MANUSCRIPT TEXT:
A four year old boy was diagnosed with hypertrophic cardiomyopathy with
moderate degree of obstruction of the left ventricular outflow tract
secondary to asymmetric septal hypertrophy and no features of congestive
heart failure during infancy. He was also found to have myxomatous
mitral valve, systolic anterior motion of anterior mitral leaflet and
moderate mitral regurgitation (Fig 1, Video 1). In view of phenotypic
features suggestive of Noonan syndrome (Fig 3), he underwent genetic
evaluation with target gene sequencing and was detected to have a novel
heterozygous mutation in exon 13 of LZTR 1 (Leucine- zipper-like
transcriptional regulator 1) gene1. Echocardiogram on
follow up showed increase in left ventricular outflow tract obstruction
and appearance of an aneurysm in the membranous portion of
interventricular septum (Fig 3 and 4, Video 2 and 3). There were no
features of right ventricular inflow or outflow obstruction, tricuspid
regurgitation or aortic regurgitation. Membranous septal aneurysms in
children are usually seen in association with ventricular septal
defects. The appearance of the membranous septal aneurysm in this boy
may be attributed to the direction of jet arising from the point of
contact of the anterior mitral leaflet with the hypertrophied basal
septum and hitting this part of the interventricular septum. It is an
unusual mechanism for formation of membranous septal aneurysm, given its
absence in the earlier echocardiograms and absence of any left to right
shunt across the aneurysm. For membranous septal aneurysms to become
clinically important, they have to interfere with the closure mechanism
of the cardiac valves, cause a mass effect, or cause flow
obstruction2. Histopathology of resected aneurysms
have shown almost total loss of elastic fibres and extensive
accumulation of mucopolysaccharides3. This patient has
been initiated on beta blockers due to severe left ventricular outflow
tract obstruction and is planned for septal myomectomy, mitral valve
repair and membranous septal aneurysm resection due to the fear of
thrombus formation and rupture of the aneurysm.