Quantitative Evaluation of New Bone and Fibrous Tissue in the Cochlea following Cochlear Implantation in the Human

Abstract

The formation of new bone and fibrous tissue in the human inner ear following cochlear implantation was evaluated by computer-assisted 3-D reconstruction. Seven temporal bones from patients who in life had undergone cochlear implantation were prepared for histological study with the implant in situ. The specimens were sectioned in the axial plane at a thickness of 20 µm. At least every tenth section was digitally reconstructed in three dimensions and volumes of new bone and fibrous tissue were calculated per millimeter length of the cochlea. New bone and fibrous tissue were found in all seven specimens, particularly at the cochleostomy site. In addition, new bone and fibrous tissue had extended to variable lengths along the track of the cochlear implant and in some cases extended beyond the distal end of the implanted electrode. This methodology provides a quantitative tool for evaluation of new bone and fibrous tissue in the inner ear following implantation. This should assist in correlating psychophysical and speech perception tests with intracochlear pathology, evaluating both electrode design and the techniques of preserving residual auditory function.

Hearing Preservation After Cochlear Implantation May Improve Long-term Word Perception in the Electric-only Condition

“…Finally, cochlear trauma during surgery and thereby loss of residual hearing leads to reactive fibrosis and ossification inside the cochlea and around the electrode array (5). Such changes could also diminish the ability to stimulate intact neural fibers selectively and thereby be the reason for the plateau in word perception over the long term in the nHP group.…”

“…Nowadays, minimization of cochlear trauma and/or hearing preservation is attempted in all CI surgeries. Although all surgeries should reduce trauma as much as possible, the following are additional reasons for this goal: 1) in patients with considerable residual low-frequency hearing after cochlear implantation, electro-acoustic stimulation, which allows better speech understanding and music perception, is an option (2,3); 2) the benefit from future treatment options such as stem cell therapy may depend on remaining intact cochlear structures (4); 3) less cochlear trauma leads to less intracochlear fibrosis and ossification (5,6), which simplifies revision surgery.…”

The Histopathology of Revision Cochlear Implantation

“…Despite the low spiral ganglion cell counts, the patient derived benefit from the implants, with scores of 30% open-set word recognition and 66% on open-set sentences in both ears. Somdas et al [2007] developed a methodology to quantitatively evaluate new bone and fibrous tissue using three-dimensional reconstruction (Amira). They evaluated 7 temporal bones and demonstrated the greatest volume of new bone formation at the cochlear base (consistent with the present results) and at sites of trauma to the lateral cochlear wall in the ascending limb of the basal turn.…”

Psychophysical assessment of stimulation sites in auditory prosthesis electrode arrays

“…One variable might be the distances from the electrodes to the sites of action-potential initiation. These distances depend on a number of conditions that occur in the deafened, implanted cochlea including the position of the electrodes within the scala tympani with respect to the modiolar wall (Saunders et al, 2002); the presence of fibrous tissue and new bone within the scala tympani that obstructs the current path between the electrodes and the neurons (Somdas et al, 2007); and neural pathology that varies along the length of the cochlea, influencing the position of the remaining excitable neurons with respect to each stimulation site (Hinojosa and Lindsay, 1980;Nadol, 1997;Fayad and Linthicum, 2006). Current levels decrease as a function of the distance between the electrodes and the sites of action-potential initiation.…”

“…Histological studies have revealed several conditions that could lead to variation in the temporal and spatial patterns of responses in neurons stimulated by each of the implanted electrodes. These conditions include various patterns of nerve loss, and the growth of fibrous tissue and new bone in the implanted cochleae (Hinojosa and Lindsay, 1980;Nadol, 1997;Fayad and Linthicum, 2006;Somdas et al, 2007).…”