Hypothesis of the circannual and circadian variation in onset of intracerebral haemorrhage (CH) was verified, by means of single cosinor method and chi‐square test for goodness of fit, in 161 consecutive patients (94 men and 67 women) admitted into the Institute of Neurosurgery of Ferrara Hospital, Italy, over 9 years. The majority of CH occurred in the morning between 06.00 AM and 12.00 noon (36.7% of cases, p<0.001); when considering the specific anatomical sites, typical supratentorial haemorrhages showed a similar pattern (37.4%, p= 0.01). A similar morning behavior was found when considering subgroups by sex (men 36.2%, women 37.3%), age ≥60 years (42.5%), no presence of hypertension (39.7%), no presence of diabetes mellitus (33.3%) and non‐smokers (30.4%). The results by cosinor analysis yielded a circadian rhythmicity both for total sample and, for the men's subgroup, with a morning peak at 11.44 and 11.25, respectively. For women, however, spectral analysis found a significant ultradian cycle, having a period of 12 h (p = 0.01). A circannual periodicity, with a prevalent peak in February, was found for total sample and males subgroups, too. The results of this study confirm that intracerebral haemorrhages present a characteristic circadian and circannual pattern in onset. Copyright © 1994, Wiley Blackwell. All rights reserved
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