Ventricular system with third ventricle highlighted red Ventricular system with fourth ventricle highlighted red CT scan CT scans are used to visualize the structure of the inside of the body without needing to make any incision. For the purposes of diagnosis<unk> , a scan is performed on a patient's brain. Images showing an enlarged third ventricle along with a normally sized fourth ventricle (in a lateral view) is generally considered to be an indication of<unk> , but this is still only presumption. CT scans are typically used after a shunt treatment in order to analyze ventricle size and determine if the device is working. One complication associated with this analysis (as well as when analyzed by MRI) is that images of a small ventricle do not always correspond with a functioning shunt as a small ventricle would seem to imply. The reduced ventricle size can sometimes be due to a condition called slit ventricle syndrome. Another complication is that if the<unk>  is caused by tumor compression, there is a possibility that the scan will miss detecting small brainstem tumors. MRI imaging MRI is considered the best method of detecting<unk>  because it can visualize the entire length of the aqueduct, can clearly depict tumors, and can show ventricle enlargement or other deformations. It is helpful in determining the extent of the<unk>  obstruction, particularly when multiple masses or lesions are present, and thereby aids in determining the most appropriate treatment method (i.e. surgery, shunt, or ETV). 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. For example, CISS can be used to determine if a thin membrane interfering with CSF flow is present. Other 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. If no flow is seen, this is a reliable diagnosis of<unk>  as it implies that there is a blockage of CSF. Ultrasonography can be used in utero to diagnose<unk>  by showing dilation of the lateral and third ventricles. A retrospective study found that diagnosis can be made as early as 19 weeks of gestation, and that on average diagnosis is made at 33 weeks.
Aqueductal stenosis
Chiari malformation
Dandy–Walker malformation
Cranio-lenticulo-sutural dysplasia
Acrocallosal syndrome
Septo-optic dysplasia
Basilar invagination
Periventricular leukomalacia