Suresh Mukherji
Inner ear malformations are one of the most challenging and confusing topics in all of neuroradiology (and radiology for that matter). The topic has “haunted” radiology residents for years, and I remember being a petrified fourth-year resident in the spring of 1992 (last century!), preparing for the oral boards and being completely flummoxed by the temporal bone. I remember asking one of my neuroradiology faculty about how to approach the temporal bone for the oral boards. His answer was, “If they show you a weird temporal bone CT, just say Mondini malformation and go to the next case!” Based on my conversations with many colleagues since that time, I believe many adopted this strategy!
The most widely accepted approach to categorizing inner ear malformations for many years was published by Jackler et al1 in 1987. It was a very practical approach that was based on the embryonic development of the inner structures. The inner malformations were categorized according to when the arrest in fetal development occurred. The most “benign” of these malformations is the abnormality reported by Mondini in his seminal 1791 article, which occurs at a late stage in inner ear development.2–4
Technical improvements in CT and MRI have resulted in our ability to visualize detailed structures of the inner ear that previously could only be identified in histology textbooks. Lemmerling et al5 and Davidson et al6 published 2 very important papers in the late 1990s that identified subtle malformations of the modiolus causing subtle contour abnormalities of the cochlea in patients with enlarged vestibular aqueducts. These important works were the first to describe modiolar malformations previously documented by Schuknecht in his classic textbook.7
Sennaroglu and Saatci8 introduced their classification of inner ear malformations in 2002. Their approach was a modification of Jackler’s classification but introduced the term “cystic cochleovestibular malformation” to describe an inner ear malformation that had an incompletely formed cochlea and vestibule. This malformation was also referred to as “incomplete partition type I (IP-I).” The classic Mondini malformation was called “incomplete partition type II (IP-II).”
This edition of the AJNR News Digest contains several important articles that review the current classification of inner ear malformations, identify ways to detect subtle cochlear malformations, highlight potential genetic associations with inner ear anomalies, and highlight the role of 7T MRI in furthering our understanding of the normal anatomy and subtle malformations.
Huang et al9,10 present a state-of-the-art review of sensorineural hearing loss and review the current Sennaroglu classification of inner ear malformations. Booth et al11 and Reinshagen et al12 expand the seminal findings reported by Lemmerling et al and Davidson et al and describe different measurements to detect subtle cochlear IP-II malformations that could otherwise be easily overlooked. The article by Verheij et al13 discusses the anatomic malformations associated with 22q11.2 deletion syndrome.