Hyperinflation

00:01 So in this lecture, we'll be discussing hyperinflation which is another very commonly seen abnormality within the lungs.

00:06 Emphysema or hyperinflation is destruction of a portion of the airway distal to the terminal bronchiole.

00:15 You can have multiple radiographic findings that can let you know that there is hyperinflation.

00:21 You have flattening of the heimdiaphragms.

00:23 You have an enlarged retrosternal airspace.

00:26 You can have an increased AP diameter of the chest which is best seen on a lateral radiograph.

00:31 The heart appears small because you have so much air within the lungs and you may have hyperlucency or blackness of the lungs.

00:38 On a CT, you have slightly more findings because it is more sensitive than radiography.

00:44 You may have low-density areas within the lungs that don't have walls and we'll take a look at what all of these findings look like.

00:51 So this is an example of hyperinflation.

00:55 On the left, you see the radiographic findings and on the right, you see the CT findings.

00:59 So this is an example of a hyperinflated lung on the left versus the normal on the right.

01:07 So let's take a look here.

01:09 You can see that the diaphragms are very flat in the hyperinflated lung.

01:13 On the right, you have normal curvature of the diaphragm.

01:17 You actually have a lung that appears significantly larger on the left than it does on the right and you have this slightly diffuse haziness that's seen within the lungs as well.

01:28 On the lateral view, you have an increased diameter of the thorax compared with the normal and you can also see that there is more prominence of the aorta and of the heart and that just looks a little bit more prominent because you have more air within the lungs.

01:45 You also see the flattening of the hemidiaphragms very well on the left.

01:49 So again, this is the comparison of a hyperinflated lung versus the normal lung and you can see the differences between the two.

01:57 So how about the CT findings? There are three major types of emphysema.

02:04 There's centrilobular emphysema, which results in destruction of the respiratory bronchiole, there's paraseptal emphysema which causes destruction of the alveolar ducts and the sacs and there's panlobular emphysema which causes destruction of the entire alveolus distal to the terminal bronchiole.

02:20 So let's begin with panlobular emphysema.

02:25 The most common cause of this is Alpha1-antitrypsin abnormality.

02:29 You see diffuse areas of low density as you can see on this axial CT image.

02:34 The entire lung just looks like it's very low density.

02:36 It's difficult to actually find areas of normal lung within it.

02:40 You don't see the normal interstitium that you would in a normal-appearing lung.

02:44 Centrilobular emphysema is more caused by cigarette smoking.

02:51 This is one of the most commonly seen types of emphysema.

02:54 It's usually seen predominantly in the upper lobes and it causes centrally located lucencies so as you can see pointed out here, there are multiple lucencies throughout the lungs and the rest of the lung appears again somewhat hazy.

03:07 Paraseptal emphysema is actually the least common form.

03:11 This is also associated with cigarette smoking.

03:13 This causes peripherally located lucencies as you can see here and these can actually lead to bulla formation which can result in a pneumothorax.

03:23 So what are bulla and blebs? They are actually focal air-containing spaces that can be seen within the lungs.

03:31 So as you can see on this CT image, you have multiple lucent spaces within the lungs and these represent bulla and blebs.

03:38 On a radiograph, you have a large bulla, you can almost mistake it for a pneumothorax because you have a lucency in that area that doesn't have normal lung parenchyma.

03:47 So bulla is usually greater than 1cm in size.

03:52 It has a very thin wall and it's located in a subpleural location.

03:57 Usually, this is seen with paraseptal emphysema and occasionally can be seen with centrilobular emphysema as well.

04:03 Blebs are smaller.

04:04 They are less than about a centimeter in size and they're located within the visceral pleura.

04:09 Usually, these are located apically and these can actually lead to pneumothorax because of their location within the visceral pleura.

04:16 So this diagram actually shows you the difference between a bulla and a bleb.

04:22 So you can see here, a bulla is larger and it's a result of destruction of the alveoli.

04:27 A bleb, you have normal alveolar spaces here and the bleb comes arises from the visceral pleura.

04:34 So you have intact alveoli and then an air-filled space which can then result in a pneumothorax.

04:41 So we've discussed some common findings of emphysema.

04:44 This is a very common thing to see on a chest radiograph and hopefully this will give you a basis when we look at further radiographs.