What is echogenic lesion in ovary?how serious it is?how should be treated?

Depends: "echogenic" means the lesion is "bright" on u/s. A simple cyst is "hypoechoic" or dark on u/s. A cyst that has bled (hemorrhagic cyst), an endometrioma or other solid ovarian lesion can be echogenic. These usually require short term follow up u/s and/or MRI to make sure they are not something serious. Some lesions may go away on their own, others may require treatment.