Ultrasound Case 082


A 43 year old male develops minor scrotal discomfort and an ultrasound is requested. He had a vasectomy 8 years previously, lives in Australia, has not traveled internationally for many years, and has no risk factors for sexually transmitted disease.

Image 2 and 3

Describe and interpret these scans

Image 1: Longitudinal view right testis.

The testis is seen in long section with the mediastinum testis the more echogenic linear structure in the centre. At the cranial end of the testis is the epididymal head. Here one can see rapid movement of what appear to be spermatozoa; you can see the head and tail. The head of a sperm measures 3 x 5µm and the tail 55µm, too small for ultrasound resolution.

The mysterious case of the Megasperm.

A Youtube search “sperm at 100x magnification” (perhaps avoid a work computer) reveals a remarkably similar appearance.

Ultrasound Case 082 02 Key to image 1 Megasperm
Key to image 1 Megasperm

Image 2 & 3: Just for a bit of fun, the last two clips are of a tadpole my daughter was raising, who later happily turned into a frog, and after is was established he was not going to turn into a prince, was released back into the swamp from whence he came…


Dancing megasperm

Similar cases have been described in the literature. The “filarial dance sign” looks a bit like this, with what are presumed to be microfilariae “dancing” in dilated and blocked lymphatics.

However others have noted this appearance in patients who do not have filariasis. The term “dancing megasperm” has been used to describe the appearance which tends to occur within epididymides that have been blocked by vasectomy, prior infection or trauma.

The exact cause of the sonographic appearance remains uncertain but hypotheses abound. It is likely spermatozoa rapid movements within an ideal acoustic medium causes the appearance, and part of their reflectivity may be due to turbulence within the surrounding fluid created by their movements. We can after all see moving contrast microbubbles at an average diameter of 2.5µm.

An alternative theory suggests the megasperm may represent clumps of agglutinated sperm within dilated ducts; we do see clumps of red cells in slow moving blood – spontaneous echo contrast. Authors raise the possibility of trapped sperm developing grossly enlarged heads; sounds scary but unlikely.

Finally they suggest the phenomenon of acoustic streaming accounts for the movement of the sperm within a dilated epididymis – but again I am not convinced – streaming should always occur away from the transducer and in this example at least some of the megasperm are definitely seen swimming towards it.

Anyway whatever the cause don’t be alarmed if you see megasperm. Consider the diagnosis or filariasis in endemic areas or in patients with risks, but otherwise just marvel at the mystery of ultrasound!



An Emergency physician based in Perth, Western Australia. Professionally my passion lies in integrating advanced diagnostic and procedural ultrasound into clinical assessment and management of the undifferentiated patient. Sharing hard fought knowledge with innovative educational techniques to ensure knowledge translation and dissemination is my goal. Family, wild coastlines, native forests, and tinkering in the shed fills the rest of my contented time. | SonoCPDUltrasound library | Top 100 | @thesonocave |

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