Whether bifocal
germinomas (BFGs) synchronously presenting within the pineal region and the hypothalamo-neurohypophyseal axis (HNA) are primary
germinomas of dual-origin remains to be elucidated. We analyzed MRI images and clinical features of 95 neurohypophyseal
germinomas and 21 BFG patients and developed a tentative definition of the BFGs. We found dual-primary BFGs (true BFGs) do exist. The fundamental difference between primary and metastatic HNA
germinomas was the direction of
tumor growth. For a true BFG, the primary HNA
tumor grew from the neurohypophysis toward the hypothalamus and almost invaded the whole pituitary stalk. For a false BFG (primary pineal
germinoma with HNA
metastasis), the metastatic HNA
tumor first appeared at the third ventricular floor (TVF), grew toward the neurohypophysis, but commonly did not invade the inferior pituitary stalk. Compared to false BFGs, true BFGs commonly had
diabetes insipidus as the first symptom, dysfunction of the anterior pituitary, no high-intensity MRI signal at the posterior pituitary, a larger extension of the HNA
tumor, and fewer numbers of remote lesions from cerebrospinal fluid seeding. Accordingly, 12.8% (12/96) of our
germinoma patients had true BFGs, and of these, 58.3% (7/12) were free of remote
metastases and warranted treatment with limited
radiotherapy. True BFGs with remote
metastases and all false BFGs should be treated with
craniospinal irradiation. We provided evidence for the diagnosis of true BFGs that is useful for
radiotherapy strategy, suggesting that the existence of
metastasis to other locations is not a diagnostic criterion for a true BFG.