Four cases with the association of occlusive arteriopathy and brain tumor are presented. A clinical analysis of these cases and cases reported in the literature revealed that occlusive arteriopathy at the base of the brain was often associated with a slowly growing basal tumor in children. Possible causes of occlusive arteriopathy in these cases were compression of the circle of Willis by a slowly growing basal tumor, secondary artial occlusive changes by radiation therapy for a basal tumor, or vasculopathy associated with neurocutaneous syndrome. Symptoms of sudden onset or episodic nature suggest the presence of occlusive arteriopathy rather than the mass effect of a tumor. Cerebral angiography is mandatory whenever computerized tomography (CT), performed to rule out recurrence of a basal tumor, shows an ischemic lesion with low-density areas without any evidence of mass effect of the tumor. Cerebral angiography is also necessary when a basal tumor is suspected in children, particularly in cases associated with neurocutaneous syndrome and a basal tumor. Care should be taken not to scarify the abnormal vascular network at the base of the brain at the time of operation, because it is considered to be functioning as collateral circulation. The potential hazards of radiotherapy to radiation-induced occlusive changes of the circle of Willis must be considered in treating a benign basal brain tumor in children. Even in adults, repeated large doses of irradiation could cause occlusive arteriopathy.

SynopsisI t has been found that tack values of pressure-sensitive adhesives are dependent on the surface energies for adherends. The parabolic curves with maxima are obtained from the plots of tack values versus crit,ical surface tensions for the substrates. The maximum occurs a t the region where the two surface tensions are almost similar. On the other hand, tack is measured as a dynamic value indicated as the force necessary to deform the adhesive mass. To explain why the tack values is controlled by the surface character of the adherend, a mechanism is proposed for adhesive bond breaking. Primarily, bonding occurs by wetting the surface with adhesive. When the adhesive bond breaks by external force, unbonding proceeds from the viscoelastic deformation of the adhesive mass around the wetted spots on t,hc surface of the adherend. A? the total area of wetted spots is determined by surface energy, the tack value is dependent on the crib ical surface tension of the adherend.

synopsisCritical surface tension values yc were measured for poly(n-alkyl methacrylates) and copolymers of stearyl methacrylate with methacrylonitrile. Surface tension values y~ of n-alkyl methacrylate increase with increasing side chain length: Y L = 23.2 dynes/cm for methyl methacrylate to 33.2 dynes/cm for stearyl methacrylate, but yo values of poly(n-alkyl methacrylate) decrease with increasing side chain length: yc = 36.3 dynes/cm for poly(methy1 methacrylate) to 20.8 dynes/cm for poly(steary1 methacrylate). The decrease in yc is attributed to a tighter packing of the alkyl chain with a greater concentration of the pendent --CHI group at the air/solid interface. Values of yc of copolymers hardly depended on the methacrylonitrile content in copolymers and did not satisfy the equation yc = Nlyc, + Nzycz proposed by Lee. The difference in yc values for casting, annealing, and quenching films of poly(steary1 methacrylate) and the surface structure of copolymers were discussed using electron microscopy and measurement of melting point, heat of melting, and yc.

synopsisThe relationship between wetting and pressure-sensitive adhesion was studied using an adhesive composed of poly(buty1 acrylate) and various adherends of different surface tension. The amount of adhesive deposit was determined quantitatively by tracer technique although the unbonding process was apparently observed as interface failure. The adhesive force and amount of deposit were both dependent on the critical surface tension of the adherends. Maximum tack value and contamination were observed with adherends whose critical surface tension was close to that but a little higher than that of the adhesive. The adhesive force obtained was lower than cohesive strength of adhesive. From this evidence, a mechanism for pressure-sensitive adhesion WBS discussed: the bond breaks in the addesive mass around the very minute spots where interaction is a t work between adhesive and adherend. Inasmuch as the density of the minute spots per unit area depends on the surface tension, the adhesive force also depends on the surface tension.

SynopsisThe surface structure of pressure-sensitive adhesives consisting of natural rubber and pentaerythritol ester of hydrogenated rosin has been studied using the single-stage replica method.The fibril structure with average diameter of about 50 A was observed on the surface of an adhesive consisting of 40 to 60 wt-% resin at which maximum tack is obtained. The role of fibrils in adhesion is discussed.