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.