ARE THERE "VARIATIONS IN THE COURSE OF THE FACIAL NERVE HAVING BEARING

I'

UPON THE MASTOID OPERATION"?

BY B. ALEX. RANDALL, M.A., M.D., PHILADELPHIA.

(With Text-plate I.)

N our operative work upon the carious middle ear several of the former bugbears have sunk out of view and it may now be said that the operator often prefers to encounter the dura by laying bare the sigmoid sinus and the middle fossa, so little does he fear ill-result from this as compared with the danger of failing to evacuate extradural pus at these points. It remains otherwise with the facial nerve, however; and while we occasionally lay it bare in cases where its function is already destroyed or in other cases curette its carious canal at known risk of causing such injury, it is yet to be sedulously avoided in the great majority of operations. Were it possible by watching for twitchings of the face, as is sometimes claimed, to get timely warning that we are approaching it dangerously, we might rest upon this precaution; but I feel sure that severe and persistent injury is too often inflicted unheralded by any such warning. We must, therefore, base our safety from this distressing accident upon a good comprehension of the anatomy of the parts.

In a recent paper (A. f. O., lvii., p. 96) Schwartze presses further his claims as to variability of the course of the facial canal, and figures specimens which he has prepared to show that the descending portion of the nerve as it passes down may be steep or very oblique in its outward trend or may occupy a middle relation--"Schrägverlauf,"-differences which may count for much as to its vulnerability in respect

FIG. 1. Posterior half of Temporal vertically sectioned in the axis of the external meatus and with the Facial canal chiselled open to show its relation to the tympanic Annulus (Author's preparation).

FIG. 2.-Skull with Reid's base line and vertical indicated and a probe impacted in the descending portion of each Facial canal.

to the removal of the back wall of the ear canal.

"While

the Facial lies far internal to the upper part of the margo tympanicus, it passes in its downward course so far outward . . that it can come not only into the plane of the lower part of the tympanic margin (Steilverlauf) but even far outside of the lower part of the margo tympanicus (Flachverlauf)." "The facial can come so near the surface of the mastoid process that even by the first chisel-strokes an injury of it is possible." The latter claim is incomprehensible; but as to an outward course of the facial, others have more vaguely urged the same view, and I believe it is quite generally held.

So far as I know, I stand alone in stating that the descending portion of the facial canal is almost exactly vertical (Fig. 1), and forms one of the most constant features of the temporal bone. It is by this that we can most surely as well as most conveniently orientate the detached bone. This view has been impressed firmly upon me by all my studies and has long constituted a positive point in my teaching; so the publication of Schwartze's contradictions of it forces me to an immediate review of the question.

As a first step I have measured the first hundred skulls of the Hyrtl Collection in the Mütter-Museum as to the direction of this portion of the canal. To gain the desired information I have simply inserted straight probes into the stylo-mastoid foramina of the inverted skulls (Fig. 2), allowing them to penetrate by gravity if possible and confirming or correcting the accuracy of their placing in the axes of the canals before making a final reading. With Reid's base-line held parallel to a distant horizontal line, it is easy to note the least deviation of the probes from the perpendicular, and then by similar comparison of the skull viewed from the occiput to measure (by a large protractor if desired) any inward or outward direction of the probes. This group of skulls is especially convenient for such mensuration, since they have already been carefully measured in respect to their general configuration and dimensions and especially as to the direction of their external auditory canals'; but I expect to press Transactions, American Otological Society, 1892, p. 235: These ARCHIVES, ? Transactions, American Otological Society, 1894.

1894.

the study to much larger numbers before offering more than this preliminary report.

Suffice it now to state that in the sagittal plane the deviations from the exact perpendicular were absent, while they were rather more frequent in the transverse plane of the skull than I had expected, since only 58 of the 100 showed no recognizable departure from this position. In no case was this deviation more than 10 degrees and in but 30 was it more than 1 or 2 degrees; and in 27 of these the direction was inward towards the vertebral column, not outward as generally claimed. Taking every case in which the least outward tendency could be assumed, I noted 4 in which it was not measurable, 5 of 1-2 degrees, and only 3 where it was notable-twice 10 degrees and once 5 degrees outward. Even thus much confirmation of Schwartze's claim is worthy of careful consideration; but closer study of these three cases shows that slight over-development of the para-mastoid process had in each encroached slightly upon the exit of the canal, and that the probe did not fairly indicate the really vertical direction of the canal within.

Another point which may enhance but now seems to neutralize all force of Schwartze's claim is brought out in this series of studies. The external auditory canal is the natural structure with which clinically to compare the direction of the facial, since it is in the removal of its back wall that there is most surgical importance in precisely locating the nerve. The direction of the meatus I have shown' to vary notably both in the vertical and in the horizontal plane -the extreme differences in each direction being sometimes 20 degrees, with an average direction of 10 degrees upward and 10 degrees forward as it passes inward. This direction seems to vary somewhat with the development of the skull and somewhat with its long-head or broad-head configuration; but to neither of these nor to the estimated direction of the Facial canal has it shown in my studies, so far as they have been carried, any definite relation.

In the paper of Seldon Spencer' to which reference is

1 Transactions, American Otological Society, 1894, p. 87.

2 Medical Bulletin, Washington University, April, 1902.