INIS-mf —11OO6 COMPUTED TOMOGRAPHY OF THE PETROUS BONE IN OTOSCLEROSIS AND MENIERE'S DISEASE J.A.M.DEGROOT ' '. i. i ./„.. COMPUTED TOMOGRAPHY OF THE PETROUS BONE IN OTOSCLEROSIS AND MENIERE'S DISEASE Cover design: Rene Smoorenburg DRUKKERIJ ELINKWIJK BV - UTRECHT RUKSUNIVERSITEIT UTRECHT COMPUTED TOMOGRAPHY OF THE PETROUS BONE IN OTOSCLEROSIS AND MENIERE'S DISEASE Computertomografie van het rotsbeen bij otosclerose en bij de ziekte van Meniere (Met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor in de geneeskunde aan de Rijksuniversiteit te Utrecht, op gezag van de rector magnificus Prof.Dr. J.A. van Ginkel, volgens besluit van het college van dekanen in het openbaar te verdedigen op dinsdag 14 april des namiddags te 4.15 uur in het hoofdgebouw der universiteit door Johan Antonius Maria de Groot geboren te Utrecht Promotores: Prof. dr. E.H. Huizing Prof. dr. P.F.G.M. van Waes Aan Corrie Harry Trudy ACKNOWLEDGEMENTS This dissertation was produced in the Departments of Otorhinolaryngology and of Radiology of the Utrecht University Hospital, Utrecht, the Netherlands. The author wishes to thank Prof. dr. Egbert H. Huizing (Head of the Department of Otorhinolaryngology) who has spent so much time in supervising this work, and Prof. dr. Paul F.G.M. van Waes (Department of Radiology) for his support and enthusiasm. Many thanks are due to Mr. Frans W. Zonneveld M.Sc. (Philips Medical Systems), whose scientific and technical contribution has been essentially for this study, to Dr. Henk Damsma (Department of Radiology) for his evaluation of the CT scans and to Dr. Jan E. Veldman (Department of Otorhinolaryngology) for his valuable corrections and suggestions. He would like to thank Prof. dr. A.C. Kiinkhamer (Head of the Department of Radiology), Prof. dr. S.A. Duursma (Head of the Department of Internal Medicine, bone metabolism), Prof. dr. W.J. van Doorenmaalen (Head of the Laboratory of Anatomy) and Prof. dr. P. Bretlau (Head of the Department of Otorhinolaryngology of the University of Copenhagen) for their suggestions and scientific judgement. Many thanks are also due to Mr. Marcel Metselaar for his help in the realization of the photographical part, Dr. Frank Besamusca for his initial and Mrs. Gayle Johnson for her final listinguic corrections and to Dr. Kobus Dijkhorst for his support in matters of soft- and hardware. Finally, the author is very grateful for the moral support of all who have followed the proceedings of this work with interest. Utrecht, April 1987 John de Groot CONTENTS PART I Computed Tomography of the petrous bone 1 PART II CT investigation of the cochlear capsule in otosclerosis 33 PART III CT investigation of the vestibular aqueduct in Meniere's disease 95 Summary in Dutch - Samenvatting in het Nederlands 137 Curriculum Vitae 143 GENERAL INTRODUCTION In this study the pathology of the cochlear capsule in otosclerosis and of the vestibular aqueduct in Meniere's disease was investigated by means of high-resolution CT scanning. Computed Tomography (CT) can be considered as the most important improvement in the area of X-ray diagnostics during the last twenty years. Technical developments have resulted into an increase in spatial resolution. The 'high-resolution' scanner of the third generation facilitates the visualization of the more delicate structures in the temporal bone. Previous studies on otosclerosis and Meniere's disease (by means of classical polytomography) have presented a more or less confusing picture. In this study we tried to find out if CT scanning of the temporal bone can clarify some of the questions raised by polytomographical studies. In order to analyze these problems, this study is divided into three parts: PART I : Normal radiographical 3natomy of the temporal bone as examined by CT PART II : CT investigation of the cochlear capsule of patients with otosclerosis PART III : CT investigation of the vestibular aqueduct in patients with Meniere's disease. In PART I a brief description is given of the high resolution CT scanner used in this study. Some principles of computed tomography are explained in relation to the analysis of anatomical and pathological details of the temporal bone. The specific otoradiological planes are described, in particular those planes used in our patient study. The normal anatomy of the temporal bone is presented in six otoradiological planes. In each plane seven consecutive CT slices are given. In PART II a short introduction is presented to the clinical aspects and the histopathology of otosclerosis, followed by a review of the literature. In our own study we have tried to find an answer to the next main questions: - In which otoradiological planes can the cochlear capsule be optimally visualized with CT? - What is the normal density of the labyrinthine capsule? Is it dependent on age? - Is it possible to detect foci of otospongiosis and otosclerosis by means of CT? - Is there a correlation between the degree of demineralizaiion in a focus and the degree of bone conduction hearing loss? - Is a correlation present between the location of density loss in the cochlear capsule and the magnitude of inner ear impairment for the place corresponding frequency? This study concerns a CT investigation of the labyrinthine capsule in 35 normal ears and 134 ears of 84 patients with surgically confirmed otosclerosis. CT scans are judged by the naked eye and by densitometry. The maximum and minimum density of the cochlear capsule is measured both in normal and patients' ears. Bone density is also measured at six predefined points within the cochlear capsule. The results of densitometry are correlated with the inner ear impairment as measured by bone conduction audiometry. In PART III the clinical aspects of Meniere's disease are summarized including histopathology, anatomy and pathophysiology of the endolymphatic duct within the vestibular aqueduct. Earlier research on polytomographical visualization of the vestibular aqueduct is reviewed. The purpose of this part of the study is to investigate, by means of CT, visibility and length of the vestibular aqueduct and to compare our results with the inconsistent (and often controversial) results in the literature. Therefore we have defined strict inclusion and exclusion criteria in diagnosing Meniere's disease. The following questions are studied: - Which otoradiological planes are optimal for visualization of the vestibular aqueduct? - Is it possible to find a qualitative method to establish the dimensions of this aqueduct? - Does the visibility and length of the vestibular aqueduct in affected ears of patients with Meniere's disease differ from that in normal ears? - Is there a difference in visibility and length of the vestibular aqueduct between affected and non-affected ears in patients with unilateral Meniere's disease? - Do the dimensions of the aqueduct correlate with age, duration of the disease or degree of hearing loss? In 55 patients with unilateral or bilateral Meniere's disease (104 ears) the vestibular aqueduct is investigated by CT. A visibility scale for classification of the vestibular aqueduct is developed and the results, obtained in affected and non-affected ears of patients with Meniere's disease, are presented and compared with the CT findings in 50 normal ears. The same comparisons between Meniere's ears and control ears are made as to the length of the vestibular aqueduct. The results are compared with those from previous polytomographic and dissection studies. IPAOTK COMPUTED TOMOGRAPHY OF THE TEMPORAL BONE I. CT of the temporal bone CONTENTS OF PART I 1. INTRODUCTION 3 1. Some principles of computed tomography in relation to the analysis of temporal bone details 3 1. Hounsfield Unit scale 3 2. Image reconstruction 4 3. Partial volume averaging 5 4. Slice thickness 8 5. Geometrical enlargement 8 2. The Philips Tomoscan 310/350 8 2. OTORADIOLOGICAL PLANES 10 1. Transverse plane (Hirtz) 10 2. Sagittal plane 13 3. Coronal plane 13 4. Axio-petrosal plane (Poschl) 14 5. Semi-axial plane (Guillen) 14 6. Semi-longitudinal plane (Zonneveld) 14 3. CT ATLAS 15 Legends 16 Visibility matrix 17 1. Transverse plane (Hirtz) 18 2. Sagittal plane 20 3. Coronal plane 22 4. Axio-petrosal plane (Poschl) 24 5. Semi-axial plane (Guillen) , 26 6. Semi-longitudinal plane (Zonneveld) 28 4. REFERENCES 30 I. CT of the temporal bone - Introduction INTRODUCTION During the last ten years the technology of computed tomography has developed rapidly. Since details smaller than 1 mm can be visualized, CT has been applied more and more to examine the temporal bone (Hanafee et al, 1979; De Smedt et al, 1980; Shaffer et al, 1980; Littleton et al, 1981; Zonneveld et al, 1981; Rettinger et al, 1981; Zonneveld & Damsma, 1982; Valvassori etal, 1982; Swartz, 1983; Zonneveld, 1983). The term 'high resolution' has to be considered as a relative qualification. At this moment it means that details of about 0.5 mm can be visualized (Zonneveld, 1985). The so called 'third generation' scanner was introduced in 1974 as a brain scanner. It was an entirely new type as compared to the first and second generation scanners. The number of detectors was increased and varies from 300 to 700. Therefore the fan angle is widened so that it can incorporate the whole body cross section. A translating motion (as was necessary in former generations) is no longer needed. These rotate-only scanners work much faster than second generation scanners. As a consequence of continuous data aquisition the influence of the patient's motion artifacts is much smaller. SOME PRINCIPLES OF COMPUTED TOMOGRAPHY in relation to the analysis of temporal bone details. 1. Hounsfield Unit Scale The local attenuation characteristic of tissue for X-rays is the product of a number of interacting processes between X-rays and matter such as photoelectric absorption and Compton scatter. X-ray tubes produce radiation in a spectrum of wavelengths.