Cardiothoracic ratio (CTR) is a simple, cheap and reproducible tool used as a classic index of cardiac size in screening for cardiovascular diseases. The study aims to establish the cardiothoracic ratio (CTR) of non-hypertensive patients using posteroanterior (PA) chest radiographs in an indigenous Nigerian population and correlate it with age and gender. This was a 12 months retrospective study of all the posteroanterior (PA) chest radiographs of 250 non-hypertensive patients retrieved from departmental archives of the Radiology department of the Benue state university Teaching Hospital (BSUTH), Makurdi from August 2018 to September 2019. The indication for the study as well as the patients` age, gender, and location were obtained. Measurements for maximum transverse cardiac diameter (MTCD)and the maximum internal thoracic width (MITW) were obtained and used to calculate the cardiothoracic ratio (CTR).Data was entered into statistical package for social science (SPSS) version 26 software for analysis, with the p value taken as <0.005. A total of 250 chest radiographs of   non-hypertensive patients were used to assess the cardiothoracic ratio (CTR) in which 132(52.8%) were males and 118(47.2%) females. Routine medical check-up was the commonest indication, followed by peptic ulcer disease (PUD) in 126(50.4%) and 26(10.4%) patients who presented for chest X-rays respectively. In both cases, males were in the majority. The presumed “small heart” with a cardiothoracic ratio (CTR) less than 42%, was observed in a total of 29(11.6%) patients made up of 16 females and 13 males. Normal chest X rays (CXR) with a cardiothoracic ratio (CTR) between 42-50% was seen more in males than in females (111:100). “Borderline”, but still abnormal cardiothoracic ratio (CTR) of between 51-55% was recorded for 10(4%) patients, while no patient presented with a cardiothoracic ratio (CTR) greater than 55%. The mean cardiothoracic ratio (CTR) increases steadily with age up to the 4<sup>th</sup> decade, with a lull at the 5<sup>th</sup> and then a slight spike after the 6<sup>th</sup> decade, with the males generally having greater values than the females. The mean cardiothoracic ratio (CTR) of the study population were 45.6%, 45.9% and45.3% for the general population, males and females respectively, with a statistically significant correlation (p=0.000) between male and female cardiothoracic ratio (CTR). The result of this study has established the cardiothoracic ratio (CTR) of indigenous Nigerian population in Makurdi as 45.6%.It has also shown the relationship between cardiothoracic ratio (CTR),and the patients` age and gender. These are necessary for comparison with similar findings elsewhere nationally and internally.

Keywords: Cardiomegaly, Cardiothoracic ratio (CTR), Indigenous Nigerian, Maximum transverse cardiac diameter (MTCD), Maximum internal thoracic width (MITW), Radiography.

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Dr Chia Daniel Msuega

Department of Radiology, College of Health Sciences, Benue State University, Makurdi