[Surgical approach to the petrous bone and related tumors. The neurosurgeon's viewpoint].
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Definition and technique of the Dulac 7 incidence. Diagrams 1 and 2 give details of the anatomical orientations which define this incidence. It is:--centered on the head of the malleus,--orientated in the plane of the ossicules or in the neighbouring plane of the ear-drum,--parallel to the general axis of the ossicules,--close to the perpendicular to the tegment tympani. This incidence is easy to obtain with our technique, using a fixed intracranial centering point, The transversal linear scanning is very effective and can be completed in a very short period. It should be noted, however, that in obese subjects with short necks, the entry point of the incidence is difficult to obtain as there is interposition of the neck muscles. Under these conditions, one should try to be as close to this entry point as possible, knowing that the results are still valid. Tomographic anatomy. A close examination of the text of figures 6, 7, and 8 will familiarize the reader with the tomographic anatomy of this incidence. To summarize the important information obtained from the Dulac 7 incidence we should note that in tomographies of normal petrous bones:--the attic is always perfectly visible, expecially its internal and external walls throughout their total length, and more especially the anterior wall;--the ossicles (head of the malleus, body of the incus, and their articulation) are always perfectly visible and distinct;--the inferior processes of the malleus and incus are always visible;--the external wall of the attic is visible throughout its length, more especially the anterior and posterior portions;--the anterior and posterior contours of the external auditory canal are particularly well-defined. Finally, this incidence also gives clear images of the temporo-mandibular joint, the antral region, the superior canal, and the internal auditory canal. A large experience of this incidence is required before interpreting the image of the foramen ovale. Tomographic pathognomonic signs. The texts of figures 9 to 24 are sufficiently demonstrative of the richness of the pathological data obtained from this incidence, without needing to repeat them here. We would only add that the degree of calcification of the ossicles and the anterior wall of the attic can be precisely determined. This incidence, therefore, gives valuable information in almost all middle ear affections. It is also necessary in order to study the external auditory canal.
The purpose of this method is to improve the reproduction of the petrous bone area in cephalometric lateral head roentgenograms. Metal screens are used to project a high-voltage x-ray beam only to this area. Two techniques using a lead screen or a copper filter screen are described. Reproduction of the points porion and basion and of the temporomandibular joint is considerably improved.
Two cases of Paget's disease presenting with deafness are described. Tomography of the petrous bones showed, in both cases, an upward tilt of the long axes of the bones including their auditory canals, generalized sclerosis of the petrous pyramids and enlargement of the ossicles. In one case, there was narrowing of the internal auditory canal. Review of the literature revealed three radiological phases in Paget's disease of the temporal bone:--(i) early changes consisting mainly of demineralisation; (ii) an intermediate phase consisting of diminishing visibility of the semicircular canals and cochlea; and (iii) a late phase consisting of complete blotting out of the structures of the optic capsule and replacement of the ossicles by Pagetic bone. Our two cases fall within the last phase.
Some investigation has been made in recent years of radiation dose to the eye during radiological procedures. A comparative survey has been made of eye dose during petrous bone tomography in different departments on different tomographic units and during different types of examination. Doses of up to 4 rad per exposure have been recorded and various methods of reducing the dose have been investigated, the most successful being the use of 1 mm lead eyeshields or examining the patient in the posteroanterior position.
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Three cases of keratosis obturans, which were studied by tomography of the petrous temporal bone, are described. The widening of the deep bony part of the external auditory canal by pressure erosion of an impacted benign slowly-growing mass is the key radiological finding. Erosion was so severe as to involve the facial nerve canal in one and the temporo-madibular joint in two cases. The theories of causation are reviewed. Tomography using elliptical tube movement was valuable in diagnosis, pre- and post-operative management.
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41 benign tumor of the temporal bone are reported. 33 glomustumors, originating from the middle ear or from the lower temporal bone. According to their origin they present different surgical problems. Neurinomas are less common. Surgery is the therapy of choice. Symptoms and properties of these tumors are discussed briefly.
A characteristic "notch" in the petrous bone is described in relation to the superior outline of the jugular foramen. This notch seems to be a congenital anomaly and has a close relationship with ectasia of the dome of the internal jugular vein, as was demonstrated in two patients.
This paper has described an unusual case of osteoclastoma of the petrous temporal bone which presented with multiple cranial neuropathies. A radical course of radiotherapy reversed the neuropathies but it is too early to comment on possible cure.