Diseases Of The Nose Throat And Ear

CHAPTER 69
OTOSCLEROSIS

In normal conditions the membranous labyrinth is surrounded by two dis-
tinct layers of bone: (1) The inner of these two, the labyrinth capsule proper,
is composed of dense bone directly derived from the cartilaginous capsule
of the otic vesicle in the embryo. For good hearing it is necessary that the
nerve structures of the inner ear should be immediately surrounded by this
layer of dense non-vascular bone. (2) Enclosing this cartilaginous bone, but
distinct from it, there is the ordinary lamellar bone derived from the muco-
periosteum of the middle ear and from the osteogenic layer of the dura
mater. These two layers are partially separated from one another in the
embryo, and also in infants, by a well-marked lymph space. In young sub-
jects, remains of fetal cartilage are sometimes to be found in the promontory
near the anterior margin of the oval window (Fig. 194).

Otosclerosis is a very common disease. Probably 1 person in every 200
suffers from the affection. In many cases Otosclerosis is present, unsuspected,
in the labyrinth capsule and only becomes manifest when it involves the
hearing mechanism.

AETIOLOGY. The disease is much more common in the female than the
male sex. There is marked hereditary tendency to Otosclerosis in certain
families, and in nearly 50 per cent of cases a history of deafness in the family
can be obtained. The disease usually becomes manifest between the ages
of 18 and 30, but it may begin earlier. There appears to be a close relation-
ship between the onset of deafness and the onset of puberty or the occur-
rence of pregnancy.

PATHOLOGY. The bony changes vary according to the duration of the
disease. At first the normal bone is absorbed and replaced by vascular
spongy osteoid tissue. The process advances along the blood vessels. Later
the new bone becomes thicker and less vascular. The most common site of
disease is the promontory in the region of the anterior margin of the oval
window (Figs. 195, 196), and in advanced cases the stapes becomes anky-
losed in position by a mass of spongy new bone. Various reasons have
been given to explain this 'site of election' for bone disease in Otosclerosis.
It may be worthy of note that there is in this region an anastomosis between
the vessels of the middle ear and those of the labyrinth capsule. Of greater
possible significance is the fact that in this area is located the fistula ante
fenestram, a vestigial structure which frequently contains cartilaginous
remnants and which is particularly prone to otosclerotic change.

SYMPTOMS. The chief symptoms are gradually increasing deafness and
tinnitus. The noises are often referred to the head rather than the ear and
occasionally cause the patient more discomfort than the deafness. If tinnitus
is marked, the case is likely to progress rapidly. Paracusis Willisii is frequently

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