The Multifaceted Human Round Window Anatomical Aspects and Clinical Relevance

There is an increasing clinical interest in the human round window region through the arise of novel medical treatments such as cochlear implantation (CI), middle ear pharmacotherapy, and gene therapy strategies. Here, we analyzed anatomic variations of the round window niche (RWN) and membrane (RWM) using synchrotron phase-contrast imaging (SR-PCI) of human cadaveric specimens. Results were combined with light (LM) and electron microscopy (TEM) investigations of optimally preserved human tissue.

SR-PCI and 3D reconstructions of the round window region were accomplished in 66 human cadaveric temporal bones. RWN and RWM morphology was analyzed and correlated with light and electron microscopy studies of human cochleae.

SR-PCI showed the wide variations in both size and shape of the human RWN. A pseudomembrane was present in 80% of the specimens, of which 20% were complete. In 3%, the RWN contained dense tissue or secrete plugs partly or entirely obstructing the niche. Bone channels communicated between the spiral ganglion and RWM and were found in all specimens. Tympanic-meningeal fissures and infra-labyrinthine clefts are described.

The human RWN forms a highly variably shaped corridor to the RWM and cochlear base. It may be subdivided and partially closed by a pseudomembrane or soft tissue obscuring the RWM. The RWM seems to be invariably reached by channels containing neural or stretch-receptor-like structures from the spiral ganglion believed to be involved in perilymph pressure regulation.