Is 1.7 cm Kidney Hydronephrosis Considered Severe?

When evaluating kidney hydronephrosis, medical professionals typically rely on ultrasound imaging to determine the severity. Two widely used grading systems are the Anterior-Posterior Diameter (APD) measurement and the Society for Fetal Urology (SFU) classification system. In general, a renal pelvis diameter between 0–10 mm is considered normal and referred to as "pelviectasis" rather than true hydronephrosis. When the APD exceeds 10 mm, it is classified as mild hydronephrosis; values above 15 mm indicate moderate hydronephrosis, and those surpassing 20 mm are categorized as severe. Since 1.7 cm equals 17 mm, this falls into the moderate hydronephrosis range based on APD criteria alone.

Why One Measurement Isn't Enough

Determining the seriousness of kidney swelling requires more than just measuring the width of the renal pelvis. The extent of calyceal dilation—meaning how much the inner chambers of the kidney (calyces) are stretched—and the thickness of the renal cortex (the functional outer layer of the kidney) are equally critical indicators. If imaging shows significant dilation of the calyces or noticeable thinning of the renal cortex, this suggests ongoing damage and points toward a more serious condition—even if the APD is only 17 mm.

The Role of Renal Cortical Thickness

Renal cortical thinning often reflects chronic obstruction or long-term pressure on kidney tissue, which can impair its ability to filter blood and produce urine. A thinner cortex usually correlates with reduced kidney function and may signal irreversible damage over time. Therefore, radiologists and urologists carefully assess cortical integrity when staging hydronephrosis and planning treatment.

Assessing Kidney Function: The Nuclear Medicine Perspective

To gain deeper insight into kidney health, doctors often perform a renal scan with differential function assessment, such as a MAG3 or DMSA scan. These tests measure how well each kidney contributes to overall renal function. Normally, each kidney should account for approximately 50% of total function. If one kidney functions below 40%, it indicates impaired performance that could require surgical intervention. When function drops below 10%, the kidney may be non-functional or severely compromised, and in some clinical cases, removal (nephrectomy) might be recommended to prevent complications like infection or hypertension.

Putting It All Together: A Comprehensive Evaluation

In summary, while an APD of 1.7 cm places the case in the moderate hydronephrosis category, severity cannot be determined by size alone. A full diagnostic picture includes imaging details like calyceal involvement and cortical thickness, combined with functional data from nuclear scans. Only through this multidimensional approach can physicians accurately judge whether the condition poses a significant risk and what steps—ranging from monitoring to surgery—are appropriate.

Patients diagnosed with moderate hydronephrosis should maintain regular follow-ups with a urologist or nephrologist to monitor changes over time. Early detection and timely management significantly improve long-term outcomes and help preserve kidney function.