Dilatation of the collecting system during pregnancy: physiologic vs obstructive dilatation

Dilatation of the collecting system is a classical phenomenon during pregna ncy, due to hormonal and extrinsic compressive factors. Imaging has to; dif ferentiate a physiological dilatation and a pathological obstruction due to urolithiasis. Presently, sonography, using both, B-mode and color Doppler, has the potential to demonstrate the physiological compression of ureters at the level of the pelvic brim. A pathological obstruction is considered e ither when a stone is detected above the usual site of compression or when the ureter appears dilated beyond. Color Doppler helps in localizing the si te of ureteral compression against the vessels and in differentiating urete rs from veins. Magnetic resonance urography, with strongly T2-weighted sequ ences, also may show the site and type of obstruction without contrast agen t administration. These two non-radiating techniques make it possible to av oid the use of X-rays in most cases for management of these patients. The t ype of treatment is based mostly on the level of pain and the presence or a bsence of stone.