Pagets Disease

tributed. X-rays of temporal bone specimens show the well-defined lesion as a patch of mottled translucen-cy (Fig. 8.17).

The histological characteristic of otosclerosis is the presence of trabeculae of new bone, mostly of the woven type with marked vascularity. This contrasts with the well-developed lamellar bone under the outer periosteum, the endochondral middle layer and the endosteal layer of the otic capsule, a sharply demarcated edge between normal and otosclerotic bone being a prominent feature. In most places osteocytes are very abundant within the woven bone. The footplate of the stapes is often invaded by otosclerotic bone, and the lower end of the anterior crus of the stapes is sometimes invaded (Fig. 8.18). Otosclerotic bone sometimes reaches the endosteum of the cochlear capsule. In some cases it may lead to a fibrous reaction deep to the spiral ligament. These changes are probably the basis of the sensorineural hearing loss that is also occasionally found in cases of otosclerosis.

Stapedectomy with insertion of a prosthesis to replace the fixed stapes and so reinstate the mobility of the ossicular chain is frequently performed as a treatment for otosclerosis. If the specimen of stapes is composed of the head and crura only microscopical examination will not show the changes of otosclerosis. On the other hand, if the whole stapes is removed, as is usually the

Paget's disease (osteitis deformans) is a common condition affecting particularly the skull, pelvis, vertebral column and femur in people over 40 years of age. The cause is not yet certain, but the presence in many cases of paramyxovirus-like structures seen within osteo-clasts has prompted the suggestion that Paget's disease may be of viral aetiology and the measles virus and canine distemper viruses have been under scrutiny as candidates. The pathological change is one of active bone formation proceeding alongside active bone destruction. The affected bones are enlarged, porous and deformed. Microscopically, bone formation is seen in trabeculae of bone with a lining of numerous osteo-blasts. A mosaic appearance is formed by the frequent successive deposition of bone, cessation of deposition resulting in thin, blue "cement lines", followed again by resumption of deposition and its cessation, and so production of further cement lines. Bone destruction is shown by the presence of numerous, large osteoclastic giant cells with Howship's lacunae. Areas of chronic inflammatory exudate intermixed with the bone are common.

In the temporal bone the petrous apex, the mastoid and the bony part of the Eustachian tube are most frequently affected [23, 79]. The periosteal part of the bony labyrinth is the first to undergo pagetoid changes and the pagetoid changes spread through the bone towards the membranous labyrinth, usually with a sharp line of

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