Can testicular cancer be missed on ultra scan?

Yes: If a testicular cancer is very small, doesn't look different from the remainder of the testicle, or is "burned out" it may not be seen. "burned out" means the tumor has shrunken in the testicle (often leaving nothing but a scar or calcification) and the tumor is only found by patient metastases, often enlarged lymph nodes. Lastly, an inexperienced sonographer can just not see it.