Could an internal hernia, in the mid-abdomen, be missed on ct scan? is mri more accurate? thank you.

No: An internal hernia can only be suspected post surgery when signs of partial bowel obstruction develops due to a loop entering a defect in mesentery or equivalent and bowel dilatation develops which can be defined by both CAT and MRI

Surgery: The only way to definitively diagnose (and treat if it exists) an internal hernia is an operation, typically done laparoscopically. While CT and MRI can diagnose it, a "negative" study does not rule it out. Symptoms are typically intermittent pain, occasionally progressing to bowel obstruction. Intussusception can also have the same symptoms. Hope this helps!