Purpose: Thrombolysis in acute stroke is time limited. Onset time is unknown in a large number of patients. We wanted to classify acute stroke patients with unknown time of onset into less than or more than 4.5 hours onset, using CT scan and National Institute of Health Stroke Scale(NIHSS).
Methods: Acute stroke patients with NIHSS ≥8 and CT within 24 hours of onset were included. The control group included 100 normal CT. Two reviewers blinded to clinical information independently reviewed all images. CT was graded as 0-normal, grade-I poorly-demarcated hypodensity and grade-II well-demarcated hypodensity. Hounsfield unit (HU) calculated in the area of interest using 0.5-1 cm area and compared with the contralateral side (n=44). The diagnosis was confirmed from follow-up scans.
Results: A total 120 CT-scans were reviewed. There were 65% males, age ranged from 39-90 years. < 4.5 hour group: Sixty-nine CT were graded as <4.5-hours, 87%(n=60) were correctly graded (p<0.0001) and 13%(n=9), false negative) were incorrectly assigned to > 4.5 hours category. Both observers were incorrect on same eight CT-scans. Five of the false negative (assigned to >4.5-hours) were in 2.30-3.0 hours range with average NIHSS of 13. Four patients under two hours developed hypodensity, assigned to >4.5 hour category with average NIHSS of 21. Average NIHSS of the group was 15. > 4.5 hours group: Fifty-one CT were over 4.5 hours. Forty-four (86%) were correctly graded as >4.5-hours (p<0.0001) and seven (14%) patients were incorrectly assigned to <4.5 hour category (false positive). Six false positive patients were in 3.30-4.10 time range, average NIHSS of 15. Average NIHSS of >4.5-hour group was 14. Eleven incorrectly categorized scans [false negative (n=5) and positive (n=6)] tend to fall in the 2.45-4.10 hours range. Twenty-five (21%) CT scans were normal, all under three hours except one with NIHSS ≥8 at seven hours. HU were measured in 44 patients. Average HU of patients in <4.5 hour category (n=20) was 3.5 and >4.5 hour category (n=24) was 7.5.
Conclusion: Acute stroke with unknown time of onset, NIHSS >8 and CT scan changes of grade 0-I indicate <4.5 hours stroke onset. Higher NIHSS patients can develop early hypodensity, incorrectly suggesting >4.5 hours onset (false negative).