The most common cause of congenital hydrocephalus is aqueductal stenosis, which occurs when the narrow passage between the third and fourth ventricles in the brain is blocked or too narrow to allow sufficient cerebral spinal fluid to drain. Fluid accumulates in the upper ventricles, causing hydrocephalus.Other causes of congenital hydrocephalus include neural-tube defects, arachnoid cysts, Dandy–Walker syndrome, and Arnold–Chiari malformation. The cranial bones fuse by the end of the third year of life. For head enlargement to occur, hydrocephalus must occur before then. The causes are usually genetic, but can also be acquired and usually occur within the first few months of life, which include intraventricular matrix hemorrhages in premature infants, infections, type II Arnold-Chiari malformation, aqueduct atresia and stenosis, and Dandy-Walker malformation. Hydrocephalus has also been seen in cases of congenital syphilis.In newborns and toddlers with hydrocephalus, the head circumference is enlarged rapidly and soon surpasses the 97th percentile. Since the skull bones have not yet firmly joined, bulging, firm anterior and posterior fontanelles may be present even when the person is in an upright position.The infant exhibits fretfulness, poor feeding, and frequent vomiting. As the hydrocephalus progresses, torpor sets in, and infants show lack of interest in their surroundings. Later on, their upper eyelids become retracted and their eyes are turned downwards ("sunset eyes") (due to hydrocephalic pressure on the mesencephalic tegmentum and paralysis of upward gaze). Movements become weak and the arms may become tremulous. Papilledema is absent, but vision may be reduced.
The most commonly involved tooth in localized microdontia is the maxillary lateral incisor, which may also be shaped like an inverted cone (a "peg lateral"). Peg laterals typically occur on both sides, and have short roots. Inheritance may be involved, and the frequency of microdontia in the upper laterals is just under 1%. The second most commonly involved tooth is the maxillary third molars, and after this supernumerary teeth. Causes
There are many potential factors involved. Congenital hypopituitarism
Ectodermal dysplasia
Down syndrome
Ionizing radiation to the jaws during tooth development (odontogenesis)
Chemotherapy during tooth development
Marshall syndrome
Rieger syndrome
Focal dermal hypoplasia
Silver-Russell syndrome
Williams syndrome
Gorlin-Chaudhry-Moss syndrome
Coffin–Siris syndrome
Salamon syndrome
Cleft lip and palateOthers include trichorhinopharyngeal, odontotrichomelic, neuroectodermal and dermo-odontodysplasia syndromes. Treatment
Unerupted microdonts may require surgical removal to prevent the formation of cysts. Erupted microdonts, peg laterals especially, may cause cosmetic concern. Such teeth may be restored to resemble normal sized teeth, typically with composite build ups or crowns. Orthodontics may be required in severe cases to close gaps between the teeth. Epidemiology
Females are affected more than males, and the condition occurs in permanent (adult) teeth more than deciduous (baby teeth or milk teeth). References


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