Role of Computed tomography brain scan in complex febrile seizure: Number Needed to Screen (NNS)

Febrile seizures are common neurological conditions, with complex febrile seizures accounting for about 30% of cases. Neuroimaging has a low diagnostic yield, with positive findings reported in less than 1% in many settings. The number needed to screen (NNS) estimates how many patients must undergo neuroimaging to detect one clinically significant abnormality, helping assess the appropriateness of imaging strategies in paediatric practice. Because CT exposes children to ionizing radiation and may require sedation in some cases, its use should be carefully justified. Methods We performed a retrospective review of children aged 6 to 60 months admitted to a tertiary paediatric unit in Hong Kong for complex febrile seizures between 2019 and 2024 who underwent CT imaging. Results Among 581 febrile convulsion cases, 117 met criteria for complex febrile seizures. Eight patients (6.83%) had significant CT abnormalities, yielding an overall NNS of 15. Prolonged seizure duration >30 minutes (OR 75, 95% CI 6.32–890.25, p = 0.001) and developmental delay (OR 50, 95% CI 4.50–555.83, p < 0.001) were significantly associated with abnormal imaging. The concordance index was 0.887. When these predictors were incorporated into the model, all abnormalities were identified and the NNS was reduced to 2. Conclusion Prolonged seizures lasting more than 30 minutes and developmental delay were strong predictors of abnormal neuroimaging in children with complex febrile seizures. These findings may help refine imaging indications, improve resource allocation, and support evidence-based paediatric neurology practice.