Atelectasis pathophysiology: Difference between revisions

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Latest revision as of 15:00, 21 March 2018

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sudarshana Datta, MD [2]

Overview

The pathophysiology of obstructive and non-obstructive atelectasis can be better explained by understading underlying pathology. Obstructive atelectasis, the most common type of atelectasis, occurs due to obstruction at any level from the trachea to the alveoli. Foreign bodies, tumors, and mucus plugs are the most common causes of obstructive atelectasis. Non obstructive atelectasis occurs due to severe lung scarring caused by necrotizing pneumonias or granulomatous diseases leading to cicatrisation atelectasis. Lung infiltration by a tumor (bronchoalveolar carcinoma) may cause replacement atelectasis, thoracic space occupying lesions can cause compression atelectasis, diminished levels of surfactant can lead to adhesive atelectasis presenting as ARDS. Passive atelectasis occurs due to absence of contact between the parietal and visceral pleurae due to fluid (pleural effusion), air (pneumothorax), blood (hemothorax) etc. Patients undergoing upper abdominal and thoracic procedures may develop postoperative atelectasis which may arise as a complication of surgery or anaesthesia leading to decreased surfactant activity and dysfunction of the diaphragm.

Pathophysiology

Pathogenesis

It is understood that atelectasis is the result of obstructive and non-obstructive etiologies.
The pathophysiology of obstructive and non-obstructive atelectasis is determined by several factors.

Pathogenesis of Obstructive atelectasis

Obstructive atelectasis is the most common type of atelectasis
Obstructive atelectasis occurs due to obstruction at any level from the trachea to the alveoli.
Ventilation defect
- Bronchial obstruction leads to resorption of alveolar gas by the blood circulating in the alveolar capillary membrane.
- Alveolar gas reabsorption due to obstruction leads to diminished lung volume and subsequent atelectasis.^[1]

Perfusion defect
- Perfusion of under ventilated lung tissue leads to hypoxemia due to shunt formation. leading to obstruction
- Following bronchial obstruction, complete collapse of the affected lung is prevented by secretions that fill up the spaces of the alveoli.
- The adjacent lung distends to prevent collapse of the part of the lung undergoing atelectasis.
- The mediastinum shifts towards the affected side.
- Diaphragmatic elevation of the diaphragm leads to flattening of the chest wall.
The extent of atelectasis depends upon the level of obstruction.
- Lobar atelectasis occurs due to lobar bronchus obstruction.
- Segmental atelectasis arises from segmental bronchus obstruction.

The rate and pattern of development of atelectasis depends on collateral ventilation and gas composition of inspired air.

Pathogenesis of Non obstructive atelectasis

Non obstructive atelectasis occurs due to severe lung scarring caused by necrotizing pneumonias or granulomatous diseases leading to cicatrisation atelectasis.
Lung infiltration by a tumor (bronchoalveolar carcinoma) may cause replacement atelectasis, thoracic space occupying lesions can cause compression atelectasis, diminished levels of surfactant can lead to adhesive atelectasis presenting as ARDS.
Passive atelectasis occurs due to absence of contact between the parietal and visceral pleurae due to fluid (pleural effusion), air (pneumothorax), blood (hemothorax) etc.
Atelectasis of the upper lobe commonly occurs due to pneumothorax, whereas atelectasis of the middle and lower lobes occurs due to pleural effusion.
Rounded atelectasis, which presents at a mean age of 60 years, arises due to formation of fibrous bands which adhere the lung to the pleura.
- There is a high association of rounded atelectasis in asbestosis due to the formation of fibrous pleural plaques.

Middle lobe syndrome

Middle lobe syndrome (Fixed or recurrent atelectasis of the lingula/right middle lobe) occurs due to Sjogren’s syndrome.
Intraluminal or extraluminal obstruction (compression of the bronchi by adjacent structures) results in middle lobe syndrome.^[2]^[3]
Patients with lower respiratory tract infections, PE and hypoventilation may develop obstruction of the small bronchus, leading to formation of small atelectatic areas within the lung.
This may be due to respiratory stressors such as toxins, hyperoxia, hypoxia, ischemia leading to impaired surfactant production and impaired regional ventilation. Intrapulomary shunt formation and ventilation perfusion mismatch may arise to due to development of this platelike atelectasis.
Patients undergoing upper abdominal and thoracic procedures may develop postoperative atelectasis which may arise as a complication of surgery or anaesthesia leading to decreased surfactant activity and dysfunction of the diaphragm.
Postoperative atelectasis is segmental and basilar in distribution.

Associated Conditions

Common conditions associated with atelectasis include:

Gross Pathology

On gross pathology, pleural folds with deep invaginations are characteristic findings of atelectasis.^[4]

Microscopic Pathology

On microscopic histopathological analysis, fibrosis and pleural invaginations are characteristic findings of atelectasis.^[4]
If there is an existing pathology leading to atelectasis, characteristic features of the underlying disease may also be seen on microscopic pathology.

References

↑ "Atelectasis - Symptoms and causes - Mayo Clinic".
↑ Chen HA, Lai SL, Kwang WK, Liu JC, Chen CH, Huang DF (2006). "Middle lobe syndrome as the pulmonary manifestation of primary Sjögren's syndrome". Med. J. Aust. 184 (6): 294–5. PMID 16548837.
↑ Rosenbloom SA, Ravin CE, Putman CE, Sealy WC, Vock P, Clark TJ, Godwin JD, Chen JT, Baber C (1983). "Peripheral middle lobe syndrome". Radiology. 149 (1): 17–21. doi:10.1148/radiology.149.1.6611925. PMID 6611925.
↑ ^4.0 ^4.1 "Pathology Outlines - Round or rounded atelectasis".

Template:WH Template:WS

[urlAtelectasis_-_Symptoms_and_causes_-_Mayo_Clinic-1] "Atelectasis - Symptoms and causes - Mayo Clinic".

[pmid16548837-2] Chen HA, Lai SL, Kwang WK, Liu JC, Chen CH, Huang DF (2006). "Middle lobe syndrome as the pulmonary manifestation of primary Sjögren's syndrome". Med. J. Aust. 184 (6): 294–5. PMID 16548837.

[pmid6611925-3] Rosenbloom SA, Ravin CE, Putman CE, Sealy WC, Vock P, Clark TJ, Godwin JD, Chen JT, Baber C (1983). "Peripheral middle lobe syndrome". Radiology. 149 (1): 17–21. doi:10.1148/radiology.149.1.6611925. PMID 6611925.

[urlPathology_Outlines_-_Round_or_rounded_atelectasis-4] 4.0 ^4.1 "Pathology Outlines - Round or rounded atelectasis".

[1]

[2]

[3]

[4]

@@ Line 1: / Line 1: @@
 __NOTOC__
 {{Atelectasis}}
-{{CMG}} ;
+{{CMG}}; {{AE}}{{Cherry}}
 ==Overview==
-There are several types of atelectasis according to their underlying mechanisms or the distribution of alveolar collapse; resorption, compression, microatelectasis and contraction atelectasis.
+The pathophysiology of obstructive and non-obstructive atelectasis can be better explained by understading underlying pathology. Obstructive atelectasis, the most common type of atelectasis, occurs due to obstruction at any level from the [[Vertebrate trachea|trachea]] to the [[Pulmonary alveolus|alveoli]]. [[Foreign bodies]], [[Tumor|tumors]], and [[Mucus|mucus plugs]] are the most common causes of obstructive atelectasis. Non obstructive atelectasis occurs due to severe lung scarring caused by [[Pneumonia|necrotizing pneumonias]] or [[Granulomatous|granulomatous diseases]] leading to cicatrisation atelectasis. Lung infiltration by a [[tumor]] ([[bronchoalveolar carcinoma]]) may cause replacement atelectasis, thoracic space occupying lesions can cause compression atelectasis, diminished levels of [[Pulmonary surfactant|surfactant]] can lead to adhesive atelectasis presenting as [[Acute respiratory distress syndrome|ARDS]]. Passive atelectasis occurs due to absence of contact between the [[Parietal pleura|parietal]] and [[Visceral pleura|visceral pleurae]] due to fluid ([[pleural effusion]]), air ([[pneumothorax]]), blood ([[hemothorax]]) etc. Patients undergoing upper abdominal and thoracic procedures may develop postoperative atelectasis which may arise as a complication of surgery or [[Anesthesia|anaesthesia]] leading to decreased surfactant activity and dysfunction of the [[Thoracic diaphragm|diaphragm]].
-The exact pathogenesis of [disease name] is not fully understood.
-OR
-It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
-OR
-[Pathogen name] is usually transmitted via the [transmission route] route to the human host.
-OR
-Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
-OR
-[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
-OR
-The progression to [disease name] usually involves the [molecular pathway].
-OR
-The pathophysiology of [disease/malignancy] depends on the histological subtype.
 ==Pathophysiology==
 ===Pathogenesis===
-*The exact pathogenesis of [disease name] is not fully understood.
+*It is understood that atelectasis is the result of obstructive and non-obstructive etiologies.
-OR
+*The pathophysiology of obstructive and non-obstructive atelectasis is determined by several factors.
-*It is understood that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
-*[Pathogen name] is usually transmitted via the [transmission route] route to the human host.
-*Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
-*[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
-*The progression to [disease name] usually involves the [molecular pathway].
-*The pathophysiology of [disease/malignancy] depends on the histological subtype.
-Obstructive atelectasis:
-Obstructive atelectasis is the most common type of atelectasis
-In case of obstruction from the trachea to the alveoli at any level, alveolar gas reabsorption may occur leading to diminished lung volume and subsequent atelectasis.
-The extent of atelectasis depends upon the level of obstruction:
-Lobar atelectasis: due to lobar bronchus obstruction
-Segmental atelectasis: leads to segmental bronchus obstruction
-Causes of obstructive atelectasis:
-Foreign body
-Tumor
-Mucus plugs
-The rate and pattern of development of atelectasis depends on collateral ventilation and gas composition of inspired air.
-Non obstructive atelectasis:
-Non obstructive atelectasis may occur due to severe lung scarring caused by necrotizing pneumonias or granulomatous diseases (cicatrisation atelectasis) or infiltration (replacement atelectasis), extrinsic
-lung compression (due to thoracic space occupying lesions), diminished levels of surfactant (adhesive atelectasis presenting as ARDS), and passive atelectasis due to absence of contact between the parietal and visceral pleurae due to fluid (pleural effusion), air (pneumothorax), blood (hemothorax) etc.
-Atelectasis of the upper lobe commonly occurs due to pneumothorax, whereas atelectasis of the middle and lower lobes occurs due to pleural effusion.
+==== <u>Pathogenesis of Obstructive atelectasis</u> ====
-Rounded atelectasis:
+*Obstructive atelectasis is the most common type of atelectasis
-This is a form of atelectasis that is characterized by formation of fibrous bands which adhere the lung to the pleura. There is a high association of rounded atelectasis in asbestosis due to the formation of fibrous pleural plaques.
+*Obstructive atelectasis occurs due to obstruction at any level from the [[Vertebrate trachea|trachea]] to the [[Pulmonary alveolus|alveoli]].
-Mean age of presentation is 60 years.
+*'''Ventilation defect'''
-Middle lobe syndrome (Fixed or recurrent atelectasis of the lingula/right middle lobe): due to Sjogren’s syndrome
+**Bronchial obstruction leads to resorption of [[Alveolus|alveolar gas]] by the blood circulating in the [[Alveolar|alveolar capillary membrane]].
-Intraluminal or extraluminal obstruction (compression of the bronchi by adjacent structures) may result in middle lobe syndrome.
+**[[Alveolus|Alveolar gas]] reabsorption due to obstruction leads to diminished lung volume and subsequent atelectasis.<ref name="urlAtelectasis - Symptoms and causes - Mayo Clinic">{{cite web |url=https://www.mayoclinic.org/diseases-conditions/atelectasis/symptoms-causes/syc-20369684 |title=Atelectasis - Symptoms and causes - Mayo Clinic |format= |work= |accessdate=}}</ref>
-Non obstructive causes may also lead to atelectasis of the middle lobe.
+*'''Perfusion defect'''
+**Perfusion of under ventilated lung tissue leads to [[hypoxemia]] due to shunt formation. leading to obstruction
+**Following [[Bronchiole|bronchial]] obstruction, complete collapse of the affected lung is prevented by secretions that fill up the spaces of the [[Pulmonary alveolus|alveoli]].
+**The adjacent lung distends to prevent collapse of the part of the lung undergoing atelectasis.
+**The [[mediastinum]] shifts towards the affected side.
+**Diaphragmatic elevation of the [[Thoracic diaphragm|diaphragm]] leads to flattening of the chest wall.
+* The extent of atelectasis depends upon the level of obstruction.
+** Lobar atelectasis occurs due to lobar [[bronchus]] obstruction.
+** Segmental atelectasis arises from segmental [[bronchus]] obstruction.
-Pathophysiology:
+* The rate and pattern of development of atelectasis depends on collateral [[Ventilation (physiology)|ventilation]] and gas composition of inspired air.
-The pathophysiology of obstructive and non-obstructive atelectasis is determined by several factors.
-Obstructive atelectasis
+==== <u>Pathogenesis of Non obstructive atelectasis</u> ====
-Bronchial obstruction leads to resorption of alveolar gas by the blood circulating in the alveolar capillary membrane.
+* Non obstructive atelectasis occurs due to severe lung scarring caused by [[Pneumonia|necrotizing pneumonias]] or [[Granulomatous|granulomatous diseases]] leading to cicatrisation atelectasis.
-This leads to diminished lung volume and lung retraction. Perfusion of unventilated lung tissue leads to hypoxemia due to shunt formation.
+* Lung infiltration by a [[tumor]] ([[bronchoalveolar carcinoma]]) may cause replacement atelectasis, thoracic space occupying lesions can cause compression atelectasis, diminished levels of [[Pulmonary surfactant|surfactant]] can lead to adhesive atelectasis presenting as [[Acute respiratory distress syndrome|ARDS]].
-Following bronchial obstruction, complete collapse of the affected lung is prevented by secretions that fill up the spaces of the alveoli. The adjacent lung distends to prevent collapse of the part of the lung undergoing atelectasis. The mediastinum shifts towards the affected side. Diaphragmatic elevation of the diaphragm leads to flattening of the chest wall.
+* Passive atelectasis occurs due to absence of contact between the [[Parietal pleura|parietal]] and [[Visceral pleura|visceral pleurae]] due to fluid ([[pleural effusion]]), air ([[pneumothorax]]), blood ([[hemothorax]]) etc.
-Nonobstructive atelectasis
+* Atelectasis of the upper lobe commonly occurs due to [[pneumothorax]], whereas atelectasis of the middle and lower lobes occurs due to [[pleural effusion]].
-This is primarily due to loss of contact between the parietal and visceral pleurae (due to pneumothorax or pleural effusion), leading to passive or relaxation atelectasis. While pneumothorax primarily affects the upper lobe, pleural effusions affect the lower lobes.
+* Rounded atelectasis, which presents at a mean age of 60 years, arises due to formation of fibrous bands which adhere the lung to the pleura.
-Lung surfactant is composed of phospholipid dipalmitoyl phosphatidylcholine, which reduces alveolar surface tension. Absence or inactivation of surfactant leads to development of adhesive atelectasis. This can occur in case of ARDS, blunt trauma to the lung, alveolar collapse and radiation pneumonitis. Cicatrization atelectasis may develop due to scar formation in the lung parenchyma.
+** There is a high association of rounded atelectasis in [[asbestosis]] due to the formation of fibrous [[Mesothelioma|pleural plaques]].
-Infiltration of the lung lobe by a tumor (bronchoalveolar carcinoma) may lead to replacement atelectasis.
-Patients with lower respiratory tract infections, PE and hypoventilation may develop obstruction of the small bronchus, leading to formation of small atelectatic areas within the lung. This may be due to respiratory stressors such as toxins, hyperoxia, hypoxia, ischemia leading to impaired surfactant production and impaired regional ventilation. Intrapulomary shunt formation and ventilation perfusion mismatch may arise to due to development of this platelike atelectasis.
-Postoperative atelectasis: Upper abdominal and thoracic procedures lead to postoperative atelectasis which may arise as a complication of surgery or anaesthesia leading to decreased surfactant activity and dysfunction of the diaphragm.  This leads to atelectasis which is segmental and basilar in distribution.
-==Genetics==
+==== Middle lobe syndrome ====
-*[Disease name] is transmitted in [mode of genetic transmission] pattern.
+* Middle lobe syndrome (Fixed or recurrent atelectasis of the lingula/right middle lobe) occurs due to [[Sjögren's syndrome|Sjogren’s syndrome]].
-*Genes involved in the pathogenesis of [disease name] include [gene1], [gene2], and [gene3].
+* Intraluminal or extraluminal obstruction (compression of the [[Bronchus|bronchi]] by adjacent structures) results in middle lobe syndrome.<ref name="pmid16548837">{{cite journal |vauthors=Chen HA, Lai SL, Kwang WK, Liu JC, Chen CH, Huang DF |title=Middle lobe syndrome as the pulmonary manifestation of primary Sjögren's syndrome |journal=Med. J. Aust. |volume=184 |issue=6 |pages=294–5 |year=2006 |pmid=16548837 |doi= |url=}}</ref><ref name="pmid6611925">{{cite journal |vauthors=Rosenbloom SA, Ravin CE, Putman CE, Sealy WC, Vock P, Clark TJ, Godwin JD, Chen JT, Baber C |title=Peripheral middle lobe syndrome |journal=Radiology |volume=149 |issue=1 |pages=17–21 |year=1983 |pmid=6611925 |doi=10.1148/radiology.149.1.6611925 |url=}}</ref>
-*The development of [disease name] is the result of multiple genetic mutations.
+* Patients with [[Respiratory tract infections|lower respiratory tract infections]], [[Pulmonary embolism|PE]] and [[hypoventilation]] may develop obstruction of the [[Bronchus|small bronchus]], leading to formation of small atelectatic areas within the lung.
+* This may be due to respiratory stressors such as [[Toxin|toxins]], [[Oxygen toxicity|hyperoxia]], [[Hypoxemia|hypoxia]], [[ischemia]] leading to impaired [[Pulmonary surfactant|surfactant]] production and impaired regional [[Ventilation (physiology)|ventilation]]. [[Shunt|Intrapulomary shunt]] formation and [[Ventilation-perfusion mismatch|ventilation perfusion mismatch]] may arise to due to development of this platelike atelectasis.
+* Patients undergoing upper abdominal and thoracic procedures may develop postoperative atelectasis which may arise as a complication of surgery or [[Anesthesia|anaesthesia]] leading to decreased surfactant activity and dysfunction of the [[Thoracic diaphragm|diaphragm]].
+* Postoperative atelectasis is segmental and basilar in distribution.
 ==Associated Conditions==
+Common conditions associated with atelectasis include:
+*[[Lower respiratory tract infection|Lower respiratory tract infections]]
+*[[Pneumonia]]
+*[[Bronchiectasis]]
+*[[Chronic obstructive pulmonary disease|Chronic obstructive pulmonary disease (COPD)]]
+*[[Cystic fibrosis|Cystic Fibrosis]]
+*[[ARDS]]
 ==Gross Pathology==
-*On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
+*On gross pathology, pleural folds with deep invaginations are characteristic findings of atelectasis.<ref name="urlPathology Outlines - Round or rounded atelectasis">{{cite web |url=http://www.pathologyoutlines.com/topic/lungnontumorroundedat.html |title=Pathology Outlines - Round or rounded atelectasis |format= |work= |accessdate=}}</ref>
 ==Microscopic Pathology==
-*On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
+*On microscopic histopathological analysis, [[fibrosis]] and pleural invaginations are characteristic findings of atelectasis.<ref name="urlPathology Outlines - Round or rounded atelectasis">{{cite web |url=http://www.pathologyoutlines.com/topic/lungnontumorroundedat.html |title=Pathology Outlines - Round or rounded atelectasis |format= |work= |accessdate=}}</ref>
+*If there is an existing pathology leading to atelectasis, characteristic features of the underlying disease may also be seen on microscopic pathology.
 ==References==