\[ \boxed { \left ( \left ( y \left ( x \right ) \right ) ^{2}+{x}^{2}+a \right ) y \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) + \left ( \left ( y \left ( x \right ) \right ) ^{2}+{x}^{2}-a \right ) x=0} \]
Mathematica: cpu = 0.024003 (sec), leaf count = 149 \[ \left \{\left \{y(x)\to -\sqrt {-\sqrt {a^2+4 a x^2+4 c_1}-a-x^2}\right \},\left \{y(x)\to \sqrt {-\sqrt {a^2+4 a x^2+4 c_1}-a-x^2}\right \},\left \{y(x)\to -\sqrt {\sqrt {a^2+4 a x^2+4 c_1}-a-x^2}\right \},\left \{y(x)\to \sqrt {\sqrt {a^2+4 a x^2+4 c_1}-a-x^2}\right \}\right \} \]
Maple: cpu = 0.046 (sec), leaf count = 125 \[ \left \{ y \left ( x \right ) =\sqrt {-{x}^{2}-a-\sqrt {4\,a{x}^{2}+{a}^ {2}-4\,{\it \_C1}}},y \left ( x \right ) =\sqrt {-{x}^{2}-a+\sqrt {4\,a{ x}^{2}+{a}^{2}-4\,{\it \_C1}}},y \left ( x \right ) =-\sqrt {-{x}^{2}-a- \sqrt {4\,a{x}^{2}+{a}^{2}-4\,{\it \_C1}}},y \left ( x \right ) =-\sqrt {-{x}^{2}-a+\sqrt {4\,a{x}^{2}+{a}^{2}-4\,{\it \_C1}}} \right \} \]