Adult primitive neuroectodermal tumor: proton MR spectroscopic findings with possible application for differential diagnosis. 
To assess the utility of proton magnetic resonance (MR) spectroscopy in the clinical categorization of primitive neuroectodermal tumors (PNETs) in adults.  In vivo proton MR spectroscopy was performed with an echo time of 136 msec in nine adults with PNET, and findings were retrospectively compared with spectroscopic findings of 22 meningiomas, 12 low-grade astrocytomas, eight anaplastic astrocytomas, 23 glioblastomas, and 21 metastases.  Nine resonances were semiquantitatively evaluated.  Statistical analysis was performed by using Kruskal-Wallis and Mann-Whitney U tests.  The Hochberg correction was applied for multiple comparisons.  Results were prospectively validated in 24 tumors of the six types included in the study.  The resonances of choice for identifying PNET were alanine (P <.001) and glutamate and glutamine (P =.004), both decreased with respect to meningioma; choline increased with respect to low-grade (P <.001) and anaplastic astrocytoma (P =.055); and lipids at 1.30 ppm decreased and choline and other trimethyl-amine-containing compounds increased with respect to glioblastoma (P <.001 and P =.004, respectively) and metastasis (P <.001 and P =.021, respectively).  We developed an algorithm for bilateral differential diagnosis between PNET and other tumor types.  The leave-one-out method was used to test the five possible differential situations in the retrospective data set, with the following results: PNET versus meningioma, 31/23/5/3 (number of total/correct/unclassifiable/incorrect procedures); PNET versus low-grade astrocytoma, 21/19/2/0; PNET versus anaplastic astrocytoma, 17/6/9/2; PNET versus glioblastoma, 32/28/2/2; and PNET versus metastasis, 30/27/1/2.  In total, 131 consecutive procedures produced 103 (79%) correct classifications and nine (7%) misclassifications.  Twenty-five (78%) of 32 possible procedures in the prospective independent test set produced correct classifications and four (13%) produced incorrect classifications.  In vivo proton MR spectroscopy provides useful information in clinical differentiation between PNETs and common brain tumors in adults.