On May 29, 2016, the patient – a woman of 30 years old, was accepted to the Sechenov University Clinical Hospital No. 1 with occasional pulling pain in left hypochondrium, nausea, and low-grade fever. The examination revealed a cyst in the spleen. The reaction of Kasoni and ELISA for Human Cystic echinococcosis was negative. The diagnosis of NSC was established. On June 13, 2016, the patient was admitted to the Department of Surgery for the surgery. A percutaneous puncture and MWA of the splenic cyst were performed under the control of ultrasound and X-ray fluoroscopy. At admission: The spleen is of 20 × 10 cm, with the lower pole being palpated in the area of the mesogastrium, of dense consistency, and painless during palpation. During examination: The blood and urine test results were within normal ranges, except for the erythrocyte sedimentation rate (ESR), which was 29 mm/h. Thrombocytopenia was not detected, with the values of platelets of 315 thousand/μl. Ultrasonography and computer tomography (CT) of abdominal organs: The spleen is of 20 × 10 cm, with clear, even contours, and homogeneous structure. In the upper pole of the spleen, a cyst is defined with clear smooth contours of 7.5 × 7.5 × 5 cm, uniform content, without septa or additional inclusions (). There were no signs of color Doppler mapping in the walls of the cyst. Conclusion: cyst of the spleen is not excluded. Previously, spleen surgery had not performed. During the surgery, a percutaneous puncture and MWA of the splenic cyst were performed under the control of ultrasound and X-ray fluoroscopy. Under intravenous anesthesia (Propofol 150 mg, Phentanylum 0.2 mg), an MWA catheter (MedWaves Incorporated, AveCure®) was inserted percutaneously into the cyst of the spleen's upper pole, accessing via the left mid-axillary line in the 9th intercostal space. In the epigastrium on the left anterior axillary line, a percutaneous puncture of the cyst of the upper pole of the spleen was made using a 18 gauge needle. After removal of the stylet, about 140 ml of a green turbid liquid was evacuated, which was sent for biological and cytological examination. Then, a radiopaque preparation (Urografin® 76% - 20 ml + NaCl 0.9% 120 ml) was injected into the cyst. During X-ray, a neoformation of clear, even contours, and of uniform contrast was determined at the left subphrenic region. No contrast in the abdominal cavity or the vessels of the spleen was detected. MWA of the cysts was performed using a MWA catheter placed in the cavity at the center of the cyst, with the frequency of 902–928 Hz delivered during 5 minutes. The installed 18 G needle allowed the evacuation of the residual high temperature liquid during the MWA. Then, both the catheter and needle were removed. Biological and cytological examination of the fluid obtained during the surgery revealed the presence of a cylindrical epithelium and the absence of abnormal cells. The postoperative period was uneventful, and no analgesics required. The abdominal ultrasound examination performed on day 2 post-surgery, did not reveal the residual cavity of the cyst in the region of the upper pole of the spleen. The patient was discharged under the supervision of a general practitioner, with recommendations to abstain of physical activity for 3 months, and to perform ultrasound examinations every six months. Four months post-surgery, on October 22, 2018, the patient underwent the control examination. There were no complaints reported. CT scan of the abdominal cavity in the region of the upper pole, has revealed the residual cavity of the cyst with dimensions of 3 × 1.7 × 1.9 cm (volume 4.8 ml) ().