A radiologic study of the tympanic bone: anatomy and surgery.

OBJECTIVE: The aim of this study was to obtain data on the anatomic structure of the tympanic bone using parasagittal reformatted images created from high-resolution axial computed tomographic scans. In particular, the thickness of the bone in the region of the temporomandibular joint and the floor of the external auditory canal was assessed. The findings are discussed with particular emphasis on the relevance to surgery in this area. BACKGROUND: Surgical management of the tympanic bone forms the basis of canalplasty, which is an essential step in the management of disorders of the external auditory canal. Adequate canalplasty is also crucial in the provision of access for tympanoplasty and to ensure optimal cavity geometry in canal wall down mastoidectomy. Tympanic bone removal is a major step in approaches to the lateral skull base and infratemporal fossa. The tympanic bone is also important because it has critical neurovascular relations in this region of the skull base. METHODS: Computed tomography of the tympanic bone (parasagittal reformatted images) in 54 consecutive adults. RESULTS: The mean thickness of the anterosuperior, anteroinferior, and inferior aspects of the tympanic bone are 2.6, 2.8, and 8 mm, respectively. CONCLUSION: Canalplasty is safely performed in the regions outlined. The technique of canalplasty described in this article is essential for good exposure in external ear, middle ear, mastoid, and skull base surgery.

The CT diagnosis of acute appendicitis.

In clinically equivocal cases of acute appendicitis, CT performed after the opacification of the terminal ileum and the cecum offers a significant improvement in diagnostic accuracy when compared to diagnosis based on clinical signs and symptoms alone. The method employed to opacify the bowel has been the subject of discussion in the literature. We believe that the oral administration of contrast, without the use of rectal or intravenous contrast, provides the best combination of diagnostic accuracy and convenience. The CT signs of acute appendicitis are described. Ways of minimizing the difficulties of diagnosing a ruptured appendix are discussed. Because of the radiation involved, CT should not be used routinely in acute appendicitis, but should be reserved for clinically equivocal cases.