Pathology of Pulmonary Vascular Disease and Pleural Disease

Question 1

Describe the pulmonary circulation

Answer 1

LOW PRESSURE system with a DUAL BLOOD SUPPLY:
Pulmonary arteries (deoxygenated blood) - receive entire cardiac output
Bronchial arteries

Question 2

Vessels of the pulmonary circulation

Answer 2

Thin-walled vessels with a low incidence of atherosclerosis (at normal pressures)

Question 3

What is pulmonary oedema?

Answer 3

Abnormal accumulation of fluid IN THE LUNG:
In the interstitium, firstly
Then in the alveolar spaces

Causes a RESTRICTIVE PATTERN of disease with PFTs

Question 4

Causes of pulmonary oedema?

Answer 4

1. Haemodynamic (hydrostatic pressure increase - less water out of vessels/plasma osmotic pressure decrease - less water back into vessels)
2. Due to cellular injury to:
   Alveolar lining cells
   Alveolar endothelium

Question 5

Causes of increased hydrostatic pressure and decreased plasma osmotic pressure?

Answer 5

Increased hydrostatic pressure:
Left ventricular failure (causes backwards pressure increase and fluid leaks out, into interstitium and then into alveolar spaces)

Decreased plasma pressure:
Low albumin levels

Question 6

Effects of pulmonary oedema?

Answer 6

Localised - pneumonia

Generalised - Adult Respiratory Distress Syndrome (ARDS)

Question 7

What is ARDS?

Answer 7

AKA Diffuse Alveolar Damage Syndrome (DADS) and shock lung

Causes:
Sepsis
Diffuse infection (viruses, mycoplasma, etc)
Severe trauma
Oxygen - O2 therapy can be dangerous due to oxygen free radicals being produced by leukocytes

Question 8

Pathogenesis of ARDS?

Answer 8

Characteristic hyaline membranes (fibrinous exudate lining alveolar walls)
Cellular regeneration
Inflammation

Injury, e.g: with a bacterial endotoxin, leads to:
Infiltration of inflammatory cells
Cytokines
Oxygen free radicals production by leukocytes
Injury to cell membranes

Question 9

Outcomes of ARDS?

Answer 9

Tissue death
Resolution (potential with ventilation, vascular support in ICU, etc)
Fibrosis (chronic restrictive lung disease)

Question 10

What is neonatal RDS?

Answer 10

Occurs in PREMATURE infants, who are deficient in SURFACTANT (secreted by type 2 alveolar lining cells) - increased surface tension leads to stiff lungs

So, increased effort in expanding lungs leads to physical cell damage

Question 11

What is an embolus?

Answer 11

Detached intravascular mass carried by blood to a site in the body distant from its point of origin

Most are thrombi; others are gas (bone through skin - exposure to air), fat, foreign bodies, tumour clumps

Question 12

What is a pulmonary embolus?

Answer 12

Cause of sudden death and pulmonary hypertension
Common and often sub-clinical

95% ARE THROMBOEMBOLI
Source of most pulmonary emboli is a DEEP VENOUS THROMBOSIS (DVT) of lower limbs

Question 13

Risk factors for PE?

Answer 13

Same as for DVT; VIRCHOW’S TRIAD:

1. Factors in vessel wall, e.g: endothelial hypoxia
2. Abnormal blood flow, e.g: venous stasis
3. Hypercoagulable blood, e.g: in cancer patients, post-MI, etc)

Question 14

Effects of PE?

Answer 14

Sudden death
Severe chest pain/dyspnoea
Haemoptysis
Pulmonary infarction
Pulmonary hypertension

Question 15

What do the effects of a PE depend upon and give examples?

Answer 15

Size of embolus
Cardiac function
Respiratory function

Large emboli:
Death
Infarction
Severe symptoms

Small emboli - tend to be clinically silent but, if recurrent, can lead to pulmonary hypertension

Question 16

What is a pulmonary infarct?

Answer 16

Ischaemic necrosis
Embolus is necessary for this but not everybody with an embolus infarcts
BRONCHIAL ARTERY supply COMPROMISED, e.g: in cardiac failure

Question 17

Types of pulmonary hypertension?

Answer 17

Primary (rare but tends to be in young women)

Secondary

Question 18

Mechanisms of pulmonary hypertension development?

Answer 18

HYPOXIA - vascular constriction
Increased flow through pulmonary circulation - congenital heart disease (shunting of blood from left to right)
Blockage (PE) or loss (emphysema) of pulmonary vascular bed
Back pressure from left-sided heart failure

Question 19

Morphology of pulmonary hypertension?

Answer 19

Medial hypertrophy of arteries
Intimal thickening (fibrosis)
Atheroma
Right ventricular hypertrophy
Extreme cases, e.g: congenital heart disease, primary pulmonary hypertenson) - plexogenic change (plexiform lesions - complex vascular formations originating from remodeled pulmonary arteries) /necrosis

Question 20

What is Cor Pulmonale?

Answer 20

Pulmonary hypertension complicating lung disease:
Right ventricular hypertrophy
Right ventricular dilatation - can cause cardiomegaly
Right-sided heart failure (causing swollen legs, congested liver, etc)

Question 21

What are the pleura?

Answer 21

Mesothelial surface lining lungs and mediastinum; have mesothelial cells designed for fluid absorption

Question 22

What are pleural effusions?

Answer 22

HALLMARKS OF DISEASE

Accumulation of fluid in pleural space

Question 23

Types of pleural effusion?

Answer 23

Transudate (low protein/low albumin levels) - caused by cardiac failure and in hypoproteinaemia

Exudate (high protein) - caused by either an inflammatory process in pleura, e.g: pneumonia, TB, connective tissue disease, or malignancy (primary/metastatic)

Question 24

What is a purulent effusion?

Answer 24

Full of acute inflammatory cells and contain pus, e.g: in an:
Empyema (can be a pneumonia complication and can become walled off, leading to an abscess)
Can become chronic

Question 25

What is a pneumothorax?

Answer 25

Air in pleural space due to:
Trauma, e.g: fractured rib punctures pleura)
Spontaneous (rupture of bulla)

Question 26

Types of pleural neoplasia?

Answer 26

Primary:
Benign pleural neoplasias are rare
Malignant mesothelioma

Secondary - spread from elsewhere and are common, e.g: from adenocarcinomas in lung, GIT, ovary, etc)

Question 27

What is mesothelioma?

Answer 27

Primary malignant tumour of pleura that is ASBESTOS-RELATED - bad prognosis
Mixed epithelial/mesenchymal differentiation (looks between a carcinoma and sarcoma in appearance, i.e: are BIPHASIC TUMOURS)

METASTASES IN PLEURA CAN MIMIC A MESOTHELIOMA

Question 28

Determining differential diagnosis of malignant effusions?

Answer 28

Difficult to differentiate between primary and secondary tumours but can use:
Cytology, biopsy
Immunohistochemistry for lineage specific antigens may help
Medicolegal importance