Purpose Primary and secondary conditions that cause thiamine deficiency can result in similar symptoms in children, including acute episodes of encephalopathy and bilateral symmetrical brain lesions. In this study, we investigated the role of mammillary body (MB) involvement in SLC19A3-BTBGD patients and the differentiation between BTBGD and Wernicke's encephalopathy based on Magnetic Resonance Imaging (MRI) findings.Methods We conducted a retrospective study of 90 patients with genetically confirmed BTBGD. Two certified neuroradiologists independently reviewed the brain MRI scans, focusing on the involvement or sparing of specific regions such as the mesencephalon, cerebellum, caudate nuclei, globus pallidi, putamina, thalami, cortical and subcortical regions, MBs, and deep white matter.Results Clinically, all patients developed acute/subacute encephalopathy triggered by nonspecific febrile illnesses or mild trauma. MRI scans showed bilateral caudate lesions, putamen lesions, cortical-subcortical areas of the cerebral hemispheres, ventromedial region of the thalamus, cerebellar lesions, brainstem lesions, periaqueductal region, spinal cord lesions, and lesions in the globus pallidus. However, none of the patients had any mammillary lesions.Conclusion We found no MB involvement in 90 patients with BTBGD caused by the same homozygous variant of SLC19A3. Differentiating between BTBGD and Wernicke's encephalopathy based on MRI findings is critical for clinical decisions about treatment, prognosis, and genetic counselling. This study provides a crucial point in ruling out Wernicke's encephalopathy, especially in adults, and favouring BTBGD before the results of genetic testing are available. MRI is of utmost importance in the diagnosis and differentiation of these conditions.