Scrotal Ultrasound:
Recent Advances Including Color Doppler

by James A. Machin, M.D.

The Acute Scrotum
The two chief diagnostic considerations in the acutely painful scrotum are torsion and epididymitis. Differentiation of the two is critical, since delayed diagnosis of torsion results in a nonviable testis. Surgery is most effective when performed within 6 hours of onset of symptoms.

Testicular Torsion
Torsion is most common in adolescents, but can be found at any age. The predisposing condition is the presence of a short mesenteric attachment of the testis, the so call "bell clapper" deformity, allowing excessive mobility of the testis. This form of torsion is intravaginal. Treatment is immediate orchiopexy of the affected testis. The contralateral testis is also explored, since the abnormality is bilaterla in 50-80% of patients. Patients status post orchiopexy for undescended testis have a tenfold increased incidence of torsion. Extravaginal torsion is most common in newborns.

Prior to the development of color Doppler, the nuclear medicine flow studies were the procedures of choice in the diagnosis of testicular torsion. More recently, color Doppler has been proven superior, due to improved spatial resolution and better anatomic detail, and improved sensitivity to slow flow.

The keys to Doppler diagnosis of torsion are: high frequency (7 mHz or greater) probes with maximized doppler sensitivity settings, low filter and pulse repetition settings, and a well trained operator. The opposite testis should be examined to determine if flow is detectable prior to making the diagnosis of torsion. In addition, if cessation of flow due to torsion is incomplete, arterial signals may be present, but will have a high resistance doppler signature. For this reason, gray scale doppler should be obtained.

Epididymitis and Orchitis
Epididymitis is the most common cause of acute scrotal pain in post pubescent men. It is usually caused by lower urinary tract infection. The epididymis is swollen and tender (which is also the case in torsion). On ultrasound, the epididymitis is enlarged and hyperemic, with the arterial waveform changing from its normal triphasic to a low resistance monophasic pattern.

With orchitis, the testis becomes involved, resulting initially in a swollen, hyperemic, hypoechoic testis. If the disease progresses, areas of necrosis or abscess may develop. Due to the confining nature of the tunica albuginea, ischemia may result from increased intratesticular pressure, with findings indistinguishable from chronic torsion.

Trauma
Traumatic rupture is an unusual occurance, with early diagnosis key to the survival of the testis. The fracture plane is rarely seen, however, the ruptured testis usually has an irregular contour. Surgery is needed within 72 hours to maintain viability of the testis.

Testicular Masses

Germ Cell Tumors
Germ cell tumors are most common in young men in the third and fourth decades. Genetic factors and cryptorchidism are predisposing factors, however, the magnitude of the risk associated with cryptorchidism is unclear.

Seminoma
Seminoma is the most common single cell type of germ cell tumors, accounting for about 40% of all germ cell tumors. Seminoma is very sensitive to radiation, with cure rates of 80 - 95%, depending on stage at time of discovery.

Embryonal Cell Carcinoma
The second most common cell type is usally found in mixed cell tumors, usually with yolk sac and/or teratoma. This tumor is usually seen in a slightly younger age group. They are more aggressive than seminoma, with 5 year survival rates of 25% to 35%.

Teratomas
Teratomas are usually well differentiated and have a favorable prognosis, with 5 year survival rates of approximately 70%.

Choriocarcinoma
This is the rarest type of germ cell tumor and is found almost exclusively as a component of mixed tumors.

Mixed Tumors
Mixed tumors account for approximately the same number of germ cell tumors as seminoma, with combined teratoma and embryonal cell carcinoma (formerly teratocarcinoma) most common. Cystic change is common in these tumors.

Ultrasound Of Testicular Tumors
The ultrasound appearance of germ cell tumors is nonspecific. There may be songle or multiple masses, which are uaully hypoechoic relative to normal testis. Cystic change or hyperechoic areas of hemorrhage may be present. Of particular importance is the presence of 2 - 5 mm calcifications which have been termed macrocalcifications. These may be seen either in the presence or absence of a mass. The presence of macrocalcification should be assumed to represent germ cell tumor, prompting testing for tumor markers and search for metastases.

Ultrasound is indicated for the evaluation of clinically occult masses in patients with metastatic GCT. In addition, ultrasound is indicated in patients with palpable scrotal mass of uncertain origin, or in patients with prior contralateral orchiectomy for GCT with elevated tumor markers and no evidence of tumor elsewhere.

Lymphoma and Leukemia
Involvement of the testis with lymphoma is usually unilateral but may be bilateral. In leukemia, the testis is frequently involved in patients during chemotherapy, felt to be due to the relative impermeance of the testis to chemotherapeutic agents.

Miscellaneous Masses
Sertoli and Leydig cell tumors are generally benign stromal origin tumors, accounting for approximately 5% of all testicular tumors. They may produce excessive estrogen or testosterone, resulting in precocious virilization, or feminization.

Cryptorchidism
Cryptorchidism is relatively common, with approximately 3 - 4% of term infants, with 10 - 25% being bilateral. Approximately 30% of premature infants are affected. Approximately 80% of cryptorchid testis arre found in the inguinal canal, with 4 - 10% agenesis, and 10% intraabdominal. The intraabdominal testis can be found as high as the renal pedicle. There is a significant incidence of later development of germ cell tumor in the undescended testis.

Miscellaneous Conditions
Hydroceles are commonly encountered fluid collections between the layers of the tunica vaginalis. A small amount of fluid is a normal finding.

Hernias are not uncommonly encountered. Ultrasound can be used to differentiate hernia from other masses, and evaluate for the presence of bowel in the hernia sac.

Calcifications of the tunica vaginalis are common, and of no significance. Testicular microlithiasis is an uncommon condition with innumerable minute calcifications 1 - 3 mm in diameter, which are usually diffuse and symmetric, but may be more focal and asymmetric. The condition can be seen in cryptorchidism, Down's syndrome, pulmonary alveolar microlithiasis, intratubular germ cell neoplasia (IGN), or can be an isolated finding. It may be associated with subnormal fertility. A recent multicenter study demonstrated a 40% incidence of coexistent germ cell tumor.

Mediastinal Cysts representing dilated rete testis can be seen, usually with coexistent epididymal abnormalities (cysts, spermatocele or epididymitis).

References

"Cystic Testicular Mass Caused by Dilated Rete Testis: Sonographic Findings in 31 Cases", Brown, DL, et. al. AJR 158: 1257-1259, June 1992

"The Scrotum", Diagnostic Ultrasound, Mosby Yearbook Publishers, 1991. Chapter 26. Stewart, R, and Carroll, BA.

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"Color Doppler Ultrasound of the Scrotum", Horstman, WG, et. al. RadioGraphics 1991;11:941-957

"Color Doppler Sonography of the Scrotum", Ralls, PW, et. al. Seminars in Ultrasound, CT and MR, 1991;12:109-114

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"Ultrasound of the Nonacute Scrotum", Doherty FJ. Seminars in Ultrasound, CT, and MR 1991;12:131-156.

"Neoplasms of the Bladder, Prostate and Testis", Heiken JP, Forman HP, Brown JJ. Radiologic Clinics of North America, 1994;32:81-98.

"Testicular Microlithiasis: Sonographic and Clinical Features", Janzen DL, et. al. AJR 1992;158:1057-1060.

"Testicular Germ Cell Tumors: Review of Contemporary Evaluation and Management", Steinfeld AD. Radiology 1990;175:603-606.

"Testicular Microlithiasis: Imaging Appearance and Pathologic Correlation", Backus ML, Mack LA, Middleton WD, King BF, Winter III TC, True LD. Radiology 1994;192:781-785.