#Traumatic Cephal-hydrocele.#--Certain rare cases of simple fracture of the vault occurring in early childhood have been followed by the development beneath the scalp of a localised fluid swelling, which varies in size from time to time and is partly reducible by pressure. The swelling results from laceration of the membranes, and sometimes of the brain substance, so that the cerebro-spinal fluid of the sub-arachnoid space, or even of the lateral ventricle, escapes through the opening in the skull and bulges beneath the scalp. In a majority the swelling pulsates synchronously with the heart, and becomes tense on exertion. A distinct opening in the skull may sometimes be felt. When associated, as it frequently is, with mental deficiency or the occurrence of fits, the cyst may be tapped or its neck ligated (Hogarth Pringle). Otherwise it should be left alone. HYDROCEPHALUS An excess of cerebro-spinal fluid may collect in the arachno-pial space surrounding the brain, or in the interior of the ventricles, constituting in the former case an _external_, and in the latter an _internal hydrocephalus_. Hydrocephalus may be acute or chronic. #Acute hydrocephalus# is practically synonymous with tuberculous meningitis, although it may result from other forms of meningeal infection. The excess of fluid is found both in the arachno-pial space and in the ventricles. This condition only calls for mention here as attempts have been made to treat it by surgical measures, such as lumbar puncture, or drainage through the occipital fossa. The results, however, have not been encouraging. #Chronic Hydrocephalus.#--_Chronic external hydrocephalus_ is rare, and usually results from some definite intra-cranial lesion, such as meningitis, tumour, or cerebral atrophy. It is not amenable to surgical treatment. _Chronic internal hydrocephalus_, on the other hand, is a comparatively common condition. It may be of congenital origin, or may develop in young rickety children, usually as a result of some chronic inflammatory process in the membranes at the base, the choroid plexuses, or the ependyma of the ventricles, causing obstruction to the outflow of blood through the internal cerebral veins of Galen. In the acquired form the communication between the ventricles and the sub-arachnoid space, by way of the foramen of Magendie, is obstructed, so that the cerebro-spinal fluid is pent up in the ventricles and gradually distends them. The pressure causes the head to enlarge, the fontanelles to bulge, and the bones to be separated from one another, the interval between the bones being occupied by a thin translucent membrane. The cerebral tissue is greatly thinned out, but the cerebellum and cranial nerves usually remain unaffected.