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.
It can be diagnosed prenatally on ultrasound as early as 14 weeks of gestation, although it is usually diagnosed postnatally by MRI. It is diagnosed within the first year of life 41% of the time, normally due to increasing signs of hydrocephalus, but 28% of the time it is discovered in adolescence or adulthood due to mental health problems, such as psychosis or mood disorder. Criteria and classification
The precise diagnostic criteria and classification systems of DWM are not agreed upon, and significant dispute exists as to which terms or criteria should be used. The core criteria of DWM are hypoplasia of the cerebellar vermis and an enlarged fourth ventricle and posterior fossa (the space behind the cerebellum), though the specific degree of hypoplasia or cystic enlargement for diagnosis of DWM is not agreed upon. Additionally, there are several similar conditions which have at various times been grouped with DWM on a continuum by some authors and separated as distinct by others, further complicating diagnosis.In 1976, Harwood-Nash and Fitz proposed the term Dandy–Walker variant (DWV) for a malformation in which the posterior fossa is not enlarged but the cerebellar vermis is hypoplastic. In 1989, Barkovich et al. proposed the term Dandy–Walker complex (DWC) to include classic DWM and DWV (under type A) plus a third malformation (under type B) in which the cerebellar vermis remains large enough to sit between the fourth ventricle and the cisterna magna beneath it, and instead it is mostly the cisterna magna that is enlarged.