SINGLE-VOXEL PROTON MR SPECTROSCOPY OF NONNEOPLASTIC BRAIN-LESIONS SUGGESTIVE OF A NEOPLASM

BACKGROUND AND PURPOSE: MR spectroscopy is used to characterize bioche mical components of normal and abnormal brain tissue, We sought to eva luate common histologic findings in a diverse group of nonneoplastic d iseases in patients with in vivo MR spectroscopic profiles suggestive of a CNS neoplasm. METHODS: During a 2-year period, 241 patients with suspected neoplastic CNS lesions detected on MR images were studied wi th MR spectroscopy. Of these, five patients,vith a nonneoplastic diagn osis were identified retrospectively; a sixth patient without tissue d iagnosis was added. MR spectroscopic findings consistent with a neopla sm included elevated choline and decreased N-acetylaspartate and creat ine, with or without detectable mobile lipid and lactate peaks. RESULT S: The histologic specimens in all five patients for whom tissue diagn oses were available showed significant WBC infiltrates,,vith both inte rstitial and perivascular accumulations of lymphocytes, macrophages, h istiocytes, and (in one case) plasma cells. Reactive astrogliosis was also prominent in most tissue samples. This cellular immune response w as an integral component of the underlying disorder in these patients, including fulminant demyelination in two patients, human herpesvirus 6 encephalitis in one patient, organizing hematoma from a small arteri ovenous malformation in one patient, and inflammatory pseudotumor in o ne patient, Although no histologic data were available in the sixth pa tient, neoplasm was considered unlikely on the basis of ongoing clinic al and neuroradiologic improvement without specific therapy. CONCLUSIO N: Nonneoplastic disease processes in the CNS may elicit a reactive pr oliferation of cellular elements of the immune system and of glial tis sue that is associated with MR spectroscopic profiles indistinguishabl e from CNS neoplasms with current in vivo MR spectroscopic techniques. Such false-positive findings substantiate the need for histologic exa mination of tissue as the standard of reference for the diagnosis of i ntracranial mass lesions.