Spheno-orbital Lesions-A Major Review of Nonmeningioma Causes.

PURPOSE: To review the imaging features of the broad range of nonmeningioma lesions of the greater wing of the sphenoid (GWS) bone and adjacent orbit to assist clinicians in differentiating these lesions from each other and from the most common lesion of the GWS and adjacent orbit, meningioma. METHODS: We reviewed 32 cases of spheno-orbital lesions involving the GWS from our own practice, as well as 109 published cases (total 141), with emphasis on available imaging features on computerized tomography (CT) and MRI. Features that might assist in differentiating meningioma from its mimics were analyzed for each lesion, including the presence of an osteoblastic or hyperostotic response, bone erosion or osteolysis, homogeneous hypo- or hyperintensity on T2-weighted MRI, leptomeningeal involvement, and the absence of a "dural tail" on contrast-enhanced MRI. The clinical and imaging features were also briefly summarized for each diagnostic group. RESULTS: The largest diagnostic group was metastasis (67 cases, 47.5%). The most useful imaging features that helped differentiate meningioma from its mimics were the presence of bone erosion and the absence of a "dural tail." Other features were helpful in a small minority of cases only. Metastatic prostate cancer was the largest single group (21 cases), and 18 (85.7%) of these were osteoblastic and most closely mimicked meningioma. Prostate cancer patients were generally older than males with GWS meningioma. Almost all other (44/46, or 95.7%) metastatic lesions showed evidence of bone erosion. Almost half (30 of 61, 49.2%) of patients with metastasis presented without a known diagnosis of malignancy. Among children 16 years of age and less, Langerhans cell histiocytosis (10 cases), dermoid cyst (5), and Ewing's sarcoma (5) were the most common diagnoses. CONCLUSIONS: A combination of a careful history and both CT and MRI gives information, which can best guide the management of patients with spheno-orbital lesions. Metastatic prostate cancer to the GWS most closely mimics GWS meningioma but can in most cases be differentiated on clinical and imaging features. Older males with hyperostotic lesions of the GWS should be investigated for prostate cancer. Other metastatic lesions and primary tumors of the GWS, as well as benign and structural lesions can readily be differentiated from meningioma on clinical and imaging features.

1H-MRS evaluation of metabolism in Alzheimer's disease and vascular dementia.

Proton magnetic resonance spectroscopy (1H-MRS) allows major metabolites to be measured noninvasively in defined regions of the living brain, and can detect biochemical abnormalities where conventional structural imaging appears normal. MRS can be performed in 10 min as part of a clinical MRI examination. Biochemical abnormalities in Alzheimer's Disease (AD), vascular dementia (VaD) and other primary degenerative dementias have been investigated using MRS. Characteristic and consistent abnormalities in AD are decreased N-acetyl aspartate (NAA) and elevated myo-inositol (mI) in the mesial temporal and parieto-occipital cortex. These are thought to represent neuronal loss/dysfunction and gliosis, in anatomic distributions which reflect early pathological involvement and atrophy patterns in AD. Less consistent disturbances of glutamine and glutamate (Glx) and choline-containing compounds (Cho) have also been reported. Similar changes are seen in VaD; mostly in white matter, whereas in AD they predominate in cortical grey matter. The regional distribution of grey matter involvement may differ between AD and other degenerative dementias. Hence, both the nature and anatomic distribution of metabolite abnormalities contribute to diagnostic discrimination with MRS. NAA/mI ratios from short echo time spectra of the posterior cingulate region cortex discriminate reliably between AD subjects, normal individuals and those with VaD, and provides a useful clinical test, as an adjunct to structural imaging. Elevated mI is detected in mild cognitive impairment (MCI) and quantitative metabolite measures correlate with degrees of cognitive impairment in AD; these suggest a possible role for MRS in early diagnosis and for surrogate biochemical markers for monitoring disease progression and therapeutic response.