If trephining has been necessitated, the bone-disk is not replaced, thus allowing of subsequent tappings through the trephine-hole, this gap now taking the place of a patent postero-lateral fontanelle.
Keen’s method of ventricular puncture presents many advantages over other methods, though still open to the objection that the actual central puncture is done blindly.
Ventricular-subdural drainage.
A point is mapped out on the scalp which corresponds to the surface-marking of the descending horn of the lateral ventricle (see [p. 3]), and, with this point as a guide, a scalp-flap is framed, the base of which lies immediately below the indicated spot whilst its convexity is situated between 11⁄2 and 2 inches above. This flap should not include the pericranium. The flap is turned down to its base, the pericranium stripped aside and a disk of bone removed, at the upper part of the exposed bone, with a 1⁄4 or 1⁄2 inch diameter trephine. The bone is usually very thin.
A
B
Fig. 26. Diagrammatic Representation of the Author’s Operation for Hydrocephalus Internus. A. The osteoplastic exposure of the brain (A, The bone; B, Upper two-thirds of trephine hole; C, Dura mater; D, The four dural flaps; E, Site of brain perforation; F, The brain; G, Line of fracture of bone-flap; H, The bone-flap; I, The Scalp; J, Lower third of trephine hole). B. Ventriculo-subdural drainage (s., The scalp; b., The bone; d., The dura mater; v., The lateral ventricle; t., The drainage medium between the ventricular cavity and the subdural space; s.l.s., Superior longitudinal sinus; f.c., Falx cerebri).
When this disk is removed, the dura is separated from the bone, and, with the aid of a strong pair of scissors, the bone is cut in such a manner as to form a bone-flap, the margins of which lie well within those of the scalp-flap (see [Fig. 26]). This flap is broken across at its base, turned down, and covered with gauze.