Pleural and Mediastinal Pathology

Question 1

What can lead to a pleural effusion?

Answer 1

Accumulation of fluid (>15mL) in the pleural space secondary to:

• Increase in hydrostatic pressure
  
  • congestive heart failure, lymphatic blockage due to tumor
• Decreased osmotic pressure
  
  • nephrotic syndrome
• Increased vascular permeability
  
  • pneumonia

Question 2

How does a pleural effusion clinically manifest?

Answer 2

• Dyspnea, pleuritic pain, cough
• Enlarged hemithorax
  
  • dullness on percussion
  • decreased or absent breath sounds
• Compression of the lung
  
  • atelectasis leading to respiratory distress

Question 3

How is a pleural effusion diagnosed and treated?

Answer 3

• Chest X-ray
• Thoracentesis
• Analysis of pleural fluid
  
  • Chemistry
  • Culture
  • Cytology
• Pleural biopsy (percutaneous, open)
• Treatment of underlying cause

Question 4

Common Causes of Pleural Effusion:

Answer 4

1. Infections
   
   • Bacterial pneumonia
   • Viral disease
   • Tuberculosis
2. Pulmonary embolism
3. Malignant neoplasms
4. Trauma
5. Systemic conditions
   
   • Congestive heart failure
   • Cirrhosis
   • Nephrotic syndrome
   • Collagen vascular diseases

Question 5

List the different types of pleural effusions:

Answer 5

1. Inflammatory Pleural Effusions:
   
   • Serofibrinous
   • Suppurative (empyema)
   • Hemorrhagic
2. Non-Inflammatory Pleural Effusions:
   
   • Hydrothorax
   • Hemothorax
   • Chylothorax

Question 6

What are causes of inflammatory pleural effusions?

Answer 6

1. Serous, fibrinous and serofibrinous: inflammatory conditions such as pneumonia, T.B., lung infarcts, abscesses
2. Purulent exudate (empyema): localized accumulation of pus due to organisms
3. Hemorrhagic pleuritis: coagulopathies, rickettsial disease, malignant neoplasms

Question 7

• What is an empyema (pylothorax)?
• What is done to treat it?

Answer 7

• Purulent pleural effusions complicating lung infections
  
  • pneumococci, staphilococci and streptococci
  • A.k.a. “suppurative pleuritis”
• Pleural surface is coated by shaggy thick fibrin layer admixed with greenish purulent exudate
• Organization produces adhesions and loculation circumscribing the pus and limiting lung expansion
• Surgical decortication is treatment of choice

Question 8

What are the differences between the non-inflammatory pleural effusions?

Answer 8

1. Hydrothorax: clear serous fluid
   
   • cardiac failure, pulmonary congestion and edema, cirrhosis, uremia, renal failure
2. Hemothorax: hemorrhagic fluid
   
   • ruptured aortic aneurysm, trauma
3. Chylothorax: milky fluid
   
   • thoracic duct trauma or lymphatics occlusion secondary to malignancy

Question 9

• What is a pneumothorax?
• What is it most commonly associated with?
• What are the two types of pneumothorax?

Answer 9

• Presence of air or gas within the pleural cavity
  
  • Spontaneous – traumatic – therapeutic
• Most commonly associated with emphysema, asthma and tuberculosis
• Two Types:
  
  1. Spontaneous idiopathic pneumothorax
  2. Tension pneumothorax

Question 10

What mechanisms can form a pneumothorax?

Answer 10

• Perforation of the visceral pleura and entry of air from the lung
• Penetration of air from the chest wall, diaphragm, mediastinum or esophagus
• Gas-forming organisms in empyema

Question 11

Pneumothorax

Clinical Symptoms

Answer 11

• Chest pain, dyspnea
• Absent breath sounds on auscultation
• Tympanitic percussion (hyper-resonance)
• Contralateral deviation of the trachea on CXR
• Compression and collapse of lung parenchyma with atelectasis
• Marked respiratory distress

Question 12

What are the clinical signs and causes of a spontaneous pneumothorax?

Answer 12

• Encountered in young individuals secondary to rupture of small apical lung blebs or bullas
• Trachea is deviated to the ipsilateral side
  
  • usually subsides spontaneously
• Causes:
  
  • Idiopathic (unknown cause)
  • Bronchopleural fistula
  • Bullous emphysema

Question 13

What are the clinical signs and causes of a tension pneumothorax?

Answer 13

• Due to penetrating trauma to the lungs
  
  • Produces increased pleural cavity pressure with compression and atelectasis
  • Flap-like pleural defect acts like a valve allowing air in but not out
• Sudden onset of respiratory distress (medical emergency)
• Trachea deviated to contralateral side of pneumothorax

Question 14

Example of Pleural Neoplasms:

1. Benign:
2. Malignant:

Answer 14

1. Benign:
   
   • Solitary fibrous tumor (pleural fibroma)
2. Malignant:
   
   • Metastases from other organs
   • Malignant mesothelioma

Question 15

• Describe a solitary fibrous tumor:
• What is it associated with?

Answer 15

• Polypoid, well-circumscribed, pedunculated
• Composed of fibroblasts with abundant collagenized stroma
• Benign tumor, cured by simple excision
• Mostly asymptomatic and discovered incidentally on chest X-rays
• Associated with hypoglycemia and clubbing of the fingers

Question 16

• Define malignant mesothelioma:
• What age group is it most common in?

Answer 16

• Neoplastic proliferation of mesothelial cells lining serosal surfaces
  
  • Affects 15-20 persons per million/per year in the general population
• Most common in adults over 50

Question 17

What are etiologies of malignant mesothelioma?

Answer 17

• Asbestos exposure
• Idiopathic (up to 50% of cases)
• Radiation
• Chronic inflammation
• Viral infections (SV40 simian virus in old polio vaccines)

Question 18

What is the incidence of asbestos-related mesothelioma?

Answer 18

• Epidemiologic studies (coastal areas of US and GB and mining areas in Canada and So. Africa)
• Lifetime risk for developing mesothelioma is up to 10% in patients with a history of heavy exposure
• Long latency period (20-40 years)
• Occupational exposure: millworkers, roofing materials, textiles, insulation, shipyard workers

Question 19

Abestos-related Mesothelioma:

Clinical Symptoms

Answer 19

• Insidious, slow growing neoplasm
• Recurrent pleural effusions
• Chest pain and dyspnea in more advanced stages
• Only 20% of patients have pulmonary fibrosis (asbestosis)
• Fatal malignancy; median survival 18 months

Question 20

How does mesothelioma appear histologically?

Answer 20

• Tumor characteristically spreads along mesothelial surfaces
• Composed of bland-appearing cuboidal cells that resemble normal mesothelial cells (well-differentiated neoplasm)
• Very difficult for pathologist to distinguish mesothelioma from metastatic carcinoma to the pleura
• Can also involve other serosal surfaces like peritoneum, tunica vaginalis and pericardium

Question 21

________ ______ are more common than primary malignancies in the pleura

Answer 21

Metastatic tumors are more common than primary malignancies in the pleura

Question 22

Describe how metastatic tumors spread:

Answer 22

• Lung is the most frequent source of metastases to the pleura
  
  • ​other tumors include breast and ovarian cancer, pancreas, kidney
• Spread is by blood, lymphatics or direct extension
• Metastases are often multiple and bilateral

Question 23

What are the mediastinal compartments?

Answer 23

1. anterior/superior
2. medial
3. posterior

Question 24

What are the different types of mediastinal inflammation?

Answer 24

1. Acute mediastinitis
   
   • Complication of conditions affecting neighboring organs
   • esophageal perforation, perforation of lung abscess, sternal osteomyelitis, etc
2. Granulomatous mediastinitis
   
   • Chronic disorder secondary to fungal or mycobacterial infection
3. Idiopathic sclerosing mediastinitis
   
   • Unknown etiology

Question 25

What causes **granulomatous mediastinitis**?

Answer 25

1. Histoplasmosis 2. Tuberculosis 3. Cryptococcosis 4. Atypical mycobacteria 5. Aspergillosis

Question 26

**Tumors of the Mediastinum** Anterior/Superior

Answer 26

1. **Metastatic tumors** 2. **Thymoma, thymic CA** 3. Lymphomas 4. Germ cell tumors 5. Sarcomas 6. Congenital thymic cysts

Question 27

**Tumors of the Mediastinum** Medial

Answer 27

1. **Metastatic tumors** 2. **Pericardial cyst** 3. **Bronchogenic cyst** 4. Lymphomas

Question 28

**Tumors of the Mediastinum** Posterior

Answer 28

**Neurogenic tumors** 1. Schwannoma 2. Neurofibroma 3. Ganglioneuroma 4. Neuroblastoma

Question 29

**Congenital Cysts** * Clinical Presentation:

Answer 29

* Usually **unilocular** * _Children aged 5 to 15 years_ * Lined by _simple cuboidal epithelium_ * May be filled with _serous fluid_

Question 30

What is **thymic lymphoid follicular hyperplasia** associated with?

Answer 30

**myasthenia gravis** and other autoimmune disorders

Question 31

**Myasthenia Gravis** * Associated with: * Pathogenesis: * Symptoms:

Answer 31

* May be associated with **thymic lesions** – * Thymic hyperplasia * Thymoma (30-40% of patients with thymoma develop MG) * Thymic carcinoma * **Auto-antibodies form to acetylcholine receptor** in neuromuscular junction * Autosensitization to AChR is initiated in the thymus due to defective confrontation of ACh-secreting thymic myoid cells with T-lymphocytes * **Symptoms:** weakness, fatigability, ptosis, diplopia

Question 32

What is a **thymoma**? * What is its clinical presentation? * How does it appear histologically?

Answer 32

* **Neoplastic proliferation of thymic epithelial cells** * Usually contains abundant immature T-lymphocytes (non-neoplastic) * Frequently associated with **myasthenia gravis** and other paraneoplastic syndromes * May be composed of **spindle cells or round epithelioid cells** * type A (spindle cells) * type B (round cells) * type AB (mixture of both) * Slow-growing tumor that may recur but rarely metastasizes

Question 33

**Thymoma** * Symptoms: * Paraneoplastic syndromes:

Answer 33

* Symptoms: * Asymptomatic in 30% of patients * Cough, dyspnea, chest pain * **Superior vena cava syndrome** * **​**obscures or obstructs the SVC * Paraneoplastic syndromes: * **Myasthenia gravis** * Pure red cell aplasia * Hypogammaglobulinemia * Agranulocytosis; white blood cell aplasia * Polymyositis; SLE * Pemphigus vulgaris, disseminated herpes

Question 34

What is the clinical behavior of a thymoma?

Answer 34

* Depends on the status of the capsule * Encapsulated tumors ⇒ cured by complete surgical excision * Invasive tumors ⇒ tend to recur repeatedly and may eventually metastasize * Recurrent tumors may progress to thymic carcinoma

Question 35

* What is the histology of thymic carcinoma? * How is a diagnosis made?

Answer 35

* _Resemble other types of carcinoma occurring in other organs_ (squamous, small cell, adenocarcinoma, etc) * _Diagnosis of exclusion_ (i.e., there are no specific features that permit definite histologic diagnosis)