OPERATIONS ON CRANIUM AND SCALP.
TREPHINING AND TREPANNING are the names given to operations for the
removal of portions of the cranium by circular saws which play on a
centre pivot. When the motion is given to the saw simply by rotation of
the hand of the operator, as is common in this country, it is called
_trephining_; when (as used to be the case in this country, and still is
on the Continent) the motion is given by an instrument like a
carpenter's brace, the operation is called _trepanning_.
The nature of the operation varies according to the nature of the case
for which it is performed. Thus (1.) it may be performed through the
uninjured cranium in the hope of evacuating an abscess of the diploe or
dura mater, or of relieving pressure caused by suppuration in the brain
itself, or by extravasation into the brain or membranes; or (2.) it may
be required in cases of punctured and depressed fracture for the purpose
of removing projecting corners of bone and allowing elevation of the
depressed portions; or (3.) it is sometimes used to remove a circular
portion of bone in cases of epilepsy in which pain or tenderness is felt
at some limited portion of the cranium.
1. _In cases where the cranium and its coverings are entire._--There are
certain positions where, if it is possible, the trephine should _not_ be
applied. These are the longitudinal sinus, the anterior inferior angle
of the parietal bone, where the middle meningeal artery is in the way,
the occipital protuberance, and the various sutures. These being
avoided, a crucial incision is to be made through the skin, and its
flaps reflected. The pericranium should then be raised from the centre,
for a space large enough to hold the crown of the trephine. The
pericranium should never be removed, but carefully raised and preserved,
as its presence will greatly aid in the restoration of bone.[80] The
centre pin should then be projected for about the eighth of an inch and
bored into the bone. On it as a centre the saw is then worked by
semicircular sweeps in both directions alternately, till it forms a
groove for itself. Whenever this groove is deep enough the pin should be
retracted, lest from its projection it pierce the dura mater before the
tables of the skull are cut through. Were the cranium always of the same
thickness, and even of similar consistence, the operation would always
be exceedingly easy; but in both these particulars different skulls vary
much from each other, and thus by a rash use of the instrument the dura
mater may possibly be injured. The tough outer table is more difficult
to cut than the softer and more vascular diploe, and the inner table is
denser than either, but more brittle. In many old skulls, however, the
diploe is wanting altogether, and the two tables are amalgamated, and
often very thin.
Great care must be taken in every case to saw slowly, to remove the
sawdust, and examine the track of the saw by a probe or quill, lest one
part should be cut through quicker than another. The last turns of the
instrument must specially be cautious ones. When the disk of bone does
not at once come away in the trephine, the elevator or the special
forceps for the purpose will easily remove it. If the abscess,
extravasation, or exostosis be then discovered and removed, all that
remains is to remove any sawdust or loose pieces of bone, and possibly
to smooth off any sharp edges of the orifice by an instrument called the
lenticular. This is very seldom required, and now hardly ever used.
2. _In cases of depressed or punctured fracture_ the trephine is
occasionally required (when symptoms of compression are present) for the
purpose of enabling the depressed portion to be elevated. It is unsafe
to apply it to the depressed or fractured bone, lest the additional
pressure of the instrument should cause wound of the dura mater or
brain. It is generally applied on some projecting corner of sound bone
under which the depressed portion is locked, and hence it is rarely
necessary to remove a complete circular portion. In fact very many cases
of such displacement may be remedied more easily by a pair of strong
bone-forceps, or a Hey's saw, applied to remove the projecting portion
of sound bone. The same precautions must be used as in the operation
already described, and the sawing must be done even more cautiously, as
it is rarely more than a semicircle that requires cutting.
In former days trephining was a much more frequent operation than it is
now, and apparently more successful. The reason of the greater apparent
success can easily be found in the fact that it was performed in many
cases merely as a precautionary measure against dreaded inflammation of
the brain, which probably never would have appeared at all, and that the
operation itself is one by no means dangerous. Very numerous
applications of the trephine have been made in the same individual--two,
four, six, and even in one case twenty-seven disks having been removed
from the same skull, and yet the patients have survived.
TUMOURS OF THE SCALP, _Removal of_.--By far the most frequent are the
encysted tumours, or wens. These consist of a thick firm cyst-wall,
which contains soft, curdy, or pultaceous matter, sometimes almost
fluid, at others dry and gritty. They are loosely attached in the
subcutaneous cellular tissue, and unless they have become very large, or
have been much pressed on, are non-adherent to the skin.
The treatment is thus very simple. They should merely be transfixed by a
sharp knife, the contents evacuated, and the cyst seized by strong
dissecting forceps and twisted out.
If they have once become adherent, they must be dissected out in the
usual manner, after the adherent portion of skin has been defined by
elliptical incisions.
In the case of large wens on visible parts of scalp or face, the author
avoids scar, by the following plan:--
Make a small incision, two lines at most, through skin only, then with a
blunt probe separate the cyst from the skin subcutaneously; then,
pulling it to the wound with catch-forceps, empty the cyst and gradually
pull it out, as if taking out an ovarian cyst. No scar but a dimple will
remain.
FOOTNOTES:
[80] See case by the author in the _Edin. Med. Jour._ for June 1868.