Effect of stenosis on wall motion. A possible mechanism of stroke and transient ischemic attack.

The mechanism by which atherosclerotic plaque causes stroke and transient ischemic attack is not fully understood. One possibility is that the plaque stenosis may set up hemodynamic conditions causing local arterial wall collapse. Arterial wall collapse may, in turn, affect the integrity of the plaque. This study was designed to define the effects of stenosis on the production of arterial wall collapse using a latex tube model. Stenoses ranging up to 81% by diameter were tested in a Starling resistor chamber under pulsatile pressure conditions upstream of the tube. Increasing the degree of stenosis progressively decreased the external pressure necessary to produce collapse, from 37 mm Hg with the 0% stenosis to 24 mm Hg for the 81% stenosis. The stenoses greater than 70% produced a new phenomenon of "systolic wall collapse" just distal to the stenosis. The maximum diameter decrease was 2.83 mm from the baseline diameter of 6.41 mm. Cyclic wall motion just downstream of the stenosis increased with the increased degree of stenosis from 0.34 mm at 0% stenosis to -1.28 mm at 75% stenosis. The phenomena are discussed in terms of simplified Bernoulli pressure drops. We conclude that local arterial stenosis can produce conditions favorable for wall collapse and increased wall motion at physiologic pressure and flow. This collapse may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization.

Optimal graft diameter: effect of wall shear stress on vascular healing.

Arterial walls tend to adapt to maintain a specific wall shear stress. The formation of neointimal hyperplasia and endothelial cell healing of polytetrafluoroethylene grafts may also be governed by wall shear stress, which suggests that an optimal graft diameter may exist. To test this, 40 polytetrafluoroethylene grafts with internal diameters of 3, 6, and 8 mm were inserted end to end in the femoral and carotid arteries of 10 mongrel dogs. Total flow and diameter were measured, and grafts were stained with Evans blue dye, fixed by pressure perfusion, and analyzed by computer for anastomotic neointimal thickening, graft pseudointimal thickening, and degree of endothelial coverage. Mean calculated shear stress was 41 dyne/cm2 for the 3 mm grafts, 7 dyne/cm2 for the 6 mm grafts, and 3 dyne/cm2 for the 8 mm grafts. Fifteen weeks later the patency rate was 0 of 10 for the 3 mm grafts, 16 of 20 for the 6 mm grafts, and 7 of 10 for the 8 mm grafts. The mean graft shear stress was calculated to be 10 dyne/cm2 for the 6 mm grafts and 4 dyne/cm2 for the 8 mm grafts. Pseudointima lining the graft was composed of disorganized protein and cell remnants. The rough surface contained no overlying endothelium. Anastomotic neointima contained a layer of well-organized smooth muscle cells covered by a single layer of polygonal-shaped endothelial cells. A transition zone of thrombus, which is sandwiched by a wedge of smooth muscle cells near the graft surface and covered by endothelial cells, is described. Mean thickness of pseudointima of the patent 8 mm grafts was 150 microns thicker than that of the 6 mm grafts. Anastomotic neointimal thickness was 110 microns thicker in the 8 mm grafts compared with the 6 mm grafts. Among the 6 mm grafts, the carotid grafts had an average initial shear stress of 10 dyne/cm2, whereas the femoral grafts averaged a lower 5 dyne/cm2 and yielded pseudointima and neointima that were 40 microns thicker. The percent graft surface area covered with neointima did not differ among the grafts of differing diameter either proximally or distally. Lower shear stresses produced greater amounts of pseudointimal thickening within polytetrafluoroethylene grafts and neointimal thickening at their anastomoses. Conversely, the high shear stress from small-diameter grafts was associated with poor graft patency. These results suggest that an optimal graft diameter may help to prevent neointimal hyperplasia and graft thrombosis.

Fine needle aspiration cytology in lieu of open biopsy in management of primary breast cancer.

Fine needle aspiration (FNA) can be used in place of open breast biopsy in most patients with primary breast cancer. This report summarizes our experience with 398 patients who had FNA of the breast. There was a total of 136 cancers, of which 100 (74%) were diagnosed by FNA. Seventy-one patients had mastectomy without frozen section. Thirteen had an excisional biopsy before mastectomy by preference of the surgeon. These cases occurred early in this series, before the surgeons became confident in the technique. The presence of locally advanced disease was confirmed by FNA in 12 patients and metastases to the breast were confirmed in four. There were no false-positives. Fine needle aspiration was interpreted as "suspicious" but not diagnostic of malignancy in 31 patients and open biopsy was requested. Biopsies demonstrated primary breast carcinoma in 22 patients and metastatic cancer in one. There were 103 patients with FNA negative for cancer who had open biopsy; 102 were confirmed negative, and one was positive for cancer. Fine needle aspiration yielded insufficient material in 38 patients, and 12 of these were found to have carcinoma with open biopsy. Advantages of FNA: It is safe, atraumatic and rapid, and permits definitive discussion about treatment planning at the initial office visit. It obviates the need for frozen section, reducing anesthesia and operative time. Our experience shows that FNA is highly accurate in the diagnosis of breast malignancy if rigorous criteria are used. Although a negative FNA requires biopsy to exclude malignancy, a FNA that is positive for cancer eliminates the need for open biopsy and allows the surgeon to proceed to mastectomy with confidence.