Difficult to say without examining the ultrasound myself.
1) It is likely that a bilateral varicocele is two seperate varicoceles.
2) Bilateral varicoceles are common, occuring in 1/3 of patients with varicoceles. If all the other testing and imaging are negative, it is unlikely that a serious cause is behind the varicocele.
3) One can consider a semen analysis - since uncommonly varicoceles are associated with infertility.
As for the cause of varicoceles, I will quote from UptoDate:
"The left spermatic (gonadal) vein is one of the longest veins in the body, entering the left renal vein at a perpendicular angle. The intravascular pressure in the left renal vein is higher than on the right because it is compressed between the aorta and the superior mesenteric artery coming off the aorta above the renal vein, thereby producing a "nutcracker effect." This phenomenon causes increased pressure in the left gonadal vein, which can dilate and cause incompetence of the valve leaflets, leading to retrograde flow of blood toward the testis in the erect position. The venous complex in the scrotum dilates and produces anything from minimal fullness on Valsalva maneuver to a large soft scrotal mass ("bag of worms") that decompresses and disappears in the recumbent position."
4) It is not uncommon for a varicocele to present after the age of 30.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_b
Bibliography:
Eyre. "Evaluation of nonacute scrotal pathology in adults". UptoDate 2005.