Incidental Diagnosis of Complete Agenesis of the Corpus Callosum in a 62-Year-Old Man Presenting With Dizziness.

Agenesis of the corpus callosum (ACC) is a congenital malformation most commonly identified in prenatal or early childhood imaging, with adult diagnoses being relatively rare. We present the case of a 62-year-old man with a history of intellectual disability who was incidentally found to have complete ACC during evaluation for dizziness and chest discomfort. Initial noncontrast computed tomography (CT) of the brain demonstrated ventricular enlargement concerning for hydrocephalus, prompting further evaluation. Subsequent magnetic resonance imaging (MRI) clarified the diagnosis, revealing classic radiographic features of ACC, including colpocephaly, the "moose head" configuration on coronal views, "racing car ventricles" on axial imaging, and the "sunray" (or "sunrise") sign on sagittal views. The patient had no prior neuroimaging and was previously unaware of this congenital anomaly. This case highlights the potential for delayed diagnosis of ACC in individuals with lifelong intellectual disability and emphasizes the importance of recognizing characteristic imaging findings to avoid misinterpretation. Additionally, it underscores the clinical and social relevance of identifying structural brain abnormalities later in life.