THE HILUM AND MEDIASTINUM

Hilum

The normal hilar shadow is for 99% composed of vessels - pulmonary arteries and to a lesser extent veins .

The vessel margins are smooth and the vessels have branches.

The left hilum should never be lower than the right hilum.

The left pulmonary artery runs over the left main bronchus, while the right pulmonary artery runs in front of the right main bronchus, which is usually lower in position than the left main bronchus.

Hence the left hilum is higher than the right.

Only in a minority of cases the right hilus is at the same level as the left, but never higher.

In this illustration the lower lobe arteries are coloured blue because they contain oxygen-poor blood.

They have a more vertical orientation, while the pulmonary veins run more horizontally towards the left atrium, which is located below the level of the main pulmonary arteries.

Both pulmonary arteries and veins can be identified on a lateral view and should not be mistaken for lymphadenopathy

Sometimes the pulmonary veins can be very prominent.

The left main pulmonary artery passes over the left main bronchus and is higher than the right pulmonary artery which passes in front of the right main bronchus.

These images are thick slab sagittal reconstructions of a chest-ct to get a better view of the hilar structures.

The lower lobe pulmonary arteries extend inferiorly from the hilum.

They are described as little fingers, because each has the size of a little finger .

On the right side the little finger will be visible in 94% of normal CXRs and on the left side in 62% of normals.

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Study the CXR of a 70-year old male who fell from the stairs and has severe pain on the right flank..

Notice on the PA-film the absence of the little finger on the right and on the lateral view the increased density over the lower vertebral column.

What is your diagnosis?

There is a right lower lobe atelectasis.

Notice the abnormal right border of the heart.

The right interlobar artery is not visible, because it is not surrounded by aerated lung but by the collapsed lower lobe, which is adjacent to the right atrium.

On a follow-up chest film the atelectasis has resolved.

We assume that the atelectasis was a result of post-traumatic poor ventilation with mucus plugging.

Notice the reappearance of the right little finger (red arrow) and the normal right heart border (blue arrow).

Hilar enlargement

The table summarizes the causes of hilar enlargement.

Normal hili are:

    Normal in position - left higher than right

    Equal density

    Normal branching vessels

Enlargement of the hili is usually due to lymphadenopathy or enlarged vessels.

In this case there is an enlarged hilar shadow on both sides.

This could be the result of enlarged vessels or enlarged lymph nodes.

A very helpful finding in this case is the mass on the right of the trachea.

This is known as the 1-2-3 sign in sarcoidosis, i.e. enlargement of left hilum, right hilum and paratracheal.

Here some more examples of sarcoidosis.

    Lymphadenopathy and groundglass appearance of the lungs

    Lymphadenopathy, 1-2-3 sign

    Bulky lymphadenopathy

    1-2-3 sign

    Nodular lung pattern, no lymphadenopathy

    Hilar and paratracheal lymphadenopathy

Mediastinum

Here is just a brief overview of Mediastinal masses.

The mediastinum can be divided into an anterior, middle and posterior compartment, each with it's own pathology.

Mediastinal lines

Mediastinal lines or stripes are interfaces between the soft tissue of mediastinal structures and the lung.

Displacement of these lines is helpful in finding mediastinal pathology, as we have discussed above.

Azygoesophageal recess

The most important mediastinal line to look for is the azygoesophageal line, which borders the azygoesophageal recess.

 This line is visible on most frontal CXRs.

The causes of displacement of this line are summarized in the table.

A hiatal hernia is the most common cause of displacement of the azygoesophageal line.

Notice the air within the hernia on the lateral view.

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Another common cause of displacement of the azygoesophageal line is subcarinal lymphadenopathy.

Notice the displacement of the upper part of the azygoesophageal line on the chest x-ray in the area below the carina.

This is the result of massive lymphadenopathy in the subcarinal region (station 7).

There are also nodes on the right of the trachea displacing the right paratracheal line.

On the PET we can appreciate the massive lymphadenopathy far better than on the CXR.

There are also lymphomas in the neck.

this is an important finding, since these nodes are accessible for biopsy.

Continue with images of CT and ultrasound.

Here we see a CT-image.

The azygoesophageal recess is displaced by lymph nodes that compress the left atrium.

The final diagnosis of small cel lungcancer was made through a biopsy of a lymphnode in the neck.

First study the chest x-ray.

Then continue reading.

Notice the following:

    There is displacement of the azygoesophageal line both superiorly an inferiorly.

    There is an air-fluid level (arrow).

    Combined with the above this must be a dilated esophagus with residual fluid. The final diagnosis was achalasia.

    The density on the left in the region of the lingula is the result from prior aspiration pneumonia.

Here we have a prior CXR of this patient.

The AP-film shows a right paratracheal mass.

The azygoesophageal recess is not identified, because it is displaced and parallels the border of the right atrium.

The large round density in the left lung is the result of aspiration.

Notice the massive dilatation of the esophagus on the CT.

Aortopulmonary window

The aortopulmonary window is the interface below the aorta and above the pulmonary trunk and is concave or straight laterally.

Here the AP-window is convex laterally due to a mass that fills the retrosternal space on the lateral view.

On the CT-images a mass in the anterior mediastinum is seen.

Final diagnosis: Hodgkins lymphoma.

Here another case.

On the PA-film a mass is seen that fills the aortopulmonary window.

The PET better demonstrates the extent of the lymphnode metastases in this patient.

Final diagnosis: small cell lungcarcinoma.