Four signs to guide you on CT: 1. Diaphragm Sign 2. Displaced Crus Sign 3. Interface Sign 4. Bare Area Sign

1. Dr. Vikram Patil
JSS Medical College, Mysore

2. Four signs to guide you on CT:
 Diaphragm Sign
 Displaced Crus Sign
 Interface Sign
 Bare Area Sign

3.  Pleural Effusion: Fluid is outside the confines of diaphragm.
 Ascites: Fluid is within the confines of diaphragm.

4.  Pleural effusion: Displaces crus away from vertebral body
 Ascites: Displaces crus towards the vertebral body

5.  Pleural Effusion: Hazy
 Ascites: Sharp margins
Because the diaphragm forms the interface, the organs (liver
and spleen) are well delineated by the ascitic fluid.

6.  Pleural Effusion: Unimpeded access to posterior CP sulcus, fluid is
seen in relation to the bare area also.
 Ascites: Fluid is seen in relation to the bare area. Excluded from
bare area between coronary ligament.

7.  Pleural fluid tends to rise higher along its edge producing a
meniscus shape medially and laterally.
 Usually only lateral meniscus can be seen.
 The meniscus is a good indicator of the presence of a pleural
effusion (Ellis curve).

8. The diaphragmatic contour is partially or
completely obliterated, depending on the
amount of the fluid.

9.  Sharply marginated curvilinear opacity between
aerated apical lung and the apical ribs.

10. Supine CXR shows the veil like appearance.

11.  The dark image is an effusion because it is framed within four regular
borders: the pleural line, the shadow of the ribs, and mostly the regular
deep border (the lung line – arrows).
 The quad sign is drawn at the right image. It shows the absence of local
lung impairement, since the image beyond the lung line is artifactual
 Quadrangle-4 sided
Lung line.

12.  With respiration lung comes in and out of field. On m-mode,
this makes a sinus wave.
 Sinusoid sign allows not only full confidence in the diagnosis of
pleural effusion (associated with quad sign), but also indicates
possibility of using small needle for withdrawing fluid.

13.  Color Doppler ultrasonography can help in differentiating small effusions from
pleural thickening by demonstrating the fluid-color sign (ie, presence of color
signal in the fluid collection).
 The sign is positive in pleural effusions because of the transmitted respiratory
and cardiac movements.
 The sign has a reported sensitivity of 89.2% and a specificity of 100% in
identifying small effusions.

14.  On the frontal film, the highest point of the apparent right hemi
diaphragm is displaced laterally (it is usually in the center).
 On the lateral film, there is a flat edge where the effusion meets
the major fissure.

15.  The peak of the pseudodiaphragmatic contour is more lateral than the
peak of the normal diaphragm. Sometimes, thin triangular upward
extension of the fluid can be seen medially on the left side.
 On the lateral view: Frequently, the pseudodiaphragmatic contour is
interrupted anteriorly by the major fissure, with a sharp descent into the
anterior costophrenic sulcus. Extension of a small amount of fluid
through the inferior aspect of the major fissure can be seen as well.
 On both PA and lateral views: In contrast to the normal diaphragmatic
opacity, the pulmonary vessels are poorly visualized through the
pseudodiaphragmatic contour. The gastric gas lucency is widely
separated (>2 cm) from the pseudodiaphragmatic contour in cases of
left subpulmonic effusion.

16.  Encysted fluid.
 Usully lenticular shaped.
 Loculated fluid in one or more fissure – can be seen in heart
failure.

17.  The split pleura sign is characterized by thickened pleural layers
separated by fluid.
 This sign is found primarily in empyema, and it helps to
differentiate from abscess.
 It is also frequently seen in hemothorax and talc pleurodesis.

18.  Medial displacement of the cecum and ascending colon.
 Lateral displacement of the properitoneal fat line.
 Present in more than 90% of patients with significant ascites.

19.  In 80% of patients with ascites, the lateral liver edge is medially
displaced from the thoracoabdominal wall.

20.  In the pelvis, fluid accumulates in the rectovesical pouch and
then spills into the paravesical fossa.
 The fluid produces symmetric densities on both sides of the
bladder.

21.  Diffuse abdominal haziness.
 Bulging of the flanks.
 Indistinct psoas margins.
 Poor definition of the intra-abdominal organs.
 Erect position density increase.
 Separation of small bowel loops &
 Centralization of floating gas containing small bowel.

22.  On ultrasound examination ,with massive ascites, the small
bowel loops have a characteristic polycyclic, "lollipop," or
arcuate appearance because they are arrayed on either side of
the vertically floating mesentery.

23.  Free fluid in the peritoneum and in unopacified bowel often has
a similar density at CT.
 Free fluid will forms concave margins, conforming to loops of
bowel with peaks at the apices of the margins.
 Fluid-filled loops of bowel or ovaries have convex margins
without peaks, and these can be differentiated from free fluid if
the concave margin sign is used.

24. Do mail us back at (jssmcrad@gmail.com) - if you come across more signs that can
be added to this “sign soup”.