A 28-year-old man presents with acute onset of severe testicular pain, swelling, and erythema. On examination, the spermatic cord is thickened and tender. Doppler ultrasound shows increased vascularity within the testis. Which investigation is most specific for confirming acute suppurative inflammation of the testis and excluding torsion?

Explanation

## Investigation of Choice for Acute Orchitis vs Testicular Torsion **Key Point:** Color Doppler ultrasound with spectral analysis is the most specific and widely accepted investigation to differentiate acute suppurative orchitis (increased vascularity) from testicular torsion (absent or markedly reduced flow), and is the current standard of care per Harrison's Principles of Internal Medicine and Bailey & Love's Surgery. ### Comparison of Imaging Modalities | Investigation | Sensitivity | Specificity | Mechanism | Differentiates Torsion? | |---------------|-------------|-------------|-----------|------------------------| | Color Doppler US | 95–100% | 95–100% | Real-time blood flow imaging | Yes — first-line, rapid, no radiation | | Radionuclide scintigraphy | 98% | ~100% | Perfusion imaging | Yes — but rarely available, radiation exposure, slow | | Contrast-enhanced CT | 85% | 90% | Tissue enhancement | Yes, but less specific and not standard | | LH/FSH levels | N/A | N/A | Endocrine markers | No | **High-Yield:** Color Doppler ultrasound findings: - **Acute orchitis / epididymo-orchitis:** Markedly **increased** intratesticular vascularity ("hyperemic" testis) with low-resistance spectral waveform - **Testicular torsion:** **Absent or markedly reduced** intratesticular flow; may show a "whirlpool sign" of the spermatic cord - **Epididymitis:** Increased epididymal flow with normal or mildly increased testicular flow ### Why Color Doppler Ultrasound Is the Correct Answer **Clinical Pearl:** Color Doppler ultrasound with spectral analysis combines anatomic (B-mode) and functional (flow) information in real time, without ionizing radiation, and is immediately available at the bedside. It has sensitivity and specificity of 95–100% for differentiating orchitis from torsion (Harrison's, 21st ed.; Bailey & Love, 27th ed.). The stem itself states that Doppler ultrasound already shows increased vascularity — confirming its diagnostic role. Spectral analysis adds quantitative flow data (resistive index, peak systolic velocity), further increasing specificity. **Key Point:** Radionuclide scintigraphy (Tc-99m pertechnetate) was historically considered the gold standard but is now largely obsolete in routine practice due to: (1) limited availability, especially in India; (2) radiation exposure; (3) time delay incompatible with the 6-hour window for surgical detorsion; and (4) inferior spatial resolution compared to modern ultrasound. It is not recommended as first-line in current NEET PG curricula or standard Indian surgical textbooks. ### Why Other Options Are Suboptimal 1. **Radionuclide scrotal scintigraphy** — Historically accurate but now rarely used; time-consuming, involves radiation, and not available in most Indian centers. Color Doppler has equivalent or superior specificity with practical advantages. 2. **Contrast-enhanced CT scrotum** — Provides anatomic detail but involves significant radiation; not the standard investigation for acute scrotal pathology; inferior to Doppler for vascular assessment. 3. **LH and FSH levels** — Endocrine markers entirely unrelated to acute inflammation or vascular status; do not differentiate orchitis from torsion; not useful in acute scrotal emergencies. [cite:Harrison's Principles of Internal Medicine 21e; Bailey & Love's Short Practice of Surgery 27e]