Fig. 192.—Diagram of Extra-Dural Abscess.
Fig. 193.—Pott's Puffy Tumour in case of extra-dural abscess following compound fracture of orbital margin; infected with road-dust; operation; recovery. At the time of the photograph the man was unconscious.
When associated with a punctured wound implicating the skull, an extra-dural abscess may develop within a few days of the injury, or not till after the lapse of several weeks, and it may spread over a wide area and come to encroach on the cranial cavity sufficiently to raise the intra-cranial tension and cause symptoms of compression, or even to press upon cortical centres and produce localised paralyses. As discharge can escape from the wound in the scalp, the puffy tumour does not necessarily form.
Treatment.—When the abscess is secondary to middle ear disease, the mastoid must be opened, the eroded bone exposed, and sufficient of it removed with rongeur forceps to admit of free drainage. When the infection has spread from the frontal sinus, the skull is trephined in the frontal region, the precise site being indicated by the œdematous area in the scalp, and the diseased bone is removed. In cases of compound fracture, drainage is established by enlarging the scalp wound, and removing loose, depressed, or inflamed portions of bone; if the bone is comparatively intact, it must be trephined, and further bone is removed with rongeur forceps over the entire area in which the dura has been separated.
Lepto-meningitis.—If the infection spreads to the adjacent arachno-pia (localised lepto-meningitis), adhesions usually form, and shut off the infected area from the general arachno-pial space.
Pus may form among these adhesions, constituting a sub-dural abscess, and may infiltrate the superficial layers of the cortex (purulent encephalitis, or meningo-encephalitis) ([Fig. 194]). The symptoms are similar to those of extra-dural abscess, but may be more severe; and it is seldom possible to distinguish between them before exposing the parts by operation. The treatment is carried out on the same lines.
