Conclusions
Causes of PAAs have been divided into those associated with
Eisenmenger’s physiology, pulmonic valve abnormalities, and connective
tissue disorders.4 Gupta et al also included
infectious causes such as tuberculosis (Rasmussen’s aneurysm),
vasculitis, and endocarditis.4 This rare entity has
been associated with congenital defects in almost half of
cases.2 The pathophysiology of PAAs remains poorly
understood, especially in the absence of connective tissue
disorders.2 This case report describes the rare
incidence of a normally functioning, non-stenotic bicuspid pulmonic
valve and a PAA, suggesting a developmental association versus a
hemodynamic one.
Bicuspid pulmonic valves are quite uncommon, being described in only
0.1% of donor hearts, while PAAs are even more rare, having been found
in 8 out of 109,571 autopsies.1,5-7 This rarity makes
it difficult to characterize relationships. Even on the aortic side,
despite the robust association between bicuspid aortic valves and
thoracic aortic aneurysms, the mechanism still remains unclear. It has
been postulated that with a bicuspid valve, there is an increase in
matrix metalloproteinase 2 activity and a decrease in fibrillin-1 that
leads to dilation.8 Fedak et al found this decrease in
fibrillin-1 to also be present in PAs of patients with bicuspid aortic
valves independent of valvular function.8 Abnormal
neural crest cell migration could also be a culprit since neural crest
cells are involved in both semilunar valve and vascular wall
formation.1
Previously noted relationships between bicuspid valves and PAAs has been
attributed to post-stenotic dilation.3 However, in our
patient there was no significant gradient across the bicuspid pulmonic
valve, suggesting that hemodynamics are not the primum mobile of
this association and that progression can occur in the absence of
significant pulmonic stenosis. Furthermore, the association between PAAs
and bicuspid aortic valves adds additional weight to a common
developmental abnormality, along with the more recognized relationship
between bicuspid aortic valves and aortopathies.1,9Further studies are needed to determine if the incidental finding of a
bicuspid pulmonic valve warrants routine imaging for the development of
a PAA, but given the continued enlargement of the PAA in our patient, we
will perform surveillance imaging.