Atypical mature bone in the otosclerotic otic capsule as the differentiated zone of an invasive osseous neoplasm.

CONCLUSION: A large proportion of the mature otic capsule bone in cases of otosclerosis lies in plaques in direct contiguity with active otosclerosis and, because it shows significant structural defects, it should be regarded as part of the otosclerotic process. These appearances support our previously described suggestion that otosclerosis is an invasive osseous neoplasm, the mature atypical bone representing differentiation of earlier-formed invasive neoplastic osseous tissue. OBJECTIVES: We sought structural features in differentiated bone within the otic capsules of cases of otosclerosis that might indicate a relation to the underlying disease process. METHODS: Fifty temporal bones from 42 adult patients with otosclerosis were processed into stained histological sections and the appearance of the otic capsule was compared with that of the same tissue, processed in the same way, in 10 cases that did not show otosclerosis. RESULTS: In the cochlear otic capsules of otosclerotic temporal bones, when traced back along the otosclerotic plaque from the invasive front, atypical shapes and arrangements of osteons were seen, often with otospongiosis (severe dilatation of multiple Volkmann's canals), culminating in larger differentiated osteons with irregularities in structure. In the medial region of the otosclerotic cochlear otic capsule, at a similar position to that where giant normal osteons are present in the normal temporal bone, differentiated, giant abnormal osteons were seen. In the otosclerotic vestibular otic capsule there were changes similar to those of the otosclerotic cochlea (apart from the giant osteons) and many osteons composed of clusters of atypical osteoblast-like cells around highly atypical Volkmann's canals.

Origin and growth of otosclerosis.

CONCLUSION: The external layer of the otic capsule arises from periosteal osteoblasts, which produce large numbers of Volkmann's canals as well as lamellar bone. The main plaque of otosclerosis is a histologic replica of the external layer and seems to arise from similar cells in the periosteum and to follow a defined invasive course into the footplate of the stapes, the basal coil of the cochlea and the saccule. OBJECTIVES: To determine by histologic study of the developing otic capsule and temporal bones with otosclerosis the site, tissue of origin, and pathways of growth of the disease. METHODS: Step sections of 60 celloidin-embedded temporal bones from fetuses and 24 from patients aged between 1 and 52 years were examined in the study of the development of the otic capsule. Step sections of 65 temporal bones each with 2 or more deposits of otosclerosis were surveyed to obtain data on the site, tissue of origin, and pathways of its growth. RESULTS: The otic capsule differs from other bones in that the formation of the ultimate lamellar bone tissue is accompanied by very numerous intercommunicating channels. In the middle (cartilage origin) layer these are chondro-osseous canals and Volkmann's canals (like Haversian canals, but multidirectional). In the external (periosteal origin) layer these are Volkmann's canals only. In all, 63 of the 65 temporal bones with otosclerosis that were studied showed a prominent posterior otic capsule plaque. Evidence that this is derived from the periosteum of the external canal is as follows. (a) The otosclerotic tissue of the plaque--like all otosclerotic tissue--is composed of Volkmann's canals and lamellar bone only, as does external layer tissue. (b) All posterior plaques have an edge at the periosteum bordering the processus cochleariformis and tensor tympani muscle. The presumed invasive edge of the plaque on the opposite (cochlear) side shows a variable level of its front. (c) The tissue on the cochlear side of the plaque has a darkly stained appearance with large numbers of osteoblasts and poorly differentiated Volkmann's canals, suggesting that this is an invasive front. The otosclerosis becomes progressively better differentiated away from the darkly stained zone, indicating increasing maturation, which is greatest in the suggested origin of the plaque at the processus/tensor tympani muscle region because this would be the oldest region of the plaque. The pathway of the growth indicated by this study suggests a possible time sequence in the symptomatology of otosclerosis as it moves first to stapes footplate and then through the spiral ligament of cochlea to the saccule. An anterior plaque was seen in 42 of the 65 temporal bones with multiple sites of otosclerosis examined. These showed features similar to those listed above for the posterior plaque, with a base on the periosteum bordering the canal for the internal carotid artery, dark zonation at the invasive front near the cochlea, and increasing differentiation towards the base.

The intravestibular source of the vestibular aqueduct. III: Osseous pathology of Ménière's disease, clarified by a developmental study of the intraskeletal channels of the otic capsule.

CONCLUSION: Review of the histopathological changes in the vestibular arch in Ménière's disease, after a study of development of the otic capsule, indicated a severe apoptotic loss of osteoblasts with consequent denudation of these cells from and damage to the osseous canal structure of the arch. OBJECTIVE: To review previously reported histological findings in the inner layer of the vestibular aqueduct and its intravestibular source in Ménière's disease, using newer knowledge of otic capsule development. METHODS: Temporal bone histological sections from the vestibular arch region of eight patients with Ménière's disease were reviewed in our London-based material. RESULTS: Minute granules suggesting apoptotic bodies were found in the arch in the majority of cases, giving support for the concept of an apoptotic loss of osteoblasts. Explanation for the previously described appearance of proliferation of atypical channels and of small, finely outlined empty areas in the bone was provided by the observation of denudation of osteoblasts from Volkmann's canals and microcanals. These canals had been recently described in a developmental study of the otic capsule. Dislocation of dead microcanals into blood vessels of Volkmann's canals was seen in two of the cases.

The intravestibular source of the vestibular aqueduct. II: its structure and function clarified by a developmental study of the intra-skeletal channels of the otic capsule.

CONCLUSION: A developmental histologic study of the otic capsule indicates that it grows a system of lamellar bone with abundant interconnecting intraosseous channels. These include the 'cartilage canals' in the cartilage model, the chondro-osseous and Haversian-like (Volkmann's) canals in the ossified otic capsule, the fissula ante fenestram, which seems to function as a lifelong manufacturer of the latter two channels, and the inner layer (vestibular arch) of the vestibular aqueduct, which is a complex series of Volkmann's canals and microcanals. Chemical changes, possibly produced by breakdown of cells within the channels, may provide a homeostatic environment for the functions of hearing and balance that take place in the endolymphatic fluid. OBJECTIVES: We studied the development of the otic capsule to clarify the cellular appearances that we had previously described in the normal vestibular arch and the changes in that structure in Ménière's disease. METHODS: Step sections from 84 temporal bones, including those from fetuses, children and adults from a variety of ages were examined histologically. RESULTS: Cartilage canals, bringing blood vessels and mesenchymal cells from perichondrium to the depths of the cartilage model to mediate ossification, are found early in fetal life and disappear when ossification is complete at about 24 weeks. The otic capsule is formed of chondro-osseous canals, which are composed of trabeculae of mineralized cartilage lacunae containing mesenchymal cells that undergo ossification (globuli ossei); also Volkmann's canals (like Haversian canals in long bones but multidirectional), which are produced from osteoblasts. The lumina of the latter frequently link up with chondro-osseous canals. Lamellar bone forms the background of the otic capsule. The fissula ante fenestram is present from early in the cartilage model and then throughout life. It appears to mediate bone production and the new formation of chondro-osseous channels and Volkmann's canals. The internal layer of the vestibular aqueduct (vestibular arch) is seen in the cartilage model of the otic capsule (present in early fetal life) as a vascular layer of perichondrally derived connective tissue (not cartilage) surrounding the endolymphatic duct. When endochondral ossification starts, the bone from the adjoining cochlear and vestibular sides embrace this connective tissue layer to form the outer bony layer of the vestibular aqueduct. Osteoblasts then fill the inner layer with lamellar bone and macro- and mini-Volkmann's canals. At 1 year osteoblasts in the walls of macro-Volkmann's canals, proliferating thereafter throughout life, produce large numbers of microcanals. It is possible that slow breakdown of these osteoblasts and of similar cells in the canals of the otic capsule proper may contribute to the homeostasis of the endolymphatic duct and that of the rest of the membranous labyrinth, respectively.