Tumor compression In cases of<unk>  caused by tumor compression, a brain tumor in the region of the midbrain forms. More specific anatomically, a tumor forms in the pineal region which is dorsal to the midbrain and is level with the aqueduct of Sylvius. As the tumor grows and expands, it compresses the aqueduct to eventually obstruct it. Narrow aqueduct A naturally narrow<unk> lows for it to be more easily obstructed. Narrow aqueducts have no unusual tissue characteristics, and ventricles are lined with normal epithelial cells. Narrowing can be a defect from birth that results in congenital<unk> . Developmental errors that could result in this defect include abnormal folding of the neural plate which causes the neural tube to be narrowed from birth. Forking Forking refers to an aqueduct that has become split into multiple, separate channels as a result of incomplete fusion of the median fissure. These channels may connect back together to form a single aqueduct again, or they may abruptly stop and form a dead-end. Both of these deformations disrupt the laminar flow of CSF through the ventricular system, causing the force by the aqueduct on its surroundings to be lower than the compressive force being applied to the aqueduct. This greater compressive force could effectively stop the flow of CSF if the aqueduct closes due to the force. Septum formation Formation of a septum implies that through gliosis, a membrane of glial cells has developed across the aqueduct. This abnormal membrane most commonly forms at the lower and distal portion of the aqueduct, and completely obstructs the canal. This barricade causes the portion of the aqueduct above it to become dilated with the excess CSF which in turn applies more pressure to the cells in this upper part. This increased pressure amplifies the effects of gliosis, as described in the next section. Gliosis With this condition, the aqueduct begins as partially blocked. To compensate for the partial blockage and increase the CSF flow to normal rates, the pressure in the third ventricle is increased thereby also increasing the velocity of the CSF. This in turn creates more shear stress in the aqueduct, causing more damage to the epithelial cells lining the ventricle, and resulting in gliosis and a proliferation of glial cells. This increased number of cells thus causes the blockage to worsen, necessitating more pressure and velocity, and continuing the cycle of gliosis. Other medical conditions A genetic disorder called “Brickers-Adams-Edwards syndrome” or “X-linked hydrocephalus” has been discovered that leads to<unk> . This disease is transmitted from mother to son. This disorder is caused by a point mutation in the gene for neural cell adhesion. Most males born with this have severe hydrocephalus, adducted thumbs, spastic motions, and intellectual problems. Females with this defect may have adducted thumbs or subnormal intelligence. Bacterial meningitis can also result in gliotic blockage of the aqueduct. In utero infection or infection during infancy could both result in glial cell build-up to make an obstruction.
Aqueductal stenosis
Chiari malformation
Dandy–Walker malformation
Cranio-lenticulo-sutural dysplasia
Acrocallosal syndrome
Septo-optic dysplasia
Basilar invagination
Periventricular leukomalacia