© 2008 by the American Institute of Ultrasound in Medicine
J Ultrasound Med 27:141-143 • 0278-4297
Color Doppler Sonography in Evaluation of SpermatocelesThe "Falling Snow" Sign
Akhilesh K. Sista, MD and
Roy A. Filly, MD
Department of Radiology, University of California, San Francisco, California USA.
Address correspondence to Roy A. Filly, MD, Department of Radiology, University of California, 505 Parnassus Avenue, L374, San Francisco, CA 94143-0628 USA. E-mail: roy.filly{at}radiology.ucsf.edu
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Abstract
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Objective. Doppler sonography is not commonly used in evaluation of cystic lesions with internal echoes. Here we report the use of the mechanical properties of color Doppler sonography to further characterize 3 spermatoceles. Methods. Three patients who came to University of California San Francisco Imaging Center with painless unilateral scrotal enlargement were evaluated with sonography and were found to have large spermatoceles. Color Doppler sonography was applied to these spermatoceles, and digital video clips were obtained as the color beam was instituted. Results. When color Doppler sonography was applied to each spermatocele, the internal echoes moved away from the transducer, resulting in an appearance similar to falling snow. Conclusions. The "falling snow" sign can be used to enhance the diagnosis of a spermatocele as well as to evaluate a superficial cystic lesion with echogenic fluid and internal microdebris that is difficult to distinguish from a solid mass.
Key Words: Doppler sonography • epididymal cyst • internal echoes • spermatocele
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Introduction
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Aspermatocele is a cyst arising from the epididymis that contains nonviable sperm. In contrast, epididymal cysts are simple cysts that do not contain sperm. Both lesions are benign and most often incidentally noted by a patient or detected during a physical examination.
Although occasionally found in other locations,1 most spermatoceles are located within the epididymal head and are thus palpated above the testicle. They are usually asymptomatic; however, if there is pain, swelling, discomfort, or aesthetic displeasure, open surgery is considered the standard of care, with aspiration and sclerotherapy being an alternative. The latter achieves an initial cure in approximately 60% of patients.2,3 Cyst aspiration alone is contraindicated mostly because of the widely accepted high likelihood of recurrence.2 There is also the theoretical but poorly characterized possibility of spilling locally irritating spermatozoa into the scrotal cavity.
Sonography is highly sensitive in the diagnosis of spermatoceles. The primary role of sonographic evaluation is to differentiate spermatoceles from neoplasms primarily but also from other non-neoplastic lesions such as hydroceles, varicoceles, and inguinal hernias. Although there is no real clinical importance in deciding whether a cystic lesion in the epididymis is a spermatocele or an epididymal cyst, this differentiation is sometimes difficult to make with sonography.4 However, if there are internal echoes within the cyst, the cyst is thought to be a spermatocele, with the internal echoes representing nonviable spermatozoa.
Here we describe a new sign, the "falling snow" sign, in the characterization of spermatoceles using color Doppler sonography. As well, this observation clearly discloses that the color Doppler beam is a more powerful mechanical force because it is capable of displacing small particles in fluid not displaced by the standard B-scan imaging beam. The technique may also be of value in the assessment of other superficial echogenic fluid collections that appear similar to solid masses. Finally, we wanted to illustrate this finding because of its uniqueness.
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Materials and Methods
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Three patients, patients A, B, and C, came to the University of California San Francisco Imaging Center for evaluation of scrotal swelling. Patient A was a 45-year-old man with painless scrotal swelling for several months. Patient B was a 52-year-old man with 1 month of painless scrotal enlargement. On the basis of a physical examination, the cause was thought to be a hydrocele. Patient C was a 38-year-old man who was told he had a spermatocele in the past but thought that his scrotum was enlarging.
Sonography of each scrotum was performed, and in each case, a large cyst in the epididymal head with internal echoes was found, consistent with a spermatocele. As is routine at our institution, color Doppler sonography was applied to these spermatoceles, and digital video clips were obtained as the color beam was instituted. It is important to note that given the sonographic diagnosis of a spermatocele and given the lack of symptoms, none of these patients underwent surgery.
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Results
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Videos 1–3 show cystic lesions with internal echoes that displace the ipsilateral testicle, consistent with spermatoceles. In each digital video clip, when color Doppler sonography is applied, the internal echoes move away from the transducer. The appearance is similar to that of falling snow.
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Discussion
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The typical sonographic appearance of a spermatocele is a unilocular or oligolocular thin-walled hypoechoic structure of variable size within the epididymal head that displaces the ipsilateral testis.5–7 Classically, it contains internal echoes. It should be noted that internal echoes within a cystic lesion in the epididymis may represent debris from another process, such as an infection or a hematoma. The combination of a history, a physical examination, and characteristic sonographic findings is usually sufficient to diagnose a spermatocele.
Here we describe a new sign, the falling snow sign, to enhance the presumptive diagnosis of a spermatocele. This sign can be defined as the movement of internal echoes, representing solid particles, within a superficial cystic mass away from the transducer after the application of power or color Doppler sonography. The physical principle resulting in the falling snow appearance that we describe is acoustic streaming. Although the phenomenon of acoustic streaming, or movement of fluid by ultrasonic waves, has been described extensively,8 we are not aware of any published report describing movement of solid particles within a fluid collection on Doppler sonography in the clinical setting. However, we did note a reference to movement of echoes from particulate matter in a color Doppler beam (M. Frates, MD, verbal communication, 2007). Power and color Doppler ultrasound emit a higher-intensity acoustic beam than the B-scan (B-mode) acoustic beam. Indeed, one must be cognizant that safe mechanical index levels are used when color or power Doppler acoustic beams are being transmitted into the patient, especially in pregnancy. Because the acoustic beam is of higher intensity, ultralight particles such as spermatozoa can be physically moved within a cystic cavity by power and color Doppler sound waves when they appear stationary on B-scan imaging (Videos 1–3).
Occasionally, internal echoes may be artifactual, and differentiating artifacts from true internal echoes may not be trivial. If there is a positive falling snow sign, then the internal echoes must be real. Additionally, this sign can be used to confirm that a superficial lesion represents an echogenic fluid collection and not a solid mass.
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Footnotes
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Received September 17, 2007, from the Department of Radiology, University of California, San Francisco, California USA. Revision requested September 24, 2007. Revised manuscript accepted for publication October 1, 2007.
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References
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- Davis RS. Intratesticular spermatocele. Urology 1998; 51(suppl):167–169.[Medline]
- Beiko DT, Morales A. Percutaneous aspiration and sclerotherapy for treatment of spermatoceles. J Urol 2001; 166:137–139.[Medline]
- Swartz MA, Morgan TM, Krieger JN. Complications of scrotal surgery for benign conditions. Urology 2007; 69:616–619.[Medline]
- Dogra VS, Gottlieb RH, Oka M, Rubens DJ. Sonography of the scrotum. Radiology 2003; 227:18–36.[Abstract/Free Full Text]
- Hamm B. Differential diagnosis of scrotal masses by ultrasound. Eur Radiol 1997; 7:668–679.[Medline]
- Hricak H, Filly RA. Sonography of the scrotum. Invest Radiol 1983; 18:112–121.[Medline]
- Rifkin MD, Kurtz AB, Goldberg BB. Epididymis examined by ultrasound: correlation with pathology. Radiology 1984; 151:187–190.[Abstract/Free Full Text]
- Clarke L, Edwards A, Graham E. Acoustic streaming: an in vitro study. Ultrasound Med Biol 2004; 30:559–562.[Medline]
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Abstract
Introduction