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Causes of enlarged head in an infant 1- normal variation. 2- familial large head. 3- fluid collection: a- hydrocephalus. b- subdural fluid collection. hematoma- collection of pus. c- brain edema: - infections: meningitis/ encephalitis. - toxins: lead/ tetracycline. - metabolic: galactosemia/ hypoparathyrodism. - asphyxia : cardiac arrest/ birth asphyxia. d- blood : intracranial hemorrhage. 4- thickened skull: a- chronic hemolytic anaemia. b- skeletal disorders: rickets/ osteogenesis imperfecta. 5- big brain ( megalencephaly): a- anatomic: neurocutaneous syndromes e.g. neurofibromatosis. hemimegalencephaly. b- metabolic: mucopolysaccharidosis. tay sach s disease. aminoaciduria. Tests for enlarged head in infant 1- laboratory studies: a- complete blood picture, hemoglobin, hemoglobin electrophoresis ( if you suspect hemolytic anaemia) b- metabolic studies: serum calcium, phosphorus etc, according to the clinical evaluation. c- lumber puncture & examination: to exclude acute infections & subarachnoid hemorrhage ( do CT scan first ). 2- imaging: a- plain X ray skull: - will demonstrate abulging anterior fontanel in infants. - also, bone changes due to hemolytic anaemia may be seen. b- plain X ray both wrist: for rickets. c- CT scan: identifies hydrocephalus & its cause , cysts, subdural fluid collections & brain edema. d- MRI scan: for anatomical or metabolic disorders associated with megalencephly. 3- fundus examination: for papilledema, retinal hemorrhages or pigmentations. Normal CSF circulation - CSF is mostly produced by the choroid plexus in the lateral ventricles of the brain. - from there it passes through the foramen of Monro on each side to reach the midline 3rd ventricle. - the fluid then passes downwards to the aqueduct of Sylvius ( = cerebral aqueduct) to the 4th ventricle. - the 4th ventricle has 2 lateral foramina ( of Luschka) & one medial foramen ( of Magendi), which transmit CSF to the subarachnoid space around the brain & spinal cord. - most of the fluid absorption ocurrs inside the skull through the arachnoid villi to the blood stream ( systemic circulation) Constriction of cerebral aqueduct (= aqueduct of Sylvius) - if constriction occurs in cerebral aqueduct will lead to enlargement of the 3rd ventricles & lateral ventricles. - the 4th ventricles & subarachnoid space enlargement would likely not be visible. Obstructed arachnoid vilii there will be enlargement of: 1- subarachnoid space, 2- 4th ventricles. 3- 3rd ventricles. 4- lateral ventricles.