The document describes various signs seen on imaging of the respiratory system. It defines signs such as the signet ring sign seen on CT scans of the lungs, the finger-in-glove appearance seen in allergic broncho-pulmonary aspergillosis, and the continuous diaphragm sign seen in pneumomediastinum where air outlines the entire diaphragm. It also provides details on other signs like the halo sign associated with hemorrhagic nodules, the reversed halo sign, and tree-in-bud appearance seen in conditions like tuberculosis.

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SIGNS IN
RESPIRATORY SYSTEM

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SIGNET RING SIGN
Bronchiectasis
The signet ring sign is a finding seen on computed
tomographic (CT) scans of the thorax. It consists of a small
circle of soft-tissue attenuation that abuts a ring of soft-tissue
attenuation surroundinga larger low-attenuating circle of air.

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AIR CRESCENT SIGN
Differential Diagnosis:
• Hydatid disease
• Aortic aneurysm
• Angio-invasiveaspergillosis
• Rasmussen’s aneurysm
• Tuberculosis
• Lung abscess
• Haematoma within cavity
• Pneumosistis carinii
• Pneumonia

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FINGER-IN-GLOVE APPEARANCE
Allergic BronchoPulmonary Allergosis
• Radiologic manifestations of ABPA include homogeneous, tubular,
finger-in-glove areas of increased opacity in a bronchial distribution,
usually predominantly or exclusively involving the upper lobes.
• These shadows are related to plugging of airways by hyphal
masses with distal mucoid impaction and can migrate from one
region to another.
• CT findings in allergic bronchopulmonary aspergillosis consist
primarily of mucoid impaction and bronchiectasis involving
predominantly the segmental and subsegmental bronchi of the
upper lobes

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CONTINUOUS DIAPHRAGM SIGN
Pneumomediastinum
The entire diaphragm is visualized from one side to the other in
pneumomediastinum because air in the mediastinum outlines the
central portion which is usually obscured by the heart and
mediastinal soft tissue structures that are in contact with the
diaphragm.
Other signs noted in pneumomediastinum are
• Ring around the artery sign
• Tubular artery sign
• Double bronchial wall sign
• “V” sign of Naclerio
• Spinnaker sign
• Air in the pulmonary ligaent
• Air in the azygo-oesophageal ligament

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SILHOUETTE SIGN
• Coined by Felson
• An intra-thoracic radio-opacity, if in anatomic contact with a border of
heart or aorta, will obscure that border.
• An intra-thoracic lesion not anatomically contiguous with a border or a
normal structure will not obliterate that border It can localise
abnormalities on a PA film without a lateral view. If a mass lies overlaps
the aortic knuckle and the outline of the knuckle is lost (air is no longer
adjacent to it), then the mass lies posteriorly, against the knuckle (which
represents the posteriorly placed arch and descending aorta). If the
edges of the mass and the knuckle are both visible, then the mass lies
anteriorly.
• The loss of clarity of a structure, such as the hemidiaphragm or heart
border, suggests there is adjacent soft tissue shadowing, such as
consolidated lung, even when the abnormality itself is not clearly
visualised. This is particularly valuable in some cases of lobar collapse .

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CT HALO SIGN
• The computed tomographic (CT) halo sign, also known as the halo sign, refers to a
zone of ground-glass attenuation surrounding a pulmonary nodule or mass on CT
images.
• The presence of a halo of ground-glass attenuation is usually associated with
hemorrhagic nodules . This CT appearance was described by Kuhlman et al in
patients with invasive aspergillosis.
• In severely neutropenic patients, the CT halo sign is highly suggestive of infection by
an angioinvasive fungus, most commonly Aspergillus. Vascular invasion by this
fungus results in thrombosis of small- to medium-sized vessels, which causes
ischemic necrosis. At pathologic examination, the nodules represent foci of infarction,
and the halo of ground-glass attenuation results from alveolar hemorrhage.
• Although it is less common, the halo sign may also be observed in nonhemorrhagic
nodules, in which case either tumor cells or inflammatory infiltrate account for the halo
of ground-glass attenuation.
• Nonetheless, in the appropriate clinical setting, the halo sign is considered early
evidence of pulmonary aspergillosis even before serologic tests become positive, and
it warrants the administration of systemic antifungal therapy

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REVERSED HALO SIGN
• The reversed halo sign is defined as central ground-glass
opacity surrounded by a crescent or ring of consolidation.
• In the image, High-resolution CT scan of a patient with
pulmonary paracoccidioidomycosis shows extensive
bilateral ground-glass opacities and small areas of
consolidation. Areas of consolidation are located
predominately adjacent to ground-glass opacities.
Reversed halo sign is best seen in left lower lobe (arrows).

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Golden S Sign
• The Golden S sign is a finding that can be seen not only on
posteroanterior chest radiographs, but also on computed tomographic
(CT) scans .
• Because this sign resembles a reverse S shape, which the minor
fissure sometimes assumes with right upper lobe collapse, it is also
referred to as the "reverse S sign of Golden".
• On the posteroanterior chest radiograph, the proximal or medial portion
of the minor fissure is convex inferiorly, and the distal or lateral portion
of the fissure is concave inferiorly.
• The analogous appearance at CT is a convex bulge along the fissural
margin of a collapsed lobe. Although typically seen with right upper
lobe collapse, the S sign can also be seen with the collapse of other
lobes and has been demonstrated on the lateral chest radiograph.

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Split Pleura Sign
The split pleura sign is seen on contrast material–
enhanced chest computed tomographic (CT) images.
There is enhancement of the thickened inner visceral
and outer parietal pleura, with separation by a
collection of pleural fluid

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THYMIC SAIL SIGN
• Thymus is a normal anterior mediastinal
sail shaped structure.
• The thymus assumes this shape as its
inferior border is flattened by the horizontal
fissure.

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TREE-IN-BUD APPEARANCE
• Peripheral, poorly defined, small (2–4-mm-
diameter) centrilobular nodules and branching linear
opacities of similar caliber originating from a single
stalk (the tree-in-bud pattern) in the lower lobe
(arrow).
• These findings can represent endobronchial spread
of tuberculosis among other causes.

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WESTERMARK SIGN
• The Westermark is an eponym indicating the abrupt cutoff
of pulmonary vascularity distal to a large central pulmonary
embolus. The presumed mechanism behind the image
arises from the nearly complete obstruction of blood flow to
the pulmonary artery distal to the embolic clot.
• Presumably the lack of flow to these more distal vessels
results in their radiographic transparency and an
appearance of an abrupt truncation as is shown in this
exemplary case.

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HILUM OVERLAY SIGN
• useful in distinguishing an anterior mediastinal mass from a
prominent cardiac silhouette.
• If the bifurcation of the main pulmonary artery is >1 cm medial to
the lateral border of the cardiac silhouette, it is strongly
suggestive of a mediastinal mass. If the pulmonary artery arises
from the lateral heart border, this favors an enlarged heart. In
other words, because the pulmonary arteries arise from the
heart, when the heart enlarges, then pulmonary arteries must
move laterally with the heart border
• If you can recognize the interlobar pulmonary artery, it means
that the mass seen is either in front of or behind it.
• The above is an example of dissecting aneurysm.

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CERVICOTHORACIC SIGN
• Used to determine the location of a mediastinal lesion in
the upper chest. The uppermost border of the anterior
mediastinum ends at the level of the clavicles.
• The medial and posterior mediastinum extends above the
clavicles.
• A mediastinal mass that projects superior to the level of the
clavicles must therefore be located either within the middle
or posterior mediastinum.

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DEEP SULCUS SIGN
• Represents pneumothorax in a patient in supine position.
• It shows anteromedial air in the pleural space causing a
deep anterior costophrenic sulcus.
• It outlines the medial hemidiaphragm under the heart.
• Produces an appearance of lucency in the right or left upper
abdominal quadrants.