Journal of Neuro-Oncology 59: 169–172, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. Clinical Study Failure of radiation therapy for brain involvement in Erdheim Chester disease Mario Mascalchi 1 , Patrizia Nencini 2 , Marco Nistri 1 , Cristina Sarti 2 and Riccardo Santoni 3 1 Radiodiagnostica and 3 Radioterapia, Dipartimento di Fisiopatologia Clinica, Universit` a di Firenze, Firenze, Italia; 2 Clinica Neurologica III, Universit` a di Firenze, Firenze, Italia Key words: Erdheim Chester disease, histiocytosis, proton MR spectroscopy, brain stem Summary A patient with suprasellar and brain stem involvement in Erdheim Chester disease (ECD) underwent magnetic resonance (MR) imaging and proton MR spectroscopy ( 1 H MRS) of the ventral pons before and 1, 4 and 18 months after external whole-brain (24Gy) radiotherapy. By revealing a decrease of the N -acetyl-aspartate/choline ratio in the pons, 1 H MR spectroscopy anticipated lesions growth on MR imaging. In line with the results in four patients reported in the literature, our observation indicates that external radiation therapy is not effective for intracranial involvement in ECD. Introduction Erdheim Chester disease (ECD) is a systemic form of histiocytosis [1]. Central nervous system (CNS) involvement in ECD is uncommon and its treatment is controversial [2–5]. We report a patient with brain involvement in ECD who underwent magnetic res- onance (MR) imaging and proton MR spectroscopy ( 1 H MRS) before and after external radiation therapy and reviewed the literature. Case report A 52-year-old man was admitted to hospital for pro- gressive gait unsteadiness. History included polydip- sya, polyuria and mood depression since 20 years. The neurological examination showed cerebellar ataxia and defective smooth pursuit eye movements. Blood and CSF laboratory analysis were normal. Cranial MR imaging showed mild thickening and signal change and contrast enhancement of the infundibulum. Further small areas of signal change and contrast enhance- ment were present in the pons, right middle cerebellar peduncle and right peridentate regions (Figure 1A). 1 H MRS was performed on a 1.5 T system using point resolved spectroscopy sequence (PRESS) with repetition time of 2000 msec and echo time of 272 and 136 msec. Water suppression was obtained with a selective excitation pulse. A volume of interest of 20 × 20 × 20 mm 3 was placed in the pons in order to include the widest area of signal change. Post-processing included zerofilling (2048 points), exponential broadening (-3 Hz), Gaussian filter (4 Hz), and Fourier transformation and phase cor- rection. The ratios of the areas corresponding to the resonance peaks at 2.02, 3.0 and 3.2 ppm assigned respectively to N -acetyl-aspartate (NAA), crea- tine/phosphocreatine (Cr) and choline (Cho) were com- puted and compared with those obtained in 10 healthy volunteers using the same sequence, voxel size, local- isation and post-processing. The patient’s initial spec- trum (Figure 1B) revealed low NAA/Cr (2.65) and NAA/Cho (0.93) ratios and normal Cho/Cr ratio (2.75) as compared to control values (NAA/Cr = 4.16 ±0.53; NAA/Cho = 1.61 ± 0.29; Cho/Cr = 2.64 ± 0.25) (Figure 1C and D). No abnormal peaks at 1.2–1.3 ppm consistent with lactate or lipids were observed. Skele- tal scintigraphy with 99 Tc diphosphonate showed increased uptake in the distal parts of the femurs which corresponded to sclerotic areas on X-ray films. Bone biopsy from the left distal femur revealed spindle shaped cells, multinucleated giant cells and spumous histiocytes. Immunohistochemical study of the foam cells allowed the diagnosis of ECD.