Tomography of the temporomandibular joint. Thesis. OLaF ECKERDAL Acta Radiol. Suppl. 329. 107 pages, (1973). The purpose of this thesis is to analyse the diagnostic possibilities and limitations of tomographic examination of the temporomandibular joint. The following questions are discussed: 1. Which parts of the temporomandibular joint can be demonstrated using sagittally oriented tomography? 2. The thickness of the image layer in temporomandibular joint tomography. Is the "layer thickness" a useful concept and how can it be characterized? 3. Is there an overall correspondence between the tomographic image and the morphology? 4. Are there special features of temporomandibular joint tomography, which may lead to diagnostic errors? S. What factors affect the reproducibility of details in tomography of the tempo-. romandibular joint? The investigation is based on a correlation of data from different sources. Information on the specimens was obtained mainly by tomography combined with corresponding sectioning of the specimens with a microtome. The successive anatomic sections were photographed, stained histologically and in some cases microradiographed. The individual data on a given specimen obtained from any of these methods can, by means of a
three-dimensional reference system, be related to the whole. This system permits an analytical breakdown and synthesis of the joint region, using one or more of the series of tomograms or anatomic sections. Analysis of the parts of the joint accessible for diagnosis by tomography shows that, under favourable circumstances, the central two-thirds of the joint region is clearly reproduced. Medially and laterally there are zones of increasing blur. These zones are broader medially, mainly because of superimposition from the base of the skull. Blurring is due not only to superimposition from lateral or medial extra-articular parts, but also to geometric-morphologic factors within the joint. The thickness of the tomographic layer was determined to 3 ± 1 mm using the hypocycloid movement pattern of a Polytome. The layer can be asymmetricaIly distributed in relation to the tomographic plane, especially in the medial or lateral regions of the joint, or when there is marked morphologic and/or structural incongruence between the anatomic layers in the zones tomographed. Such an incongruence can also lead to distortion. Tomography of extreme morphologic variants of the joint may also result in distortion. There is no standard orientation of the joint that can entirely eliminate all distortion phenomena. False appearances of both sclerosis and rarefaction of the bony structures of the joint are examplified. Such false images can be due to the hypocycloidal blur pattern, the layer summation and various morphologic and geometric properties of the specimen. The limits for reproduction of bone lesions, osteophytes and periarticular ossicles are examplified by specimens. It is not attempted to state the exact size of the lesions or osteophytes as the appearance is influenced by such factors as the relation of the detail to the zone of sharpness in the joint, its relation to the tomographic plane, structural relations in or around the detail, tangential relationships, the effects of superimposition, false images such as double contours and halo effects, and the exposure data used at the examination. It can be concluded that hypocycloidal tomography is well suited for examination of the temporomandibular joint. The tomographic image may contain any of a number of types of spurious phenomena. They are in part due to certain specific properties 111
of the joint region, and in part to the tomographic technique per se. Demonstration and elucidation of these factors should contribute to increased diagnostic acuity. 51 references. Hakan Hakansson, Malmo
three-dimensional reference system, be related to the whole. This system permits an analytical breakdown and synthesis of the joint region, using one or more of the series of tomograms or anatomic sections. Analysis of the parts of the joint accessible for diagnosis by tomography shows that, under favourable circumstances, the central two-thirds of the joint region is clearly reproduced. Medially and laterally there are zones of increasing blur. These zones are broader medially, mainly because of superimposition from the base of the skull. Blurring is due not only to superimposition from lateral or medial extra-articular parts, but also to geometric-morphologic factors within the joint. The thickness of the tomographic layer was determined to 3 ± 1 mm using the hypocycloid movement pattern of a Polytome. The layer can be asymmetricaIly distributed in relation to the tomographic plane, especially in the medial or lateral regions of the joint, or when there is marked morphologic and/or structural incongruence between the anatomic layers in the zones tomographed. Such an incongruence can also lead to distortion. Tomography of extreme morphologic variants of the joint may also result in distortion. There is no standard orientation of the joint that can entirely eliminate all distortion phenomena. False appearances of both sclerosis and rarefaction of the bony structures of the joint are examplified. Such false images can be due to the hypocycloidal blur pattern, the layer summation and various morphologic and geometric properties of the specimen. The limits for reproduction of bone lesions, osteophytes and periarticular ossicles are examplified by specimens. It is not attempted to state the exact size of the lesions or osteophytes as the appearance is influenced by such factors as the relation of the detail to the zone of sharpness in the joint, its relation to the tomographic plane, structural relations in or around the detail, tangential relationships, the effects of superimposition, false images such as double contours and halo effects, and the exposure data used at the examination. It can be concluded that hypocycloidal tomography is well suited for examination of the temporomandibular joint. The tomographic image may contain any of a number of types of spurious phenomena. They are in part due to certain specific properties 111
of the joint region, and in part to the tomographic technique per se. Demonstration and elucidation of these factors should contribute to increased diagnostic acuity. 51 references. Hakan Hakansson, Malmo
