The confluence of sinuses, part of the drainage system located at the far rear of the occipital lobe, is elevated due to the enlarged posterior fossa. (The adjacent cerebellar tentorium is also elevated. )Due to the inconsistency of the presence of hydrocephalus in DWM, Spennato and Klein suggested that it should not be considered a criterion for DWM. Kleins criteria differed from Spennatos mainly in that it required no apparent cerebellar hemisphere hypoplasia, but it may also have required the vermis to touch the tentorium or an absence of brainstem abnormalities. Methods
DWM can be observed prenatally on ultrasound as early as 14 weeks of gestation, though an MRI scan is the most useful method for diagnosis. MRI can delineate the shape and extent of the malformation as well as assessing additional areas for malformations such as the cerebellar hemispheres, cerebral aqueduct or corpus callosum. Cardiac-gated phase-contrast MRI can observe the flow of cerebrospinal fluid (CSF) during systole and diastole of the heart. In true DWM, this will find a flow from the cerebral aqueduct to the posterior fossa and no flow between the cisterna magna and the space behind the cervical spinal cord.CT may also be used if MRI is unavailable, but it provides less detail. Klein et al. (2003) suggested that a suspected diagnosis based on CT or ultrasound should not be confirmed until an MRI is performed, due to the large number of conditions that can present highly similarly and confound diagnosis.
Delays may lead to seizures (due to hypoglycaemia), hypotension (due to cortisol deficiency), and/or intellectual disability (due to thyroid endocrine deficits). Due to the before-mentioned factors, mortality and morbidity is higher than that of the general population, particularly during the first 2 years of life. Epidemiology
The prevalence of PSIS is unknown, however, some 1,000 cases have been reported either with or without the full triad. References


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