Ultrasound did not show the ovary operated is this normal?

After laparoscopic surgery to remove teratoma measuring around 4 cm, the doctor kept the ovary, but was asked for an ultrasound after 2 months of surgery and the doctor could not visualize the ovary operated is this normal?
Expert answer:

It depends on which ultrasound was done: by the belly the visualization of the ovary is difficult, the transvaginal visualization is easier, but it can happen that the ovary is there and the examination does not show.