=Operation.= Operations are carried out (_a_) with the object of withdrawing fluid from the distended ventricular cavities (ventricular puncture), and (_b_) to establish a communication, or short-circuit, between the ventricular space and other spaces (ventricular drainage).
_Ventricular puncture._ This operation may be carried out through the anterior fontanelle, through the frontal bone, or over the descending cornu of the lateral ventricle.
_Through the anterior fontanelle._ The region of the fontanelle is shaved and cleansed in the usual manner, after which the surrounding parts are cut off from the field of operation by a large sheet of gauze or lint, in which a hole is cut sufficing to allow of exposure of the site of election for puncture.
The patient should be in the recumbent position, the head well towards the end of the table. The operation is performed without an anæsthetic or under local anæsthesia. A site is chosen at the outer angle of the fontanelle, about 1 inch away from the median antero-posterior line, thus avoiding all possibility of injuring the superior longitudinal venous sinus. The trocar and cannula, of small size, is passed directly inwards, towards the base of the skull, for a distance of not more than 2 inches. The trocar is withdrawn and the fluid allowed to escape slowly. If the cerebro-spinal fluid escapes at high pressure, the flow should be regulated by the finger placed over the mouth of the cannula, and, in any case, it is inadvisable to allow of the withdrawal of more than 50 c.c. (approximately 1¹⁄₂ ounces) at one sitting. The cannula is withdrawn and the site of tapping covered with collodion gauze. Even when adopting all precautions the operation is not without danger, and, added to this, is the fact that few surgeons care about introducing an instrument blindly into the cerebral cortex--the risk of puncturing one of the distended superficial cerebral veins is sufficiently obvious.
_Through the frontal bone._ Tillmanns, in recommending this procedure, states that ‘the needle should be inserted about 2 centimetres from the central line and 3 centimetres from the precentral sulcus. You strike the ventricle at a depth of from 3 to 5 centimetres’. He claims that this method leads to satisfactory results. It is open, however, to all the objections of puncture through the fontanelle.