Testicular and scrotal ultrasound is the primary modality for imaging most of the male reproductive system. It is relatively quick, relatively inexpensive, can be correlated quickly with the patient's signs and symptoms, and, most importantly, does not employ ionizing radiation.
MRI is occasionally used for problem solving if the diagnosis is unclear on ultrasound. CT is only rarely needed, and is avoided because of its ionizing radiation. Nuclear medicine studies (e.g. Tc99m-pertechnetate) have also fallen out of favor because of their ionizing radiation.
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Normal ultrasound anatomy
Testis
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homogeneous echogenicity
a prepubertal testis has a slightly decreased echogenicity relative to an adult
mildly coarse echotexture
adult diameter measures between 3-5 cm, with a volume of ~20 mL
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the tunica (vaginalis/albuginea) appears as an echogenic outline of the testis:
the tunica invaginates to form the linear echogenic testicular mediastinum (a.k.a. mediastinum testis)
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the rete testis can be identified in ~20% of patients
hypoechoic region near the mediastinum
more noticeable if dilated
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appendix testis: attached to upper pole of testis, near the epididymis
not usually seen unless torsion is present or outlined by hydrocele
spectral Doppler: the testis demonstrates a low-resistance arterial waveform
Epididymis
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epididymal head: round or oblong structure located near the superior pole of the testis
isoechoic or mildly hyperechoic relative to the testis
measures 5-12 mm
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epididymal body: extends down the posterior aspect of the testis
measures 2-4 mm
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epididymal tail: curved structure at the inferior pole of the testis and becomes the proximal ductus deferens
measures 2-5 mm
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appendix epididymis: attached at the epididymal head
not normally seen unless torsion present or outlined by hydrocele
spectral Doppler: epididymis demonstrates a low-resistance arterial waveform
Scrotum
normal scrotal skin thickness varies between 2-8 mm 5
Technique
A high-frequency transducer (9-15 MHz) is usually used for evaluation of the testes and scrotum, except in certain circumstances (e.g. massive hydrocele), when a lower MHz transducer might be necessary.
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patient is supine
patient may be upright when looking for an inguinal hernia
scrotum is supported on a towel laid over the thighs
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testes should be evaluated in both long and short axes
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if a scrotal mass is found, one of the primary roles of ultrasound is to determine if it is intratesticular or extratesticular
intratesticular mass: generally malignant
extratesticular mass: 3-6% malignant
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color and spectral Doppler parameters should be set for low flow
low wall filter and low pulse repetition frequency
power Doppler may be necessary to prove testicular torsion
important: both a short axis greyscale and a color Doppler image should be obtained, in which both testes are imaged side-by-side ("buddy shot" or "sunglasses view"), to compare the size, relative echogenicity and blood flow
scrotum should be examined for extratesticular masses or processes
Tips:
use enough gel to eliminate gas trapped in the skin folds of the scrotum
do not change the setting when moving from one testis to the other
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