Medical Professional World: RADIOLOGY

Showing posts with label RADIOLOGY. Show all posts

Saturday, December 12, 2015

Chest Radiology - The Silhouette Sign

By Dr Deepu

Silhouette sign/loss of silhouette sign/ loss of outline sign.

I was always confused with the silhouette sign for its hidden meaning and failure to decode it by many medical students. So, I thought it would be apt to unravel it so that it could be handy for many medical students.

One of the most useful signs in chest radiology is the silhouette sign. This sign was described by Dr. Ben Felson. The silhouette sign is in nothing but elimination of the silhouette or loss of lung/soft tissue interface caused by a mass or fluid in the normally air filled lung. For instance, if an intrathoracic opacity is in anatomic contact with, for example, the heart border, then the opacity will obscure that border. The sign is commonly applied to the heart, aorta, chest wall, and diaphragm. The location of this abnormality can help to determine the location anatomically.

Just go through the X Ray to know the various structures seen in the chest x ray.

Let me explain this with this image.

What do we see???

There is plastic bottle which is surrounded by air, the margins of the shadow is very well demarcated from the surrounding air.

First scenario: There are two bottles, made of same material, placed apart from each other. The shadows appears separate from each other. Let us consider the right bottle to be the heart and the air surrounding the bottle as lung. The left bottle as a mass, since they are far from each other, the border of both is visible clearly.

Second scenario: Here we see the bottles are touching each other at two points and there is no gap in between and if we look at the shadow, we cannot differentiate between the two shadows, they appear like a single opacity at the upper and lower ends.

For the heart, the silhouette sign can be caused by an opacity in the RML, lingula, anterior segment of the upper lobe, lower aspect of the oblique fissure, anterior mediastinum, and anterior portion of the pleural cavity.

This contrasts with an opacity in the posterior pleural cavity, posterior mediastinum, of lower lobes which cause an overlap and not an obliteration of the heart border. Therefore both the presence and absence of this sign is useful in the localization of pathology.

want to read more in chest radiology??? Have a look at the following pages
Chest Radiology
Signs in Chest Radiology

Thursday, September 24, 2015

Chest Radiology _ A Case Of Azygous Lobe

By Dr Deepu
The lungs are normally divided into five lobes by three main fissures .
Occasionally, invaginations of the visceral pleura create accessory fissures that separate individual bronchopulmonary segments into accessory lobes .
An azygos lobe is found in approximately 0.4% of patients . In contrast to other accessory lobes, the azygos lobe does not correspond to a distinct anatomical bronchopulmonary segment .

It forms during embryogenesis when the precursor of the azygos vein fails to migrate to its medial position in the mediastinum, where it normally arches over the origin of the right upper lobe bronchus.
This gives rise to the following characteristics, which are visible on a standard chest x-ray

: the laterally displaced azygos vein lies between folds of parietal pleura, also referred to as the mesoazygos, where it assumes a characteristic teardrop shape ; the mesoazygos indents the right upper lobe, thereby creating the accessory (azygos) fissure, which is similar in shape to an inverted comma; the fissure delineates the azygos lobe, located superomedially ; laterally, the pleural folds of the mesoazygos separate before reaching the chest wall, resulting in a radiopaque triangular area ; and medially, the tracheobronchial angle appears empty .

An azygos lobe may be confused with a pathological air space such as a bulla or abscess . In addition, the abnormally located azygos vein may be mistaken for a pulmonary nodule, while a consolidated azygos lobe may be confused with a mass . An understanding of the pathogenesis and characteristic x-ray features of the azygos lobe will enable an accurate diagnosis in most cases .
If the x-ray findings are equivocal, computed tomography will be diagnostic .