lung infiltrates. These patients rapidly develop respiratory failure requiring mechanical ventilation. The prognosis is grave with a majority of patients dying within two months of onset.
Adenocarcinoma
One of the most common primary lung carcinomas, which appears to be increasing in incidence, and now may be more common than squamous cell carcinoma. This tumor is usually peripheral in location and often is associated with scarring, leading to pleural puckering. This neoplasm may vary in histologic appearance with some tumors having well formed glands, others having a papillary architecture, and yet others being less differentiated and having a solid appearance. Most pulmonary adenocarcinomas are mucin positive, a feature which may be helpful in correctly classifying poorly differentiated (solid) adenocarcinomas.
Adenosquamous carcinoma
A less frequent type of lung carcinoma that by definition has both squamous and glandular features. They are usually large bulky peripheral tumors and preliminary clinical studies indicate that this tumor is more aggressive than adenocarcinoma or squamous cell carcinoma.
Adult respiratory distress syndrome
See definition for diffuse alveolar damage. They are synonyms.
Allergic Angiitis and Granulomatosis (Churg-Strauss Syndrome)
Churg-Strauss syndrome is a rare type of systemic vasculitis that occurs almost exclusively in patients with asthma and peripheral blood eosinophilia. A lung biopsy shows an eosinophilic pneumonia, and there is vasculitis involving both the pulmonary and systemic circulation.
Alpha-1 Antitrypsin
(also known as protease inhibitor, or Pi) is a circulating glycoprotein synthesized in the liver, which normally acts to inhibit proteolytic enzymes such as trypsin, elastase, and collagenase which are capable of destroying lung tissue. Patients with alpha-1 antitrypsin deficiency have low antiproteolytic activity and are at high risk for the development of COPD, usually panlobular emphysema. The defect is genetic, and alpha-1 antitrypsin is the product of two allelles located on chromosome 14. A normal individual is pimm; homozygotes are pizz; heterozygotes are pimz.
Asbestos-related diseases
Refers to a group of diseases caused by exposure to asbestos including:
  1. pleural plaque
  2. pleural effusion
  3. pulmonary parenchymal interstitial fibrosis (asbestosis)
  4. bronchogenic carcinoma
  5. malignant mesothelioma
  6. possibly other types of tumor
Asbestosis
Refers to interstitial fibrosis of the lung caused by asbestos exposure. Histologically there is interstitial fibrosis of varying severity and asbestos bodies (which consist of asbestos fibers coated by iron containing proteinaceous material).
Aspergillosis
Is defined as infection caused by Aspergillus species (usually A. Fumigatus or A. Niger), which may present as:
  1. invasive pulmonary aspergillosis (primarily occurs in immunocompromised patients)
  2. aspergilloma (fungus ball or mycetoma - i.e., Fungus growing in a pre-existing cavity)
  3. allergic bronchopulmonary aspergillosis (a syndrome occurring in asthmatics characterized by transient pulmonary infiltrates with recurrent pneumonia, and eosinophilia of blood and sputum)
Asthma
Is a chronic obstructive disease characterized by tracheo- bronchial hyper-reactivity leading to paroxysmal airway narrowing, which may reverse spontaneously or as a result of treatment. It is characterized clinically by wheezing, dyspnea, and cough. Allergic asthma is the most common form. Other precipitating factors include infection, exercise, occupational and environmental exposures, drugs, air pollution, and emotional factors.
Atelectasis
Refers to either collapse of previously inflated lung or incomplete expansion of the lung. Significant atelectasis reduces oxygenation and predisposes to infection.
Berylliosis
Refers to a lung disease due to inhalation of Beryllium. Heavy exposure may cause acute pneumonitis. Chronic berylliosis is caused by induction of cell mediated immunity, resulting in formation of noncaseating granulomas in the lung and hilar lymph nodes, and less frequently in other organs such as the spleen, liver, and kidney. Chronic berylliosis may remain asymptomatic until many years after exposure, when patients present with dyspnea and cough.
Blastomycosis
Blastomycosis is a fungal infection caused by the dimorphic fungus Blastomyces dermatitidis, which may be asymptomatic, or present as an acute pneumonia, or as a progressive pneumonic disease.
Bronchiectasis
Bronchiectasis refers to irreversible dilatation of bronchi, which may develop in association with a variety of conditions, such as bronchial obstruction, post-infectious, or congenital defects.
Bronchiolitis Obliterans Organizing Pneumonia (BOOP)
Refers to a lung reaction characterized by polypoid plugs of loose fibrous tissue filling bronchioles and alveoli accompanied by a variable chronic inflammatory infiltrate. This reaction may be caused by various injurious agents, such as infection (viral and bacterial), inhaled toxins, drugs; or it may be associated with collagen vascular disease; some cases are idiopathic. In most cases, patients improve gradually or with steroids.
Bronchiolo-alveolar carcinoma
A distinctive variant of adenocarcinoma of the lung, which probably arises from terminal bronchioles or alveolar walls. Grossly it may appear as a solitary mass, multiple small nodules, or as a diffuse infiltrative lung disease resembling a pneumonic infiltrate. The prognosis is variable depending on the gross pattern (better for solitary tumors and poor for diffuse tumors). The histologic hallmark of this tumor is preservation of the underlying pulmonary architecture, with lepidic growth of tumor cells (cuboidal or columar cells) along the pre-existent alveolar walls.
Bronchocentric granulomatosis
A very rare disorder characterized by granulomatous and necrotizing lesions of bronchioles.
Bronchogenic cyst
A benign cyst, most frequently located in the middle or anterior mediastinum, or in the lung. It may present in childhood with respiratory distress due to compression and atelectasis, or recurrent infections; it rarely may be an incidental finding in adults. The cyst is lined by respiratory epithelium and the wall of the cyst contains muscle and cartilage.
Bulla
Are subpleural emphysematous spaces measuring greater than 1-2 cm in diameter.
Caplan syndrome
Defined as coexistence of rheumatoid arthritis and a pneumoconiosis.
Carcinoid tumor
A neuroendocrine tumor of low grade malignancy. They are usually central in location (90%), and less frequently are located in the periphery of the lung (10%). The prognosis is variable, but overall is much better than the more frequent bronchogenic carcinomas. This tumor also occurs in a younger age group than the more frequent bronchogenic carcinomas (average age about 45 years).
Centrilobular emphysema
(Also referred to as centriacinar emphysema) can be defined as enlargement and destruction of the respiratory bronchiole (i.e., The central portion of the acinus) with sparing of the distal portion of the acinus. When severe, however, it may involve the distal acinus and be difficult to distinguish from panlobular emphysema. This is the most common form of emphysema and typically involves the upper lung zones. It occurs more frequently in males than in females.
Chronic bronchitis
Defined clinically as the presence of a chronic productive cough without a discernible cause for at least 3 months out of the year, for 2 successive years. (Yes, this definition is slightly different than what is in your book, but is used widely by clinicians). There are several risk factors, but cigarette smoking is the most important. It is morphologically characterized by hypertrophy and hyperplasia of submucosal glands (which can be quantitated by the Reid Index) and mucous and goblet cell metaplasia. The key change is hypersecretion of mucus in response to chronic injury.
Chronic Eosinophilic Pneumonia
Refers to a type of eosinophilic pneumonia, that usually is associated with chronic asthma, peripheral blood eosinophilia and elevated IgE. There is a variable clinical prsentation, ranging from mild disease, to high fever, chills, and severe dyspnea. Patients respond dramatically to steroids, but may have recurrences. Causes of chronic eosinophilic pneumonia include: drugs, fungal hypersensitivity, parasites, inhalents and unknown.
Chronic obstructive pulmonary disease (COPD)
Refers to a group of diseases which have a similar disorder of function: decreased expiratory flow in the airways of the lung. Chronic bronchitis and emphysema are classic examples of COPD; some individuals also include asthma and bronchiectasis under the umbrella term of COPD.
Churg-Strauss Syndrome
See Allergic Angiitis and Granulomatosis.
Coal-Workers pneumoconiosis
A lung disease caused by exposure to coal dust, which may produce; 1) asymptomatic anthracosis 2) simple coal-workers pneumoconiosis. (characterized by coal macules and nodules containing carbon-laden macrophages), with little or no pulmonary dysfunction or 3) complicated coal-workers pneumoconiosis or progressive massive fibrosis: which is black scars in the lungs causing compromised pulmonary function
Congenital cystic adenomatoid malformation
A congenital anomaly in which the lung parenchyma is converted into multiple gland-like spaces lined by bronchiolar epithelium that are separated from each other by loose fibrous tissue, usually affecting one lobe of lung, and occasionally associated with other congenital anomalies.
Cryptococcosis
A fungal infection caused by Cryptococcus neoformans, an opportunistic yeast that is present in the soil and in pigeon droppings. Clinically, pulmonary cryptococcosis varies from an asymptomatic infection to a severe life-threatening illness. The histologic features vary depending on the patient's immune status; a granulomatous reaction is usually seen in cases with an intact immune system. This yeast is unique in that the capsule stains bright red with mucin stains, a feature that makes morphologic identification of the organism quite reliable.
Cytomegalovirus pneumonia
A viral infection which, like most viral pneumonias, produces an interstitial pneumonitis or DAD. Histologically one can see nuclear and/or cytoplasmic inclusions. In adults it occurs primarily in immunocompromised patients.
Desquamative interstitial pneumonia (DIP)
A type of chronic interstitial pneumonitis characterized histologically by the accumulation of numerous macrophages in alveolar spaces, as well as interstitial abnormalities. Patients usually present with slow onset of cough and dyspnea. Radiographic findings include bilateral lower lobe ground glass infiltrates. The etiology is unknown. Patients often respond to steroid therapy, and DIP has a more favorable prognosis and better response to steroid therapy than UIP. Some authorities question the existence of DIP and feel that it represents a very early stage of UIP.
Diffuse alveolar damage (DAD)
(synonymous with adult respiratory distress syndrome (ARDS)): A descriptive term for a syndrome caused by diffuse alveolar capillary damage, characterized clinically by rapid onset of severe life-threatening respiratory insufficiency, cyanosis, and severe arterial hypoxemia that is refractory to oxygen therapy, and that frequently progresses to extrapulmonary multisystem organ failure. DAD is a well recognized complication of numerous diverse conditions, including both direct injuries to the lungs and systemic disorders; examples include diffuse pulmonary infections, smoke inhalation, oxygen and drug toxicity, aspiration, radiation, shock, sepsis, burns etc. The average mortality is 50%; but ranges from 10% to 90% depending on the cause and severity of the lung injury.
Embolus
Usually blood clots, most commonly arising in the legs, causing occlusion of pulmonary arteries. Pulmonary emboli cause infarcts only when the circulation is already inadequate, i.e. In patients with pre-existent heart or lung disease. A variety of underlying disorders predispose to pulmonary emboli, such as cardiac disease, cancer, immobilization, and hypercoaguable states. Pulmonary emboli lead to 2 main effects; 1) respiratory compromise due to underperfusion 2) hemodynamic compromise due to increased resistance to pulmonary blood flow.
Emphysema
Emphysema is a chronic obstructive disorder of the lung characterized by abnormal permanent enlargement of the air spaces distal to the terminal bronchiole, accompanied by destruction of their walls. Enlargement of air spaces without destructive changes should be termed overinflation or hyperinflation.
Empyema
A variant of pyothorax in which thick pus accumulates within the pleural cavity, often with loculation and fibrosis.
Eosinophilic Pneumonia
The most common type of pulmonary eosinophilia, and is divided into three clinical groups (the histology is the same for all three groups):
  1. Simple eosinophilic pneumonia (Loeffler Syndrome)
  2. Tropical eosinophilic pneumonia
  3. Chronic eosinophilic pneumonia.
Farmer's lung
A type of hypersensitivity pneumonitis caused by exposure to moldy hay, typically occurring in farmers.
FEV 1
(forced expiratory volume in one second): The maximum volume of air that can be exhaled during the first second of a forced vital capacity (FVC). In a normal individual, the FEV, is 80% of the FVC.
Forced vital capacity (FVC)
One of many pulmonary function tests. The patient makes a full inspiration, and then exhales as hard and fast as possible into a spirometer. This expired volume is designated as the FVC.
Ghon complex
Refers to the initial focus of primary tuberculous infection, which consists of a parenchymal subpleural lesion, (often just above or just below the interlobar fissure between the upper and lower lobes), and enlarged caseous lymph nodes draining the parenchymal focus.
Goodpasture syndrome
(Also know as antibasement membrane antibody disease - ABMA) Characterized by a proliferative rapidly progressive glomerulonephritis and diffuse alveolar hemorrhage. It is caused by a circulating cytotoxic autoantibody to a component of basement membrane (type II immune reaction). This disease typically occurs in young men and is treated by administration of corticosteroids, cytotoxic drugs, and plasmaphoresis.
Hamartoma
A benign localized proliferation of normal tissue components (hyalin cartilage containing cleft like spaces lined by respiratory epithelium; occasionally there may also be fibrous tissue, fat, and blood vessels.) Pulmonary hamartoms are relatively common lesions which usually are discovered as an incidental finding on routine chest x-ray.
Hamman Rich Syndrome
Previously had been used synonymously with UIP (usual interstitial pneumonitis); this concept has now been changed (note this difference from your book). UIP has a chronic slowly progresive clinical course; whereas Hamman Rich Syndrome is an acute rapidly progressive fulminant disease. Hamman Rich Syndrome is an acute interstitial pneumonia (AIP) and these two terms are now used interchangeably (also see AIP definition).
Histoplasmosis
A fungal infection caused by the dimorphic fungus Histoplasma capsulatum, usually acquired by inhalation of dust particles from soil contaminated with bird or bat droppings. It most frequently occurs in the midwestern and southeastern regions of the U.S., particularly in the Mississippi and Ohio river valleys. Histoplasmosis has many clinical and pathologic similarities to tuberculosis.
Honeycomb lung
Refers to end stage fibrotic lung, which may be the result of many types of interstitial, inflammatory, or proliferative processes involving the lung such as AIP, UIP, DIP, DAD, pneumocomosis, infections, hypersensitivity pneumonitis, sarcoid, etc. The lungs become solid with alternating areas of fibrosis and restructuring of distal air spaces leading to formation of small cysts.
Hydrothorax
Refers to a pleural effusion that resembles water (transudate).
Hypersensitivity pneumonitis
(Also known as extrinsic allergic alveolitis), is an immunologic lung disease caused by exposure to a variety of inhaled antigens. The clinical presentation may be acute or chronic, and the numerous clinical syndromes are generally given names reflecting the circumstances of exposure, such as farmer's lung, air-conditioner lung, humidifier lung, and bird- fanciers or pigeon breeders lung. Histologically it shows features of chronic interstitial pneumonitis with interstitial non-necrotizing granulomas.
Hypertension, pulmonary
May be primary or secondary, but far more frequently is secondary to other conditions such as COPD, congenital or acquired heart disease, etc. Primary pulmonary hypertension is a rare condition, typically occurring in young women.
Idiopathic pulmonary hemosiderosis
A rare disease that occurs in children younger than 16 years, characterized by diffuse alveolar hemorrhage similar to Goodpasture Syndrome, but without renal disease or antibasement membrane antibodies.
Interstitial lung disease
Refers to an inflammatory, occasionally fibrosing process, that occurs predominantly within the interstices or supporting structures of the lung (alveolar walls), as opposed to a lesion in which the predominant reaction takes place within the alveolar spaces. Examples of interstitial lung disease include usual interstitial pneumonia (UIP), DIP, Sarcoidosis, hypersensitivity pneumonitis, DAD, pneumoconiosis, etc.
Langerhans cell
Refers to the diagnostic cell seen in eosinophilic granuloma (Histiocytosis X). This cell is a large histiocyte containing a bland, folded or indented nucleus, an inconspicuous nucleolus, and abundant eosinophilic cytoplasm with indistinct cell borders. In active lesions, Langerhans cells are numerous and occur in clusters. These cells stain positively with S100 protein stain (an immunoperoxidase stain).
Langhans giant cell
Refers to a multinucleated giant cell seen in granulomas in which the nuclei are arranged around the periphery of the cell in a horseshoe pattern. Not the same as a Langerhans cell (see above)
Large cell carcinoma
Refers to a group of poorly differentiated carcinomas which lack histologic features of squamous cell carcinoma, adenocarcinoma, or small cell carcinoma (i.e., This is a "waste basket" group). This group of poorly differentiated tumors could also be referred to as poorly differentiated carcinoma, non-small cell type. They usually have a solid pattern and are composed of large malignant cells having a moderate amount of cytoplasm.
Legionella pneumonia (Legionnaire's disease)
Refers to a pneumonia caused by a Gram-negative intracellular bacteria, Legionella pneumophila. This bacteria may cause a mild, self-limited fever in otherwise healthy individuals, or a severe pneumonia in smokers, the elderly, or individuals with chronic lung disease. Mortality is high (10-20%) in immunocompromised patients.
Lipid pneumonia
May be exogenous (due to chronic aspiration of exogenous oils); or endogenus (due to bronchial obstruction).
Loeffler Syndrome
Refers to one of the types of eosinophilic pneumonia characterized by fleeting pulmonary infiltrates and peripheral bood eosinophilia. It is usually a mild self-limited disease that resolves spontaneously.
Lymphoid Interstitial Pneumonia (LIP)
A rare type of chronic interstitial pneumonia characterized by a dense and diffuse interstitial infiltrate of lymphocytes, plasma cells and histocytes, that are histologically benign, polymorphous and polyclonal. LIP may be difficult to distinguish from a well- differentiated lymphocytic lymphoma.
Mesothelioma
Refers to primary pleural tumors including benign and malignant mesotheliomas. Benign mesothelioma, (also called pleural fibroma), does not produce a pleural effusion and has no relationship to asbestos exposure. Malignant mesotheliomas may arise from either the visceral or parietal pleura, and are associated with asbestos exposure and pleural effusion. Malignant mesothelioma is a diffuse tumor that invades lung and spreads widely in the pleural space. It frequently invades other thoracic structures. The prognosis is poor.
Mycoplasma
An infectious agent which causes an atypical pneumonia, characterized by peribronchiolar infiltrates of lymphocytes and plasma cells. It causes an acute self limited lower respiratory tract infection (tracheo-bronchitis and pneumonia), affecting mostly children and young adults.
Necrotizing Sarcoid Granulomatosis
Felt to represent a rare variant of sarcoid, that is characterized by sarcoid-like granulomas, but also by vasculitis and focal parenchymal necrosis. This disease responds well to steroids and has an excellent prognosis.
Pancoast tumor/syndrome
Pancoast tumor refers to lung cancer (usually squamous) located in the apex of the lung, extending to involve the eighth cervical and first and second thoracic nerves. This results in shoulder pain radiating in an ular distribution down the arm (Pancoast syndrome). A Pancoast tumor may also involve the cervical sympathetic nerves and cause Horner syndrome (enophthalmos, ptosis and miosis).
Panlobular emphysema, (also referred to as panacinar emphysema)
A type of emphysema in which the acinus is uniformly involved, with destruction of alveolar septa involving the entire acinus. It typically occurs in the lower lung zones, and is the type of emphysema associated with alpha-1 antitrypsin deficiency.
Pneumoconiosis
Refers to pulmonary diseases caused by the inhalation of inorganic dust. The most important factor in the production of pneumoconiosis is the capacity of inhaled dust to stimulate fibrosis. Other important factors include particle size, length of exposure, and individual susceptibility. Examples of pneumoconiosis include silicosis, coal workers pneumoconiosis, and asbestos related lung diseases.
Pneumocystis carinii pneumonia
A pulmonary infection typically occurring in immunocompromised patients. Histologically there is a prominent frothy foamy intra-alveolar exudate, containing the organisms. The organisms are best demonstrated on silver stains.
Pneumonia
A generic term that refers to inflammation and consolidation (solidification) of the pulmonary parenchyma. Traditionally bacterial pneumonias have been classified as lobar pneumonia,( consolidation of an entire lobe) or bronchopneumonia (scattered foci in the same or several lobes); however, these terms have little clinical relevance.
Pneumothorax
Refers to air or gas in the pleural cavities, and may be spontaneous, traumatic or iatrogenic in origin.
Protease - antiprotease hypothesis
A theory that emphysema results from an imbalance between proteases (mainly elastase) and antiproteases in the lung. Emphysema results from the destructive effect of high protease activities in individuals with low antiprotease activity.
Psittacosis (also known as ornithosis)
A self-limited pneumonic illness transmitted to humans from birds, characterized by severe systemic symptoms and surprisingly few respiratory symptoms other than cough. The causative agent is Chlamydia psittaci.
Pulmonary alveolar proteinosis
A disease of obscure etiology and pathogenesis characterized radiographically by diffuse pulmonary opacification, and histologically by accumulation of intra-alveolar dense granular material that contains abundant lipid and PAS positive material. Patients present with nonspecific respiratory difficulty and may have a variable clinical course.
Pulmonary eosinophilia
Defined as a condition in which patchy pulmonary infiltrates occur in association with eosinophilia of blood or sputum. Disorders classified as pulmonary eosinophilia include: eosinophilic pneumonia, allergic bronchopulmonary aspergillosis, mucoid impaction of bronchi, bronchocentric granulomatosis, and Churg-Strauss Syndrome.
Pulmonary eosinophilic granuloma
(also referred to as pulmonary histiocytosis X, or Langerhans cell granulomatosis) This is a proliferative disorder of histiocytes characterized by patchy nodular interstitial lesions. Clinically patients may present with cough and dyspnea, or they may be asymptomatic. Radiographically, there are multiple nodules distributed throughout both lungs. Histologically the infiltrate is composed of a variable mixture of histiocytes (Langerhans cells) and eosinophils, as well as occasional plasma cells and lymphocytes. Older lesions show a stellate pattern of fibrosis. Electron microscopy of Langerhans cells demonstrates the characteristic Birbeck granules.
Reid index
A ratio that may be used to quantitate the degree of submucosal glandular hypertrophy and hyperplasia seen in patients with chronic bronchitis. The Reid index is the ratio of the thickness of the submucosal glands divided by the thickness of the bronchial wall (measured from the basement membrane to the innermost perichondrium). The Reid index normally is less than 0.4, but in chronic bronchitis the Reid index is increased, usually in proportion to the severity and duration of the disease.
Restrictive lung disease
Refers to a group of diffuse pulmonary diseases characterized by reduced expansion of lung parenchyma, with decreased total lung capacity. This may occur in 2 general conditions:
Sarcoidosis
A chronic disease of unknown etiology in which non-caseating granulomas occur in almost any organ of the body. The lung is the most frequently involved organ, and histologically one may see multiple non-caseating granulomas scattered in the interstitium of the lung. Sarcoidosis is a protean clinical disease, and follows an unpredictable clinical course, characterized by either progressive chronicity, or periods of activity interspersed with remission (sometimes permanent), that may be spontaneous or initiated by steroid therapy. It is most common in young, black women.
Scar carcinoma
A somewhat outdated term referring to the fact that some tumors (particularly adenocarcinomas) are associated with pleural scaring. The old literature stated that these tumors arise and develop from the regenerating epithelium of pre-existent scars. More recent studies indicate that in most cases, the scar is simply a desmoplastic reaction to invasive carcinoma.
Sequestration
There are two types of pulmonary sequestration:
Silicosis
A pneumoconiosis caused by the inhalation of silicon dioxide (silica), usually in crystalline form as quart. Two forms of silicosis exist: 1) Simple nodular silicosis. 2) Progressive massive fibrosis.
Small airways disease
The concept that alterations in the distal small airways may be the earliest abnormalities in the evolution of COPD. Alterations in these small airways can result in physiologically important and early manifestations of chronic airway obstruction.
Small cell carcinoma
A highly malignant lung cancer characterized by sheets of small tumor cells, with a scanty amount of cytoplasm. This tumor is usually centrally located, and is closely associated with cigarette smoking. Most patients already have metastatic disease at the time of diagnosis; hence, chemotherapy is the usual treatment for this tumor (rather than surgical resection). Small cell carcinoma is at the malignant end of the spectrum of neuroendocrine tumors of the lung.
Squamous cell carcinoma
A common type of lung cancer which is usually central in location and closely associated with cigarette smoking. Microscopically, tumors may show keratin pearls (particularly in well differentiated tumors), individual cell keratinization or inter-cellular bridges.
Status asthmaticus
Severe acute asthma which does not respond to treatment and persists (for days or weeks). In rare instances, acute episodes can result in death.
Thymoma
A mediastinal tumor, most frequently occurring in the anterior mediastinum, with a peak incidence in the 5th decade of life. Associated diseases include myasthenia gravis, red cell hypoplasia and hypogamaglobulinemia. Most thymomas are slow growing with a relatively benign clinical behavior. The main factor that adversely affects the prognosis is evidence of invasion of surrounding structures, a feature which may be noted at the time of surgical resection.
Tropical eosinophilic pneumonia
Refers to one of the eosinophilic pneumonias that occurs in the tropics. Filarial infections are implicated etiologically and the disease responds well to antifilarial drugs.
Tuberculosis
Represents an infection with Mycobacterium tuberculosis complex, although atypical mycobacteria may mimic tuberculosis. The disease is clinically divided into primary and secondary (reactivation) tuberculosis.
Usual interstitial pneumonitis (UIP)
The most common type of idiopathic chronic interstitial pneumonitis, characterized clinically by progressive respiratory insufficiency and pathologically by interstitial inflammation and fibrosis. Clinically, UIP begins insidiously with gradual onset of dyspnea and cough. Pathologically, UIP is an inflammatory and fibrosing lesion affecting predominantly the interstitium. The single most important histologic finding that separates UIP from other interstitial pneumonias is the marked variation from field to field in degree of lung involvement and also in the nature and appearance of the cellular infiltrate.
Wegener granulomatosis
A systemic necrotizing vasculitis of unknown etiology, characterized by granulomatous lesions of the upper and lower respiratory tract (nose, sinuses, and lungs) and renal glomerular disease. Pathologically, there is necrotizing vasculitis with granulomatous inflammation and parenchymal necrosis. Treatment with cyclophosphamide produces improvement in prognosis and both complete remission and substantial disease free intervals are induced in most patients.