The middle lobe syndrome (MLS) refers to chronic or recurrent collapse of the right middle lobe and/or lingual of the left lung. The right middle lobe is relatively isolated, especially if a complete minor fissure is present. One theory for cases without obstruction is that loss of collateral ventilation results in atelectasis.


Classification of the middle lobe syndrome are divided into:

(1) obstructive causes (right middle lobe bronchus obstructed on bronchoscopy)

(2) nonobstructive causes (right middle lobe bronchus patent on bronchoscopy)


Obstructive causes:

(1) lung tumor

(2) infection

(3) foreign body


Nonobstructive causes:

(1) bronchiectasis

(2) asthma

(3) other inflammatory disease

(4) broncholithiasis


Symptoms are often nonspecific. A patient may present with dyspnea, fever, cough, chest pain or hemoptysis. The diagnosis is often not suspected until it is demonstrated by imaging studies.


Management may be medical or surgical. Surgical therapy is indicated if:

(1) a malignancy is suspected

(2) medical therapy fails


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