Silhouette and Cervico-thoracic sign

Synonyms: Obscured margin sign, Loss of outline sign

Silhouette refers to the shadow and derived it’s origin from shadow papercuts done by Etienne de Silhouette.

Principle of Silhouette sign

On a normal Chest X-ray the well-defined borders of the heart and the domes of the diaphragm are visualised because the adjacent normal air containing radiolucent lung.

Silhouette sign is based on the principle that if the two structures have approximately the same radiographic density, an are in intimate contact with each other, then the interface between them is obliterated.

If a lesion effaces one of these interfaces then the sharp margin (heart or diaphragm) is lost. The CXR appearance of a blurred or effacement is referred to as the silhouette sign.

Application of silhouette sign

It is used in localization of intrathoracic opacity like: consolidation, mass, fluid, atelectasis, etc. that are in contact with mediastinum or diaphragm.

lung segments xray

Silhouette structureLung segment
Ascending aortaRight upper lobe – Anterior segment
Aortic knob/knuckleLeft upper lobe – apicoposterior segment
Right heart borderRight middle lobe – medial segment
Left heart borderLeft upper lobe – lingular segment
Right hemidiaphragmLower lobe – anterior segment
Left hemidiaphragm
silhouette sign
Where is the intrathoracic pathology localized?
Ans: Right middle lobe

Cervico-thoracic pass sign

Upper most border of the mediastinum:

  1. Anterior mediastinum: Ends at the level of clavicle
  2. Middle and posterior mediastinum: Projects above the clavicle

cervicothoracic sign

Interpretation:

  1. The external and superior edges of the mediastinal opacity disappear above the clavicles: opacity is anterior in the superior mediastinum
  2. The superior edge of the opacity is visible in the pulmonary air: the opacity is posterior
cervicothoracic sign
Where is the pathology located – anterior or posterior?
Ans: Posterior (because the opacity projects above the ipsilateral clavicle)

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