(a) When aphasia supervenes immediately or within a few days or weeks after an injury of the anterior portion of the head on the left side. It is extremely probable that in the first case a clot or bony spiculum will be found compressing the speech-centre; in the second case, that an abscess has formed in or near it (Broca's case).
(b) When simple hemiplegia or hemiplegia with hemispasm follows an injury, however slight, in the temporo-parietal region. If the paralysis or spasm be limited to one side of the face or to one extremity, the indication to operate is even stronger. Even if in such cases the injury be not immediately over the motor area, the surgeon is justified in exploring that region.
(c) In conditions of stupor and coma after cranial injuries, sometimes without external wound, in which meningeal hemorrhage is the cause of impending death, the discovery of slight hemiplegia should justify trephining planned according to the topographic rules above laid down (Weir's case, 1882). In some cases latent hemiplegia may be discovered by the presence of an erythematous flush on one buttock and of a slightly increased peripheral temperature (taken between fingers or toes).
(d) In the very rare cases in which paralytic phenomena are found on the same side as the evident cranial injury, it would be proper to trephine on the opposite side of the skull in search of fracture or hemorrhage, the result of contre-coup.
(e) In chronic epilepsy after traumatism of the head the indication for trephining is present, but it is seldom a specific indication connected with the subject of localization. Lesions of any part of the skull and dura may be a cause of epileptic attacks, irrespective of motor centres.
(f) In cases of tumor in the motor centres, if there be not symptoms of tumors in other parts of the brain (multiple tumors) or of penetration of the tumor to the central parts of the brain, we believe trephining not only justified, but demanded in the present state of science.
Some of the contraindications to trephining may be thus stated:
(a) Whenever in apparently favorable cases there are signs of injury to the base of the brain, such as paralysis of cranial nerves, neuro-retinitis, and Cheyne-Stokes respiration (although the last symptom may occur from simple compression).
(b) When hemispasm or hemiplegia is accompanied by hemianæsthesia, thus making it probable that the lesion is deeper and farther back.
It should be added, in conclusion, that these indications and contraindications are formulated from the standpoint of the neurologist.