Atheroemboli to the brain: size threshold for causing acute neuronal cell death.

OBJECTIVE: The objective of this study was to investigate the dilemma posed by the observations that carotid angioplasty dislodges significant numbers of plaque fragments but is reported to have a low rate of neurologic consequences. We examined the fragments released by ex vivo carotid angioplasty. The smaller and most numerous were separated by size and injected into rats to determine the tolerance of the brain to microemboli. METHODS: Ex vivo angioplasty was performed on a total of 20 human carotid plaques removed en bloc. Plaques were placed within polytetrafluoroethylene grafts, and three manipulations were performed: guide wire insertion, 3.5- or 4.0-mm balloon angioplasty, and 5-mm angioplasty with or without a Palmaz stent. After each manipulation, the lumen was flushed, effluent was collected, and fragments were counted under 100x magnification. Using 200-microm and 500-microm micropore mesh, we separated fragments by size into two groups: (1) less than 200 microm and (2) 200 to 500 microm. We then injected rats with saline alone (Group A), with 100 fragments less than 200 microm (Group B), or with 100 fragments 200 to 500 microm (Group C). Animals were euthanized at 1, 3, and 7 days, and brain sections were examined for cell viability and expression of HSP- 72. RESULTS: The total number of fragments dislodged from the plaques varied from 30 to 553. The mean number of fragments released with each manipulation was as follows: guide wire passage, 24; initial balloon angioplasty, 97; second balloon angioplasty, 68; and second angioplasty plus stent, 172. Sixteen of the 20 plaques dislodged fragments that were 1 mm or more in greatest dimension. There was no evidence of brain ischemia in Group A at any time. Group B also showed no injury at 1 or 3 days. However, injection of 200- to 500-microm fragments (Group C) caused a scattered pattern of neuronal cell death. At 7 days, brain sections from both Group B and Group C animals had a scattered pattern of ischemic neurons. There were no classic wedge-shaped infarctions. DISCUSSION: The brain appears to have a surprising tolerance for microembolization in the acute setting. Thus, carotid angioplasty may dislodge plaque fragments, but there may still be a low incidence of stroke. However, even small plaque fragments, less than 200 microm, may cause neuronal ischemia at later time points. Periprocedural microemboli could cause subtle neurologic dysfunction in late follow-up.

A method for training surgeons in laparoscopic ultrasound.

With the increased use of laparoscopic surgery and the obligatory loss of palpation of solid organs, laparoscopic ultrasound will be an invaluable tool for the location and evaluation of solid or fluid-filled masses and retroperitoneal organs. Surgeons have heretofore had limited experience with ultrasound but are increasingly using other minimally invasive techniques to perform major operations. A graduated learning experience has been developed for surgeons, including a didactic introduction to ultrasound, inanimate and ex vivo training models, and finally, a live large animal model. Hepatic metastases were simulated and surgeons trained to locate and biopsy these lesions within the liver parenchyma under laparoscopic ultrasound guidance. The devised training session has allowed the participating surgeons to feel confident that they could identify and then biopsy intrahepatic lesions using minimally invasive techniques.

Laparoscopic colonic and rectal resection.

The technology that has permitted the rapid advance of minimal access surgery has now made it feasible to perform laparoscopically assisted colon resections safely. As the instrumentation improves, specimen removal problems are solved, surgeons' sewing skills improve, and other anastomotic methods are devised, an increasing amount of colonic surgery will be done using laparoscopy. It is clear that the techniques now in use are evolving, and will be substantially different a few years hence. Previously accepted surgical principles may continue to be challenged by new techniques, which must be evaluated under strict protocol before being widely accepted. These operations should be performed by surgeons who are able to achieve the same level of radical operation that they would achieve through a laparotomy. Special training in advanced laparoscopic techniques including microsurgical suturing is a distinct advantage in performing these operations successfully. It may be best for surgeons to start with palliative procedures or operations for benign diseases of the colon, to avoid the risk of jeopardizing an operation for cancer.