SYMPTOMS POINTING TO FRACTURE OF THE POSTERIOR FOSSA
=External hæmorrhages.= In fractures of the posterior fossa, blood effused into the deeper tissues of the scalp has considerable difficulty in coming to the surface and thus making itself evident. Furthermore, the resistance offered by the nuchal muscles tends to confine the blood to the subtentorial region, thus adding to the already grave prognosis of fractures in this region. On careful palpation, however, it will be noted that the nuchal tissues present a doughy or boggy condition, whilst ecchymosis becomes evident after twenty-four to thirty-six hours. A peculiar ecchymotic patch is occasionally observed, appearing in front of the mastoid process and travelling upwards in a curved direction, concavity forwards, following the outline of the ear. It is said to result from the tracking of blood along the course of the posterior auricular artery. Whether this is the case or not, the hæmorrhage usually implies a separation along the line of the masto-occipital suture.
=Escape of cerebro-spinal fluid.= } Neither of these symptoms =Escape of brain-matter.= } are present.
=Involvement of nerves.= When dealing with fractures of the middle fossa, allusion was made to the implication of the seventh and eighth pair of nerves as the result of a fracture traversing the posterior fossa of the skull towards the outer angle of the jugular foramen and cutting across the petrous bone (see p. 104).
The ninth, tenth, and eleventh cranial nerves may be injured in the same variety of fracture. These three nerves are, however, so protected by their dural sheaths that they generally escape injury.[21]
In the following cases the nerves were involved:--
The patient was admitted suffering from a fracture resulting from a blow on the posterior parietal region. During the next four days no special symptoms developed. On the fifth day, during a sudden attack of dyspnœa and dysphagia, death occurred. A fissured fracture was found which extended into the jugular foramen, a region occupied by blood-clot.
A man committed suicide by means of a pistol-bullet fired through the mouth. The bullet lodged against the under surface of the petrous bone, tearing the jugular vein and lacerating the nerves passing through that foramen.