Normal and pathologic features of the limbus spiralis and its functional significance.

The normal and pathologic morphology of the limbus spiralis was studied by light and electron microscopy. Beneath the interdental cells are stellate, mesothelial, osmiophilic, and light types of fibrocytes. Morphologic evidence suggests that the stellate type cells occupying the main body of the limbus are actively engaged in the recycling of ground substance. The loosely interwoven mesothelial cells (dark cells) continuous with those of Reissner's membrane may participate in the secretion and maintenance of perilymph. Below this superficial cell lining are the osmiophilic and light cells, which appear to serve as a partial barrier to the exchange of substances between the scala vestibuli and the limbus proper. The collective data from experiments on vascular occlusion, drug toxicity, acoustic trauma, and perilymph and endolymph fistulae indicate that these connective tissue cells, particularly the stellate type of cells, are highly susceptible to injury. The lesions are often total or nonexistent, and are common in the basal and apical turns. When the lesion is small, the region adjacent to the inner sulcus cells is most frequently affected. In severe lesions, the adjacent interdental cells and sensory cells often remain normal. When the organ of Corti is concomitantly affected, the outer hair cells are usually missing. A common factor associated with limbus cell atrophy appears to be changes in ground substance due to the contamination of perilymph. Another factor associated with fluid contamination is the permanent or temporary cessation of blood flow to the limbus capillary arcades. The limbus spiralis may serve as one of the most sensitive indicators of alterations in the chemical composition of perilymph.