Large juvenile nasopharyngeal angiofibromas are a therapeutic challenge because of their relation to major vasculature and cranial nerves at the base of the skull, and their propensity for recurrence. A classification scheme based on the growth pattern of this tumor is proposed to help the surgeon choose a procedure to access this lesion. This report describes the results obtained with the surgical removal of large (class III and IV) nasopharyngeal angiofibromas through the infratemporal fossa approach. Fourteen patients were cured and one individual developed a recurrence which was totally removed at a second procedure. Surgical morbidity was minimal and there was no mortality. Radiation therapy was necessary in only one patient who had tumor infiltration of the cavernous sinus.

While holding vast potential, diffusion tensor imaging (DTI) with single-excitation protocols still faces serious challenges. Limited spatial resolution, susceptibility to magnetic field inhomogeneity, and low signal-to-noise ratio (SNR) may be considered the most prominent limitations. It is demonstrated that all of these shortcomings can be effectively mitigated by the transition to parallel imaging technology and high magnetic field strength. Using the sensitivity encoding (SENSE) technique at 3 T, brain DTI was performed in nine healthy volunteers. Despite enhanced field inhomogeneity, parallel acquisition permitted both controlling geometric distortions and enhancing spatial resolution up to 0.8 mm in-plane. Heightened SNR requirements were met in part by high base sensitivity at 3 T. Diffusion tensor imaging (1,2) is a promising noninvasive method for studying white matter structure of the human brain in vivo. Based on the concept of anisotropic water diffusion across tissue, the measurement of 3D diffusion properties, as described by a local diffusion tensor, allows the characterization of the axonal architecture of white matter networks. For that purpose, a 3D tracking of axonal projections, known as fiber tracking (3-7), is required. However, the low SNR and the limited spatial resolution (8 -10) of the method severely impair its application. A serious resolution limit stems from the strong link between voxel size and SNR, the latter being inherently low due to diffusion weighting. Only improving the SNR of the initial diffusion-weighted (DW) images will enable better spatial resolution. Therefore, the use of high magnetic fields and the related SNR gain could considerably enhance the performance of DTI and fiber tracking.The calculation of the local diffusion tensor requires a set of DW images, acquired with diffusion gradients applied in at least six noncollinear directions, plus a reference image without diffusion weighting. The sequence most commonly used for DTI is spin-echo single-shot EPI (SE-sshEPI). It allows for whole brain coverage in an acceptable scan time and is insensitive to bulk motion due to its speed. Critical shortcomings of sshEPI are image blurring due to T* 2 decay during the EPI readout interval and off-resonance effects, caused by the long EPI echo train (11,12). Both effects scale with the main magnetic field B 0 , making the transition to higher field strength challenging. At 3 T, signal alteration and geometric distortion due to static resonance offset effects, e.g., in the vicinity of airtissue interfaces, are a serious problem when using sshEPIbased protocols.Recently, the potential of parallel imaging techniques, such as simultaneous acquisition of spatial harmonics (SMASH) (13) and sensitivity encoding (SENSE) (14), has been demonstrated for sshEPI in general (15), as well as for diffusion-weighted MRI (DWI) (16 -18) and DTI (19) at 1.5 T. Parallel imaging techniques were shown to significantly reduce EPI-related artifacts as a result of shortening the echo train by facto...

The central neurocytoma has recently been added to the differential diagnosis of intraventricular tumors. Histopathologically, this tumor is characterized by a uniform neoplastic cell population with features of neuronal differentiation. Central neurocytomas occur in young adults, develop in the area of the foramen of Monro, and are usually associated with the septum pellucidum. Initial reports appeared to indicate that these tumors are benign lesions with a favorable postoperative prognosis. The authors present clinical and neuropathological findings in a series of eight patients with central neurocytoma. An anterior transcallosal microneurosurgical approach yielded good outcomes. Postoperative radiation therapy was restricted to two patients with a malignant variant of central neurocytoma and one patient with a recurrent tumor. Observations of anaplastic variants of this neoplasm in two cases and local tumor recurrences in three indicate that the biological behavior and postoperative prognosis of central neurocytoma may not always be as favorable as previously assumed.

Fuzzy logic clustering algorithms are a new class of processing strategies for functional MRI (fMRI). In this study, the ability of such methods to detect brain activation on application of a stimulus task is demonstrated. An optimization of the selected algorithm with regard to dtfferent parameters is proposed. These parameters include (a) those defining the preprocessing procedure of the data set; (b) the definition of the distance between two time courses, considered as p-dimensional vectors, where p is the number of sequential images in the fMRl data set; and (c) the number of clusters to be considered. Based on the assumption that such a clustering algorithm should cluster the pixel time courses according to their similarity and not their proximity (in terms of distance), cross-correlation-based distances are defined. A clear mathematical description of the algorithm is proposed, and its convergence is proven when similarity measures are used instead of conventional Euclidean distance. The differences between the membership function given by the algorithm and the probability are clearly exposed. The algorithm was tested on artificial data sets, as well as on data sets from six volunteers undergoing stimulation of the primary visual cortex. The fMRl maps provided by the fuzzy logic algorithm are compared to those achieved by the well established cross-correlation technique.

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Heavily T2-weighted spin echo sequences of the brain show age-dependent low signal intensity in many extrapyramidal nuclei. Although it has been suggested that this low intensity results from non-haem iron, the specific influence of non-haem iron on the T2 relaxation time has not been quantified and remains controversial. The T2 relaxation times of the globus pallidus and putamen were measured from MRI at 1.5T in 27 healthy patients, by using a mathematical model. They were then plotted as a function of age and compared to the curve of age-dependent iron concentration determined post mortem. The curves of T2 relaxation time in the basal ganglia are congruent with published curves of iron concentration, indicating a high probability that the changes in T2 relaxation times and the low signal in the basal ganglia result from the local, age-dependent iron deposition. Individual measurements of T2 relaxation time show less variation before than after 45 years of age, indicating the influence of a second, more individual factor.

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In four cases of giant intracranial aneurysm, CT demonstrated a hyperdense open-, or closed-ring structure at the periphery of the aneurysm. Surgery in two of the cases demonstrated that this peripheral hyperdensity represents fresh clot inside the wall of the thrombosed mass. An analogy is established between giant intracranial aneurysms, chronic subdural hematomas and growing encapsulated intracerebral hematomas. The common feature of the three entities is slow growth by recurrent hemorrhages into the lesion. It is proven that growth of chronic subdural hematomas and of growing encapsulated hematomas is related to recurrent hemorrhage from capillaries sprouting within the membrane of the lesion. The highly vascularized membranous wall of a giant intracranial aneurysm seems to behave like the membrane of a chronic subdural hematoma. It is suggested that the giant intracranial aneurysm grows by recurrent hemorrhage into its wall and behaves like growing encapsulated hematomas.