Hello and thanks for trusting me to help you and Maximus today. I am a licensed veterinarian with over 25 years experience and would be happy work with you.
I am a little confused since a tear in the belly wall is a hernia, but it can occur in different spots besides the inguinal area. Are you sure that they aren't referring to a diaphragmatic hernia that they are seeing on the xray? This is the internal wall that separates the abdominal organ from the chest and is frequently damaged when there is a trauma. When it occurs, there would be no outwardly visible signs of a problem and the surgery to repair is much more costly than an inguinal tear.
It is impossible to tell what is truly going on without exploration of the inguinal region. If there was an inguinal hernia, an xray can give somewhat of an idea and if there is intestines involved, it would be seen, but why they didn't not that at the surgery, I do not know. I will tell you that when there is a hernia, the intestines are not always out and can often move in an out of the abdomen at will. If he was on his back during the surgery, it is possible they slipped back into the abdomen and that is why they didn't see them. It is also possible if there was a fat pad there, it would be obscuring visualization, but if they palpated the inguinal ring, they would likely be able to identify if a hernia was present.
If he seems stable, I would wait and have the surgeon who originally performed the surgery re-evaluate and repair.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.
My posted replies are for general education only and not meant as a diagnosis. Only after a thorough veterinary examination can a diagnosis for your pet be made and specific treatments be advised or medications be prescribed.