Aqueductal Stenosis: A Type Of Obstructive Hydrocephalus
Obstruction to normal cerebral spinal fluid pathways may involve any portion of the ventricular system. Look at the area labeled Aqueduct. The connection pathway in the ventricular system between the IIIrd and IVth ventricles is known as the Aqueduct of Sylvius or just aqueduct. Stenosis means a narrowing. Pathology arises such that CSF cannot flow through the stenotic aqueduct. The IVth ventricle remains small since minimal CSF reaches it, but the entire ventricular system preceeding the IVth ventricular CSF flow gets backed up. These parts of the ventricular system dilate from the blockage of flow. This situation is called Aqueductal Stenosis and is a type of Obstructive Hydrocephalus."
Normal Cerebral Spinal Fluid Flow vs Aqueductal Stenosis Cerebral Spinal Fluid Flow
Notice how all the ventricles are dilated with CSF in communicating hydrocephalus.
With Aqueductal Stenosis, the Aqueduct and IV ventricles are small or normal in size while the IIIrd ventricle and Lateral Ventricles are dilated.
CAT Scan Showing Communicating Hydrocephalus vs Aqueductal Stenosis
Notice in the first CAT all the ventricles (in black) are dilated. In the second CAT scan, only the lateral, III ventricles and the temporal horns are dilated. The IV ventricle is small and just starting to be seen. In the last CAT scan, the IV ventricle is normal in size.