Germ cell tumors (GCTs), a heterogeneous group of tumors that originate from the primordial germ cell (PGC), can present across a wide range of ages, sites, histologies, and clinical behaviors. GCTs can be malignant (eg, yolk sac tumors [YSTs], embryonal carcinomas, choriocarcinomas, and seminomas/germinomas) or benign (eg, teratomas and gonadoblastomas). Most children with malignant GCTs have a favorable prognosis following treatment with surgery and platinum-based chemotherapy; however, significant late effects of treatment may result.
There are 2 distinct peaks in the incidence of GCTs: 1 in young children aged 0 to 4 years, and another from the onset of puberty through young adulthood. Malignant germ cell tumors (MGCTs) represent 3% to 4% of all childhood cancers that occur before 15 years of age, making them about as common as childhood rhabdomyosarcomas or retinoblastomas. In adolescents between 15 and 19 years of age, MGCTs account for 14% of neoplasms, second only to Hodgkin lymphoma as the most common cancer in this age group. Overall, this equates to about 900 new cases of MGCTs in the United States each year in patients less than 20 years of age.
Cryptorchidism and Klinefelter syndrome are associated with an increased risk of testicular and mediastinal GCTs, respectively, in boys. Turner syndrome and androgen insensitivity syndrome are associated with an increased risk of ovarian GCTs in girls.
GCTs are thought to arise from PGCs. During normal embryo development, PGCs migrate from the yolk sac through the midline to the gonadal ridge. GCTs can occur at any point in this migration path, which explains why they may be found at either gonadal or extragonadal sites as well as near the midline of the body (eg, pineal and suprasellar regions of the brain, the mediastinum, the retroperitoneum, the ovaries or testes, or the sacrococcygeal spine).
The totipotent nature of PGCs explains the wide variety of possible GCT histologies. According to a model of GCT histogenesis, normal differentiation of PGCs leads to normal testicular or ovarian germ cells. Absent differentiation leads to the formation of seminomas (which are called seminomas when found in the testes, dysgerminomas when found in the ovaries, and germinomas when found in extragonadal sites or the central nervous system). Abnormal differentiation resembling early embryonic tissue leads to the formation of embryonal carcinomas, and further differentiation into mature somatic tissue leads to teratomas. Teratomas contain tissues from all 3 germ layers (endoderm, ectoderm, and mesoderm). PGCs can also abnormally differentiate into structures normally found outside the embryonic body: Recapitulation of the yolk sac leads to the development of YSTs and recapitulation of chorionic cells leads to choriocarcinomas. Tumors that contain multiple histologies are called mixed GCTs.
Figure 455-1 shows the 5 most common radiographic presentations of pediatric extracranial GCTs.