A child presents with periorbital and scrotal edema, and their urinalysis shows 3-4+ protein. What is the most likely diagnosis?

The presentation of periorbital and scrotal edema, along with significant proteinuria (3-4+ protein), is highly suggestive of nephrotic syndrome. In nephrotic syndrome, a series of pathophysiological changes leads to increased permeability of the glomerular filtration barrier, resulting in excessive protein loss in urine. This loss of protein results in hypoalbuminemia, which contributes to edema formation due to decreased oncotic pressure in the blood vessels.

Children with nephrotic syndrome often present with these characteristics; they may also exhibit signs such as a pronounced swelling in the face (particularly around the eyes), as well as potential generalized edema due to fluid retention. The degree of proteinuria, typically more than 3.5 grams per day in children, aligns with the urinalysis findings of 3-4+ protein.

Understanding the clinical features and laboratory findings of nephrotic syndrome is crucial and helps differentiate it from other conditions like acute glomerulonephritis, which may present with hematuria and different types of edema, or other urinary tract problems like cystitis and hydronephrosis, which do not typically present with such significant proteinuria.