The right kidney and left kidney (both) measure 10.0 cm in length without hydronephrosis or stones.
There is no need for a comma in this sentence. However, you are referring to two organs, so the verb is plural. Moreover, the organs are the same length. "Respectively" is used in the following way: The right kidney and left kidney measure 10.0 cm and 11 cm in length respectively ...", that is, it refers the order in which I give the lengths of the organs back to the names of the organs in the same order as written.
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