Muscular type VSD is caused by which developmental error?

Muscular type VSD is caused by which developmental error?

• A. Failure of mesoderm to form
• B. Migration of neural crest failed
• C. Opening at semilunar valve
• D. Increased pulmonary vascular resistance

Answer: (A)

Muscular VSD arises when the muscular part of the interventricular septum doesn’t form properly. That portion of the septum comes from ventricular myocardium, which is derived from the mesoderm. If mesoderm formation or its contribution to the ventricular wall is impaired, the muscular septum may be incompletely formed, leaving a defect between the ventricles. The other options don’t fit as the primary developmental cause. Neural crest migration affects the outflow tract and conotruncal septation (leading to defects like certain outflow tract anomalies, not specifically the muscular septum). An opening at the semilunar valve isn’t how a VSD develops, and increased pulmonary vascular resistance is a postnatal hemodynamic factor that can influence shunt direction rather than a developmental error.

Muscular VSD arises when the muscular part of the interventricular septum doesn’t form properly. That portion of the septum comes from ventricular myocardium, which is derived from the mesoderm. If mesoderm formation or its contribution to the ventricular wall is impaired, the muscular septum may be incompletely formed, leaving a defect between the ventricles.

The other options don’t fit as the primary developmental cause. Neural crest migration affects the outflow tract and conotruncal septation (leading to defects like certain outflow tract anomalies, not specifically the muscular septum). An opening at the semilunar valve isn’t how a VSD develops, and increased pulmonary vascular resistance is a postnatal hemodynamic factor that can influence shunt direction rather than a developmental error.