Prognostic Factors of Stage II Rectal Cancer / 대한소화기학회지

BACKGROUND/AIMS: We aimed to verify the prognostic factors of stage II rectal cancer and the effect of radiation therapy on the survival and local recurrence rate. METHODS: This study was undertaken in 202 patients who underwent curative resection of rectal cancer and confirmed to be stage II between July 1989 and December 1996. Univariate and multivariate (Cox's model) analyses of survival were employed to identify prognostic factors. Statistical significance was assigned by p value of <0.05. RESULTS: Overall recurrence occurred in 32 patients. Four patterns of recurrence were observed: hematogenous recurrence in 17 patients, local recurrence in 11, peritoneal seeding in two and simultaneous hematogenous and local recurrence in two cases. Overall 5-year survival rate was 85.6% and 5 year disease free survival rate was 82.8%. There was no significant difference in local recurrence rate and survival according to radiation therapy or location of cancer. In multivariate analysis, the number of harvested lymph node was only a prognostic factor. CONCLUSIONS: The number of harvested lymph nodes has prognostic value in stage II rectal cancer. Postoperative radiation therapy should be considered for stage II rectal cancer with poor prognostic factors although radiation did not decrease local recurrence rate in present study.

Kinematic Analysis of Locomotion Following Dorsal Hemisection of Spinal Cord in the Rat

Using computerized motion analysis techniques, kinematics of foot trajectories were quantitatively analyzed in twelve rats before and after dorsal spinal cord hemisection at the T6 level. Although overground locomotion in these animals returned to normal within four weeks, some kinematic variables during treadmill locomotion did not recover to pre-lesion level. Immediately following dorsal hemisection, amplitudes of both hindfeet horizontal and vertical movements were dramatically reduces. However, in three weeks, the amplitudes of horizontal movement(stride length) became significantly larger than of pre-lesion strides. On the other hand, amplitude of hindlimb vertical movement showed very little recovery. Forelimb-hindmill coordination was also disrupted initially but returned to normal within three weeks. The duration of hindlimb swing phase became significantly longer after sectioning and gradually recovered, but never to pre-lesion levels. Interestingly, amplitudes of forelimb vertical movement. which was depressed initially, became significantly largery three weeks after lesioning. A dramatic increase in the statistical variation of limb kinematics, which persisted even after motor recovery, is an important parameter for the evaluation of neural deficits in spinal cord injuries. Kinematic analysis is a sensitive technique for the detection of minor motor deficits following nerve injuries.

The Characteristic and Origin of Motor Evoked Potential in Rats

Motor evoked potential(MEP) produced by cortical surface or transcranial stimulation has evolved as a new clinical and experimental tool to monitor the integrity of motor pathways and to map motor cortex. Clinical assessment of motor system using MEP has further advanced with recent development of the magnetic stimulator. The primary concept using MEPs for test of motor pathways was based on the assumption that pyramidal neurons in the motor cortex are activated by electrical stimulation applied on the cerebral cortex and synchronized compound action potentials are conducted mainly along the corticospinal tracts in the spinal cord. However,recent studies indicated that the origins of the Meps in non primates may differ from those previously believed. In order to use MEPs as a clinical or experimental tool, it is essential to clarify the origin of MEPs. Therefore, goals of this study were : (1) to investigate the origin of MEPs, and (2) to design the most reliable but simple method to evoke and monitor MEPs. In a total of fifteen rats, MEPs were produced by cortex to cortex stimulation and were monitored using a pair of epidural electrodes. Using varying stimulus intensities, the amplitudes and latencies of MEPs were statistically analyzed. The latencies and amplitudes of the MEPs in these animals showed surprisingly large standard deviations, which were partially resulted in these animals showed surprisingly large standard deviations, which were partially resulted from convergence of neighboring waves during high stimulation intensities. Wave forms of MEPs were also varied greatly depending on the position of recording electordes. At low stimulus intensities, most consisten MEPs were obtained when the stimulating electrodes were placed on the hard palate and the temporal muscle, not on the motor cortex. This observation indicates that the primary source of MEPs is not the motor cortex in the rat. When the potentials generated by direct stimulation of motor cortex and those generated by reticular nuclei were monitored epidurally in the same preparation using the same electrodes, these potentials generated by different sources actually identical in their latencies and wave forms. However, the threshold stimulus intensities evoking these potentials were quite different in the two metholds. The threshold was much lower to evoke potentails by reticular nuclei stimulation. It suggests that MEPs are geneated by the reticular nuclei or brain structure located in the brain stem. The observation that the motor cortex play no major roles in generating MEPs was confirmed by sequential sections of neural axis from the motor cortex to brain stem in three rats. All these findings suggested that neither direct motor cortex stimulation not transcranial stimulation did evoke MEPs originating from the motor cortex in rat. These stimulating methods activate reticular nuclei by stimulus current spread to the brain stem. Since the reticular formation plays an important role in motor function in rats, MEP originated from reticular nucleus can be an important testing of the motor function in rats. Moreover, transcranial stimulation of the brain is technically easy. This technique producing MEPs originated from reticular nucleus can be useful to monitor the integrity of motor pathways.

The Intraspinal Pathways Conducting Motor Evoked Potentials in Rats

Recently, motor evoked potential(MEP) using cortical surface of transcranial stimulation have been used to monitor the integrity of motor pathways and map motor cortex in human and animal. The primary concept using motor evoked potentials(MEPs) for test of motor pathways was based on the assumtion that pyramidal neurons in the motor cortex are activated by electrical stimulation applied on the cerebral cortex and synchronized compound action potentials are conducted mainly along the corticospinal tracts in the spinal cord. However, the origins and the descending pathways of these MEPs in small animals may be different from those of potentials evoked by intracortical microstimulation because of current spread. Our previous study revealed that the origns of the MEPs in rats differed from those previously believed and may be reticular nuclei. To further clarify those results and localize the intraspinal pathways conduction MEPs, consecutive vertical and/or horizontal sections of the spinal cord were performed at T9 cord level in twelve rats. MEPs were recorded at T2/3 and L2/3 before and after each section and sequential alterations of MEPs were observed. In six rats, the stimulation was alternated between the right and left cortex and the lateralities of conduction pathways were compared. All six cases showed no differences of MEPs and pattern of wave abolition after each section between right and left brain stimulation. The alteration of MEPs after each consecutive section was categorized by analyzing latency shift, amplitude change, and disappearance of waves. We divided a cross section of T9 spinal cord into forty-six squares. If one of the categorized changes occurrd after cutting an area, the appropriate score was given for the area since more change of waves meant more significant contribution of the cut area to conduction of MEPs. The score of twelev rats were summed in each forty-six spots and map showing the distribution of MEPs was constructed. The map revealed that MEPs were conducted along the wide area of ventral and lateral funiculus of the spinal cord but mainly along the medial portion of the ventral funiculus of the spinal cord but mainly along the medial portion of the ventral funiculus and ventral portion of the larteral funiculus through which reticulospinal and vestibulospinal tracts pass. No conduction of MEPs along the corticospinal tracts was confirmed. This finding supports the result of our previous study. However, this extrapyramidal MEP conducted along ventral spinal cord in addition to somatosensory evoked potential(SSEP) which is conducted along posterior funiculus can be useful to monitor the integrity of the whole spinal cord. Moreover, the extrapyramidal MEP can be more useful than pyramidal MEP in rats because the reticular formation plays a more important role in motor function and pyramidal tract is located in posterior funiculus.