The prevalence of undiagnosed abnormalities on non-contrast-enhanced computed tomography compared to contrast-enhanced computed tomography of the brain

Background: Even though magnetic resonance imaging (MRI) is the gold standard investigation for intracranial pathology, it is not widely available in developing countries and computed tomography (CT) of the brain remains the first-line investigation for patients with suspected intracranial pathology. It is generally accepted that certain intracranial pathology can be missed on non-contrast-enhanced CT (NECT) of the brain if a contrast-enhanced CT (CECT) is not done. We have to consider on the one hand the risk of delayed or missed diagnosis and on the other hand the cost, increased radiation exposure and contrast-induced reactions. Advances in CT technology have also improved the resolution of CT scan images, making it easier to identify pathology on an NECT of the brain. To date, no study comparing NECT to CECT of the brain, utilising 64-slice CT technology, has been published. Objectives: To determine the prevalence of undiagnosed abnormalities on non-contrast-enhanced computed tomography (NECT) scans of the brain reported as normal, on a 64-slice CT scanner. Method: A descriptive retrospective study was undertaken of CT brain scans done during a 12-month period at a tertiary provincial hospital in the Northern Tshwane district of Gauteng, South Africa. The CT brain scans were evaluated by three reviewers (general radiologists). The NECT and contrast-enhanced computed tomography (CECT) scans of the brain were reviewed independently on separate occasions. Reviewers were blinded to patient history, each other's interpretation, and to their own interpretation of the NECT when evaluating the CECT and vice versa. Discrepancies in interpretation were resolved during a consensus meeting between all three reviewers. The reviewers also re-evaluated the NECT scans of the cases with undiagnosed abnormal findings during this session. A decision was made pertaining to the visibility of the abnormal findings on the NECT scan. Results: In this study, 3.28% of cases had abnormal findings undiagnosed by three reviewers on the NECT scans. Re-evaluation by the panel reduced this to 1.42%, indicating a reading error of 1.85%. Conclusion: There is a small prevalence of missed abnormal findings on the NECT scan when using only NECT. Omitting unnecessary CECT will reduce the radiation exposure to the patient and reduce the risk of adverse events from the use of intravenous iodinated contrast. Alternatively, doing only a CECT scan would reduce the risk of missing abnormal findings and would also decrease the patient's exposure to radiation.