Relation Of Hippocampal Formation Measurements From MRI To Elderly Patients' Postoperative Cognitive Dysfunction

Objective:To study the predictive value of the MRI-derive volume of hippocampal formation on elderly patients' post-operative cognitive dysfunction.Methods: We selected 41 patients aged at least 65 years, ASA II～III grade who accepted gastrointestinal tract surgery as study cases,and selected 35 healthy aged subjects as control group.MR1 was performed on the 41 patients before surgery . The volume of hippocampal formation (HF) was measured by T₁-weighted images from oblipue coronal scan based on the height of the hippocampal formation.The results was standardized according to intracranial volume. For elderly patients and healthy aged subjects,postoperative cognitive dysfunction was classified using unique neuropsychological tests and judgement.All patients completed neuropsychological tests before and 4 days after the surgery.The test battery included sensitive tests from the Wechsler Adult Memory Scale and Wechsler Adult Intelligence Scale,Trail Making Test (Part A)and the Grooved Pegboard Test. An SD unit for each test was calculated from the healthy first scores. For patients, We compared changes in performance for each test from baseline (first session) to 4 days after surgery,and divided the result by the control-group SD to obtain a Z score for each test. Large positive Z scores showed a deterioration in cognitive function.We defined a composite Z score from all of the Z scores. Patients had cognitive dysfunction when two Z scores in individual tests or the combined Z score were 1.96 or more.Then,we assigned all patients to POCD group or non-POCD group according to the results of neuropsychological tests, compared the two groups' hippocampal volume,and predicted the value of the MRI-derive volumes of hippocampal formation on elderly patients'post-operative cognitive dysfunction.Result: 36 patients completed neuropsychological tests after surgery,and we found cognitive dysfunction in 13(36.1%) of patients.In the control group,all subjects completed twice neuropsychological tests,and 5.7% (in 2 of 35 subjects)of participants had scores that showed cognitive dysfunction.False positive classifications of the neuropsy -chological tests that we chose was 5.7%. The hippocampal volume of POCD group (4.75±0.23) was smaller than that of non-POCD group (5.06±0.31) (P<0.01). Z score that showed a deterioration in cognitive function was negative correlation with hippocampal volume(r=—0.324, P<0.05) . Hippocampal volume was found to be an important predictor of post-operative cognitive dysfunction, the overall accuracy of prediction was 77.8% (in 28 of 36 subjects), with 92.3% sensitivity(in 12 of 13 subjects), 70%specificity(in 16 of 23 subjects) and 0.623 Youden index. Conclusion:1 The incidence of post-operative cognitive dysfunction of patients aged at least 65 years who accept gastrointestinal tract surgery was not small.2 The HF volume of POCD group was smaller than that of non-POCD group's.3 The hippocampal atrophy is sensitive to predict elderly patients'post-operative cognitive dysfunction.