Hrev_master Emergency Care Journal 2025 volume 21:14431 A worrying dance in the subcutaneous adipose tissue Massimo Barakat,1 Matteo Marcucci2 1Pediatric and Adult CardioThoracic and Vascular, Oncohematologic and Emergency Radiology Unit, IRCCS Azienda Ospedaliero- Universitaria di Bologna, Bologna, Italy; 2U.O.C. di Radiodiagnostica, Ospedale Generale Provinciale di Macerata, Macerata, Italy Question Given the patient’s history and US result, which is the most likely diagnosis? 1. Metastasis from breast cancer 2. Subcutaneous dirofilariasis 3. Hidradenitis suppurativa 4. Infected sebaceous cyst Answer Subcutaneous dirofilariasis is the correct answer. Dirofilariasis is a vector-borne parasitic disease caused by filarioid nematodes of the genus Dirofilaria, transmitted by various mosquito species of the family Culicidae (Aedes, Anopheles, Culex, Ochlerotatus, Coquillettidia or Mansonia).1 These nema- todes naturally infect dogs, cats and/or some wild carnivores, and humans have long been considered accidental “dead-end” hosts, because these parasites do not usually reach sexual maturity in human tissues.1 Based on its location, human dirofilariasis is clas- sified into three forms: ocular,2 subcutaneous and pulmonary.3 In most cases the presentation of Subcutaneous Dirofilariasis (SD) is highly nonspecific: an accidentally palpable nodule.4,5 Although the definitive diagnosis is histopathological,1 US can rise the sus- picion of SD by detecting worm-like structures resembling parallel hyperechoic lines within a cystic lesion (as shown in Figure 1)1 and worm movements in live ones (the so-called “filarial dance sign”, first described in 1994 and shown in Video 1).1,6 Surgical excision of the lesion is the definitive treatment for SD.1,7 Figure 1. Ultrasonography. A 37-year-old woman presented to the emergency department with a mild painful swelling in the anterior abdominal wall at the right iliac fossa; there was no associated itch- ing or rash. Five months earlier she underwent right mastectomy for infiltrating ductal carcinoma, which was still under treatment with chemotherapy (doxorubicin, cyclophosphamide, paclitaxel, per- tuzumab and trastuzumab). Her vital signs and laboratory tests were normal. Ultrasonography (US) showed a 8 x 5 mm sized anechoic lesion with multiple internal thin structures, which presented paral- lel echogenic borders and anechoic centers, in the subcutaneous adi- pose tissue (Figure 1, red arrow). These structures exhibited wrig- gling motion during real-time imaging (Video 1). Correspondence: Massimo Barakat, Pediatric and Adult CardioThoracic and Vascular, Oncohematologic and Emergency Radiology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Via Pietro Albertoni n° 15, Bologna, Italy. Tel.: +39.0512144327 E-mail: massimo.barakat@gmail.com Key words: dirofilariasis, filariasis, nematode, parasites, zoonosis, subcutaneous tissue, ultrasonography, filarial dance sign. Contributions: MB conceptualized and wrote the manuscript. MM performed ultrasonography and collected clinical data and icono- graphic material. All Authors approved the final version of the man- uscript. Conflicts of interest: the Authors declares no conflict of interest. Funding: none. Availability of data and materials: all data and materials are included in this published article. Ethics approval and consent to participate: as this was a descriptive case report and data were collected without patient identifiers, ethics approval was not required under our hospital’s Institutional Review Board guidelines. Informed consent: the patient provided consent for access to medical records at the time of admission. Received: 11 September 2025. Accepted: 22 September 2025. Early view: 10 October 2025. This work is licensed under a Creative Commons Attribution 4.0 License (by-nc 4.0). ©Copyright: the Author(s), 2025 Licensee PAGEPress, Italy Emergency Care Journal 2025; 21:14431 doi:10.4081/ecj.2025.14431 Publisher's note: all claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher. [page 60] [Emergency Care Journal 2025; 21:14431] Images in emergency [Emergency Care Journal 2025; 21:14431] [page 61] In our case the patient had no history of contact with pets or recent travel, so she was probably infected by an outdoor mosquito bite of which she had no memory at the time of admission. The lesion was excised in toto under local anesthesia. Histopathologic exam- ination showed a cyst without epithelial lining, bordered by a rim of fibroblasts and lympho-plasmacellular infiltrates, including a worm-like structure consistent with Dirofilaria. No medical thera- py was undertaken, because the parasite was completely removed with surgery. Full recovery was achieved, and the patient was dis- charged after one day of hospitalization. In the last years there has been an increase in cases of human diro- filariasis in Europe due to global climate change and international movement of people, so emergency physicians should always con- sider this condition in the differential diagnosis of subcutaneous nodules.8 References 1. Momčilović S, Jovanović A, Gasser RB. Human dirofilariasis - A potentially significant nematode zoonosis in an era of cli- mate change. J Infect 2025;90:106460. 2. Poggiali E, Dacrema A, Vercelli A. Doctor, something is stuck in my eye! Emerg Care J 2025; https://doi.org/10.4081 /ecj.2025.14036. 3. Simón F, Diosdado A, Siles-Lucas M, et al J. Human dirofilar- iosis in the 21st century: A scoping review of clinical cases reported in the literature. Transbound Emerg Dis 2022;69:2424-39. 4. Harizanov RN, Jordanova DP, Bikov IS. Some aspects of the epidemiology, clinical manifestations, and diagnosis of human dirofilariasis caused by Dirofilaria repens. Parasitol Res 2014;113:1571–9. 5. Momčilović S, Gabrielli S, Đenić N, et al. New cases of human dirofilariosis on the Balkan Peninsula – "Masked intruders" uncovered by a surgeon. Parasitol Int 2022;86:102482. 6. Amaral F, Dreyer G, Figueredo-Silva J, et al. Live adult worms detected by ultrasonography in human Bancroftian filariasis. Am J Trop Med Hyg 1994;50:753–7. 7. Joseph M, Krishna MM, Vijayan A. Human Subcutaneous Dirofilariasis. Cureus 2023;15:e35879. 8. Capelli G, Genchi C, Baneth G, et al. Recent advances on Dirofilaria repens in dogs and humans in Europe. Parasit Vectors 2018;11:663. Online supplementary materials Video 1. Ultrasonography.