Intermittent groin pain for 17 months. ultrascan in feb to rule out tc, showed nothing. still aches from time to time. could scan be wrong?

Unlikely: If the ultrasound was negative, there is unlikely to be testicular cancer present. Other things that might cause groin pain include hernias, varicocele (which can also be identified on sono), intermittent testicular torsion, and infections of the scrotal contents. If the problem is persistent, a ct of the abdomen may be suggested to rule out abdominal pathology.