Mature cystic teratomas are benign tumors of the ovary composed of mature tissue representing at least two embryonic layers (ectoderm, mesoderm or endoderm) 1. They are commonly seen in young women, with mean age of 30 years 2.
Most are asymptomatic unless a complication develops, such as torsion, rupture or malignant transformation 2. In this particular case, the calcification mimicked a renal calculus on abdominal radiography but the orientation of the long axis was atypical, while the dentiform morphology suggested a teratoma. The mass caused mild hydroureter from extrinsic compression of the distal ureter. The presence of fat confirmed on CT clinched the diagnosis.