The “BIG RIB SIGN” and “VERTICAL DISPLACEMENT SIGN” In Lateral Chest X Ray.

Pulmonary Medicine Blog By Dr Deepu

The “BIG RIB SIGN” and “VERTICAL DISPLACEMENT SIGN”- To Differentiate The Right and Left Ribs on Lateral Chest Radiographs

Today I would like to share with you two important signs in Chest X Ray- The Big Rib Sign and Vertical Displacement Sign.

Diseases of the ribs and diaphragm are often identified only at lateral chest radiography. Therefore, it is important to use a reliable technique for differentiating the right and left ribs. Two techniques—the “big rib” sign and the “vertical displacement “sign—can be used to localize the right and left ribs at lateral chest radiography. Conventially lateral radiographs are taken with left side near the film. But lateral view can be obtained as Right or left  as per clinicians request, then the principle remains the same but only the magnified sides change .

The big rib sign is a technique that exploits the difference in magnification between the right and left sides on lateral chest radiographs.



The side of the rib cage farther from the film is magnified more than the side closer to the film. On a well-positioned left lateral chest radiograph, the right ribs appear larger than the left ribs . This difference in rib size is more easily detected posteriorly where the x-ray beam is tangential to the ribs but can be appreciated at all corresponding points along the curvature of the two ribs. In addition, rotating the patient may enhance or reduce the magnification effect because, with such rotation, the x-ray beam is transmitted through different portions of the ribs, which are thin medially and thick laterally. In a left lateral projection, when the posterior portions of the right and left ribs appear comparable in size, the hemidiaphragm traceable to the most anterior ribs is the right hemidiaphragm. Otherwise, the significantly larger ribs are the right ribs, which are farther from the film.

The big rib sign is very useful but is not perfect because the magnification difference between the right and left ribs is only 10%. For example, if the width of a rib is 5 mm, the observed difference between sides is only 0.5 mm, which is not always sufficient to enable differentiation of the two sides. Furthermore, the big rib sign is not applicable when the posterior ribs are superimposed.

Another Sign is the vertical displacement sign, which is an easy, reliable, and precise method for differentiating the right and left ribs on lateral radiographs .

 The vertical displacement sign is based primarily on the vertical divergence of the x-ray beam rather than on the magnification of the ribs. Because the right rib cage is farther from the film, the projection of the right ribs on a lateral radiograph will fan out and diverge in a vertical direction to a greater degree than that of the left ribs. Thus, the right side can be distinguished from the left by the vertical displacement of the paired ribs.

The vertical displacement sign is usually applicable even when the posterior ribs are partially superimposed. It is usually possible to identify which rib is higher or lower even when they overlap. The vertical displacement sign can be used as an alternative when the big rib sign is not applicable.

Also Read

Air Bronchogram Sign.


The ‘Dark Bronchus’ Sign


reference:
1. http://pubs.rsna.org/doi/pdf/10.1148/radiographics.19.1.g99ja02105
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Air Bronchogram Sign.

Pulmonary Medicine Blog By Dr Deepu

Air bronchogram

An air bronchogram is a tubular outline of an airway made visible by filling of the surrounding alveoli by fluid or inflammatory exudates. It is almost always caused by a pathologic airspace/alveolar process, in which something other than air fills the alveoli.

 Six causes of air bronchograms are
Lung consolidation
Pulmonary edema
Nonobstructive pulmonary atelectasis
Severe interstitial disease
Neoplasm
Normal expiration.
In The Image Air Bronchogram is seen.
The Magnified Image Showing Air Bronchogram On CXR and Confirmed With HRCT


The phenomenon is Characterised by  air-filled bronchi (dark) being made visible by the opacification of surrounding alveoli (grey/white). It is almost always caused by a pathologic airspace/alveolar process, in which something other than air fills the alveoli.
 Air bronchograms will not be visible if the bronchi themselves are opacified (e.g. by fluid) and thus indicate patent proximal airways.
Air bronchograms that persist for weeks despite appropriate antimicrobial therapy should raise the suspicion of a neoplastic process. CT may be planned in such cases.

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The ‘Dark Bronchus’ Sign: For diagnosis of PCP

Pulmonary Medicine Blog By Dr Deepu

Today I will discuss the importance of the ‘dark bronchus’ sign in the diagnosis of uniform, diffuse ground glass opacification on high resolution computerized tomography (HRCT). This sign is useful to identify diffuse ground glass opacity on HRCT in cases of Pneumocystis carinii pneumonia who may present with a normal or equivocal chest radiograph in the early course of disease.

Chest radiograph is the initial investigation in HIV patients with chest symptoms. But even in patients with proven PCP, radiographic findings may be normal in up to 20-40%. Low incidence of PCP in patients with normal or equivocal findings on chest radiograph despite high clinical suspicion emphasizes the need for a noninvasive and widely available investigation in such cases.

Various modalities to investigate symptomatic HIV patients with normal, equivocal or nonspecific radiographic findings include carbon monoxide diffusion in lung (DLCO), gallium citrate lung scanning and HRCT. A DLCO of less than 80% of the predicted value has a sensitivity of up to 98% for PCP, but the specificity is less than 50% and the measurement is not always available. Although gallium scanning has a sensitivity of up to 100% for PCP in patients with abnormal radiographs, it has never been prospectively studied in patients with normal or equivocal radiographic findings. In addition, this investigation requires a 48- to 72-hour delay in imaging, is not readily available and has a high cost.



    On the other hand, HRCT is a widely available and noninvasive investigation for PCP. Patchy or diffuse ground glass opacity is the most frequent finding. Other findings include cystic changes (33%), centrilobular nodules (25%), lymphadenopathy (25%) and pleural effusion (17%). HRCT has been found to be especially important in the assessment of symptomatic patients with normal, equivocal or nonspecific radiographs. In such cases, it shows high sensitivity (100%), specificity (86%) and accuracy (90%) for PCP, using only the presence or absence of ground glass opacity as the criterion for positivity.
The Arrow Shows The Dark Bronchus Relative to The Surrounding Lungs

Patchy ground opacity or mosaic attenuation, which is observed in up to 92% of the patients, can be easily identified on HRCT. However, subtle ground glass opacification, especially when bilateral and diffuse, may be difficult to diagnose. This is because of bilateral uniform increase in lung attenuation with absence of normal lung parenchyma for comparison. In such cases, the ‘dark bronchus’ appearance is a useful sign to identify diffuse ground glass opacity. This finding refers to the presence of air-filled bronchi appearing ‘too black’ relative to the surrounding lung parenchyma, which is filled with inflammatory alveolar exudates. This subtle finding may help in identification of patients with ‘possible PCP’ despite a normal or equivocal chest radiograph. Subsequently direct test for PCP (i.e., broncho-alveolar lavage) may be initiated for definitive diagnosis and treatment.
Hence the importance of the ‘dark bronchus’ sign in the diagnosis of uniform, diffuse ground glass opacification on HRCT. This is especially useful in the presence of a normal chest radiograph and ‘near normal’ HRCT. HRCT offers an accurate and early diagnosis in patients with normal chest radiographs; it alters patient management and facilitates early therapy.

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BASICS OF CHEST X RAY-PART 5, THE HILUM AND MEDIASTINUM

Hello, Welcome to the fifth part of chest Xray Reading, today we shall know about the hilum and mediastinum
spare time to go through the other posts on chest X ray
Here are the links

The Part 2 has over a lakh views, please go through it.


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.
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