Scrotal Scintigraphy⁹⁹ᵐTc-pertechnetate

Quick Answer

Scrotal scintigraphy uses a Tc-99m-pertechnetate bolus (flow + blood-pool imaging) to assess testicular perfusion in acute scrotal pain. Acute torsion shows decreased/absent perfusion to the affected testis; missed (late) torsion shows a photopenic testis with a hyperemic rim ("rim/halo sign"); epididymitis shows increased perfusion. In modern practice, color Doppler ultrasound is first-line, and scintigraphy is a problem-solver when ultrasound is equivocal or unavailable.

Mechanism & Physiology

Free Tc-99m-pertechnetate is a blood-pool/perfusion tracer (it is not taken up by testicular tissue), so the study images arterial flow and capillary blood pool to the hemiscrotum. In torsion, the spermatic cord twists and first occludes the low-pressure venous then arterial supply, producing a photopenic (cold) testis; surrounding dartos and scrotal-wall reactive hyperperfusion creates the rim. In epididymitis, inflammatory vasodilation increases flow. The clinical stakes are time-driven: testicular salvage exceeds ~90% if detorsion occurs within ~6 hours, falls sharply by 12 hours, and is rare beyond 24 hours — which is why imaging must never delay surgery when torsion is likely.

Findings

• Acute torsion: reduced flow and blood-pool activity in the affected hemiscrotum (± a small "nubbin" of activity at the cord from the twist point) — a surgical emergency.
• Missed/late torsion: central photopenia with a surrounding hyperemic rim ("rim/halo/bull's-eye" sign) from reactive dartos/scrotal-wall flow.
• Epididymitis/orchitis: increased flow and blood-pool activity (inflammatory hyperemia), sometimes a curvilinear lateral-to-medial pattern.
• Torsion of a testicular appendage ("blue-dot"): usually normal or mildly increased perfusion — a mimic that does not need surgery.
• Spontaneous torsion-detorsion: transiently increased perfusion after untwisting — can mimic epididymitis.

Technique

Radionuclide angiogram (flow phase, 2–3 s frames) immediately after IV bolus, then static blood-pool images with a scrotal/perineal lead shield and skin markers; a pinhole or converging collimator improves resolution of the small testes. Symmetry with the contralateral side is the reference.

Reporting Checklist

• State the flow and blood-pool findings by side, and classify: decreased (torsion) / rim (late torsion) / increased (epididymitis).
• Note mimics (hydrocele/hematoma photopenia, appendage torsion, detorsion).
• Emphasize that a torsion-suspicious study warrants immediate urologic evaluation.

Perfusion direction tells torsion from infection

Scrotal scintigraphy assesses testicular perfusion in acute scrotal pain: decreased/absent perfusion = acute torsion (a time-critical surgical emergency); a photopenic testis with a hyperemic rim ("rim/halo sign") = missed/late torsion (shrinking salvage window); increased perfusion = epididymitis/orchitis. Color Doppler ultrasound is first-line — scintigraphy is the problem-solver when US is equivocal or unavailable, and imaging must never delay urologic evaluation when torsion is clinically likely.

Salvage is time-critical: detorsion within ~6 h salvages >90%, dropping sharply by 12 h and rarely successful beyond 24 h — so a torsion-suspicious history mandates surgery, not more imaging. The rim/halo (bull's-eye) sign marks missed/late torsion, where the salvage window has usually closed.

Watch the mimics: torsion of a testicular appendage ("blue-dot") shows normal/mildly increased perfusion and is managed conservatively; spontaneous detorsion produces reactive hyperperfusion mimicking epididymitis; and a large hydrocele or hematoma can cause photopenia that falsely suggests torsion. Pertechnetate images blood pool/perfusion only (no testicular uptake), so interpretation rests on flow symmetry versus the contralateral side.

High-Yield Pearls

• Decreased perfusion = torsion (emergency); increased perfusion = epididymitis; rim sign = missed torsion.
• Salvage >90% if detorsed <6 h; rare beyond 24 h — do not delay surgery for imaging.
• Doppler ultrasound is first-line; scintigraphy resolves equivocal cases.
• Appendage torsion and post-detorsion hyperemia are the classic mimics.

Common Pitfalls

• A large hydrocele or hematoma causing photopenia mimicking torsion.
• Appendage torsion / spontaneous detorsion mimicking epididymitis (increased flow).
• Delay — do not let imaging postpone urologic evaluation when torsion is clinically likely.

Related Pages

• Related: color Doppler ultrasound (first-line); pitfalls: Pearls, pitfalls & normal variants.

Self-Check