Exostoses vary greatly both in size and consistency. Some are densely hard—ivory exostoses—others possess a covering of compact bone, whilst their interior is made up of cancellous tissue continuous with that of the bone from which they arise. The denser variety seldom attain any considerable size, but the less compact, growing in the direction of least resistance, often attain such dimensions as to be both unsightly and dangerous. Thus, a frontal exostosis may invade the frontal air sinus and grow into the orbital cavity, obliterating the sinus, interfering greatly with ocular movements, causing protrusion of the globe and even destruction of the eye.
An aural exostosis may block up the external auditory meatus, compress the facial nerve, and lead to the development of a mastoid empyema.
It might also be added that there are a few cases on record in which a frontal exostosis, by reason of extensive inward growth, has produced cerebral symptoms—general compression and intellectual deterioration.
Treatment.
In considering the question of treatment, it must be accepted that, although of slow growth, some of these exostoses are definitely progressive, tending to interfere with the character and functions of the region with which they are anatomically situated. There is also reason to believe that those secondary changes—sarcomatous, myxomatous, &c.—which are occasionally observed in the exostoses of long bones are also liable to develop in those cranially situated. The question of treatment hinges, therefore, to a large extent on the nature and position of the tumour.
When of the ivory type and growing from the flat bones of the skull, but so situated that no marked deformity or pressure symptoms are likely to ensue, they may be left alone, but when definitely progressive and situated in accessible regions, they should be removed. Their exposure is carried out by the formation of a suitable scalp-flap—designed as far as possible so as to be subsequently hidden by the hairy scalp—and the exostosis removed by the application to its base of a Gigli saw. This method is greatly superior to the older procedures whereby the tumour was chiselled away with hammer and gouge.
Occasionally the tumour is so dense and presents so wide a basal attachment that it becomes necessary to attack from a more distant line, cutting out a trench, deepened to the diploic tissue, circumferentially around the tumour and levering away the central mass. When the tumour extends more deeply, involving nearly the whole thickness of the skull, it may be removed by the application of a small trephine immediately to one side of the tumour, followed by the use of de Vilbiss forceps circumferentially around the main mass, thus freeing it from its surroundings. The resultant gap in the skull may be protected by one or other of those measures enumerated in [Chapter VI].
Frontal and mastoid exostoses often necessitate formidable operations insomuch as their size and anatomical relations present considerable difficulties (see [Fig. 94]).
The indications for operation in the case of aural exostoses are as follows[78]:—
1. If there is middle-ear suppuration and signs of retention of pus.