Extensive Osmotic Demyelination Syndrome With a Concomitant Cytotoxic Lesion of the Corpus Callosum in Hyperemesis Gravidarum: A Case Report.

Osmotic demyelination syndrome (ODS) is a rare neurological disorder classically associated with rapid correction of hyponatremia but increasingly recognized in the setting of complex osmotic disturbances. Its radiological spectrum includes central pontine and extrapontine myelinolysis, with variable clinical and imaging presentations. The coexistence of cytotoxic lesions of the corpus callosum (CLOCCs) in this context remains exceptional and poorly understood. We report the case of a 35-year-old pregnant woman presenting with severe hyperemesis gravidarum complicated by profound electrolyte imbalance and marked fluctuations in serum sodium levels. Initial brain magnetic resonance imaging (MRI) was unremarkable despite progressive neurological deterioration. A follow-up MRI performed two weeks later revealed extensive symmetric T2-weighted/fluid-attenuated inversion recovery (FLAIR) hyperintensities involving the pons, basal ganglia, thalami, hippocampi, internal and external capsules, and bilateral cerebellar hemispheres. Diffusion-weighted imaging (DWI) demonstrated heterogeneous findings, with restricted diffusion limited to the capsular regions. Additionally, a focal lesion in the corpus callosum with marked diffusion restriction was identified, consistent with a CLOCC. Mild contrast enhancement was observed within the pontine lesion. Extensive pontine and extrapontine involvement combined with CLOCC represents a rare but significant manifestation of osmotic brain injury. Recognition of this association and awareness of delayed imaging findings are essential for accurate diagnosis and management.