Enlarged thalamostriate vein causing unilateral Monro foramen obstruction. Case report

Causes of unilateral hydrocephalus resulting from an obstruction at the Monro foramen include foraminal atresia, tumors, gliosis, contralateral shunting, and infectious and inflammatory conditions. However, few reports in the literature cite vascular lesions as the cause of the obstruction. To their knowledge, the authors present the first report of unilateral hydrocephalus occurring due to an abnormally enlarged thalamostriate vein independent of an arteriovenous malformation or developmental venous angioma. The condition was treated successfully by endoscopic septum pellucidum fenestration. A 28-year-old man was referred for evaluation due to a 10-year history of chronic headaches that worsened in severity over the past year. A CT scan of the head revealed unilateral right ventricular dilation. Cranial MR imaging with and without contrast administration showed a dilated right thalamostriate-internal vein complex without any evidence of associated arteriovenous malformation or venous angioma. Endoscopic exploration of the right lateral ventricle showed an enlarged subependymal thalamostriate vein obstructing the Monro foramen. An endoscopic fenestration of the septum pellucidum was performed, resulting in alleviation of the patient's symptoms. Abnormally enlarged venous structures may cause obstructive unilateral hydrocephalus and can be a rare cause of chronic, intermittent headaches in adults. Endoscopic fenestration of the septum pellucidum is an effective treatment.