Abstract
We report a case of obstructive hydrocephalus caused by a transitional (shunting) developmental venous anomaly not previously reported in the literature. Both thalami in this patient drain into a midline vein in the floor of the third ventricle that crosses the cerebral aqueduct and exerts mass effect. While this patient's hydrocephalus was managed by a ventriculoperitoneal shunt catheter, their hospital course was complicated by a spontaneous intraparenchymal bleed of the left thalamus thought to be caused by their vascular malformation. Given the risk of venous infarcts, this transitional venous anomaly could not be treated safely.