Can thread veins be too small to inject?

The fine, thread-like veins on your legs are spider veins.  Most of these can be treated with sclerotherapy and/or topical lasers or ohmic thermolysis.  If they are short, faint veins, skin laser procedure or ohmic thermolysis may work very well without the need for sclerotherapy injection.

Sclerotherapy (injection) or laser treatment can successfully eliminate spider veins- it might be best to get a second opinion regarding your particular condition but an experienced physician can offer laser therapy if he feels injection is not a viable option