Primary reflux is a congenital abnormality of the normally oblique insertion of the ureter through the bladder wall at the ureterovesical junction and is not associated with urinary tract or other congenital anomalies. Primary VUR usually resolves spontaneously during the first decade. Although the likelihood of resolution exceeds 80% when the VUR is mild, discovered in the first year of life, and unilateral, even the most severe reflux has a 40 to 50% spontaneous resolution rate. Patients with primary reflux rarely develop significant clinical sequelae such as proteinuria, hypertension, or renal insufficiency.

Secondary reflux develops from elevated intravesicular pressure that may result from abnormal voiding patterns or anomalies, including urinary tract obstruction. In one cause of secondary reflux, known as Hinman syndrome or psychological nonneuropathic bladder ,apparently functional incoordination between detrusor contraction and relaxation of the external sphincter is acquired and leads to incomplete voiding, incontinence, and elevated intravesicular pressures culminating in VUR, hydronephrosis, and reflux nephropathy. Resolution of secondary VUR is less predictable and based on treating the underlying cause. Patients with secondary reflux are at greatest risk for long-term renal sequelae.
The true incidence of reflux in the general population is unknown, but limited data suggest 1 to 2%. The risk for siblings is as high as 50% depending on the age of the child.
The relationship between VUR and renal scarring is controversial. In children with UTI and VUR, 20 to 40% will develop renal scars, but the cause-and-effect relationship of this association is not proven.

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