Epididymo- orchitis

Epididymitis or Epididymo orchitis is the commonest cause of acute painful scrotum in adolescent boys and adults [1]. The epididymis is the organ primarily involved and the infection ascends in a retrograde manner from the tail of the epididymis to head of epididymis and finally developing orchitis in 20% to 40% of cases due to direct spread. Involvement of the epididymis and Testis usually is diffuse but focal involvement may occur in both [1]. Bilateral orchitis without the involvement of epididymis is seen in patients with Mumps [2].
Causative agent in adolescent and men younger than 35 years are usually considered as Chlamydia trachomatis and Nisseria gonorrhoeae, whereas E.coli and Proteus mirabilis are frequently the infective organism for prepubertal boys and men older than 35 years of age [1]. Less common causes of epididymitis and orchitis include Granulomatous conditions such as Tuberculosis, Sarcoidosis and Brucellosis and chemical epidimytis in reflux of sterile urine, amiodarone therapy or prostate brachytherapy[3]. When epididymitis occur in children less than two years of age a predisposing condition is usually identified, such as imperforated anus, uretaral ectopia to seminal vesicles, bladder extrophy, and posterior urethral valves [4].
Patients with epididymo-orchitis usually present with acute scrotal pain and usually demonstrate Prehn sign, which may help differentiate it from torsion of the testis [5].
Complications of epididimo orchitis are abscess formation, pyocele, infarct, gangrene, infertility, atrophy and chronic pain [1,5].
In Grey scale ultrasound the normal adult testis has homogenous echotexture with intermediate echogenicity. Normal echogenicity of the head of the epididymis is Isoechoic to the testis whereas body and tail will be hypoechic [1].
Grey scale findings in epididymo-orchitis are non specific. In Epididymitis the epididymis will be enlarged and can be Hypoechoic or Hyperechoic with a reactive Hydrocele, pyocele and scrotal wall thickening.In orchitis testicular involvement may be diffuse or focal. Diffuse testicular involvement manifest as testicular enlargement, inhomogeneous echotexture and Hypoechoic or heterogenous echogenicity. When the involvement is focal there will be focal areas of heterogenous echogenicity and these lesions need to be followed to demonstrate a complete resolution because 10% of testicular tumors can also present with acute epidydimo- orchitis features [1].
In orchitis the edema in the testicular interstitium may give rise to the appearance described as striated testis in which, linear bands of varying appearances radiate within the testis perpendicular to its long axis in Grey scale sonography. [2].
Color or power Doppler imaging is the most helpful modality for diagnosing scrotal inflammation. Color Doppler sonography reliably demonstrates intraepididymal and intratesticular flow within the normal epididymis and testis. In epididymo orchitis there is epididymal or testicular hypervascularity when compared with the normal side[1].
The normal spectral waveform of testis and epididymis shows a low resistance pattern with RI index of testis measuring .5 and RI of epididymis measuring .7. Due to inflammation these indices will decrease and also the peak systolic velocity of intratesticular arteries increases. Another important clue will be the easily detectable venous flow which is difficult to find in healthy people [1].

In MR imaging the normal testis has homogenous and intermediate signal intensity on T1W sequences and high signal intensity on T2W images relative to skeletal muscle. The epididymis has similar signal intensity to Testis on T1W images but lower signal intensity on T2W sequences. In epididymo orchitis the testis and epididymis will have heterogenous low signal intensities on T2W images. The epididymis will be enlarged and hyperenhancing with contrast on T1W studies. The testis may show inhomogenous enhancement with hypoinense bands. [6].

Radioneucleotide studies using 99mTc Pertechnatate scan of testis can be used in testicular diseases. The findings will depend on the blood flow to the scrotum and its contents.The normal scrotum will show Iliac and Femoral arteries and faint but symmetrical tracer uptake in both testis and scrotum. In epididymo orchitis the dynamic phase will show increase activity in the spermatic cord vessels, and the delayed soft tissue images will show increase uptake of tracer within the scrotum. These findings are always compared with the clinical finds as the asymmetry of uptake can be due to decrease blood supply to the contralateral testis due to torsion. [7].