EMBRYOLOGY

The testes originate from the gonadal ridge, derived from intermediate mesoderm. Initially located in the posterior abdominal wall, they descend through the inguinal canal into the scrotum guided by the gubernaculum testis, carrying layers of the abdominal wall that form the testicular coverings.

Fig 1: Abdominal wall derivatives forming the layers of the testis. Adapted from: Netter, F. H. (2019). Atlas de Anatomía Humana (7a ed.). Elsevier.

ULTRASOUND ANATOMY OF THE TESTES

The testes, suspended in the scrotum, are ovoid and obliquely oriented, with the left usually slightly lower. On ultrasound, adult testes measure 3–5 cm in length, 2–4 cm in width, ~3 cm anteroposteriorly, with an average volume of 15–20 mL.

• Grey-scale: adult testes show homogeneous, medium-level echotexture with smooth, well-defined margins.

Fig 2: Illustration of testicular anatomy.

Testicular coverings

Tunica albuginea:

Dense fibrous capsule that envelops the testicular parenchyma, providing structural support and protection.

• Grey-scale: appears as a thin, continuous echogenic line demarcating the testis. Intact tunica albuginea is a key imaging feature in the assessment of scrotal trauma.

Fig 3: Normal tunica albuginea. Longitudinal grayscale ultrasound of a normal testis demonstrates a thin echogenic line (arrow) surrounding the testis, corresponding to the tunica albuginea. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

 Tunica vaginalis

Serous membrane derived from the processus vaginalis that envelops the tunica albuginea, forming a closed peritoneal sac with visceral and parietal layers.

• Grey-scale: appears as a fine echogenic line; the layers are usually indistinguishable unless fluid, as in hydrocele, separates them.

 Intratesticular parenchyma

Seminiferous tubules:

Convoluted tubules continuing as straight tubules (tubuli recti) that converge toward the mediastinum testis and drain into the rete testis. Functional units of spermatogenesis.

Collecting duct system

Rete testis:

Network of channels connecting the tubuli recti to efferent ductules; appears on grey-scale ultrasound as small, clustered anechoic or hypoechoic tubular or cystic spaces without mass effect.

Efferent ductules: approximately 10–20 ductules originate from the rete testis and project toward the epididymal head, opening into the epididymal duct to form the ductus deferens

Fig 4: Illustration of the testicular parenchyma and collecting duct system.

 Mediastinum testis

Thickened region at the posterosuperior aspect of the testis.

• Grey-scale: appears as a linear or band-like hyperechoic structure along the longitudinal axis of the testis.

Fig 5: Normal mediastinum testis. Longitudinal grayscale ultrasound of a normal testis demonstrates a linear echogenic structure (arrow) along the long axis of the testis, corresponding to the mediastinum testis. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Vascularization of the testes 

Arterial supply:

Mainly from the testicular arteries (abdominal aorta), with contributions from the cremasteric artery and artery of the ductus deferens. Capsular arteries supply the tunica albuginea and branch centripetally and centrifugally to perfuse the parenchyma and seminiferous tubules.

Venous drainage:

Testicular veins form the pampiniform plexus; the right drains into the inferior vena cava, the left into the left renal vein. Scrotal veins drain via the inferior epigastric and deep pudendal veins at the deep inguinal ring.

Fig 6: Illustration of the arterial and venous drainage of the testes.

ULTRASOUND ANATOMY OF THE EPIDIDYMIS

Is a 6–7 cm tubular structure along the superolateral border of the testis, divided into three parts:

• Head: converging efferent ductules at the superior pole, extending posteriorly; heterogeneous, isoechoic/slightly hyperechoic to testicular parenchyma; 5–12 mm diameter.
• Body: along the posterior testicular margin; isoechoic to testicular parenchyma; 2–4 mm diameter.
• Tail: at the inferior pole, continues as the ductus deferens; echogenicity similar to testis; 2–5 mm diameter.

Fig 7: Illustration of the epididymis showing its head, body, and tail.

Fig 8: Normal epididymis. A, C. The epididymal head is visualised at the superior pole of the testis, demonstrating its characteristic pyramidal configuration and normal echogenicity. It measures approximately 6 × 8 mm. B. Colour Doppler imaging of the epididymis shows a normal vascular pattern. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

TESTICULAR AND EPIDIDYMAL APPENDAGES

Vestigial derivatives of the mesonephric (Wolffian) system, with no functional significance.

• Appendix of the epididymis: remnant at the epididymal head; typically isoechoic on grey-scale.
• Appendix of the testis (hydatid of Morgagni): ovoid structure at epididymal head/superior pole; isoechoic to slightly hypoechoic on ultrasound.
• Paradidymis: superior to the epididymal head.
• Aberrant inferior duct: blind-ending diverticulum from the epididymal tail

Fig 9: A. Illustration of the tunica vaginallis that shows its visceral and parietal layer. b. Illustration of appendages.

ANATOMY OF THE SCROTAL SAC

The scrotum is a cutaneous sac enclosing a testis, its epididymis, and the distal segment of the spermatic cord. Its layers include:

1. Skin: Thin, extensible, with transverse folds and a median raphe.
2. Dartos tunic: Smooth muscle forming the suspensory apparatus and scrotal septum; contributes to contraction, contour, and thermoregulation.
3. External spermatic fascia: from the external oblique aponeurosis.
4. Cremasteric fascia and muscle: from the internal oblique muscle; envelops the spermatic cord.
5. Internal spermatic fascia: Continuation of the transversalis fascia; forms the scrotal ligament (gubernaculum remnant).
6. Tunica vaginalis

Fig 10: Illustration of the scrotal layers surrounding the testes. Adapted from: Netter, F. H. (2019). Atlas de Anatomía Humana (7a ed.). Elsevier.

ANATOMY OF THE SPERMATIC CORD

Extends from the testis to the deep inguinal ring, enclosed by fascial layers from the anterior abdominal wall. It contains the ductus deferens, testicular and cremasteric arteries, pampiniform plexus, nerves, and lymphatics.

• Grey-scale: appears as a homogeneous tubular structure with parallel serpiginous channels representing the vessels and ductus deferens.

Fig 11: Normal spermatic cord. A. Grayscale ultrasound demonstrates the spermatic cord as an elongated tubular structure composed of multiple parallel, serpiginous hypoechoic elements. B–C. Colour Doppler imaging of the spermatic cord shows vascular structures with normal flow characteristics. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

ULTRASOUND ASSESSMENT OF THE ACUTE SCROTUM

Comprehensive evaluation includes grey-scale, colour, power, and spectral Doppler of the testes, epididymides, and scrotal contents.

Technique:

• Patient positioning: Supine, hips and knees flexed in external rotation; scrotum elevated on a folded towel; penis draped against the lower abdomen.
• Equipment: High-frequency linear transducer (7–14 MHz).
• Scanning planes: Longitudinal and transverse images of each testis; comparative transverse view at the midline for simultaneous evaluation.
• Parameters: Morphology, size, echogenicity, and vascular flow.

Initial assessment: Examine scrotal skin for symmetry, thickening, or edema. Start with the asymptomatic testis to optimize Doppler and compare findings with the contralateral side.

Fig 12: Normal testis. A. Longitudinal ultrasound view of the left testis. B. Transverse ultrasound view of the left testis. C. Comparative view of both testes demonstrates preserved morphology and normal dimensions, with smooth, well-defined contours and homogeneous echogenicity. No focal parenchymal lesions, areas of abnormal echotexture, or signs of testicular disruption are identified. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

DOPPLER EVALUATION

Assessment of testicular perfusion is a critical component in acute scrotal pain.

Technical optimization:

• Use the lowest velocity scale and low wall filter to detect slow flow.
• Maximise colour gain for sensitivity, avoiding excessive noise.

Flow characteristics:

• Intratesticular arteries: Low-resistance waveform with continuous diastolic flow; peak velocities 3–5 cm/s; RI 0.4–0.7.
• Cremasteric and deferential arteries: High-resistance patterns.
• Veins: Non-pulsatile, low-velocity continuous flow.
• Centripetal and transmediastinal arteries: Low-resistance patterns.

Fig 13: Normal arterial flow. Spectral Doppler of the testicular artery demonstrates a pulsatile waveform with low-resistance characteristics (resistive index [RI] 0.6), consistent with normal arterial perfusion. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

ACUTE SCROTUM

It is a urological emergency marked by sudden scrotal pain, swelling, and erythema, requiring prompt evaluation to prevent testicular loss. Etiologies include vascular, inflammatory, and traumatic disorders.

Vascular Disorders

Testicular torsion:

Twisting of the testis around the spermatic cord, leading to vascular compromise.

Types:

• Supravaginal or extravaginal (<5%): Common in neonates
• Intravaginal (≈95%): Associated with the “bell-clapper deformity

Time-sensitive management: testicular salvage is 100% if detorsion occurs within 6 hours, ~75% at 12 hours, and <50% between 12–24 hours.

Clinical features: Sudden pain radiating to the ipsilateral fossae, swelling, absent cremasteric reflex, negative Prehn’s sign, and horizontal orientation.

Grey-scale:

• Early (<6 h): normal echogenicity
• Acute (<6 h): testis enlargement, thickened scrotal coverings, reactive hydrocele, altered epididymal echogenicity or position.
• Late: reduced size, heterogeneous echotexture; hypoechoic areas

Doppler findings:

• Degree of torsion:
  • Complete (≥360°): Usually absent intratesticular flow.
  • Partial (<360°): Residual intratesticular flow may be detectable.
• Spectral Doppler: Increased resistive index (RI) and possible diastolic flow reversal, whirlpool sign of spermatic cord
• Late (>24 h): Periscrotal hyperaemia reflects inflammation.

Fig 14: Spermatic cord torsion with ischemic changes. A. Ultrasound demonstrates a well-defined lesion with regular margins and heterogeneous, predominantly hypoechoic echogenicity, showing the characteristic “whirlpool” configuration of the spermatic cord (pink arrow). A–B. Colour Doppler shows absence of vascular flow within the twisted cord (A) and the ipsilateral testis (B), consistent with ischemic changes due to torsion. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Fig 15: Incomplete testicular torsion. A. Ultrasound of the spermatic cord demonstrates crowding of the vessels with a spiral configuration, known as the “whirlpool sign.” B–C. Colour and spectral Doppler confirm vascular flow within the twisted cord, with preserved intratesticular perfusion in the ipsilateral testis, consistent with incomplete testicular torsion. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Appendiceal Torsion 

• Clinical features: focal upper-pole scrotal pain, firm non-mobile testis, “blue dot sign.”
• Grey-scale: well-defined ovoid extratesticular mass, hyperechoic with central hypoechoic area, reactive hydrocele, normal testis echotexture
• Doppler findings: avascular appendage, preserved testicular perfusion, perilesional hyperaemia.

Fig 16: Torsion of the left testicular appendix. A. Grayscale ultrasound identifies the left testicular appendix (red arrow) adjacent to the epididymal head, which shows an incidental simple epididymal cyst measuring 15 mm (asterisk). B–C. Colour Doppler ultrasound demonstrates absence of vascular flow within the testicular appendix (yellow arrow), consistent with torsion. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Testicular infarction

Grey-scale: 

• Acute phase: mild enlargement with preserved echogenicity.
• Advanced phase:
  • Ischaemic infarction: Focal, well-defined hypoechoic areas, with homogeneous echotexture.
  • Haemorrhagic infarction: Heterogeneous echotexture with hyperechoic foci.

Doppler findings:

• Absent/reduced intratesticular arterial flow, diastolic flow reversal
• Elevated resistive index (RI > 0.7).

Fig 17: Testicular ischaemia. A. Ultrasound of the left testis demonstrates normal size (estimated volume 10 cc) with heterogeneous echotexture, poor delineation of the epididymis, and diffuse inflammatory changes in the scrotal wall. B–C. Colour and power Doppler ultrasound shows absence of vascular flow within the left testis, consistent with ischaemia. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Inflammatory Disorders

Epididymo-orchitis

The most common cause of acute testicular pain in adults. 

• Clinical findings: tender enlarged testis, scrotal wall thickening, erythema, fever, positive Prehn’s sign, preserved cremasteric reflex.
• Grey-scale: Enlarged heterogeneous epididymis, testicular enlargement with heterogeneous hypoechogenicity, reactive hydrocele.
• Doppler: Diffuse hyperaemia, low-resistance arterial flow (RI: epididymis <0.7, testis <0.5).

Fig 18: Epididymo-orchitis. A–B. Colour Doppler ultrasound of the left testis (A) demonstrates increased vascularity compared with the normal contralateral testis (B). C. The left epididymal body shows marked hyperaemia. Findings are consistent with epididymo-orchitis. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Intratesticular Abscess

Complication of untreated epididymo-orchitis.

• Grey-scale: Round/ovoid intratesticular or intraepididymal lesions, poorly defined, heterogeneous.
• Doppler: Avascular lesion with peripheral hyperaemia

Fig 19: Epididymo-orchitis with abscess formation. A–B. Colour Doppler ultrasound of the left testis (B) demonstrates increased vascularity compared with the normal contralateral testis (A), consistent with orchitis. C. A well-defined, predominantly hypoechoic lesion with heterogeneous content and peripheral vascularity is observed in the left epididymal head, compatible with an epididymal abscess associated with epididymo-orchitis. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Pyocele:

Infected hydrocele post-inflammation or trauma.

• Grey-scale: Loculated fluid collection with echogenic debris, reactive hydrocele and scrotal wall thickening
• Doppler: Peripheral hyperaemia, absent internal flow.

 Fournier`s Gangrene

Necrotising fasciitis of genitalia and perineum, often in diabetics (~50%). Ultrasound is valuable for early evaluation of testicular viability.

• Grey-scale: Thickened, oedematous scrotal layers; echogenic foci and acoustic shadowing from gas.
• Doppler: Increased scrotal wall vascularity; preserved intratesticular flow.

Fig 20: Fournier’s gangrene. A 42-year-old man with type 2 diabetes mellitus. A–B. Ultrasound of the perineal soft tissues demonstrates a well-defined collection with irregular margins and heterogeneous, predominantly hypoechoic content, measuring 55 × 30 × 30 mm (volume: 25 mL), with posterior acoustic enhancement. C. Colour Doppler shows no internal vascularity, consistent with an abscess in the setting of Fournier’s gangrene. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Traumatic Disorders

Testicular trauma

Extratesticular lesions

• Hydrocele: anechoic fluid between tunica vaginalis layers; no Doppler flow.

Fig 21: Hydrocele. Grayscale ultrasound demonstrates a homogeneous anechoic fluid collection freely distributed within the scrotal sac (arrow), consistent with a simple hydrocele. No septations, echogenic debris, or solid components are identified. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

• Hematocele: heterogeneous fluid collection with echogenicity varying by chronicity; no internal flow. Large collections may reduce testicular perfusion by compression.

Fig 22: Haematocele. A 28-year-old man sustained blunt scrotal trauma in a motor vehicle accident. A. Ultrasound demonstrates discontinuity of the tunica albuginea (green arrow). B. Extrusion of testicular parenchyma is evident (asterisk). C–D. A heterogeneous fluid collection is present at the superior pole of the testis (blue arrows), consistent with a haematocele. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.

Intra-/extratesticular lesions

• Hematoma: well-defined avascular lesion; echogenic in the acute phase, hypoechoic in the chronic phase.

Intratesticular lesions

Integrity of the tunica albuginea determines management:

• Testicular fracture: Intact tunica albuginea, linear hypoechoic band, preserved peripheral flow.
• Testicular rupture: Disrupted tunica albuginea with parenchymal extrusion, heterogeneous echotexture, absent/reduced flow.

Fig 23: Testicular fracture with hematoma. B-mode ultrasound of the left testis demonstrates multiple lacerations in the superior pole (pink arrows), loss of contour of the inferior pole of the tunica albuginea (blue arrow), and an associated contained hematoma with fibrin deposits around the testis, consistent with testicular fracture. Case courtesy of the Department of Radiology, Fundación Cardioinfantil – LaCardio, Bogotá, Colombia.