0:00

So if you come across a case

0:02

of diffuse nodule lung disease,

0:04

it can be a little bit daunting.

0:05

But the best way to do it,

0:07

just like any diffuse lung disease, is

0:09

to use your algorithm.

0:10

And the algorithm here really is to try

0:13

to subdivide based on the anatomy.

0:15

So is it a random anatomic pattern?

0:17

Is a perilymphatic anatomic pattern

0:20

or is a central lobular anatomic pattern

0:22

where these nodules are living.

0:25

And so the random nodules really mean entropic nodules.

0:28

So they have no respect

0:30

for the underlying secondary pulmonary lobular anatomy.

0:34

They're just gonna go anywhere and everywhere.

0:36

It's like if you put the nodules like a, in like a shotgun,

0:39

you, you kind of shot it.

0:41

Some will be closer together, some will be further apart.

0:43

Again, they do not care about

0:44

the underlying pulmonary anatomy.

0:46

And so that implies that these nodules got into the lung

0:49

hemato 'cause all portion of lungs need blood to survive.

0:52

So that's actually very helpful to you.

0:54

And usually the differential diagnosis is dichotomous.

0:56

Either there's gonna be some sort of hematogenous infection

0:59

or hematologist metastases.

1:01

So random nodules,

1:03

usually these are not diagnostic conundrums.

1:06

Now imperial lymphatic nodules,

1:07

these nodules are gonna be clustered

1:09

where the lymphatics are richest.

1:11

And so where is that on a chest ct is gonna be along the

1:14

interocular septa, the subpleural lung.

1:17

'cause subpleural lung really is part

1:18

of the inter lior septa along fissures

1:21

'cause fissures are really just part

1:22

of subpleural lung sometimes along the central central Lior

1:26

core structure and along the bronchovascular tree.

1:29

So anywhere where we saw those squiggly green lines

1:32

on the previous image, that's

1:34

where we're gonna see these perilymphatic nodules.

1:37

And so when you see perilymphatic nodules,

1:39

very commonly it's gonna be due to sarcoidosis,

1:41

whether it's idiopathic or secondary.

1:44

And every once in a while it's gonna be due

1:46

to lymphocytic carcinomatosis.

1:48

Usually. History is quite helpful here.

1:50

If someone has a history of malignancy

1:54

and there's some paralympic nodularity,

1:57

but there's other findings of progression

1:59

of malignant disease

2:00

or metastatic disease, it's probably just gonna be lympho,

2:04

genetic carcinomatosis.

2:05

But if a patient in whom, let's say they have a history

2:07

of malignancy or maybe they don't have a history

2:09

of malignancy with a history of malignancy, uh,

2:11

these patients, maybe the other macroscopic findings

2:14

of metastatic disease are improving

2:16

and you see these perilymphatic nodules,

2:17

then it's probably a secondary cause of sarcoidosis.

2:20

Certainly you need to follow up that patient,

2:22

but this is kind of how you have to sort

2:24

of combine the clinical setting and the clinical history

2:27

and presentation with the imaging findings, which is,

2:30

as you know, quite common in the setting of chest imaging.

2:34

The last pattern here is central lobular nodules.

2:37

When we're talking about diffuse nodule lung disease,

2:40

it is when those nodules are really clustering in the center

2:43

of the secondary pulmonary nodule.

2:44

So very AP name. And so

2:46

by definition they'll give you subpleural sparing.

2:49

So subpleural sparing these is on along the margins

2:51

of interlobular septa.

2:53

So they give you subpleural sparing.

2:55

And so the differential diagnosis

2:57

for central lobular nodules, unfortunately

2:59

It's pretty broad, but most

3:00

of the time it means it got there through the airways.

3:03

Every once in a while it got

3:04

there through the pulmonary arteries.

3:05

You can get pulmonary arterial disease causing that,

3:08

whether it's something that maybe is injected intravenously

3:11

or or some other etiology.

3:13

But most of the time, central lab

3:14

nodules are airway related.

3:16

So we start thinking about aspiration

3:17

or infection in the acute setting.

3:19

But other things can cause us as well.

3:21

There are some subsets of central lab

3:23

and nodularity in which the differential

3:25

diagnosis is a little more compact.

3:27

And we'll discuss that in just a bit.