The involvement of nerves.
The following nerves may be involved in anterior fossa fractures:—
(a) The olfactory nerve.
The great majority of anterior fossa fractures traverse the cribriform plate, necessarily injuring the fine branches of the olfactory bulb. The bulb itself may be lacerated, with or without injury to the under surface of the frontal lobes. Sir Prescott Hewitt considered that anosmia, or loss of smell, resulted most frequently from blows applied to the back of the head, the frontal region being injured by contre-coup. From my own experience it would appear, however, that anosmia, whether uni- or bilateral, whether transient or permanent, generally results from direct injuries of the cribriform plate with associated lacerations of the olfactory nerves. It is difficult to estimate the presence or degree of immediate loss of smell on account of the general condition of the patient and because the nostrils are usually more or less filled with blood coagulum. Experience shows, however, that early loss of smell is the rule and total and permanent anosmia the exception. Anosmia is usually associated with some degree of loss of taste.
(b) The optic nerve.
Many cases have been recorded in which visual defects resulted from blows applied to the head. The blindness may be partial or complete, immediate in onset or developing at some future date. In the latter case, the loss of vision is due to retinal changes or results from post-neuritic atrophy.
The occurrence of complete or partial blindness as the immediate result of the injury is, at first sight, difficult to explain, for the vast majority of anterior fossa fractures avoid the immediate vicinity of the optic foramina, passing by preference between the two foramina or diverging towards the sphenoidal fissures. Small fissured fractures not infrequently radiate through the optic foramina, usually, however, of so slight a nature as to be incapable of leading to any gross lesion of the optic nerves. Hæmorrhage into the sheath of the nerve is probably responsible for a certain proportion of cases, more especially those in which there is a peripheral concentric loss of vision, the more central fibres escaping. It is possible, also, that cases evidencing temporal or nasal blindness may be due, as J. J. Evans[17] thinks, to a contre-coup contusion of the nerve through it being forcibly driven against the bony boundaries of the foramen. Taking into consideration, however, the very frequent presence of a fracture through the anterior clinoid process (see [p. 82]), and the usual displacement of that process, it would appear probable that immediate and more or less complete loss of vision results from the compression and crushing of the optic nerve by reason of the pressure exercised by a displaced clinoid process.
The following statistics add confirmation to this view. Thus, Callen collected 17 cases in which the optic nerve was compressed by osseous fragments in the region of the optic foramen, whilst Holder observed injury to the bones entering into the formation of the foramen in 53 out of 86 cases of fracture involving this region.
The prognosis varies according to the cause of the blindness. When resulting from concussion of the nerve trunk or from hæmorrhage into its sheath, certain fibres may regain their function. In the majority of cases, however, that have come under my own observation, blindness of the affected eye was immediate and permanent.