Background and Clinical Significance: Cavum septum pellucidum (CSP) and cavum vergae (CV) are anatomical variations that may persist into childhood, adolescence, or adulthood. When these cavities become abnormally large, they are classified as cysts. The mechanism leading to expansion is poorly understood. Although rare, symptomatic CSP and CV cysts can present with a wide range of clinical manifestations. Case Presentation: A 20-year-old Caucasian male presented with progressively worsening symptoms over several months including persistent headaches and dizziness. Neurological evaluation showed no abnormalities, with intact cranial nerve function, normal muscle strength, and no signs of paresis. Imaging identified CSP and CV cysts causing obstructive hydrocephalus. MRI findings confirmed progressive cyst enlargement and obstruction of intraventricular foramen. The patient underwent neuroendoscopic fenestration of the cyst with resolution of both hydrocephalus and the symptoms. A CT and MRI scan of the brain performed 12 years before revealed a developmental variant, showing no evidence of cyst formation or ventricular enlargement and without hydrocephalus at that time. This case provides a rare opportunity to observe cyst growth dynamics over time. Conclusions: This case presents the importance of recognizing symptomatic CSP and CV cysts as rare but significant causes of obstructive hydrocephalus. The progression from a developmental variant to cyst formation over time illustrates the value of long-term imaging follow-up in such cases. Neuroendoscopic fenestration provided complete resolution of symptoms, demonstrating the effectiveness of surgical intervention in such cases.

Background. Cavum septum pellucidum (CSP) and cavum vergae (CV) are anatomical variations that may persist into childhood, adolescence, or adulthood. When these cavities become abnormally large, they are classified as cysts. The mechanism leading to expansion is poorly understood. Although rare, symptomatic CSP and CV cysts can present with a wide range of clinical manifestations. Case report. A 20-year-old Caucasian male presented with progressively worsening symptoms over several months, including persistent headaches and dizziness. Neurological evaluation showed no abnormalities, with intact cranial nerve function, normal muscle strength, and no signs of paresis. Imaging identified CSP and CV cysts causing obstructive hydrocephalus. MRI findings confirmed progressive cyst enlargement and obstruction of foramen Monro. The patient underwent neuroendoscopic fenestration of the cyst with resolution of both hydrocephalus and the symptoms. A CT and MRI scan of the brain performed 12 years before revealed a developmental variant, showing no evidence of cyst formation or ventricular enlargement and without hydrocephalus at that time. This case provides a rare opportunity to observe cyst growth dynamics over time. Conclusion. This case presents the importance of recognizing symptomatic CSP and CV cysts as rare but significant causes of obstructive hydrocephalus. The progression from a developmental variant to cyst formation over time illustrates the value of long-term imaging follow-up in such cases. Neuroendoscopic fenestration provided complete resolution of symptoms, demonstrating the effectiveness of surgical intervention in such cases.