Hatim Attar, MD
MRI scans are the gold standard imaging modality for diagnosing acute cerebrovascular injury. The purpose of performing them in Transient Ischemic Attack (TIA) patients is to determine presence of infarction, which lends information on prognosis and risk of recurrence. This novel Japanese study has investigated Diffusion Weighted Imaging (DWI) latency from symptom onset and false negative MRI scans in TIA patients. Shono et al have determined the optimal timing of obtaining MRI scans in TIA patients to limit false negative results.
73 clinically confirmed TIA patients were included. All patients had an MRI at arrival and then again at 24 hours. They were divided into 2 groups. Group 1, which included 9 patients, had an initial negative MRI but positive DWI sequence after 24 hours. Group 2 included 64 patients that had both MRIs positive for DWR (25 patients) or both negative (39 patients). Patients in Group 1 had imaging within 1 to 2.8 hours from symptom onset, whereas patients in Group 2 ranged from 0.58 to 12 hours from onset. The false negative rate was determined for each 1 hour interval after symptom onset. The probability of false negative scans decreased with each 1-hour interval with no false negatives after 3 hours. The analysis resulted in 3 statistically significant independent factors for false negative MRI scans — DWI latency less than 2 hours, NIHSS at admission and prior TIAs.
The authors used a 3 Teslon MRI, as compared to prior studies that have used 1.5 Teslon scanners, which would decrease the false negative rates. This study also had shorter latency periods of initial MRI scans. Though there were only 9 patients in Group 1, the overall results are comparable with other studies. Constantly evolving technology is expected to become more sensitive for detecting cerebral ischemia. This, in turn, will warrant future studies with large sample sizes.
Improved healthcare access and ease of obtaining MRI scans on patients with sudden neurological deficits has resulted in early imaging. We often find DWI negative scans in patients who are clinically consistent with TIAs. If index of suspicion is high, treat as a TIA. But if the diagnosis is questioned, or other diagnoses like seizures or complicated Migraine cannot be ruled out, repeat imaging is of paramount importance.
