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Anatomy of the
Transmastoid Endolymphatic Sac Decompression
in the Management of Ménière’s Disease
Richard Robert Locke
Submitted for the degree of Doctor of Philosophy
The University of Glasgow
Faculty of Biomedical and Life Sciences
© Richard R Locke, 2008
Ménière’s disease affects 1 in 1000 people and produces vertigo and hearing loss
(Morrison, 1981). Endolymphatic sac decompression has been advocated on the basis that endolymphatic hydrops is the underlying pathology. The endolymphatic sac is said to be the terminal dilatation of the membranous labyrinth. It has been proposed that endolymph flows from the semicircular canals and cochlea to the endolymphatic sac.
Portman (1927) devised a procedure for ‘decompressing’ the endolymphatic sac by removal of the bone from the posterior cranial fossa to relieve the symptoms of Ménière’s disease. Surgery on the endolymphatic sac remains controversial.
Shea (1979) and Bagger-Sjöbäck et al (1990, 1993) have studied the endolymphatic sac using different techniques. There are discrepancies in the results between the two studies.
The hypothesis that the endolymphatic sac can be safely approached and decompressed by a transmastoid route was tested. A total of thirteen cadaver heads and ten isolated temporal bones were used. A series of dissections were performed to examine the endolymphatic sac, perform measurements and analyse surgical approaches to the sac.
Histological and electron microscopic study were performed.
The lumen of the endolymphatic sac was not always identifiable in the dura of the posterior cranial fossa or it frequently lay over the sigmoid sinus. In the dura of the posterior cranial fossa where the endolymphatic sac is located was a thickening of the dura. This thickening was present even in the absence of the endolymphatic sac. The endolymphatic sac can be safely approached by a transmastoid approach, if there is an extraosseous component to the endolymphatic sac. The proximal endolymphatic sac can be approached by posterior cranial fossa route.
ACKNOWLEDGEMENTI wish to thank all the staff of the Laboratory of Human Anatomy at the University of Glasgow for their help and support in producing this thesis. In particular I am very grateful for the assistance of Andrew Lockhart with the processing of histology specimens, David Russell for assistance with the electron microscopy and Antony Patton with gross specimens. I would especially like to thank my supervisors, Dr John Shaw- Dunn and Mr Brian O’Reilly.
I am very grateful to the staff at the Massachusetts Eye and Ear Infirmary especially Dr Saumil Merchant for their help and advice in the processing of human temporal bones. I would also like to thank them for allowing me to examine specimens from the Temporal Bone collection and allowing photographs of specimens to be included in this thesis.
I would like to thank Dr Robin Reid and Mr Peter Kerr from the department of pathology at the Western Infirmary, Glasgow, for advice and their help in the processing of temporal bones for analysis.
Finally I would like to thank my family and friends for their support and patience whilst I worked on this thesis, especially my Father, Robert, and my friends, Sara and Mark for proof reading the thesis. Finally a thank you to Paul Rea for his friendship and support, my colleague and my friend.
As I come to the end of producing this thesis I have the opportunity to think back on the work I have done and the places that it has taken me. I am grateful for the opportunity given to me to study at the University of Glasgow and in part at Harvard University Massachusetts. Whilst writing this thesis I have worked as an associate lecturer at the University of Glasgow and completed my Basic Surgical Training. This study of the temporal bone has taken more time than I and my colleagues first anticipated, however I am reminded of a quote from the New York Times: An unhurried sense of time is itself a form of wealth. Time is the simplest thing as Clifford Donald Simak said.
To my gran, Helen Brown, whom I dearly miss.
Since I was a second year medical student studying anatomy at the University of Glasgow I have always had an interest in head and neck anatomy. As my career progressed I developed a keen interest in Ear, Nose and Throat surgery. After graduating and completing my house officer year I had the unique opportunity to return to the University and demonstrate in Anatomy. It was here that I was able to embark on a course of study. Initially I began with a project studying the temporal bone. This quickly flourished into a formal research project and then into this PhD thesis. With a particular interest in the temporal bone I met with Mr O'Reilly, consultant neuro-otologist. We felt that looking at the endolymphatic sac could provide further scientific evidence in the debate over the role of surgery on the sac and Ménière’s disease.
My research led me to the Massachusetts Eye and Ear Infirmary in Boston where I had the privilege of examining the temporal bone collection founded by Harold Schuknecht.
I was given the opportunity of presenting some of my work at the British Association of Clinical Anatomists meeting where I was awarded the Conrad Lewin Prize. This thesis which was begun whilst I was demonstrating in anatomy was completed when I was working as a senior house officer in ENT, having passed my Intercollegiate Membership of the Royal College of Surgeons and completed my Basic Surgical Training.
I hope to demonstrate the reasons why surgery on the sac may or may not be of benefit in the management of Ménière’s disease. Ultimately I want to show that careful analysis of the sac and patient selection may theoretically improve outcomes in endolymphatic sac decompression surgery.
This work has been presented in part at the Scottish Otolaryngological Society and the British Association of Clinical Anatomists and won the Conrad Lewin Prize. It has been published as an
in Clinical Anatomy: LOCKE, Richard R., SHAW-DUNN, John, O’REILLY, Brian. Clinical Anatomy 17; 5, 444 Anatomy of surgical access to the endolymphatic sac for the management of Ménière’s Disease
It is commonly believed that patients with Ménière’s disease have endolymphatic hydrops, a dilatation of the membranous labyrinth. It is thought that increased volume within the endolymph compartment results in tinnitus and sensorineural hearing loss, with typical resolution when an area of the membranous labyrinth ruptures allowing the endolymh to mix with surrounding perilymph. The normal membranous labyrinth has a dilated blind ending projection that extends out of the petrous temporal bone into the dura of the posterior cranial fossa called the endolymphatic sac (Hall-Craggs, 1993).
Surgical treatment of Ménière’s disease can include decompression of the endolymphatic sac in cases unresponsive to medical management. There is great debate as to the structure and function of the endolymphatic sac and the surgery of decompression (Thomsen et al, 1981). Surgery of the endolymphatic sac is designed to relieve the symptoms of hydrops by decompressing the endolymphatic sac and thereby decompress the endolymphatic compartment. Portmann (1927) described the first procedure to decompress the endolymphatic sac via a transmastoid approach; this remains the standard approach to decompress the endolymphatic sac to this day.
Table 1 Endolymphatic sac measurement results Table 2 Endolymphatic sac measurement results 2 Table 3 Age, sex and cause of death of cadavers