These typical symptoms include: headache, nausea and vomiting, cognitive difficulty, sleepiness, seizures, balance and gait disturbances, visual abnormalities, and incontinence.

More specific anatomically, a tumor forms in the pineal region which is dorsal to the midbrain and is level with the aqueduct of Sylvius.

[3] Forking refers to an aqueduct that has become split into multiple, separate channels as a result of incomplete fusion of the median fissure.

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 number of cells thus causes the blockage to worsen, necessitating more pressure and velocity, and continuing the cycle of gliosis.

However, some studies also argue that cases of aqueductal stenosis not involving a brain tumor are actually a result of communicating hydrocephalus, rather than a cause of it.

When a patient has communicating hydrocephalus, the lateral ventricles and medial parts of the temporal lobes expand and compress the aqueduct.

[2][3] CT scans are typically used after a shunt treatment in order to analyze ventricle size and determine if the device is working.

[3] When constructive interference in steady state (CISS) or fast imaging employing steady-state acquisition (FIESTA) sequence are used, subtle abnormalities or partial obstructions in the aqueduct can be depicted in the MRI.

[10] Phase contrast-MRI is an imaging method that is more sensitive than MRI for analysis of the pulsatile CSF flow in the ventricular system.

This method takes multiple images of the ventricles within one cardiac cycle to measure the flow of CSF running past the area of acquisition.

[11] Problems which can necessitate a secondary surgery to fix them include: mechanical failure, incorrect catheter size, inappropriate valve drainage pressure, and infection.

[12] An endoscopic third ventriculostomy (ETV) is a procedure where an incision is made in the bottom of the third ventricle to make a drainage point for CSF to flow out of.

[4] Ideally this procedure can be performed near the midline of the brain with minimal side-to-side motions of the endoscope so as to not tear tissues and cause further complications.

[10] Research has found that this procedure has a 75% success rate,[13] that 72% of ETV surgeries are still correctly functioning after 15 years, and that patients have shorter hospital stays recovering as compared to shunting.

[4] If the procedure does not successfully cure the aqueductal stenosis, a second surgery can be performed to enlarge the incision or implant a shunt.