|
Echocardiography
in Practice
A Case Oriented Approach
by Susan Wiegers, Ted Plappert, and Martin St. John Sutton
Chiari Network - Normal Variant
Susan E. Wiegers, MD
A 70-year old man presented with the sudden onset of hemiparesis. The
magnetic imaging angiogram was highly suggestive of a thrombus
in the middle cerebral artery. Because the transthoracic
echocardiogram did not reveal a potential cardiac source of embolus,
he underwent a transesophageal echocardiographic study. No
cardiac source of embolism was demonstrated.
 |
Figure 12.1
Transesophageal echocardiogram from the mid-esophagus in
the longitudinal plane (imaging angle 90° ). The
superior vena cava is seen on the right of the image
entering the right atrium. There is a thread-like
structure within the right atrium (RA) which was highly
mobile in real time. |
Discussion
The Chiari network was first described in 1897 in an
autopsy series by Dr Chiari. It was noted to be present
in 2-3% of the population. This embryonic remnant has
no known purpose and is not pathological. Entrapment
of right cardiac catheters has been reported. The Chiari
network appears to be a web-like structure with a variable number
of thread-like components. It is characterized
by whip-like motion within the right atrium and
attachment to the wall of the right atrium in close
proximity to the entrance of the inferior vena
cava. It
was detected in approximately 1.5% of transthoracic
studies in a series in 1984. However, technical improvements
in image quality may have increased the incidence
of its detection.
 |
Figure 12.2
Similar transesophageal view to that in Figure 12.1, but
the
transesophageal probe has been advanced slightly. The attachment
of the structure to the wall near the entrance of
the inferior vena cava is evident. It is obvious from
comparing Figures 12.1 and 12.2 that the structure is highly
mobile. This represents a Chiari network, which is a normal
structure, although in this patient it is particularly prominent. |
Figure 12.3
Transesophageal echocardiogram from the level of the midesophagus
in the transverse plane (imaging angle 0°). This
view reveals that the network on some levels appears as a
ring. The net-like structure has variable attachments in the
right atrium. The whip-like motion and its thin thread-like
characteristics distinguish it from a thrombus or other
mass. |
 |
 |
Figure 12.4
Close-up view of the right atrium from the transesophageal
image in Figure 12.3. The Chiari network appears to be a
latticework of threads. There appears to be thickening at the
end of the network closest to the tricuspid valve. However,
this represents an oblique cut of the multiple threads within
the structure. In real time, it was easily appreciated that
there was no thickening. |
While the Chiari network has no clinical significance,
it must be
distinguished from other pathological masses in the right atrium
including thrombus, vegetation, and myxoma. The characteristic
features should allow this differentiation. Another embryonic remnant
in the right atrium is a persistent sinus venosus valve or Eustachian
valve. This ridge along the posterior wall of the right atrium
runs from the right side of the inferior vena cava to the interatrial
septum, where it joins the Thebesian valve at the fossa ovalis.
In the fetal circulation, the Eustachian valve directs the oxygenated
blood from the inferior vena cava across the interatrial septum
to the left side of the heart. This membrane usually regresses,
but can be quite prominent and can occasionally be mistaken for
other masses.
References
1. Panidis I, Kotler M, Mintz G, et al. Clinical
and echocardiographic features of right atrial masses. Am Heart
J 1984;107:745-58.
2. Werner J, Cheitlin M, Gross B, et al. Differentiation
from right heart pathology, Circulation 1981;63:1104-9.
|
