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Pathology - Malignant mesothelioma
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It is a malignant tumor originating in the pleura from mesothelial cells, characterized by a diffuse growth pattern throughout the pleural surfaces.
Epidemiology • The majority of occurrences occur in males over 60 years of age. • The incidence continues to increase owing to the prolonged incubation period between asbestos exposure and tumor formation.
• The incidence is anticipated to reach its zenith between 2015 and 2020.
Aetiology Over 90% of instances can be directly linked to asbestos exposure. Amphibole asbestos is the most potent kind, succeeded by chrysotile, and subsequently amosite. • Additional potential causes encompass non-asbestos mineral fibers and therapeutic radiation.

Pathogenesis • Inhaled asbestos fibers stay permanently lodged in the lung. • The majority do not elicit a tissue response, and they are likely the fibers responsible for carcinogenic effects. A minority become enveloped in iron, resulting in the formation of asbestos bodies.

Presentation • Dyspnea, frequently resulting from a significant unilateral pleural effusion, accompanied by thoracic pain. • Marked weight loss and malaise are commonly observed.

Macroscopy • Initially, several tiny nodules are observed on the parietal pleura. • As the tumor progresses, the nodules coalesce to create a tumor mass that envelops the entire lung and adheres to the chest wall.

Cytopathology • Epithelioid mesotheliomas are more prone to disseminate into pleural fluid, where malignant cells are observed organizing into sheets, clusters, and papillae.

Histopathology • Epithelioid mesothelioma consists of spherical cells that create tubules and papillae. Sarcomatoid mesothelioma consists of elongated spindle-shaped cancerous cells. Biphasic mesothelioma comprises a combination of epithelioid and sarcomatoid variants. Desmoplastic mesothelioma is a variation characterized by a limited number of malignant cells embedded in highly dense collagenous tissue.

Prognosis: Extremely unfavorable

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Pathology – Pneumothorax
Definition • The accumulation of air in the pleural cavity.

Epidemiology: Prevalent. • Males are impacted more significantly than females.

Aetiology
Spontaneous pneumothorax generally manifests in slender, tall young males. The phenomenon is believed to originate from the rupture of small, fragile apical blebs in lung tissue caused by lung expansion. • Preexisting pulmonary conditions, such as COPD, asthma, pneumonia, tuberculosis, cystic fibrosis, sarcoidosis, lung cancer, and idiopathic pulmonary fibrosis (IPF). Uncommon disorders frequently linked to pneumothorax encompass pulmonary Langerhans cell histiocytosis, pulmonary lymphangioleiomyomatosis, and thoracic endometriosis. • Trauma, such as penetrating thoracic injury and rib fractures. • Iatrogenic, for instance, subclavian vein cannulation and lung biopsy.

Pathogenesis
Air escapes from the compromised lung into the pleural cavity until the pressures equilibrate. The lung collapses to a varying extent, contingent upon the magnitude of the pneumothorax. • Infrequently, the tissues next to the pulmonary lesion function as a unidirectional valve, obstructing pressure equalization. The persistent accumulation of pressure and volume in the pleural cavity displaces mediastinal structures, resulting in cardiorespiratory arrest (tension pneumothorax).

Presentation:
• Abrupt onset of unilateral pleuritic thoracic discomfort. • Breathlessness may occur, contingent upon the magnitude of the pneumothorax. Individuals with preexisting pulmonary conditions typically observe an exacerbation of their symptoms.

Radiology
• Air is present in the pleural space alongside various degrees of lung collapse. Histopathology: Apical lung tissue removed from patients with spontaneous pneumothoraces has one or more bullae linked to subpleural alveolar collapse and fibrosis. The superficial visceral pleura exhibits reactive mesothelial hyperplasia and inflammation, frequently characterized by an abundance of eosinophils.
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Prognosis: Approximately one-third of patients with spontaneous pneumothorax experience recurring episodes, typically on the same side.


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Pathology - Diseases of the oral cavity
Candidiasis • A fungal illness prevalent among immunosuppressed individuals. • Clinically characterized by erythema and pseudomembrane development.

Actinomycosis • Gram-positive anaerobic bacteria that constitute a component of the normal oral flora, colonizing tonsillar crypts, dental plaque, and gingival tissues. • Pathological infection may arise if these organisms penetrate deeper tissues via trauma (e.g., tooth extraction).

Lichen planus • Frequently affects the oral cavity.Pemphigus vulgaris typically affects the oral cavity.

Mucous membrane pemphigoid, also referred to as cicatricial pemphigoid. Autoimmune blistering disease mostly impacting mucosal regions. • Manifestations occur between the ages of 50 and 70 years, characterized by mouth blistering. • Involvement of the conjunctiva, upper respiratory tract, and skin is also common. Histological examination reveals detachment of the squamous epithelium from the subjacent connective tissue accompanied by a heterogeneous inflammatory infiltrate. Direct immunofluorescence reveals linear deposition of IgG and C3 along the basement membrane zone.

Squamous papilloma • Benign exophytic growth of squamous epithelium. • Predominantly observed in people aged 30 to 50 years. • Preference for hard and soft palates, as well as the uvula. • Histological examination reveals papillary fronds covered by mature squamous epithelium.

Fibroma • Nonmalignant expansion of fibrous tissue due to inflammation. • The majority manifest as a painless oral mass in adults aged 30 to 50 years. Histological examination reveals a subepithelial mass composed of thick collagenous tissue.

Pyogenic granuloma • A benign vascular lesion more accurately referred to as 'lobular capillary hemangioma'. • Exhibits a dark red polypoid mass that frequently undergoes ulceration. • Histological examination reveals a lobulated proliferation of tiny blood vessels.
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Squamous cell carcinoma • The most prevalent cancer of the oral cavity. • Significant correlation with alcohol consumption and tobacco use. • 30% present with regional lymph node metastases. • Cumulative 5-year survival around 50%


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Pathology - Pulmonary hypertension
Definition: A mean pulmonary artery pressure above 25 mmHg at rest or 30 mmHg during exertion.
Categories Secondary pulmonary hypertension is a consequence of chronic pulmonary or cardiac conditions. Primary pulmonary hypertension manifests in the absence of chronic pulmonary or cardiac conditions.
Epidemiology
• Secondary pulmonary hypertension is prevalent. Primary pulmonary hypertension is uncommon.

Aetiology
Common etiologies of secondary hypertension encompass COPD, interstitial lung disease, left ventricular failure, and chronic pulmonary thromboemboli. Primary pulmonary hypertension may be idiopathic or linked to specific medications, HIV infection, collagen vascular disorders, and congenital systemic-to-pulmonary shunts.

Pathogenesis: Chronic hypoxia and obliterative pulmonary fibrosis contribute to elevated pressure in the pulmonary arterial circulation.
Presentation • Secondary pulmonary hypertension exacerbates the symptoms of the pre-existing illness, resulting in increased breathlessness. • Primary pulmonary hypertension manifests as exertional dyspnoea and exhaustion. Dizziness and syncope are prevalent as well.

Macroscopy • The identification of atherosclerosis in major pulmonary arteries indicates potential underlying pulmonary hypertension. • Right ventricular hypertrophy may also be observed.
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Histopathology: All cases have muscular hypertrophy and intimal proliferation of tiny pulmonary arteries, together with muscularization of pulmonary arterioles. • Severe instances have plexiform lesions, marked by the proliferation of slit-like vascular gaps originating from the arterial wall. • Extremely severe cases may present with fibrinoid necrosis of the arterial wall.
Prognosis • Secondary pulmonary hypertension typically indicates substantial cardiac or pulmonary pathology with a bad prognosis. The prognosis for primary pulmonary hypertension is bleak, with 5-year survival rates ranging from 25% to 50%.


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Pathology - Pulmonary thromboembolism
Definition: Occlusion of a pulmonary artery by an embolic thrombus.
Epidemiology: Highly prevalent and frequently underdiagnosed.
Aetiology • Pulmonary emboli arise from deep vein thromboses, thus sharing identical risk factors, including immobility, acute medical conditions, recent surgical procedures, malignancy, pregnancy, and both inherited and acquired thrombotic diseases.
Pathogenesis: A piece of a detached thrombus from deep vein thrombosis embolizes via the right side of the heart into the pulmonary arterial circulation and becomes lodged in a pulmonary artery.
The clinical presentation is contingent upon the size of the pulmonary artery obstructed by the embolus. • Blockage of a large pulmonary artery usually leads to rapid death due to a sudden massive rise in pulmonary arterial pressure, acute right ventricular failure, and cardiac arrest. • Occlusion of medium-sized arteries results in a region of ventilation-perfusion imbalance in the lungs, leading to dyspnea. • Minor pulmonary emboli may produce mild manifestations of dyspnea, thoracic discomfort, and vertigo; these symptoms can often remain undetected.

Macroscopy
• Emboli appear as thrombi pieces within pulmonary arteries. • Thrombi are solid and brown, with the sliced surface potentially displaying discernible bands (lines of Zahn). Histopathology: Fresh thromboemboli consist of a composite of fibrin and interwoven blood cells, frequently organized in alternating linear bands that align with the macroscopic lines of Zahn. • Thromboemboli undergo organization after 2–3 days, characterized by the proliferation of granulation tissue consisting of fibroblasts and capillaries derived from the vessel wall. • Aged thromboemboli may manifest as fibrous nodules protruding from the vessel wall or as fibrous bands traversing the lumen of a pulmonary artery.

Prognosis
• Approximately 30% of all patients succumb to pulmonary embolism. • The mortalityz risk significantly increases if the diagnosis is not promptly established.


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Pathology – Asthma
Definition
• A chronic inflammatory condition of the major airways marked by recurring episodes of reversible airway constriction.
Epidemiology: Highly prevalent, impacting over 10% of children and 5% of adults.
Aetiology • The majority of cases are linked to atopy, a hereditary predisposition of the immune system to generate IgE in reaction to prevalent environmental allergens. • The aetiology of non-atopic asthma remains ambiguous; nevertheless, some propose a connection with gastro-oesophageal reflux syndrome.
Pathogenesis: Atopic individuals react to prevalent environmental allergens by generating substantial quantities of allergen-specific IgE, which attaches to the surface of mast cells. • Subsequent exposure to the allergen results in the cross-linking of allergen-specific IgE antibodies and the degranulation of mast cells. Degranulated mast cells provoke airway inflammation and bronchospasm. Chronic inflammation leads to hypersensitive airways that respond to many stimuli, such as physical exertion, cold air, and tobacco smoke. Presentation: Intermittent episodes of dyspnea, wheezing, and chest constriction. Coughing, especially during nocturnal hours, is prevalent.
Macroscopy • The lungs of the majority of asthmatics may appear macroscopically normal. • In severe illness, thick mucus plugs may be observed in the airways.
Histopathology • The airways exhibit signs of inflammatory activity characterized by the presence of eosinophils, which are typically absent in normal airways. • Additionally, there may be thickening of the basement membrane, hyperplasia of goblet cells, and pronounced smooth muscle.
Prognosis: Generally favorable with suitable treatment. • A minor fatality rate is linked to severe acute asthma.


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Pathology - Bacterial pneumonia
Definition: An infection of the lung parenchyma induced by bacterial pathogens.
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Classification • Acquired inside the community. • Nosocomial. • Aspiration. • Immunosuppression.

Epidemiology • Extremely prevalent.

Microbiology • Community-acquired pathogens: Streptococcus pneumoniae, Mycoplasma pneumoniae, Haemophilus influenzae, Legionella pneumophila. • Hospital-acquired: Gram-negative bacteria, such as Klebsiella, Escherichia coli, and Pseudomonas. • Aspiration: a combination of aerobic and anaerobic bacteria. • Immunosuppression: all previously stated possibilities, including viral, mycobacterial, and Pneumocystis infections. Coexisting infections frequently occur in immunosuppressed individuals.

Pathogenesis Bacterial bypass the lung's defenses and initiate infection within the alveoli.

Presentation: • Productive cough, dyspnea, thoracic discomfort, and pyrexia. Macroscopy • The infected lung parenchyma exhibits a firm texture and a yellowish hue. • Purulent exudate may be expelled from minor air passages. The superficial pleura may exhibit signs of pleuritis. Histopathology The alveolar gaps are occupied by an inflammatory infiltrate abundant in neutrophils. Bacterial colonies are frequently discernible within the exudate. • In instances of aspiration pneumonia, alimentary substances may be found within the lung parenchyma. • Severe instances compounded by abscess formation exhibit loss of lung tissue, replaced by confluent sheets of neutrophils.

Prognosis • Recovery is typically anticipated with suitable antibiotic therapy in an otherwise healthy individual.


Complications encompass respiratory failure, septicaemia, pleural effusion, empyema, and lung abscess. These occurrences are more probable with pathogenic organisms or in people with concurrent cardiac and pulmonary conditions.


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Pathology - Chronic obstructive pulmonary disease (COPD)
Definition: A chronic pulmonary ailment marked by dyspnea resulting from poorly reversible and increasing airflow restriction.

Epidemiology • Extremely prevalent. Primarily a condition affecting middle-aged to older adult smokers.

Aetiology • The majority of instances are attributable to smoking. • Instances in younger individuals may result from A-1-antitrypsin deficiency. Pathogenesis Inflammation and scarring of tiny bronchioles are considered the primary cause of airflow obstruction. • An imbalance between proteases and antiproteases leads to the degradation of lung parenchyma, resulting in the dilatation of terminal airspaces (emphysema) and air trapping. • Hyperplasia of mucous glands and the irritative effects of smoking contribute to a productive cough (chronic bronchitis).

Presentation • Abrupt emergence of dyspnea during exertion, occurring against a history of chronic cough and sputum expectoration. • Spirometric analysis generally reveals a diminished FEV1 and a reduced FEV1/FVC ratio (Fig. 5.1). Macroscopy • The lungs exhibit hyperinflation, characterized by thick mucus in the airways and dilated terminal airspaces. • Bullae may be observed.

Histopathology • Persistent inflammation and fibrosis of tiny bronchioles (chronic obstructive bronchiolitis). • Highly pigmented macrophages in respiratory bronchioles (respiratory bronchiolitis). • Enlarged terminal airspaces (emphysema). Larger airways may exhibit mucus gland hyperplasia
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Prognosis • Progressive deterioration of lung function accompanied by bouts of acute exacerbation resulting from infection, pneumothorax, or pulmonary embolism. • Subsequently, pulmonary hypertension and right ventricular failure manifest. Left ventricular failure frequently coexists with ischemic heart disease. • Mortality frequently associated with a conjunction of respiratory and heart failure


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Pathology - Pathologies of the larynx
Vocal chord nodules are benign neoplasms of the laryngeal mucosa. Nodules mainly occur in young women and are linked to vocal abuse. • Exhibit alterations in vocalization. • Minor lesions located in the central third of both vocal cords. Histology reveals a lump with an edematous stroma that subsequently turns fibrotic.
Vocal fold polyp is a non malignant proliferation of the laryngeal mucosa. • Manifestations can arise at any age and are equally prevalent among genders. • Exhibits alterations in vocal quality. • Pertains to the ventricular space or Reinke's space of a single vocal chord. Histology reveals a polyp characterized by a stroma that may exhibit variable oedema, myxoid, hyaline, or fibrous properties.

Laryngeal amyloidosis is a localized variant of amyloidosis. • Typically occurs in the false vocal cords. • Manifestations include alterations in vocal quality. Histological analysis reveals the accumulation of amorphous eosinophilic substance behind the epithelium. Amyloid exhibits staining with Congo Red and reveals chromatic alterations under polarized light. The amyloid typically originates from light chain immunoglobulins.

Squamous papillomas is a predominant benign laryngeal neoplasms. • Linked to human papillomavirus (HPV) types 6 and 11. Bimodal age of incidence: under 5 years and between 20 to 40 years. • Exhibit alterations in vocalization. Histology reveals branching exophytic papillary fronds enveloped by non-descript squamous epithelium. • Pediatric patients typically exhibit a more aggressive disease with early recurrences and an increased likelihood of metastasis outside the larynx. • Adult patients generally demonstrate a more favorable prognosis with less frequent recurrences.
Squamous cell carcinoma is a predominant malignant tumor of the larynx. • Predominantly affects older persons, with a preference for males. • Correlation with tobacco and alcohol misuse. • Exhibits alterations in vocal quality. Histological examination reveals infiltrating nests of malignant epithelial cells with squamous differentiation. • Prognosis is contingent upon the stage of the tumor at presentation.


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Pathology - Nasopharyngeal Diseases
Nasopharyngeal angiofibroma is a rare benign soft tissue tumor that only affects young guys, with a peak onset age of 15 years. • Histology reveals a highly vascular neoplasm with variable diameter arteries surrounded by a cellular fibrous stroma. The lesion is covered by an intact sinonasal epithelium. Local recurrence occurs in 720% of cases after surgery.

Nasopharyngeal carcinoma is a malignant epithelial tumor that develops in the nasopharynx. Adults may have nasal congestion, hearing loss, or tinnitus. • Incidence varies geographically, with southern China, Thailand, and the Philippines having higher rates. • Strong link between EBV and nutrition. • Histology classifies tumors into three types: non-keratinizing, keratinizing, and basaloid. Radiation therapy is typically used to treat the majority of instances. 5-year survival rate: 60%


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