- Hydrocephalus (HP:0000238): Hydrocephalus is an active distension of the ventricular system of the brain resulting from inadequate passage of CSF from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:217)
- Macrocephaly (HP:0000256): Occipitofrontal (head) circumference greater than 97th centile compared to appropriate, age matched, sex-matched normal standards. Alternatively, a apparently increased size of the cranium. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:217)
- Prominent occiput (HP:0000269): Increased convexity of the occiput (posterior part of the skull). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:217)
- Dandy-Walker malformation (HP:0001305): A congenital brain malformation typically characterized by incomplete formation of the cerebellar vermis, dilation of the fourth ventricle, and enlargement of the posterior fossa. In layman's terms, Dandy Walker malformation is a cyst in the cerebellum (typically symmetrical) that is involved with the fourth ventricle. This may interfere with the ability to drain cerebrospinal fluid from the brain, resulting in hydrocephalus. Dandy Walker cysts are formed during early embryonic development, while the brain forms. The cyst in the cerebellum typically has several blood vessels running through it connecting to the brain, thereby prohibiting surgical removal. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:217)
- Platybasia (HP:0002691): A developmental malformation of the occipital bone and upper end of the cervical spine, in which the latter appears to have pushed the floor of the occipital bone upward such that there is an abnormal flattening of the skull base. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:217)
- Cerebellar hypoplasia (HP:0001321): Cerebellar hypoplasia is a descriptive term implying a cerebellum with a reduced volume, but a normal shape and is stable over time. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Frontal bossing (HP:0002007): Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Dilated fourth ventricle (HP:0002198): An abnormal dilatation of the fourth cerebral ventricle. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Enlarged posterior fossa (HP:0005445): Abnormal increased size of the posterior cranial fossa. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Aplasia/Hypoplasia of the cerebellar vermis (HP:0006817): Absence or underdevelopment of the vermis of cerebellum. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Mild fetal ventriculomegaly (HP:0010952): A kind of ventriculomegaly occurring in the fetal period and usually diagnosed by prenatal ultrasound. Cerebral ventriculomegaly is defined by atrial measurements 10 mm or more. Mild ventriculomegaly (MVM) is defined as measurements between 10 and 15 mm. Measurements are obtained from an axial plane at the level of the thalamic nuclei just below the standard image to measure the BPD (PMID:16100637). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Enlarged fetal cisterna magna (HP:0011427): The cisterna magna is measured on a transaxial view of the fetal head angled 15 degrees caudal to the canthomeatal line. The anterior/posterior diameter is taken between the inferior/posterior surface of the vermis of the cerebellum to the inner surface of the cranium. An enlarged cisternal magna is defined by an anterior/posterior diameter of 10 mm or more (PMID:16100637). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:217)
- Cleft palate (HP:0000175): Cleft palate is a developmental defect of the palate resulting from a failure of fusion of the palatine processes and manifesting as a separation of the roof of the mouth (soft and hard palate). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Intellectual disability (HP:0001249): The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Motor delay (HP:0001270): A type of Developmental delay characterized by a delay in acquiring motor skills. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Encephalocele (HP:0002084): A neural tube defect characterized by sac-like protrusions of the brain and the membranes that cover it through openings in the skull. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Increased intracranial pressure (HP:0002516): An increase of the pressure inside the cranium (skull) and thereby in the brain tissue and cerebrospinal fluid. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Aplasia/Hypoplasia of the corpus callosum (HP:0007370): Absence or underdevelopment of the corpus callosum. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:217)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:217)
- Truncal ataxia (HP:0002078): Truncal ataxia is a sign of ataxia characterized by instability of the trunk. It usually occurs during sitting. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:217)
These phenotypes are associated with the disease Isolated Dandy-Walker malformation (ORPHA:217).