Considerations in Graft Healing

The normal tympanic membrane has a complex layered structure consisting of thin stratified squamous epithelium on the lateral surface, flat respiratory epithelium on the medial surface, and two fibrous layers, one radial and one longitudinal, between the two epithelial layers. The fibrous layers also contain vascular elements. successful, functional repair of the tympanic membrane requires reconstitution of the epithelial layers and enough of a fibrous middle layer to provide satisfactory mechanical support.

When a tympanic membrane heals spontaneously without grafting, the perforation is often closed by the squamous epithelium before fibrous elements develop. The fibrous layer may be attenuated or even lacking. The resultant tympanic membrane has an area that lacks the tensile strength, elasticity, blood supply, and resistance to future perforation of a fully reconstructed tympanic membrane. such areas are referred to as "dimeric" because the squamous epithelium lies against the mucous membrane without intermediate fibrous elements.

The healing process after grafting appears to be initiated by angiogenesis within the tympanic membrane remnant, especially at the margin of the perforation. During healing the fascia is a scaffold for epithelialization. The margins of the freshened edges of the perforation (see below) are the sources for the migrating epithelia. Fascia is composed of fibroblasts in a collagen matrix. Its low metabolic rate and its extracellular matrix permit it to persist until it becomes vascularized.

A critical problem early in the development of tympanoplasty was finding a suitable material for tympanic membrane grafting. Since the 1950s, several tissues have been proposed for donor graft materials, including split-thickness skin, full-thickness skin, vein, allograft tympanic membranes, and prepared collagen materials.

This chapter describes the use of temporalis fascia, which is now the most widely used mate-rial.5,6 Temporalis fascia results in rapid, reliable healing of an appropriately thin tympanic membrane. It can be obtained from the same operative field, often from the same incision used for access to the ear (Fig. 3-1). Epidermal growth factors have been used to enhance healing experimentally.22

Medial grafting techniques take advantage of the ability of respiratory epithelium (unlike squamous epithelium) to incorporate the graft material when the graft is placed against it. The squamous and respiratory epithelial layers and the fibrous layer are in contact with the rest of the tympanic membrane after healing.23,24

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Responses

  • Valerio Panicucci
    Why healed tympanic membrane lack fibrous layer?
    4 years ago

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