Otitis media is one of the most common of all diseases, particularly in young children. The disease is usually caused by bacterial infection, Haemophilus influenzae and Gram-positive cocci usually being incriminated in the acute form and Gram-negative bacilli in the chronic form. The clinical forms of the acute and chronic conditions correspond to the pathological changes, but intermediate or mixed states are frequent. Perforation of the tympanic membrane may occur at any phase of otitis media, but an effusion, accompanied by all of the other manifestations of chronic otitis media, is often present behind an intact tympanic membrane, a condition known as serous otitis media.
The appearances of the middle ear mucosa in acute otitis media may be seen in the bone chips removed at mas-toidectomy. There is congestion and oedema of the mucosa of the mastoid air cells. Haemorrhage may be severe and the mucosa and air cells are filled with neutrophils. Pus destroys bone, the actual dissolution being carried out by osteoclasts. At the same time new bone formation takes place, commencing as osteoid, later becoming woven and finally lamellar. Fibrosis may also be active even in the acute stage. Acute inflammatory changes are also prominent in other parts of the middle ear. The tympanic membrane shows marked congestion, the dilated vessels distending the connective tissue layer. Pus cells fill the middle ear cavity. The acute inflammation may spread deep into the temporal bone as osteomyelitis.
The chronic form of otitis media is associated with necrosis, caused by the bacterial infection. There is, as in the acute form, marked congestion. The latter results in haemorrhage in many cases. Because of the poor lymph drainage in the middle ear old haematoma becomes converted into cholesterol granuloma, with cholesterol clefts surrounded by foreign body-type giant cells, and haemosiderin.
Associated with these changes and representing an important part of the pathological picture, is prolifera-tive activity of middle ear tissue. The columnar epithelium of the middle ear has, in the presence of inflammation or other pathological changes in the middle ear, the remarkable property of invaginating itself to produce glands, which often develop luminal secretion. The glandular transformation of the middle ear mucosa, known as glandular metaplasia, may be seen in any part of the cleft, including the mastoid ear cells. The se cretion of the glands contributes to the exudate in otitis media with effusion. Fibrous tissue proliferation may also occur in combination with glandular transformation - a process which, in the advanced state, has been called "fibrocystic sclerosis" .
A specific form of reparative reaction following inflammation is the development of granulation tissue. In this process, the endothelium of blood vessels and fibroblasts are the newly formed cells. Mononuclear inflammatory cells usually accompany the latter. The granulation tissue is usually particularly prominent in the middle ear under the mucosa covering the promontory from which it frequently protrudes into the external canal through a perforation of the tympanic membrane, forming an aural polyp that is covered in pseudostratified columnar, ciliated respiratory or stratified squamous epithelium. Fibroblasts and collagen are abundant in the terminal phase of the reparative stage.
A normal degree of fibroblast cellularity in the fibrous reaction is seen in adhesive otitis media. A peculiar form of scar tissue production occurs in the middle ear, in which the collagen is poorly cellular and hyalinised. This condition, known as tympanosclerosis, is also characterised by deposition of calcium salts in the hyaline fibrous tissue. The bony walls of the middle ear also frequently react to the inflammatory process with a new formation of bone. This is woven in the early stages and lamellar later.
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