Testicular (Scrotal) Scintigraphy
Scrotal scintigraphy with ⁹⁹ᵐTc-pertechnetate assesses testicular perfusion in the acute scrotum. Torsion shows reduced or absent flow with a photopenic (“cold”) testis — sometimes a reactive hyperaemic rim on later/missed torsion — whereas epididymo-orchitis shows increased flow. Colour-Doppler ultrasound is usually first-line, but scintigraphy is a functional alternative where Doppler is equivocal.
Torsion of the spermatic cord cuts off testicular blood supply, creating a photopenic testis; inflammation increases perfusion. Because the salvage window is short, the study answers a time-critical surgical question.
When to image
- Acute scrotum where ultrasound Doppler is equivocal and the diagnosis is uncertain.
- Differentiating testicular torsion from epididymo-orchitis.
- Assessing viability at delayed/atypical presentation.
How to read it
- Torsion: decreased/absent flow with a photopenic testis; a surrounding hyperaemic rim suggests missed/late torsion.
- Epididymo-orchitis: increased perfusion and blood pool.
- Compare sides and correlate with clinical timing.
Protocol
- Flow (dynamic) and static blood-pool images after ⁹⁹ᵐTc-pertechnetate.
- Position and shield to compare both hemiscrota symmetrically.
Pitfalls
- Spontaneous detorsion restores flow — can mask torsion.
- The rim (“doughnut”) sign of missed torsion is not specific — abscess, haematoma or tumour can look similar.
- Do not delay surgery for imaging when torsion is clinically clear.
Evidence & guidelines
- Scrotal scintigraphy reliably separates ischaemic from inflammatory causes of the acute scrotum.
- Colour Doppler ultrasound is first-line (ACR Appropriateness Criteria, acute scrotal pain, 2024 update); scintigraphy is a functional problem-solver.
In depth
- ⁹⁹ᵐTc-pertechnetate scrotal scintigraphy is highly sensitive (about 90–100%) for testicular torsion. In boys with equivocal presentations it matched colour Doppler ultrasound for sensitivity and was more specific (97% vs 77%), but Doppler ultrasound is now the usual first-line test.
- Adult activity is typically about 185–740 MBq (5–20 mCi) depending on local protocol; children receive a weight-scaled activity, and pinhole (magnification) imaging helps in small children.
- A dynamic flow phase (a few seconds per frame for about 1 min) is followed by static tissue-phase images of the scrotum.
- Salvage is time-critical: about 90–100% of testes are salvaged when detorsion is performed within 6 h, falling to around 20% after 12 h, and few are viable beyond 24 h.
- Early torsion shows a photopenic testis without reactive hyperaemia; the 'nubbin' sign is increased flow in the spermatic cord vessels up to the point of the twist, with an abrupt cut-off.
- Missed (late) torsion produces the rim, doughnut or halo sign (a hyperaemic peritesticular rim around a photopenic testis), and the testis is usually no longer viable. The rim sign is non-specific and is also seen with abscess, tumour and trauma.
- Epididymo-orchitis shows increased perfusion to the cord and hemiscrotum, typically lateral where the epididymis lies, with preserved testicular activity. Torsion of a testicular appendage is common and is the most frequent cause of acute scrotum in many paediatric series; its scintigraphic appearance is variable.
Sources: PMID 9530319 (Paltiel, Radiology 1998) · Saleh et al., IMJM 2012 · 11:9 · PMID 16356796 (Jana & Blaufox 2006) · Saleh et al., IMJM 2012 (5–10 mCi protocol) · PMID 10565787 (Connolly, J Nucl Med 1999) · Saleh et al., IMJM 2012 (16 × 4-s flow frames then a 3-min static image) · Saleh et al., IMJM 2012 (citing Kapoor)