Proton Magnetic Resonance Spectroscopy Detection of High Lipid Levels and Low Apparent Diffusion Coefficient Is Characteristic of Germinomas

The differentiation of germinoma from other tumors by conventional magnetic resonance imaging (MRI) can be very difficult. The purpose of our study was to determine whether diffusion-weighted imaging (DWI) and single-voxel proton magnetic resonance spectroscopy (1H-MRS) could provide additional useful information for a definitive diagnosis of germinomas. Our hospital's Institutional Review Board approved this retrospective study. We reviewed imaging studies of 26 patients with histologically confirmed germinomas who were treated at our hospital between 2003 and 2016. We also studied 25 patients with pineal tumors, which included 14 nongerminomatous germ cell tumors (NGGCTs), 9 pineal parenchymal tumors (PPTs; including 3 pineocytomas, 4 PPTs of intermediate differentiation [PPTID], and 2 pineoblastomas) and 2 meningiomas. Patients underwent conventional MRI and advanced MRI, including DWI and/or 1H-MRS. The germinoma group comprised 24 males and 2 females, ranging in age from 9.1 to 37.7 years (average, 17.5 years; median, 14.6 years). The NGGCT group was all male, ranging in age from 5.4 to 51.9 years (mean, 20.1 years; median, 14.1 years). In the PPT group, patient age ranged from 4.5 to 64.7 years (mean, 29.9 years; median, 30.7 years). High lipid peaks detected on 1H-MRS were observed in 16 of 16 examined germinomas. In contrast, in the pineocytomas, PPTID, pineoblastomas, and meningiomas, lipid peaks were small or absent in 10 of 10 examined tumors. In the NGGCT group, high lipid peaks on 1H-MRS were observed in 11 of 12 examined tumors; however, no tumors showed high intensity on DWI, with all low to high mixed intensity. ADC was statistically lower in the germinoma group compared with the NGGCT group (P = 0.0002). Lower ADC values and high lipid peaks detected on 1H-MRS are characteristics of germinomas.