Do brushite kidney stones appear on imaging studies such as plain radiographs, non‑contrast CT, and ultrasound?

Brushite Kidney Stones on Imaging

Yes, brushite kidney stones are visible on all standard imaging modalities including plain radiographs (KUB), non-contrast CT, and ultrasound, because brushite is a radiopaque calcium-containing stone (calcium hydrogen phosphate dihydrate).

Imaging Performance by Modality

Non-Contrast CT (Gold Standard)

• Non-contrast CT detects virtually all kidney stones with 97% sensitivity, including brushite stones, and is the reference standard for stone detection 1
• Brushite stones, being calcium-based, appear as high-density structures on CT with Hounsfield units typically >700 HU 2
• Low-dose CT protocols maintain 97% sensitivity while reducing radiation exposure 1, 3
• CT provides accurate stone size measurements critical for treatment planning using coronal reformations, bone window settings, and magnified views 1, 3

Plain Radiography (KUB)

• Brushite stones are radiopaque on plain KUB radiographs because they contain calcium 1
• However, KUB has limited overall sensitivity: only 78% for stones >5 mm and just 8% for stones ≤5 mm 1, 3
• Digital radiography shows 72% sensitivity for large (>5 mm) stones in the proximal ureter but only 29% sensitivity overall for stones of any size in any location 1
• Factors affecting KUB sensitivity include stone size, location, patient body habitus, and overlying bowel contents 1
• If a brushite stone is visible on CT planning images (scout film), it will be 100% visible on formal KUB radiography 2

Ultrasound

• Ultrasound has poor direct stone detection with only 24-57% overall sensitivity compared to CT 1, 3
• Sensitivity for ureteral stones is even lower at 45-61%, though specificity remains 100% 1, 4
• Ultrasound is 95-100% sensitive for detecting secondary signs of obstruction (hydronephrosis), which may be the primary finding rather than direct stone visualization 1, 4
• Within the first 2 hours of presentation, secondary signs may not have developed yet, further limiting ultrasound utility 1, 3

Clinical Algorithm for Brushite Stone Detection

Initial Imaging Choice

• Order non-contrast CT abdomen/pelvis as first-line imaging for suspected brushite or any kidney stone 1, 3, 5
• Reserve ultrasound as first-line only for pregnant patients, pediatric patients, or those with renal impairment requiring contrast avoidance 3, 4

Follow-Up Imaging

• Use plain KUB radiography for monitoring known brushite stones over time, as they are radiopaque 6, 7
• This minimizes cumulative radiation exposure from repeated CT scans 6
• Perform yearly KUB for asymptomatic calyceal stones under observation 6

Critical Distinction: Brushite vs. Radiolucent Stones

Brushite stones differ fundamentally from radiolucent stones (uric acid, some cystine stones):

• Uric acid stones are "radiolucent" on plain KUB but remain visible on CT with lower attenuation values 5
• Brushite stones are radiopaque on both KUB and CT due to their calcium content 2, 7
• This radiopacity is clinically important because it allows for fluoroscopic guidance during extracorporeal shockwave lithotripsy (ESWL) 7

Common Pitfalls to Avoid

• Do not assume a negative KUB excludes a brushite stone—KUB misses 22% of stones >5 mm and 92% of stones ≤5 mm 1, 3
• Do not rely on CT scout images alone for treatment planning; obtain formal KUB to confirm radiopacity and accurate stone measurements 2, 8
• Plain abdominal x-ray is 48% sensitive versus scout CT at only 17% sensitive for detecting stones visible on formal CT 8
• Do not use ultrasound as the sole imaging modality when clinical suspicion for stone disease is high—proceed to CT if ultrasound is negative 3, 4
• Be aware that stones with Hounsfield units <742, located in the distal ureter, or in patients with anterior-posterior depth >26 cm may be less visible on KUB despite being radiopaque 2