Size, Shape and Relations of the Structures of Thoracic inlet in CT Sections

Abstract

Over the past decade, faster CT scan, thinner collimation, and the development of multi detector computed tomography (MDCT), coupled with the increasing capability of computers to process large amounts of data in short periods of time, have lead to an expansion in the ability to create diagnostically useful two-dimensional (2D) and three-dimensional (3D) images within the thoracic inlet. Applications within the thorax include, but are not limited to, evaluation of systemic vasculature, and the trachea, and delineation of thoracic inlet disease. Multiplanar (MPR) images increased understanding of thoracic inlet anatomy. Because there are strengths and weaknesses to all the reconstruction algorithms, the utility of any given technique is dependent on the clinical question to be answered. For instance, although maximum intensity projection imaging (MIP) is helpful in the evaluation of blood vessels, it is of little value in the diagnosis of enlarged lymph nodes. The importance of this study comes from the importance of thoracic inlet because it is a common area to obtain venous access for renal dialysis, or CT guided biopsy and has many structures with variations in appearance which iii mimic pathological changes. It is important to have a clear understanding of the anatomy of the thoracic inlet structures and their relationship to each others to avoid accidently arterial puncture or nerve damage in CT guided biopsy or misinterpretation of normal structures e.g non opacity blood vessel as enlarged lymph nodes. Computed tomography is an excellent method to delineate the anatomy of thoracic inlet structures. Variations in the anatomy of the thoracic inlet structures and their correlation to the x-ray findings. This study aims to objectively evaluate the variations in the anatomy of thoracic inlet structures, the structures sizes, appearance and their relations to each others. A total of 328 patients were evaluated using MDCT imaging. The measurements and identifications of thoracic inlet structures were done at five levels, 7th cervical vertebra, 1st, 2nd, 3rd, and 4th thoracic vertebra. The average size of main thoracic inlet structures, trachea, esophagus, internal jugular vein IJV, common carotid artery CCA subclavian artery and neural canal was measured. The percentages of identifying small vessels, lymph nodes, thyroid gland, thyroid isthmus, thymus gland, neck muscles, thoracic duct, right lymphatic duct and nerve were recorded and analyzed. The study showed differences in sizes of some of thoracic inlet anatomical structures, between males and females group. In bilateral structures e.g the right internal iv jugular vein (RIJV) was more often larger than the left internal jugular vein (IJV). With reference to the common carotid arteries (CCA), 78.5% of the IJV were found in the lateral position, 20.5% anteriorly 1.0 % posteriorly. There were significant differences in appearance of identified structures at different levels. The appearance of lymph nodes, was more in tumor patients (36%) followed infection patients (9%). Thymus remnant was more identified in yang patients, (76.6%) in age group 30to 40 years, (65. 5 %) in age group, 41 to 50 years, and only (10.5 %) in group above 50 years.