✓ Mathematica : cpu = 0.186808 (sec), leaf count = 71
DSolve[-(y[x]*(a + x^2 + y[x]^2)) + x*(-a + x^2 + y[x]^2)*Derivative[1][y][x] == 0,y[x],x]
✓ Maple : cpu = 0.096 (sec), leaf count = 112
dsolve(x*(y(x)^2+x^2-a)*diff(y(x),x)-y(x)*(y(x)^2+x^2+a) = 0,y(x))