"The renal pelvicalyceal systems are dilated bilaterally" in MRI report

[amirrrr]

HI
I have 52 years old and i am woman. Last week I felt heavy pain in my left leg from top to bottom. Doctor said it is because of Sciatica and told me to do MRI from my Reins and spinal cord. The report is as below:

All the lumbar disci show disc dehydration without herniation.
Vertebral bodies show small high signal fatty foci in the endplates.
Alignment of vertebras show increased lordosis.
Cord and nerve roots are normal.
At L5-S1 level minimal spondylolisthesis [5%] is seen.
The renal pelvicalyceal systems are dilated bilaterally .Correlation with sonography is recommended.
---------------------------------
What is the meaning of the last two sentences of this repor about Sonography? Is it dangerous? Is it normal problem?
I am really worry about it.