Hydronephrosis describes a condition where one or both kidneys swell due to urine buildup. This occurs because urine cannot drain properly, causing it to back up and distend the kidney’s collecting system. It can affect individuals of any age, often identified in fetuses during routine pregnancy ultrasounds, but also appearing in children and adults with various underlying causes.
The Purpose of a Grading System
Doctors use a grading system for hydronephrosis to standardize how they describe its severity. This provides a clear, objective measure that helps medical professionals communicate consistently about a patient’s condition. A standardized grade also aids in predicting the likelihood of the condition improving on its own. Knowing the grade helps determine which cases might resolve spontaneously and which ones may require closer monitoring or treatment.
Explaining the Hydronephrosis Grades
The most widely accepted method for classifying hydronephrosis is the Society for Fetal Urology (SFU) grading system, which uses ultrasound imaging to assess the degree of swelling. This system divides hydronephrosis into five grades, from 0 to 4, based on the appearance of the renal pelvis, calyces, and the thickness of the kidney’s functional tissue.
Grade 0 indicates no dilation, with internal collecting structures of the kidney appearing normal. Grade 1, considered mild, shows a slight enlargement of the renal pelvis, the central urine-collecting area, but without any expansion of the smaller calyces. The kidney tissue remains unaffected.
Grade 2, also mild, involves a mild dilation of both the renal pelvis and the calyces. Despite this expansion, the typical branching pattern of the calyces is still visible, and there is no thinning of the kidney’s functional tissue.
Grade 3, which is moderate, the renal pelvis and calyces show more pronounced dilation, and the tips of the calyces may appear blunted or flattened. At this stage, a slight thinning of the kidney’s outer functional layer, the cortex, might be observed.
Grade 4 represents severe hydronephrosis, where the renal pelvis and calyces are grossly dilated. The distinct borders between the renal pelvis and calyces are lost due to swelling. This grade is also characterized by noticeable thinning and atrophy of the kidney’s functional tissue.
How Grading Influences Medical Follow-Up
The assigned hydronephrosis grade influences the medical follow-up plan. For lower grades, such as SFU Grades 1 and 2, a common approach is “watchful waiting” or active surveillance. This typically involves scheduled follow-up ultrasounds to monitor the condition, as many mild cases can resolve on their own, especially in infants.
As the grade increases to SFU Grade 3 or 4, further diagnostic tests become more likely to assess kidney function and determine if there is an obstruction. A common test is a MAG3 diuretic renal scan, which evaluates urine drainage and measures individual kidney function. These scans help identify blockages and their impact on kidney function.
If higher grades of hydronephrosis persist or worsen, or if diagnostic tests indicate a significant obstruction or declining kidney function, medical or surgical intervention may be considered. For instance, a reassuring MAG3 scan in high-grade cases can still allow for continued observation. However, if the condition progresses despite a reassuring scan, a repeat scan might be performed to re-evaluate the need for intervention.