Hydranencephaly is a condition in which the brains cerebral hemispheres are absent to a great degree and the remaining cranial cavity is filled with cerebrospinal fluid. "Cephalic" is the scientific term for "head" or "head end of body". Hydranencephaly is a type of cephalic disorder. These disorders are congenital conditions that derive from damage to, or abnormal development of, the fetal nervous system in the earliest stages of development in utero. These conditions do not have any definitive identifiable cause factor. Instead, they are generally attributed to a variety of hereditary or genetic conditions, but also by environmental factors such as maternal infection, pharmaceutical intake, or even exposure to high levels of radiation.Hydranencephaly should not be confused with hydrocephalus, which is an accumulation of excess cerebrospinal fluid in the ventricles of the brain. In hemihydranencephaly, only half of the cranial cavity is affected. Signs and symptoms
An infant with hydranencephaly may appear normal at birth or may have some distortion of the skull and upper facial features due to fluid pressure inside the skull. The infants head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal, depending on the severity of the condition. However, after a few weeks the infant sometimes becomes irritable and has increased muscle tone (hypertonia). After several months of life, seizures and hydrocephalus may develop, if they did not exist at birth.
Complications like leukemia and other cancers among those who survive are managed as usual. Short term outcomes depend on the dose exposure.ARS is generally rare. A single event can affect a large number of people, as happened in the atomic bombing of Hiroshima and Nagasaki and the Chernobyl nuclear power plant disaster. ARS differs from chronic radiation syndrome, which occurs following prolonged exposures to relatively low doses of radiation. Signs and symptoms
Classically, ARS is divided into three main presentations: hematopoietic, gastrointestinal, and neuro vascular. These syndromes may be preceded by a prodrome. The speed of symptom onset is related to radiation exposure, with greater doses resulting in a shorter delay in symptom onset. These presentations presume whole-body exposure, and many of them are markers that are invalid if the entire body has not been exposed. Each syndrome requires that the tissue showing the syndrome itself be exposed (e.g., gastrointestinal syndrome is not seen if the stomach and intestines are not exposed to radiation). Some areas affected are:

Hematopoietic. This syndrome is marked by a drop in the number of blood cells, called aplastic anemia. This may result in infections, due to a low number of white blood cells, bleeding, due to a lack of platelets, and anemia, due to too few red blood cells in circulation. These changes can be detected by blood tests after receiving a whole-body acute dose as low as 0.25 grays (25 rad), though they might never be felt by the patient if the dose is below 1 gray (100 rad).