Fig. 81. Exploration for a Temporo-sphenoidal Abscess. A, Above the tegmen tympani; B, Through the tegmen tympani. Occasionally these methods are combined; the bone between the openings being also removed. (After Hunter Tod.)
2. When the evidence points to implication of the middle fossa, the scalp incision is prolonged upwards for about 1 inch and the soft parts retracted. The supra-tegmental extra-dural space can be exposed either by chiselling away the osseous roof of antrum and middle ear, or by means of a separate opening above the level of the supramastoid crest. In the event of the discovery of an extra-dural collection of pus, the purulent material is gently wiped away, free drainage supplied, and the wound closed.
In both this and the preceding case, the progress of the case during the ensuing twenty-four to forty-eight hours will prove whether adequate measures have been adopted.
When the symptoms are suggestive of brain abscess, when no extra-dural collection is discovered, and when the dura mater is tense and discoloured, then it becomes necessary to explore the brain. This can be carried out through an opening made in the tegmen or above the level of the supramastoid crest. Which route should be utilized depends on the local conditions. As a general rule, it is advisable to explore through the tegmen when a sinus exists in that situation, and above the supramastoid crest under all other circumstances.
Fig. 82. Exploration for a Cerebellar Abscess. A behind, and C in front of the lateral sinus; B, Lateral sinus. (After Hunter Tod.)
In the latter case, the dura mater is incised crucially and the bulging brain explored in the manner indicated on [p. 266]. The mastoid region should first be cleansed and packed with gauze, but, even with such precautions, it is obvious that there is some risk of contaminating membranes and brain in the event of failure to discover the abscess cavity—an argument in favour of exploring through the ‘clean’ squamous region (see [p. 264]).
3. When the evidence points to implication of the posterior fossa, an incision is carried backwards, from the mid-point of the post-aural incision, for about 2 inches, and the soft parts retracted upwards and downwards. With the chisel (or gouge) and hammer, the bone is freely cut away so as to expose (1) the lateral sinus, and (2) the dura mater below and behind the curve of the sinus. As soon as the sinus is exposed, the dura mater may be separated from the bone and the subsinus region exposed with the aid of craniectomy forceps.
The extra-dural space between the posterior aspect of the petrous bone and the lateral sinus region is first inspected, and, in the event of the discovery of a collection of pus, this is gently wiped away and further exploration postponed till the occasion should prove the necessity.
When the indications are of such a nature as to demand exploration of the cerebellum, the mastoid region is first cleansed and packed with gauze, after which the dura mater is incised either in front or behind the sinus according to the probable situation of the abscess cavity. After the evacuation of the abscess a drainage tube is stitched in position in the manner previously indicated.