MRI has traditionally been employed to rule out alternative diagnoses in unilateral acute vestibular syndrome (UAVS), but delayed 3D-FLAIR sequences offer the potential for imaging to contribute to both diagnosis and management. This study aimed to assess abnormalities on delayed 3D-FLAIR MRI in UAVS patients and correlate these findings with clinical outcomes. A retrospective multicenter study was conducted between January 2018 and May 2024 at a university hospital and a private vestibular clinic, representing a diverse clinical setting. It included 92 patients with UAVS (47 women, 45 men; mean age 50.6 years) diagnosed according to Bárány Society guidelines, with acute vertigo lasting at least 24 h, spontaneous horizontal-rotatory nystagmus, and a reduced vestibulo-ocular reflex (VOR) on the affected side, without auditory or neurological symptoms. The MRI findings were blindly assessed to identify potential blood-labyrinth barrier (BLB) impairment, nerve enhancement, or canal fibrosis. These imaging abnormalities were then correlated with initial and follow-up video head impulse test (vHIT) results. BLB impairment was found in 63% of patients and canal fibrosis in 14.1%, with no nerve enhancement detected. BLB impairment significantly correlated with initial VOR deficits and was linked to poorer vHIT recovery, suggesting its role in predicting persistent vestibular dysfunction. These findings suggest that delayed 3D-FLAIR MRI can identify biomarkers, particularly BLB impairment, that are predictive of vestibular recovery, highlighting MRI's role in guiding UAVS treatment.