The next step is to open the abscess. Formerly a trocar and canula were used. This method is no longer in favour for the following reasons:—If the wall of the abscess cavity be very thick, it may not be pierced; secondly, the trocar may pass through the abscess cavity and enter the brain substance beyond without draining it; and thirdly, even if the trocar enters the abscess cavity the pus may be so thick as to plug its lumen. For these reasons a fine pair of Lister’s sinus-forceps or a narrow-bladed bistoury is recommended. In the ordinary case Lister’s forceps can be used.
The direction in which the brain is explored depends upon the point at which this is done. Thus, if the procedure be carried out through the tegmen tympani, the brain is explored in an upward direction. The forceps are made to pierce the brain for about an inch; the blades are then slightly dilated and the forceps partly withdrawn. If a large abscess exists, the cavity is usually opened at once and pus flows out along the track of the forceps. If the abscess be small and deeply placed, its cavity may not be entered on the first thrust of the forceps. In this case they are closed and withdrawn. The brain is then explored by thrusting the forceps first upwards and forwards, then upwards and backwards, and finally upwards and inwards; in the latter case it is unwise to pierce the brain for more than an inch and a quarter for fear of entering the lateral ventricle.
If the brain be explored through the outer wall of the temporo-sphenoidal lobe, the first direction in which this is carried out is directly inwards. If this be not successful, the brain is further explored in a direction forwards, upwards, or backwards, the exploratory instrument at the same time pointing slightly inwards.
If exploration proves negative, it may also be necessary to explore the cerebellum. If, however, the surgeon be still convinced that a temporo-sphenoidal abscess exists, he may next pierce the brain with the bistoury, in case the forceps has failed to enter the abscess cavity, perhaps owing to its walls being very thick. If all efforts fail to find the abscess, the little finger may be inserted into the brain itself to see if the resistant wall of an abscess can be felt. This procedure, however, should be avoided if possible, as by doing so it causes destruction of a certain amount of brain tissue.
If an abscess be opened a varying quantity of pus escapes, usually evil smelling. In the more chronic cases it is thick and greenish; in the acute cases it may contain shreds of necrosed brain tissue or be intermixed with bubbles of gas. Sometimes there is also an escape of turbid cerebro-spinal fluid, which if excessive is suggestive either that the lateral ventricle has been opened inadvertently or that the abscess has already burst into it. In these cases the patient is usually comatose or in the state of muttering delirium at the time of the operation.
After the abscess has been opened, the forceps or bistoury should be retained in position until the pus has drained away. A large tube is then pushed into the abscess cavity along the line of the forceps or bistoury. It is only permissible to withdraw the instrument with which the abscess has been opened after the end of the tube is well within the cavity. The outer end of the tube should be flush with the surface of the wound. To prevent it slipping too far into the brain, it may be anchored to the edge of the skin wound by a silkworm-gut suture. If the abscess be drained through the tegmen tympani, it will be difficult to bring the tube out into the wound without kinking it. For this reason I prefer to incise the brain substance slightly outwards after the abscess cavity has been reached, so that a tube can be inserted obliquely upwards and inwards at a point corresponding to the angle between the tegmen tympani and the squamous portion of the temporal bone. If the exploratory puncture has been made above the tegmen tympani and an abscess discovered, the question arises whether another drainage tube should not also be inserted into the brain through an opening in the roof of the antrum so as to drain the abscess from below. This, however, I do not think necessary.
In addition to the rubber tube, many varieties of drainage tubes have been suggested, such as decalcified chicken bone, as originally used by Macewen, and glass or silver tubes; the object of the latter being to resist the pressure of the brain, which may compress a rubber tube. The rubber tube is the simplest form of drainage, and if sufficiently thick it should be employed. To make more certain of free drainage, some surgeons use two tubes placed side by side. I think, however, one large tube (half an inch in diameter) is better than two small ones.
Irrigation of the abscess cavity is still a matter of opinion. If the abscess be small and circumscribed, the best method is to open it with as little disturbance as possible to the surrounding parts, insert a large drainage tube, and to do nothing further.
If, however, the abscess be large and irregular in shape, so that the drainage is not free, and especially if it be very septic and contains necrosed brain tissue, irrigation is justifiable if gently carried out. The best method is to insert a fine tube along the lumen of the large one and allow some warm saline solution to flow slowly along it into the abscess cavity, the fluid returning along the larger tube. If two tubes have already been inserted into the abscess cavity, the fluid injected through one will escape by the other. Whatever method is employed, care must be taken that there is free exit for the fluid, as otherwise the abscess cavity may become over-distended, and in consequence rupture of a portion of its wall may take place, especially the inner, which perhaps only consists of a thin layer of brain tissue separating the abscess from the lateral ventricle. During the act of irrigation there is a risk of some of the fluid, now loaded with septic particles, escaping between the surface of the brain and the dura mater and thus setting up a secondary meningitis.
