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UNGUARDED TRICUSPID
VALVE (1-11) |
Unguarded tricuspid orifice is a rare abnormality of the
tricuspid valve and its differentiation from Ebstein's
anomaly may be difficult by echocardiography (1).
Marked thinning of the right ventricular myocardium is
present in this condition.
Castellanos et al. postulated that a
primary pathogenetic step occurs in the wall of the
right ventricle and this prevents the morphogenesis of the tricuspid valve from
the ventricle (2).
ULTRASOUND |
The diagnosis has been made antenatally
in a 15 week fetus (11).
·
The
septal cusps, chordae tendinae
and papillary muscles are absent (3).
·
Due
to the absence of the tricuspid valve and associated pulmonary atresia, there
is to and fro flow across the tricuspid orifice.
·
Enlargement
of the right ventricular cavity is secondary to pulmonary narrowing.
·
The
annulus normally appears echogenic and should not be mistaken for the valve
leaflet.
·
The
right-sided chambers appear as an elongated single chamber due to the absence
of the valves.
·
The
left atrium and ventricle appear relatively small due to reduced filling of the
chambers.
Unguarded tricuspid valve can rarely be partial, in which
case it becomes difficult to differentiate from Ebstein's
anomaly (1).
Unguarded tricuspid valve orifice, both partial and
complete agenesis of valvular tissue with normal
right ventricular outflow tract, can manifest late in childhood or rarely in
adulthood (4-7).
DIFFERENTIAL DIAGNOSIS |
The differential diagnosis for this anomaly includes Ebstein's anomaly, Uhl's disease
and arrhythmogenic right ventricular dysplasia.
In Ebstein's malformation:
·
there
is annular attachment of the septal and mural leaflets within the right
ventricle rather than at the atrioventricular
junction due tofailure of liberation of these
leaflets from the ventricular wall.
·
The
septal leaflet is therefore low and dysplastic but
the anterosuperior leaflet is placed normally (8).
·
Ebstein's malformation has an extremely variable natural history
depending on the degree of abnormality of the tricuspid valvular
apparatus, which may range from mild to severe (9).
·
The
routine four-chamber view of the heart at 18-20 weeks of gestation reveals a
dilated right atrium with a rudimentary mural leaflet of the tricuspid valve.
·
On
color Doppler, marked tricuspid regurgitation is present during systole due to
abnormal closure of the mural leaflet. The right ventricular chamber appears
small. Less severe forms of Ebstein's anomaly can
appear normal in the early weeks of gestation and can present with dilated
right atrium and tricuspid regurgitation in the third trimester or postnatally.
In Uhl's anomaly:
·
There
is total absence of myocardium of the right ventricle with normal septal trabeculations and normal structure of tricuspid and
pulmonary valves (9).
Arrhythmogenic right ventricular dysplasia:
·
There
is degeneration of the right ventricular myocardium with replacement of fibrofatty tissue (10).
·
The
tricuspid valve appears normal.
REFERENCES |