Multi-Detector Computed Tomography for Evaluating Characteristics, Distribution and Extension of Mediastinal Masses

Background: The area in the thorax between the lungs is Mediastinum which is surrounded above by thoracic inlet, in front by sternum, below by diaphragm, back by vertebral column laterally by pleura of both lungs. Multiple classification systems are used by doctors. Shields classification system is most commonly used, however the conventional Fraser and Paré, Felson, and other categorization are in daily use in radiology. The present schemes used in practice of radiology is more of nonanatomic divisions based primarily on the chest radiograph. So a typical classification based on multi detector CT is demanded to describe mediastinum and make to the purpose differential diagnoses. This study aims to assess characteristics, distribution and extension of Mediastinal masses by MDCT and correlate the histopathological diagnosis to CT scan findings. Methodology: This will be a prospective study conducted at AVBRH, Wardha. Total 100 patients with Mediastinal Masses diagnosed clinically and on Chest X ray will be enrolled in the study. Contrast CT scan of all patients will be done. Histopathology reports of masses (FNAC/Biopsy) will be collected. Results: Significant accuracy of mediastinal CT in diagnosing the mediastinal masses and a Study Protocol Jayprakash et al.; JPRI, 33(64A): 415-421, 2021; Article no.JPRI.80860 416 significant corelation to FNAC/biopsy reports is expected. Conclusion: MDCT will prove to be an useful evaluation method for diagnosis and classification of mediastinal masses.


INTRODUCTION
Mediastinum is the area in the thorax in between the lungs and surrounded above by thoracic inlet, in front by sternum, below by diaphragm, back by vertebral column laterally by pleura of both lungs. Multiple classification systems are available and used by doctors. Shields classification system is most commonly used, however the conventional Fraser and Paré, Felson, and other categorization are in daily use in radiology. The present schemes used in practice of radiology is more of nonanatomic divisions based primarily on the chest radiograph, so a typical classification based on multi detector CT is demanded to describe mediastinum and make to the purpose differential diagnoses .Hence to resolve this issue the experts have come up with International Thymic Malignancy Interest Group (ITMIG) have come up with classification of Mediastinal Compartments into the threedivisions as Prevascular, Visceral, and Paravertebral compartments [1].
MDCT along with intravenous contrast is the diagnostic technique of choice for assessment and depiction of many mediastinal masses. Hence the ITMIG uses MDCT as a gold standard for defining mediastinal compartments [2]. Mediastinal lesions include a wide range of pathologies namely tumours, benign or malignant they can be cysts, vascular congenital anomalies, lymph node pathologies and diaphragmatic hernias. These lesion are challenging for a radiologist and often a plain x ray is inadequate to locate and identify the lesion. CT is preferred for defining the accurate location, size, extent and characterizing the nature of mediastinal lesions. Both CT and MRI have cross-sectional description of the mediastinum, CT has greater spatial resolution and shorter imaging time than MRI, besides being less expensive and more widely available. In addition CT guided biopsies further help in identifying the lesion [3]. Hence we propose to study the role of MDCT in identifying, localising mediastinal masses and to determine the differential diagnosis.
Noriyuki Tomiyama et al. [5] in their study about anterior mediastinum masses accuracy of CT, MRI in diagnosis quoted that mediastinal masses account for 3% of the chest tumours and nearly 50% of all mediastinal masses are anterior mediastinal tumours.
Nicholas C. Saenz et al. [6] studied posterior mediastinal masses in children and quoted that most tumours were arising from nervous system in 89% of cases, in that neuroblastoma had much higher incidence and 60% had malignancy.
Ramakant Dixit et al. [7] in their study stated that 68.3% cases are confined to the anterior mediastinum, 16.5% cases to the middle, and 2.5 % cases to the posterior mediastinum. In 7.1%cases two or more than two compartments of the mediastinum were simultaneously involved.
Guang-Shing Cheng et al. [9] stated that the occurrence of primary mediastinal masses was hard to find out. In their survey of 9000 plus cases of a lung cancer CT screening, the rate of a coincidentally recognized mediastinal mass was 0.77%, on repeat annual examination, the rate was 0.01%. Commonest masses in adult age group were thymoma, developmental cysts accompanied by neurogenic tumours and lymphoma, according to the data by Silverman and Sabiston in around 2400 subjects. Recently studies indicated a similar trend, also Cohen and associates observed the increasing occurrence of mediastinal masses. An increasing number of lymphoma and malignant neurogenic tumours was also observed by them over a span of 45years.Among all mediastinal masses 60% were thymoma, neurogenic tumors and developmental cysts. Lymphomas and germ cell tumors were about 25% and rest 15% included other benign as well as malignant tumours.
Rationale: Computed Tomography has good role in diagnosis of mediastinal lesions. It is one of the best non-invasive imaging modality available for thoracic imaging. Computed Tomography has good spatial resolution and shorter imaging time, besides being less costly and being more widely available. It is possible in defining the accurate anatomical details and characterizing the nature, site and extent of the disease. Mediastinal abnormalities, changes such as calcification, necrosis within the lesions can be easily appreciated with the use of MDCT. It gives more details of disease. This also underlines the importance of close cooperation with the histopathologist and the clinicians in diagnosis and management.

Objectives
Where, ‫אּ‬ 2= chi square test value for I degree of freedom at desired probability level is 3.84 at 5% level of significance P = 50% proportion C= confidence interval of choice (95% CI) Sample size = 100 patients needed in the study.
Preparation of patient: Patients will be kept nil orally 6 hrs prior to the CT scan to avoid complications , due to administration of contrast medium. Risks of the procedure and contrast administration will be explained to the patient and consent will be obtained prior to the study.
Technique: Initially, routine anteroposterior topogram of the thorax will be taken in the supine in all patients. An axial section of 5 mm thickness will be taken from the level of thoracic inlet to the level of suprarenal glands. In all cases precontrast study will be followed by post-contrast study, image acquisition will be done with intermittent suspended inspiration. For postcontrast study, 80-130ml of dynamic intravenous injection of iopromide will be administered with pressure injector and axial section taken from thoracic inlet to the level of suprarenal arterial phase will be after 35 to 40 seconds after contrast infusion , venous phase after 80 seconds of contrast infusion and delayed phase after 3 -5 mins. Sagittal section and coronal section reconstruction images will be used wherever necessary. The scan will be studied on console at different window width settings i.e. soft tissue/mediastinal window of level 30 HU-50 HU ,width 350 HU-500 HU. Lung window of level 700 HU along with width of 1500 HU. Similarly, bone window level of 2400 HU and width 200 HU to study different tissue density. The pre and post contrast findings will be studied [10].

DISCUSSION
In a study by Sergi Juanpere et al. [11] in 2012 in their article A diagnostic approach to the mediastinal masses described various lesion of mediastinum including fatty masses, cystic masses, thymic hyperplasia, thymoma, lymphoproliferative disorders, uncommon mediastinal masses and concluded that location and composition of a mass is important in diagnosing ruling out differentials all this could be done much more easily with help of CT.
In a study by Brett W. Carter et al. [12]  In a study by Somshankar Pandey et al.
Hence this study is designed in such a manner that the outcome of this study will be compared with above mentioned research.

CONCLUSION
The data obtained through this study can be used to understand the importance of MDCT in conveniently diagnosing mediastinal masses and study their correlation with age, sex, clinical symptoms and FNAC/biopsy findings where ever possible.

ETHICAL APPROVAL
As per international standard or university standard written ethical approval will be collected and preserved by the author(s).

CONSENT
Patients willing to give consent for the study.