Residency · Residency · Nuclear Medicine

Renal Cortical Scintigraphy: DMSA Scan

Overview

Tc-99m DMSA (dimercaptosuccinic acid) is the gold standard for renal cortical imaging. It binds to proximal tubular cells, with 40 to 50% of the injected dose localizing in the renal cortex by 2 to 4 hours. The primary indications include detection of renal scarring, acute pyelonephritis, ectopic kidneys, and assessment of differential renal function. Although it is predominantly a pediatric study, it is used in adults for specific indications.

Radiopharmaceutical

Tc-99m DMSA is a cortical binding agent that is not excreted into the collecting system. The adult dose is 3 to 5 mCi, while pediatric dosing is weight-based according to the EANM dosage card or SNMMI guidelines. Imaging is performed at 2 to 4 hours post-injection to allow cortical binding and blood pool clearance. The result is a high target-to-background ratio that provides excellent cortical detail.

Technique

Planar imaging includes a posterior view as the primary projection, with additional posterior oblique and anterior views for ectopic kidneys. A pinhole collimator may be used for higher resolution in children. SPECT or SPECT/CT improves sensitivity for small cortical defects and allows precise localization. The low-dose CT component aids in distinguishing cortical defects from normal variants such as fetal lobulation and columns of Bertin.

<image>Normal Tc-99m DMSA scan showing homogeneous cortical uptake in both kidneys on posterior planar view with smooth contours and symmetric differential function</image>

Clinical Applications

Acute Pyelonephritis

The DMSA scan is the most sensitive imaging modality for detecting acute pyelonephritis, with a sensitivity of 85 to 95%, which is far superior to ultrasound at 40 to 60%. Findings include focal or multifocal areas of decreased cortical uptake without volume loss. Diffuse involvement produces globally reduced uptake with a preserved renal contour. Wedge-shaped cortical defects extending from the papilla to the capsule are characteristic. The study is valuable for differentiating upper urinary tract infection (pyelonephritis) from lower tract infection (cystitis).

Renal Scarring

Permanent cortical scars from prior pyelonephritis appear as focal cortical thinning or photopenic defects with associated volume loss and cortical retraction. They are distinguished from acute pyelonephritis by the presence of volume loss and cortical contour irregularity. Scanning should be performed at 4 to 6 months after the acute infection to accurately assess for permanent scarring. The clinical significance of scarring is that it increases the risk of hypertension and chronic kidney disease.

Vesicoureteral Reflux (VUR) Workup

The DMSA scan identifies renal scarring as a complication of VUR with recurrent pyelonephritis. Findings guide management decisions, as kidneys with significant scarring may not benefit from anti-reflux surgery. DMSA results influence whether conservative management or surgical intervention is pursued. AAP guidelines recommend a DMSA scan after febrile UTI in children under 2 years when ultrasound is abnormal or there is recurrent UTI.

Differential Renal Function

DMSA provides an accurate measurement of relative cortical function through ROI-based calculation from posterior images or geometric mean of anterior and posterior views. Normal values are approximately 45 to 55% for each kidney. DMSA has advantages over MAG3 for differential function assessment in that it is not affected by hydration status or collecting system dilation, making it useful when MAG3 differential function is unreliable, such as in severe hydronephrosis or impaired drainage.

Ectopic and Horseshoe Kidneys

The DMSA scan confirms the presence and location of functioning renal tissue. It identifies ectopic kidneys including pelvic and crossed fused ectopia. It evaluates the functioning cortical mass in horseshoe kidneys and other congenital anomalies.

<image>DMSA scan in a child with recurrent UTI showing a photopenic defect in the upper pole of the left kidney with cortical thinning consistent with renal scarring from prior pyelonephritis</image>

DMSA vs. Ultrasound for Pyelonephritis

DMSA Advantages

DMSA has higher sensitivity for acute pyelonephritis (85 to 95% versus 40 to 60% for ultrasound). It detects cortical involvement that is invisible on ultrasound, quantifies differential renal function, and is more sensitive for detecting renal scarring.

Ultrasound Advantages

Ultrasound requires no radiation exposure, is readily available and low cost, detects hydronephrosis, stones, and structural anomalies, and can be repeated without radiation concerns. It remains the first-line imaging study for UTI in children per AAP guidelines.

Interpretation Pitfalls

Normal Variants Mimicking Pathology

Fetal lobulation produces smooth cortical indentations between calyces and is a normal developmental variant. Prominent columns of Bertin represent hypertrophied cortical tissue extending into the medullary region and appear as areas of increased uptake, not defects. The dromedary hump is a focal cortical bulge on the lateral left kidney from splenic impression. A duplex kidney has two moieties with different function and may appear as an elongated kidney with a cortical cleft.

Artifacts and Technical Issues

Motion artifacts are common in young children, and sedation may be necessary. Improper ROI placement affects differential function calculations. Background subtraction errors can occur. Delayed imaging beyond 6 hours may show urinary tract activity that confuses cortical assessment.

<image>SPECT/CT DMSA showing a focal cortical defect in the lower pole of the right kidney on SPECT, with the CT component confirming cortical thinning and distinguishing it from a normal variant (fetal lobulation)</image>

Pediatric Considerations

Most DMSA scans are performed in children between 1 month and 5 years of age. Weight-based dosing follows the EANM dosage card. Sedation may be needed for children under 3 to 4 years who cannot remain still for the 20 to 30 minute acquisition. SPECT improves detection of small defects but requires longer acquisition time. Radiation dose is a concern in children, and the clinical benefit must justify the study.

Timing of DMSA After UTI

In the acute phase within 2 weeks of infection, the DMSA scan detects acute pyelonephritis as focal cortical defects without volume loss. At 4 to 6 months, the follow-up scan detects permanent scarring as defects with volume loss. If only one scan is to be performed, the follow-up scan is more clinically relevant for long-term management. Some centers perform an early scan to confirm pyelonephritis and guide VCUG and antibiotic prophylaxis decisions.

Clinical Pearls

DMSA is the most sensitive test for renal cortical pathology. A normal DMSA effectively excludes significant pyelonephritis or scarring.

SPECT or SPECT/CT should always be used when available for improved sensitivity over planar imaging.

In neonates, renal cortical function is immature, and DMSA scans should be deferred until after 1 month of age for reliable results.

The presence of renal scarring on DMSA should prompt screening for hypertension and proteinuria during follow-up.

DMSA differential function is more accurate than MAG3 when collecting system dilation confounds the MAG3 cortical phase.

Columns of Bertin are a common normal variant that should not be confused with cortical masses.

References

• Defined Role of DMSA Scan in Pediatric UTI. Pediatric Nephrology, 2017.
• AAP Guidelines: Diagnosis and Management of UTI in Febrile Infants and Children 2-24 Months.
• SNMMI/EANM Procedure Guideline for DMSA Scintigraphy.
• Piepsz, A., et al. "Renal Cortical Scintigraphy in Children." Seminars in Nuclear Medicine, 2006.

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