Normal pregnancy or neoplasia?

A 24 year old woman, gravida 1 para 1, presented with a request for contraception four months after delivery of a healthy baby and a normal placenta. She did not breastfeed, was asymptomatic, and did not have a return of menses (postpartum amenorrhea). A urinary pregnancy test was performed, which was positive. Transvaginal ultrasonography showed no intrauterine or extrauterine pregnancy; the endometrium was regular, 3 mm thick; and the ovaries were normal. The concentration of serum human chorionic gonadotrophin (hCG) was 92 713 IU/l (normal <5 IU/l), and one week later it was 117 056 IU/l. She underwent dilatation and curettage, and the pathological specimen showed no decidua or trophoblastic tissue. Hysteroscopy and laparoscopy showed a normal uterine cavity, tubes, and ovaries. A thoraco-abdominal computed tomography scan and magnetic resonance imaging of the brain showed no abnormality.