Imaging the Mediastinum

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MediastinumMediastinum Bounded laterally by parietal pleura of each lung Superior margin is thoracic inlet

Defined by plane of 1st ribs Inferior margin is diaphragm Tissue planes extend superiorly into neck

around great vessels, trachea and esophagus Connects to abdominal cavity via esophageal,

caval and aortic hiatuses Connects to lungs along hilar vessels and

bronchi

MediastinumMediastinum Radiologic anatomy

CXR CT

Normal or not? Compartments and their pathologies:

Anterior Middle Posterior

Radiologic AnatomyRadiologic Anatomy

Landmarks to look for on the chest radiograph: Trachea Paratracheal stripe Descending aortic contour Azygo-esophageal contour

Pneumomediastinum with Pneumomediastinum with cervical emphysemacervical emphysema

Tracheal air columnTracheal air column

Should be straight

Slight bend to right due to aortic arch on its left.

Trachea deviates to the left

Right Aortic ArchRight Aortic Arch

Right paratracheal stripeRight paratracheal stripe

Extends from thoracic inlet to azygos vein

Widens out at azygos vein

No more than 3-4 mm thick

Aortic contourAortic contour

Azygo-esophageal recessAzygo-esophageal recess

Aortic contour and azygo-esophageal Aortic contour and azygo-esophageal recess abnormalrecess abnormal

Normal anatomy:Normal anatomy:CT/CXR correlationCT/CXR correlation

Is the mediastinum wide?Is the mediastinum wide? First ask… is it technical?

Positioning: rotated:? AP? Lordotic? Supine?

Inspiration If so, repeat the film before proceeding to CT.

Then ask…Is it new? GET OLD FILMS before getting a CT unless

time is critical.

Think about normal variants!Think about normal variants!

Vascular structures Aortic anomalies Tortuous vessels Azygos vein

Lipomatosis Fat pads

Severe asthma on long term steroids

Mediastinal lipomatosisMediastinal lipomatosis

Pericardial Fat PadPericardial Fat Pad

Tortuous brachiocephalic Tortuous brachiocephalic vesselsvessels

70 year old with dysphagia70 year old with dysphagia

Tracheal air

column

Esophageal cancer

Abnormal right paratracheal stripe

Hodgkins Hodgkins diseasedisease

Abnormal right paratracheal stripe

Check the old film!Check the old film!

2 days earlier

Hematoma from line insertion

Air fluid levelsAir fluid levels Think bowel or abscess:

Hiatal hernia Zenker diverticulum Epiphrenic diverticulum Achalasia Mediastinal abscess

AchalasiaAchalasia

Zenker diverticulumZenker diverticulum

Hiatal herniaHiatal hernia

Mediastinal abscess after Mediastinal abscess after CABGCABG

Differential diagnosis of Differential diagnosis of mediastinal massesmediastinal masses

Traditionally, we divide the mediastinum into compartments.

Likely diagnosis of mass depends on what is contained in each compartment

These are not anatomic boundaries, and masses commonly cross over into compartments where they don’t “belong”.

Posterior mediastinumPosterior mediastinum Paraspinal area Masses usually visible

on lateral film overlying spine

May obscure descending aorta contour

Posterior mediastinumPosterior mediastinum Neurogenic tumors

Schwannoma Sympathetic nerve tumors

e.g. ganglioneuroma Neurenteric cyst, lateral

meningocele Lymph nodes (unusual

as only area involved) Extramedullary

hematopoesis Vertebral tumors, spurs

SchwannomaSchwannoma

Extramedullary hematopoesisExtramedullary hematopoesis

Chronic anemias, myelodysplasias

Lateral meningocele in NF-1Lateral meningocele in NF-1

Anterior mediastinumAnterior mediastinum Space anterior to

great vessels and heart, behind the sternum

Anterior mediastinumAnterior mediastinum Most common:

Lymphoma Thymic lesions Germ cell origin tumors Thyroid masses

Also: Foregut cysts, nerve tumors, aortic aneurysm,

Anterior mediastinal massesAnterior mediastinal masses

thymic hyperplasia teratocarcinoma

teratoma lymphoma

thymoma

hemorrhage

Middle mediastinumMiddle mediastinum Contains heart, great

vessels, esophagus, trachea, lymph nodes, nerves.

CXR abnormality in paratracheal area, azygo-esophageal recess, retrocardiac area

May be difficult to see on lateral view

Middle MediastinumMiddle Mediastinum

Lymph nodes Foregut cysts Vascular lesions e.g. aneurysm Bronchogenic carcinoma Hiatal hernia, other esophageal or GI

lesions

Lymphoma Lymphoma

Cardiac evaluationCardiac evaluation Remember: cardiothoracic ratio of about

0.5 applies only to good PA chest x-rays. Knowing which chambers form which

cardiac contours can help identify what is enlarged.

Look for accompanying signs: Pulmonary venous engorgement and isolated

LA enlargement suggests mitral stenosis. Dilated aorta and LV enlargement suggests

aortic valve insufficiency.

Normal heart contoursNormal heart contours

Left atrium

Left ventricle

Right atrium

Left atrial enlargement-mitral Left atrial enlargement-mitral stenosisstenosis

Mitral valve

Left atrial enlargementLeft atrial enlargement

“Double density”

Straightened left heart border LA enlarged

LV normal

Enlarged ascending aorta in ASEnlarged ascending aorta in AS

Calcific Aortic StenosisCalcific Aortic Stenosis Enlarged ascending aorta, normal arch,

normal overall heart size

LV enlargementLV enlargement

Dilated cardiomyopathy Dilated cardiomyopathy multichanber enlargementmultichanber enlargement

The EndThe End

Imaging the Mediastinum

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