(4) Many general surgeons do not possess that intimate acquaintance with the anatomy of the ear which is necessary to carry out a complicated aural operation.
Each case must be considered on its own merits, but I am inclined to advocate the two-stage method when the diagnosis is reasonably clear that the patient is suffering from temporo-sphenoidal or cerebellar abscess, mastoid exploration being carried out as soon as the patient has recovered from the first operation. When, however, considerable doubt exists as to the position of the abscess—or the nature of the complication in general—it is then advisable to start by exploration of the mastoid and aural regions, further measures being adopted according to the conditions found at the time of operation.
1. The two-stage operation.
Trephining for temporo-sphenoidal abscess. A point is chosen on the scalp which lies between 11⁄2 and 2 inches above the centre of the external auditory meatus, and a bradawl is there introduced so as to indent the external table of the skull. A small scalp-flap is framed, one presenting an upward convexity, and all bleeding controlled. The pin of the trephine is applied to the spot previously indicated on the bone and the disk removed. On account of the absence of diploic tissue and consequent approximation of the two tables of the skull, care must be taken to avoid injury to the posterior branch of the middle meningeal artery and to the bulging dura mater.
Fig. 79. The Exposure of a Temporo-sphenoidal Abscess.
The dura is then inspected and palpated; absence of pulsation, loss of lustre and tenseness, indicate the probable adjacency of the abscess cavity. The membrane should be crucially incised, all meningeal vessels that cross the line proposed for section being first under-run on either side of that line. The scalpel is lightly applied to the membrane and, as soon as the pia-arachnoid is exposed, the section completed with the blunt-pointed scissors.
The four dural flaps are turned aside and the cortex exposed. At the very apex of the bulging brain, and avoiding all visible vessels, a large blunt-pointed trocar and cannula or, preferably, Horsley’s pus-evacuator is introduced and passed, for not more than 11⁄2 inches, in a direction inwards and slightly forwards, parallel to the roof of the middle ear. The blades of the evacuator must be opened ‘once for each quarter of an inch of brain substance penetrated’ (Macewen). If the trocar and cannula be utilized, similar precautions must be adopted.
In the event of failure to find pus at the first attempt, the evacuator is withdrawn, introduced at the same site, but now passed in other directions—directly inwards, slightly upwards, and finally, slightly backwards, in each case for not more than 11⁄2 inches.
By wide separation of the blades of the evacuator the pus is allowed to escape, to be immediately wiped away by the assistant. Irrigation of the cavity should never be attempted, not so much because of the difficulties attendant on that process, but because of the danger of infecting the neighbouring meningeal regions.