Guide to CT-Chest

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Index

1-CT-Chest .. 2

2- Mediastinal window .... 3

3-L.N. around vessels ...... 8

4-Lung window ... 9

5-Pulmonary lesions:

1- nodules ....15

2- Masses .....20

3- Cavities ....21

6-Bronchogenic carcinoma .....22

7-Hydated cyst 23

8-Mediastinum ....25

Guide to CT-Chest

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CT-CHEST Composition:

1- Mediastinal window

2-Lung window

3-Bone window? ( if not found, search it in Lung window )

Notes:

-CT with contrast .. when to ask it?

In ALL cases except:

1-Diffuse pulmonary-parenchemal diseases e.g. IPF ( if with lymphangitis CT with contrast ).

2-Bronchiactasis ( use HRCT ).

3-Scanning for lung depositis e.g. metastasis follow up.

4-Some traumatic cases of the chest except affection of one or more of the main vascular structure(s) use CT with contrast.

-Types of CT Chest .. ( scanning techniques ):

1- HRCT ( mostly used today )

2-Spiral , Helical , Volumetric CT

3-Standard examination ( NOT used today )

-CT misregistration:

.

Guide to CT-Chest

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I-Normal Lung

1- Mediastinal window:

See all mediastinal structures BUT NOT see details of the lung.

Start with Reference Point

Reference Point:

It is the level to start reading any film before moving above & below.

Characters of any Reference Point:

-Characteristic configuration i.e. known fixed shape structure.

-Easily discovered.

-Constant at any film.

-Important i.e. used to know structures around it.

In Mediastinal window, reference point is AORTIC ARCH. ) (

Step one: Start with the previous section to locat the reference point (the aortic arch ).

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Step two: Look above this section to see the 3 main branches of the aortic arch (innominate artery lt. common carotid artery lt. subclavian artery ) at the same level of the aortic arch

Step three: Between the previous 2 sections you will find:

Lt. innominate vein crosses the midline to the right side to join with rt. innominate vein to form S.V.C.

Step four: Below the reference point you will see assending aorta (above) & descending aorta (below) & aortic window inbetween (in which, pulmonary artery will appear).

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Step five: below this section you will see Pulmonary artery (the main artery & its 2 branches

^ ) (

Step six: below the previous section .. each vessel will be exchanged with the part of the heart which is drained by it i.e.:

Ascending aorta lt. ventricle

Pulmonary artery rt. ventricle

S.V.C. rt. atrium

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Step seven: below .. the section will be as follow:

N.B.: the lt. atrium has a characteristic shape ( like a moustash ) due to drainage of rt. & lt. pul. Veins.

) ( ) (superior ) ( inferior .

Step eight: then the picture will be like this:

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Step nine: below.. atria will disappear & ventricles still present:

Step ten: Finally, rt. copula of the diaphragme will appear:

* * *

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L.N. around vessels 1- Prevascular L.N. ( = retrosternal L.N.)

2- Retrocaval L.N. ( = rt. paratracheal L.N.)

N.B.: There is NO lt. paratracheal L.N.

3- Aortic window L.N.

4- Precarinal L.N.

5- Retrocarinal L.N.

N.B.: Carinal = Tracheal

6- Carinal L.N. ( = subcarinal L.N.)

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2- Lung window:

To understand the lung window, you should know anatomy of the lung.

.

1- Lateral view: Rt. lung is subdivided by 2 fissures into 3 lobes. Lt. lung is subdivided by 1 fissure into 2 lobes.

The Right lung:

The superior lobe is then subdivided by 2 imaginary lines into 3 parts:

- apical

- anterior

- posterior

The middle lobe is subdivided by 1 imaginary line into 2 parts:

- lateral

- medial

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The lower lobe is subdivided by 3 imaginary lines into 4 parts:

- apical (= superior)

- posterior

- lateral

- anterior

N.B.: Remember that we look to the lung from the lateral side of the body.

The medial part of the lower lobe is located behind the lateral one in

this view.

The Left lung:

Firstly, we drow an imaginary line horizontally which resemble the horizontal fissure on the right lung.

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The superior lobe above this line, is then subdivided by 1 imaginary line into 2 parts:

- apico-posterior

- anterior

The superior lobe below this line, is also subdivided by 1 imaginary line into 2 parts:

- superior

- inferior

The lower lobe is subdivided by 3 imaginary lines into 4 parts:

- apical (= superior)

- posterior

- lateral

- anterior

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Now, as in mediastinal window, we start with reference point

In lung window, reference point is Tracheal bifurcation.

From above downward:

1st section: Apex of the lung

2nd section: Other parts of the superior lobe of the lungs

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3rd section: Tracheal bifurcation

:

- ant. Segment of the superior lobe

- apical part of the inferior lobe

superior lobe ) (

4th section: Below that, tracheal bifurcation disappears & so, we divide the lungs into: upper 1/3 and lower 2/3 as follow:

tracheal bifurcation :

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Upper 1/3 in rt. side is then subdivided into: medial & lateral parts.

Upper 1/3 in lt. side is then subdivided into: inferior & superior parts.

The rest part ( i.e. the lower 2/3 ) is subdivided into:

In rt. side: Posterior, lateral, anterior & medial segments.

In lt. side:Posterior, lateral & anterior segments (there is NO medial segment).

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II- Pulmonary Lesions

1- Focal lesions:

1-nodules:

Def.: a rounded well defiend pulmonary opacity, less than 3 cm in

diameter ( rounded )

Characters:

- size: 3 cm

- number: single or multiple

- growth rate: by doubling time ( time needed to reach double of its previous size )

nodule .

1 month inflammatory

1 15 month benign

- central lucencies: e.g. fat lobule ..

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- calcification: mostly benign ( see later )

- margine: smoth, speculated or lobulated. ( see later )

* * *

Calcification: mostly benign

Types: laminated, central, popcorn or diffuse

: benign malignant :1ry in other organ

Prescence of Fat: mostly pulmonary hamartoma1

Hamrtoma or Tuberculoma ?

Generally, hamrtoma = calcified nodule in any site other than sites of TB.

1 Hamartoma is a benign ( NOT malignant ) focal malformation, composed of tissue elements normally found at the site of origine, which are growing in the same rate of the surrounding tissues into a disorganized mass. Mostly, hamartomas dont cause problems except by their location & in lungs,they are often asymptomatic.

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N.B.: sites of Tuberculoma: apex of upper ( or lower ) lobes

Sites of Hamartoma: middle lobe, base of the lung etc.

Fat .

Cavities: thin wall 5 mm = benign

Thick wall 15 mm = malignant

Margins: ill-defined or speculated = malignancy

Well defined & smooth = mostly benign ( with Ca+2 ) except if it is

metastatic ( without Ca+2 ).

CXR :

margins CT

Other signs of pulmonary nodules:

1- Pleural tail of bronchogenic carcinoma ) ( = infiltration of tumor cell

2- Satellite nodules surrounding a dominant nodule (Granulomatous nodule)

3- Nodules connected to the hilum by vessels ( AVM = pul. Arterio-venous fistula ).

4- Air crescent sign = intercavitary nodule ( ball in a cavity ).

5- Air bronchogram = bronchoalveolar carcinoma

6- Halo sign [ ground-glass veiling around the nodule ] = lesion with angio-invasive character (?Aspergillosis).

segment pneumonia ... pneumonia

N.B.: Tuberculoma & Hamartoma NOT more than 4 cm

lesion =br. carcinoma calcification.

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Commonest types of pulmonary nodules (summary):

1- Carcinoma: mass or ill-defined nodule.

2- Metastases.

3- Tuberculoma: single, smooth, 3 cm Calcification.

4- Fungus.

5- Hamartoma: single, smooth, 3 cm Calcification.

6- Pulmonary AVM.

N.B.: Calcification: Big &/or Central mostly Bengin

Small &/or Peripheral mostly Malignant

Tuberculoma & - Hamartoma mostly solitary and rarely multiple

Multiple calcification lesion in adult mostly multiple hamartoma

nodules.

Pulmonary lesion:

Peripheral bronchogenic carcinoma may be: 3 cm nodule

3 cm mass

nodule Peripheral bronchogenic carcinoma

when we found: margine speculated due to demoplastic reaction, mostly at upper lobe.

Deposites:

When we see the following, we suspect metastasis:

- Multiple: 10 in one patient.

- Non-calcified, rounded, 2-5 cm

- 75 % are: variable size & subpleural

) .(

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- 2.5 cm with smooth edge

if they are multiple nodules with speculated edge, are they metastasis?

( see later )

metastasis

Special types of pulmonary deposites:

Fine micronodular pattern Millary deposites

Metastases + pneumothorax osteogenic 2%

Cannon ball deposites

Supportive signs of deposites: ) (

-Mass-Vessel sign = connection between metastatic nodule & the adjacent branch of the pulmonary artery

-Zone of hypodensity distal to nodule

mass vessel

-Reticular changes around nodule

:

Any subpleural mass/nodule metastases until proven otherwise

if it is centeralized in lung parynchema Hamartoma

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Pulmonary AVMalformation:

-Simple type 80%

-Complex type 20%

-70% In lower lobe

-8-20% bilateral

-90% sharply defined lobulated/rounded mass lesion

-1 cm to few cm in size

-NO calcification

-Cord-like bands from the lesion to hilum

/ hilum

* * *

2-Msses: 3 cm

-Solid: carcinoma or metastases according to numbers

-Cystic: hydatid cyst =

-In CXR: large dense ill-defined mass br. carcinoma !

:

mass cancer / ...

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multiple speculated lesion in lung METASTASES ( ? may be lymphoma )

biopsy histopathology:

Small cell , large cell , squamous , adenoid

* * *

3- Cavities: wall thickness fluid level:

- Abscess

- Bulla

- Cyst ; -pneumatocele

-cystic bronchiactasis

* * *

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How to diagnose Hydated Cyst?

CXR CT

-Solitary 75% - Multiple 25%

-Sharply circumscribed

-1-10 cm in diameter

-Water density

-Multiple cyst in the wall of a large cyst

-Calcification is very rare

-Rupture fluid level ( wavy ) ( water lily sign ) =

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CXR

Very large solitary mass in chest

Echinococcus granulosus:

-large well circumscribed mass

-may reach 10 cm in diameter

-normal lung around it

-complication(s):

*Rupture between layers of the cyst Meniscus sign

*Rupture into a bronchus Water lily sign ( air-fluid level )

*Rupture into a pleura hydropneumothorax

* * *

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Mediastinum Divided into: superior

inferior

Borders of inferior mediastinum: below manubrium sterni anteriorly & upper border of D5 posteriorly.

Inferior mediastinum subdivisions: Anterior - Middle - Posterior according to pericardium ( heart ).

To diagnose any finding in mediastinum, we either use the regional classification or site of origin classification ( i.e. tissue affected ).

Actually, we use both of classifications for easy & accurate diagnosis.

1- Regional classification: D.D.

A: 1-Retrosternal thyroid

2-Thymic tumor

3-L.N. enlargement

4-Aortic arch aneurysm ( AAA )

5-Innominate artery tortuousity

B: 1-Teratodermoid ( tumor )

2-tissue of sternum

C: 1-Pericardial pad of fat

2-Pericardial cyst

3-Hernia of Morgagni

4-Diaphragmatic hernia

D: 1-Paratracheal hilar lymphadenopathy

E: 1-Bronchogenic cyst

2-Aortic aneurysm

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3-Central pulmonary artery aneurysm

4-Dilated veins

F: 1-Oesophageal lesions

2-Neuroenteric cysts

3-Aortic aneurysm

4-Para-aortic masses

G: 1-Hiatus hernia

2-Hernia of Bochdalek

H: 1-Neurogenic tumor

2-Paravertebral masses

2-Site of origin classification:

1-from thyroid gland

2-from thymus gland rebound thymus

3-Mediastinal cysts ( mostly, congenital or pericardial cysts)

4-from adipose tissue e.g. lipoma, liposarcoma or lipomatosis ( diffuse increase of fat

as in Cushings syndrome )

5-from lymphatic tissue: cyst or lymphangioma

6-from vascular tissue: vessels ( aorta, pulmonary artery, SVC ) or hemangioma

7-from nerves: peripheral nerves, sympathetic ganglia, paraganglion cells

8-Miscellaneous e.g. paraspinal masses, lateral thoracic meningocele, vertebral

abnormalities, oesophageal lesions

1 Thyroid: Retro-sterna goiter

High up dense in contrast due to vascular lesion

Commonest anterior mediastinal mass

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Middle aged females

Radiological signs:

Mass effects: a-Displaces trachea ( narrow trachea )

b-Displaces aorta ( laterally & inferiorly )

c-Displaces oesophagus ( backward bowing of oesophagus )

Calcification Nodular

Pattern of enhancement

2 Thymus: Normally:

from birth to puberty bilobed structure with convex border of muscle

density about 1.8 cm at long axis.

from puberty to 25 ys in size (1.3 cm), in density, concave borders

from 25 ys long involution with total fat replacement

mediastinum

*Neoplasms of thymus:

1-Thymoma:

-usually in adults in 50th 60th decade

-1/3 of patients with thymoma have Myasthenia gravis

-10% - 15% of patients myasthenia gravis have thymoma

-Types: a-Non-invasive: sharply demarcated of homogenous density rounded or

oval benign masses - may show calcification or cystic changes

:

mediastinal lesions

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b- invasive: 30% are malignant & infiltrate adjacent structures & gives

distal implants in pleura & pericardium.

2-Germ cell tumor ( extragonadal germ cell tumor ):

-2nd 4th decade

-in anterior mediastinum within or adjacent to the thymus.

-arise from one or more primitive germ cell layers.

-may be: Bengin M : F ratio is 1 : 1

Malignant M F ( seminoma or choriocarcinoma )

primary anterior mediastinum

N.B.: -Teratoma is the commonest mediastinal germ cell tumor.

-In seminoma, soft tissue is predominant in the tumor

teratoma cystic tissue

3-Thymic lymphoma: thymic enlargement 2ry to lymphatic infiltration mostly Hodjken lymphoma.

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4-Thymic neuroendocrine tumor: ( Neurogenic tumors are the commonest posterior

mediastinum masses; compare with retrosternal goiter .. see above )