[Complications of craniofacial resection in anterior skull base tumors]

INTRODUCTION

The development of new radiographic techniques and the refinement of microsurgery and reconstructive surgery have been the responsible of the establishment of craniofacial resection (CFR) as the standard treatment of anterior skull base tumors. Overall complication rates varies from 24-56%, according to a review of recently published series.

OBJECTIVES

To describe the complications of CFR in a series of 41 patients and to analyze the management and final outcome.

MATERIAL AND METHODS

From 1990 to 2002, 41 patients underwent CFR for tumors involving the anterior cranial base. The extent of the tumor was always assessed with craniofacial CT-scan and MRI. The objective of the surgical treatment was to achieve "on block" removal of the tumor.

RESULTS

The average age was 57 years with a male preponderance (63.4%). Squamous cell carcinoma was the most frequent histopathological type of tumor. The tumors were localized in paranasal sinuses in 78% of the cases. Bifrontal craniotomy was performed in 85.4% and unilateral orbitofrontal craniotomy in 14.6% of the cases. The area of facial resection included: ethmoidectomy (60.9%), ethmoido-sphenoidectomy (24.3%), maxillectomy (39%) and orbital exenteration (14.6%). The reconstruction of the floor of the anterior cranial fossa was performed using pedicled pericranial flap (100%), local (34.1%) or microvascular free flaps (21.9%) and split calvarian graft (19.5%). 20 patients (48.7%) developed post-operative complications, CSF leaks (12.1%) and meningitis (7.3%) being the most frequent major complications. The mortality rate was 7.3%.

CONCLUSIONS

CFR has become the standard approach for anterior cranial base tumors. Despite its widespread application, the complication's rate ranges between 24-50% and the procedure carries a risk of significant morbidity and even mortality. Improvement of specific aspects of surgical technique and more refined reconstructive methods will decrease the number of complications.

Inertization of pyrite cinders and co-inertization with electric arc furnace flue dusts by pyroconsolidation at solid state

The viability of a pyroconsolidation process to render pyrite cinders inert and to co-inert pyrite cinders with a hazardous polymetallic residue such as electric arc furnace flue dusts (EAF) containing Pb, Cu, Zn, As, Cr, Ni and Mo were investigated. The effects of pyroconsolidation temperature (800-1200 degrees C), milling pyrite cinders and additions of both CaO and EAF on the resulting microstructure of the pellets were determined. The microstructural changes were then compared with the results of the standard leaching tests. Full inertization of pyrite cinders was achieved after milling to < 100 micron followed by a pelletization and pyroconsolidation process at a temperature of 1200 degrees C. This process also allows co-inertization of pyrite cinders with controlled additions of EAF (up to approximately to 10%). Following pyroconsolidation at 1200 degrees C, the metallic elements were inert components in the four main phases: traces of Cr in hematite; Cr, Cu, Zn and Ni in spinel-phase; traces of Cr and Zn in calcium ferrites; and Pb and traces of Cu, Zn and Ba in K-Ca-Al-Fe glassy silicate.

Domain coarsening of stripe patterns close to onset

We study domain coarsening of two-dimensional stripe patterns by numerically solving the Swift-Hohenberg model of Rayleigh-Bénard convection. Near the bifurcation threshold, the evolution of disordered configurations is dominated by grain-boundary motion through a background of largely immobile curved stripes. A numerical study of the distribution of local stripe curvatures, of the structure factor of the order parameter, and a finite size scaling analysis of the grain-boundary perimeter, suggest that the linear scale of the structure grows as a power law of time t(1/z), with z=3. We interpret theoretically the exponent z=3 from the law of grain-boundary motion.

Adiabatic elimination and reduced probability distribution functions in spatially extended systems with a fluctuating control parameter

We obtain the stationary probability distribution functions of the order parameter near onset for the one-dimensional real Ginzburg-Landau and Swift-Hohenberg equations with a fluctuating control parameter. A perturbative expansion in the intensity of the fluctuations leads to a hierarchy of Fokker-Planck equations for conditional probability distribution functions that relate components of the order parameter that evolve in different time scales. Successive integration leads to a Fokker-Planck equation for the slowest mode, which we solve analytically for the models studied. In all cases, the probability distribution function above onset is of the form P(A0) approximately A(delta)(0)e(-gammaA20), where A0 is the slow component of the order parameter and the values of delta and gamma depend explicitly on the intensity of the fluctuations. Knowledge of P(A0) allows the calculation of an effective bifurcation threshold and of the moments of A0 above threshold.

Grain-boundary motion in layered phases

We study the motion of a grain boundary that separates two sets of mutually perpendicular rolls in Rayleigh-Bénard convection above onset. The problem is treated either analytically from the corresponding amplitude equations, or numerically by solving the Swift-Hohenberg equation. We find that if the rolls are curved by a slow transversal modulation, a net translation of the boundary follows. We show analytically that although this motion is a nonlinear effect, it occurs in a time scale much shorter than that of the linear relaxation of the curved rolls. The total distance traveled by the boundary scales as epsilon(-1/2), where epsilon is the reduced Rayleigh number. We obtain analytical expressions for the relaxation rate of the modulation and for the time-dependent traveling velocity of the boundary, and especially their dependence on wave number. The results agree well with direct numerical solutions of the Swift-Hohenberg equation. We finally discuss the implications of our results on the coarsening rate of an ensemble of differently oriented domains in which grain-boundary motion through curved rolls is the dominant coarsening mechanism.

Amplitude equation and pattern selection in Faraday waves

A nonlinear theory of pattern selection in parametric surface waves (Faraday waves) is presented that is not restricted to small viscous dissipation. By using a multiple scale asymptotic expansion near threshold, a standing wave amplitude equation is derived from the governing equations. The amplitude equation is of gradient form, and the coefficients of the associated Lyapunov function are computed for regular patterns of various symmetries as a function of a viscous damping parameter gamma. For gamma approximately 1, the selected wave pattern comprises a single standing wave (stripe pattern). For gamma<<1, patterns of square symmetry are obtained in the capillary regime (large frequencies). At lower frequencies (the mixed gravity-capillary regime), a sequence of sixfold (hexagonal), eightfold, ...patterns are predicted. For even lower frequencies (gravity waves) a stripe pattern is again selected. Our predictions of the stability regions of the various patterns are in quantitative agreement with recent experiments conducted in large aspect ratio systems.