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Biomedical subjects

D M Summers

Publications and source records attributed to D M Summers.

7 recordsLinked to original sources
PubMed2005

Third ventricular chordoid glioma: clinicopathological study of two cases with evidence for a poor clinical outcome despite low grade histological features.

Chordoid glioma of the third ventricle is a rare glial tumour whose precise histogenesis remains uncertain. We describe two cases that presented recently to our department and review the background literature. The neoplasm tends to occur in women and its clinical presentation is variable, resulting from acute hydrocephalus or impingement upon local structures. However, the radiological appearance is distinct, with an ovoid shape, hyperdensity and uniform contrast enhancement on computerized tomography and magnetic resonance imaging. Intraoperative smear diagnosis is difficult because of the lack of specific features, although the presence of metachromatic extracellular mucin may be useful. The characteristic histological appearance is that of cords and clusters of cohesive, oval-to-polygonal epithelioid cells with abundant eosinophilic cytoplasm and a mucinous background. There is often a mixed chronic inflammatory infiltrate with lymphocytes and plasma cells with Russell bodies. The main differentials for histological diagnosis include chordoid meningiomas, pilocytic astrocytomas and ependymomas. An immunohistochemical panel including antibodies to glial fibrillary acidic protein, CD 34, epithelial membrane antigen, pan cytokeratin, S100 and vimentin can be used to distinguish between these possibilities. Ultrastructurally the tumour cells have basal lamina and microvilli, reminiscent of ependymomas. The clinical outcome in our cases was poor because of the location of the lesion and its close relation to the hypothalamus. Limited follow-up after surgery with or without radiotherapy suggests that as-full-as-possible resection favours a better outcome, although surgery in this area carries significant operative risks.

Adult↗
PubMed2002

Energy and structure of inertial range turbulence deduced from an evolution of fluid impulse.

We explore numerically a very simple idea that may provide a material explanation for inertial range turbulence. We base a Lagrangian model of viscous incompressible fluid flow on an evolving ensemble of vortex doublet sheets. Initially these are randomly oriented and randomly distributed within a disk in two-dimensional space. These sheets are then actively transported (in two dimensions) according to the Oseledets equation of motion for fluid impulse. The mutual interaction of these sheets, and their diffusion, establishes a velocity fluctuation field. In a specific sense this evolution is self-affine, and we exploit this property to calculate standard statistical measures for the fluctuation field. We determine from this simple model the second-order structure function and the energy spectrum of inertial range turbulence.

Journal Article↗
PubMed1996

Numerical vorticity creation based on impulse conservation.

The problem of creating solenoidal vortex elements to satisfy no-slip boundary conditions in Lagrangian numerical vortex methods is solved through the use of impulse elements at walls and their subsequent conversion to vortex loops. The algorithm is not uniquely defined, due to the gauge freedom in the definition of impulse; the numerically optimal choice of gauge remains to be determined. Two different choices are discussed, and an application to flow past a sphere is sketched.

Journal Article↗