Objectives: In 1838, Edward Cock described the anatomic findings in 4 inner ears with a widely patent communication between the cochlea and the vestibule that is now frequently referred to as the "common cavity deformity" and is often confused with Michel's "otocyst deformity." Little is known about the anatomic characteristics, including the presence of neural elements in this malformation.
Methods: Light microscopy and 2-dimensional and computerized 3-dimensional reconstructions were used to determine the histopathology and spiral ganglion cell counts in 7 temporal bones with a widely patent cochleovestibular communication.
Results: In all 7 specimens, the cochlea, vestibule, and semicircular canals were distinguishable and a bony defect resulting in an abnormal communication of perilymphatic space between the cochlea and vestibule was present. The ductus reuniens was abnormally wide in all. The cochlear duct varied from less than 1 turn to up to 2 turns. The mean spiral ganglion cells were estimated as a percentage of age-matched normal controls at 2.3%, 16.5%, and 26.8% when the cochlea was approximately 1, 1(1/2), and 2 turns, respectively (p = .007). The cribrose area consisted of a thin membrane in 2 specimens, and Rosenthal's canal openly communicated with the cerebrospinal fluid space in 3 specimens. The stapes footplate was abnormal in all 7 specimens and consisted of a central defect bridged by a thin membrane in 4 specimens. The facial nerve was dehiscent in 5 specimens (71%) and also followed an anomalous course in 2 specimens (28%).
Conclusions: The widely patent cochleovestibular communication is a distinct inner ear malformation, recognition of which may have important clinical implications. Estimates of spiral ganglion cells can be predicted from the number of cochlear turns. Although cochlear implantation is feasible in patients with this malformation, a higher risk of cerebrospinal fluid gushers, facial nerve injuries, meningitis, and poor performance would be predicted. A better understanding of the anatomy will allow more effective surgical planning and techniques and may have a significant impact in improving outcomes.