Lymphatic filariasis of the scrotum
A 26-year-old man arrived at the outpatient clinic with a 1-month history of scrotal soreness and edema, as well as low-grade fevers. His internal temperature was 37.5°C. On inspection, the right side of the scrotum was painful and swollen. According to laboratory results, the absolute eosinophil count was 1180 per cubic millimetre (reference value, 500). A scrotal ultrasonography revealed anechoic tubular channels (arrow) around the right testis (asterisk) and epididymal head. On color-flow Doppler imaging, there was no colour flow in the channels. Within one of the channels, echogenic, linear shapes could be seen moving.
A feature in lymphatic filariasis described as the “filarial dance sign.”
Lymphatic filariasis is a parasitic infection caused by nematodes carried by mosquitos. The dance sign shows the undulations of living worms that have moved into lymphatic systems, producing dilatation and channel malfunction. Similarly, light microscopy was used to identify live microfilariae of the species Wuchereria bancrofti after an ultrasound-guided aspiration of scrotal lymphatic fluid. A peripheral-blood smear revealed the microbes as well. The patient’s symptoms improved after three weeks of oral diethylcarbamazine, and the motile microfilariae were no longer visible on ultrasonography.
The filarial dance sign refers to microfilariae (e.g., W. bancrofti) whirling in dilated lymphatic channels. It is recognised as a defining feature of scrotal filariasis.
The absence of colour flow on colour Doppler investigation identifies the dilated channels, and the microfilariae as curvilinear echogenic undulating structures inside it. 5-6 microfilariae are typically detected per channel.
It is crucial to highlight that while this symptom is highly suggestive of filarial infection in the correct clinical setting, it is not pathognomonic. It has also been seen on scrotal ultrasound in people who have no history of filariae exposure but have clinically significant epididymal blockage. Indeed, majority of the affected individuals in a large published series from the UK, a country where filariasis is not widespread, had undergone a vasectomy.
Histopathological findings
Histopathologically, the randomly moving echogenicities in one of these reported cases were composed of numerous macrophages admixed with partially-broken down clumped together spermatozoa; nevertheless, other reasons for these appearances have also been proposed.
Amaral and colleagues reported the FDS for the first time in 1994. Moreover, they reported the motions of live adult filarial worms in lymphatic arteries as linear echogenic structures with persistent, unpredictable, practically constant whirling movements on HRUS. This sign is so distinct that once found on HRUS, it cannot be misinterpreted.
However, the presence of highly comparable filariasis sonographic findings in nonendemic areas and in males with negative filariasis blood tests suggests that this indication is not limited to Filaria infection.
Literature findings
In nonendemic areas, the majority of patients had a history of vasectomy or, less frequently, bacterial epididymitis. The presence of a process generating spermatic duct constriction seems to be the common feature of males with “filarial dance” in both endemic and nonendemic places. A post-mortem examination of the epididymides in men with spermatic duct obstruction revealed dilated tubules with massive clusters of agglutinated spermatozoa.
In 22 carriers (61%), the “filaria dance sign (FDS)” indicated the presence of adult worms. Adult worms preferred the intrascrotal juxtatesticular lymphatic vessels in “nests” along the lymphatic vessels of the epididymis, spermatic cord, and paratesticular area. The number of nests ranged from one to four.
If a patient has FDS in an endemic area and microfilaria is found in a peripheral blood smear, it indicates active filariasis infection. If the patient has FDS in a non-endemic location, it indicates epididymal blockage, and microfilaria are not seen on the peripheral blood film. In endemic areas, the floating twisted dancing echogenic bodies are adult filiaria worms, but in non-endemic areas, they are moving, hyperechoic particles within cystic dilatations of an enlarged epididymis in a patient with spermatic duct obstruction. The particles are most likely agglutinated spermatozoa clusters.
FDS in endemic locations is caused by lymphatic blockage, and microfilaria in blood smears is diagnostic for Scrotal Filariasis. It has also been shown in patients with epididymal blockage.
Source: NEJM
