The thin sectional anatomy of the temporal bone correlated with multislice spiral CT

High jugular bulb: different osseous landmarks and their clinical implications

PURPOSE

The purpose of this investigation was to compare the rate of high jugular bulb (HJB) in relation to internal acoustic meatus (IAM), round window (RW) and endolymphatic sac and to study their clinical implications.

METHODS

Eighty-seven cadaveric non-pathologic human temporal bones were micro-dissected to expose the jugular fossa (JF) and RW. The minimum distance of JF from RW was measured. On the inner surface of petrous part of temporal bone, minimum vertical distance of JF from IAM and saccus endolymphaticus (E sac) was also measured. If the distance of summit of JF from RW or IAM was ≤2 mm or if there was no distance between JF and slit on which E sac opens, they were classified as HJB cases.

RESULTS

The mean minimum distance of JF from the RW, IAM and E sac was found to be 2.85 ± 1.58, 3.83 ± 2.38 and 2.06 ± 2.38 mm and the rate of HJB was 32.2, 24.1 and 41.4 % respectively.

CONCLUSIONS

The rate of HJB varies even in a particular specimen using different landmarks i.e. the RW, IAM and E sac. The preoperative awareness in relation to these landmarks will be useful in cochlear implantation, surgical removal of vestibular schwanommas and clinical findings of Meniere's disease.

Usefulness of the radiological planning for hearing preservation surgery in vestibular schwannoma

Purpose

During vestibular schwannoma surgery there is a risk of endolymphatic duct and sac injury, which may cause a loss or a deterioration of hearing. The goal of the study was to evaluate the empirical utility of presurgical planning using CT with the bone window for the hearing preservation surgery.

Methods

The study was performed on 14 human temporal bones. CT scans with the bone window were obtained in the standard position. Safe drilling line was evaluated and after that drilling distances were analysed: the lateral drilling distance, total length of internal acoustic meatus, drilled length of internal acoustic meatus. After this, a surgical exposure was performed, using size of a drill tip as measuring scale. The dura was excised and endolymphatic duct was injected with a latex. Revision of the internal acoustic meatus was performed with the use of a microscope.

Results

Mean results of safe drilling coefficients were: lateral drilling distance: 10 ± 2 mm, total length of internal acoustic meatus: 9 ± 2 mm, drilled length of internal acoustic meatus: 7 ± 2 mm. In all cases, no endolymphatic duct injury was observed.

Conclusions

Preoperative radiological planning using the safe drilling coefficients is of value for the hearing preservation surgery in vestibular schwannoma. The size of the drilling tip may be used as an intraoperative measuring scale during this procedure. However, CT with a bone window is a necessary tool for the purposes of this procedure.

Temporal Bone Measurements; A Comparison Between Rendered Spiral CT and Surgery

Background:

Accurate radiological assessment of the anatomical features of the temporal bone is crucial to prevent damage to vital elements in this area during surgery. Knowing the approximate location of specific temporal bone related landmarks in advance is very important for planning surgery.

Objectives:

This study compared findings from computed tomography images with those observed directly during ear surgery.

Patients and Methods:

Patients with various pathologies of the ear who needed surgery were referred to an imaging center for a spiral CT scan of the temporal bone. The following parameters were measured by a radiologist and also later recorded by the surgeon during surgery: 1) The distance between the postero-superior border of the outer ear canal and the sigmoid sinus; 2) The distance between the dome of the lateral semicircular canal and the mastoid cortex; and 3) The distance between the external surface of the incus and the mastoid cortex.

Results:

Twenty cases were included. In the three measurements performed in this study, only the first parameter (distance between the canal and the sigmoid sinus) was significantly different between the direct measurement made during surgery and that obtained from CT scans. There was no significant difference in the measurements of the distance between the dome of the lateral semicircular canal and the bone cortex, and the distance between the external surface of the incus and the surface of the bone cortex.

Conclusions:

Our study shows in terms of figures that measurements of features of the temporal bone made from spiral CT scan images and those directly obtained during surgery are similar to an adequate extent.

High and dehiscent jugular bulb: clear and present danger during middle ear surgery

PURPOSE

Internal jugular vein is anatomic continuation of cranial dural sinuses in the neck region. During the course of skull base the first enlarged segment of jugular vein is described as jugular bulb. The aim of this study is to evaluate the jugular bulb abnormalities and define the risk of high and dehiscent jugular bulb injury during middle ear surgery.

METHODS

This is a retrospective radiologic study of 1,010 patients (2,020 temporal bones) with various ear symptoms who had high resolution temporal bone computed tomography scans between 2007 and 2011.

RESULTS

High jugular bulb was seen in 308 (15.2 %) temporal bones. Jugular bulb dehiscence was encountered in 153 (7.5 %) temporal bones. High jugular bulb and jugular bulb dehiscence were more common in the right ears and females. Forty-one (2 %) temporal bones revealed high and dehiscent jugular bulb which can be vulnerable during middle ear surgery. High and dehiscent jugular bulb was more common in the right ears and males. Male predominance becomes more significant in the left ears. Of the 308 temporal bones with high jugular bulb, 87 (28.2 %) also had coexisting carotid canal dehiscence.

CONCLUSION

High and dehiscent jugular bulb is an important anatomic variation that can result in catastrophic outcomes during middle ear surgery. Our series show that 2 % of patients can be considered in the "high-risk" group. Precise assessment of the preoperative computed tomography scans by both the radiologist and the ENT surgeon is of utmost importance. Preoperative awareness will minimize morbidity and mortality.

Three-dimensional histological specimen preparation for accurate imaging and spatial reconstruction of the middle and inner ear

PURPOSE

This paper presents a highly accurate cross-sectional preparation technique. The research aim was to develop an adequate imaging modality for both soft and bony tissue structures featuring high contrast and high resolution. Therefore, the advancement of an already existing micro-grinding procedure was pursued. The central objectives were to preserve spatial relations and to ensure the accurate three-dimensional reconstruction of histological sections.

METHODS

Twelve human temporal bone specimens including middle and inner ear structures were utilized. They were embedded in epoxy resin, then dissected by serial grinding and finally digitalized. The actual abrasion of each grinding slice was measured using a tactile length gauge with an accuracy of one micrometre. The cross-sectional images were aligned with the aid of artificial markers and by applying a feature-based, custom-made auto-registration algorithm. To determine the accuracy of the overall reconstruction procedure, a well-known reference object was used for comparison. To ensure the compatibility of the histological data with conventional clinical image data, the image stacks were finally converted into the DICOM standard.

RESULTS

The image fusion of data from temporal bone specimens' and from non-destructive flat-panel-based volume computed tomography confirmed the spatial accuracy achieved by the procedure, as did the evaluation using the reference object.

CONCLUSION

This systematic and easy-to-follow preparation technique enables the three-dimensional (3D) histological reconstruction of complex soft and bony tissue structures. It facilitates the creation of detailed and spatially correct 3D anatomical models. Such models are of great benefit for image-based segmentation and planning in the field of computer-assisted surgery as well as in finite element analysis. In the context of human inner ear surgery, three-dimensional histology will improve the experimental evaluation and determination of intra-cochlear trauma after the insertion of an electrode array of a cochlear implant system.

Clinical Feasibility of Multiplanar Reconstruction Images of Temporal Bone CT in the Diagnosis of Temporal Bone Fracture with Otic-Capsule-Sparing Facial Nerve Paralysis

The aim of this study is to evaluate the feasibility of multiplanar reconstructive (MPR) imaging of temporal bone CT in the diagnosis of temporal bone fracture with oticcapsule-sparing facial nerve paralysis. Twelve patients with traumatic facial nerve paralysis with otic-capsule sparing and temporal bone fractures were selected. Multiplanar reconstruction images were obtained with the V-works 4.0 software program (Cybermed, Seoul, Korea) using axial scanning of high-resolution temporal bone CT of the fracture line. The clinical profiles of the patients displaying temporal bone fractures were examined in relation to the findings. Multiplanar images of the fracture line provided information regarding the direction of the external force that fractured the temporal bone. The fracture line was more continuous in the MPR images than in the axial view. All patients showed an imaginary extended fracture line directed toward the otic capsule. The direction of the fracture line toward the middle ear cavity is important, as it may suggest insult to the otic capsule. The MPR image parallel to the fracture line of the temporal bone provides a guideline for the vector of the force that induced the fracture. Thorough investigation of the critical organs during surgical exploration is recommended if the direction of the fracture in the MPR image points toward the otic capsule in the middle ear even if the fracture line relative to the otic capsule is not well defined in the axial or CT view.