Cinzia Santucciu ^1* Ashkan Hajjafari ² Soheil Sadr ³ Scilla Mastrandrea ⁴ Carlo Rettaroli ⁵ Luca Simbula ⁶ Mariano Scaglione ⁶ Salvatore Masala ⁶ Angela Peruzzu ⁷ Giovanna Masala ⁷

• ¹ WOAH and National Reference Laboratory for Echinococcosis, Istituto Zooprofilattico Sperimentale della Sardegna "G. Pegreffi", Sassari, Italy
• ² Science and Research Branch, Islamic Azad University, Tehran, Tehran, Iran
• ³ Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran
• ⁴ U.O.C. Malattie Infettive, A.O.U., Sassari, Italy, SASSARI, Italy
• ⁵ S.C. Chirurgia Generale e d’Urgenza A.O.U. Sassari, SASSARI, Italy
• ⁶ U.O.C. di Radiologia, A.O.U., Sassari, SASSARI, Italy
• ⁷ WOAH and National Reference Laboratory for Echinococcosis, Istituto Zooprofilattico Sperimentale della Sardegna 'G. Pegreffi', Sassari, Italy

Cystic echinococcosis (CE) is a zoonotic disease caused by Echinococcus granulosus sensu lato, the metacestode of a tapeworm parasite of high medical importance. The infection of the parasite lead to the development of an echinococcal cysts and the spleen can rarely be an infected organ. A 46year-old woman born and resident in Sardinia, Italy, was referred to Echinococcosis outpatient clinic at the University Hospital of Sassari (Sardinia, Italy) for a pain in the left flank. She used to live in the countryside in contact with several animals, and for two years, she has been working in a family garden, growing vegetables as a hobby. Ultrasounds and X-ray were performed and evidenced a rounded formation in the upper third of the spleen while CT scan confirmed a parasitological cyst. Immunological exams on sera samples did not detect specific antibodies against Echinococcus spp.. Following surgical exportation, the whole spleen with the cystic lesion was delivered to the WOAH and National Reference Laboratory for Echinococcosis for further laboratory analyses. Moreover, the characteristics of the cyst fluid resulted dense and shiny; its observation under a light microscope by a 400× magnification presented the formation of rectangular crystals and aggregates attributable to cholesterol molecules. Subsequently, through parasitological investigation, molecular biology investigations confirmed Echinococcus granulosus sensu stricto G1. We describe cholesterol crystals in a splenic echinococcal cyst for the first time. There is no clear explanation for how cholesterol crystals are formed in this case, but we attribute to multifactorial causes, including atherosclerosis, chronic inflammation, parasite metabolism, and host responses.