Extremely rare case of retroperitoneal “ancient” schwannoma with significant cystic change embedded in the psoas muscle

Schwannoma is a tumor derived from the Schwann cells in the periph-eral nerve system. Schwannoma located in the retroperitoneal cavity is rare and unusual. Less than 50 cases of schwannoma in the psoas muscle have been published. 1 In 1951, “ ancient schwannoma ” was termed by Ackerman and Taylor, a type of schwannoma with degenerative features acquired inside the tumor with increasing age, such as cystic necrosis or hemorrhage. 2 The almost completely cystic change in our case often leads to the misdiagnosis of malignancy. This 64-year-old woman presented with a palpable abdominal mass in the left lower quadrant. On abdominal examination, nothing was significant except a firm, immobile, non-tender globular mass in the suprapubic area,roughlythreecentimeterslefttotheumbilicus.Abdominalcomputed tomography a heterogeneous mass, about the size of 5 × 5.5 × 6 cm, adjacent to the aortic bifurcation and ureter (Figure 1A,B). There sign of vascular encasement of abdominal aorta, lessthan180degreesoftumorcontactofthevesselcircumference. Initial laparotomy Cystic