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Comparison of Computed Tomographic Hounsfield Numbers with Ultrasonographic Categorization of the Fatty Liver Disease

University of Lahore, Pakistan MBBS, FCPS, MCPS, FRCR II, Professor of Radiology, Alrazi Healthcare Lahore, Pakistan Associate Professor, Department (UIRSMIT) FAHS, University of Lahore, Pakistan Assistant Professor, Department (UIRSMIT) FAHS, University of Lahore, Pakistan MD, MS Ultrasound, Assistant Professor, Department (UIRSMIT) FAHS, University of Lahore, Pakistan B.Sc. Ultrasound, M.Sc. Ultrasound Lecturer, Department (UIRSMIT) FAHS, University of Lahore, Pakistan B.Sc. Ultrasound, M.Sc. Ultrasound Lecturer, Department (UIRSMIT) FAHS, University of Lahore, Pakistan MBBS, DMRD, PhD Radiology, PhD Ultrasound, Dean Faculty of Allied Health Sciences, The University of Lahore,


Introduction
Fatty Liver Disease (FLD) also known as Hepatic Steatosis (HS) is identified by the abnormal build-up of lipids particularly triglyceride in the cytoplasm of hepatocytes [1].
In Asia, the prevalence of FLD ranges from 12-24% with most estimates within the range of 6-14% in the general population [2]. The prevalence of FLD has been increasing worldwide most likely due to eating habits, lifestyle changes and improvements in diagnostic techniques [3].
When energy intake exceeds the required amount, the excess energy is stored in the adipose tissues in the form of fat leading to obesity. Insulin resistance associated with obesity is considered as the key factor to develop metabolic syndrome and FLD [4]. FLD is the most common reason for elevated liver enzymes throughout the world [5].
Although up to 70% of FLD patients are normal on laboratory findings [6]. Most of the patients of FLD are asymptomatic or have nonspecific findings that do not correlate with the severity of disease. The most common clinical symptoms of FLD are right upper quadrant pain, feeling of fullness and lethargy or malaise. In addition hepatomegaly can also be found on physical examination [7]. Other findings are related to metabolic syndrome, obesity or overweight [8]. (NAFLD) and Alcoholic Fatty Liver Disease (AFLD) [9].
NAFLD is defined as FLD in the absence of hepatic damaging factors including alcohol use, hepatitis viruses and metabolic disorders [10]. In Pakistan the prevalence of NAFLD in general population is 18% [11,12]. In western countries the prevalence of NAFLD in adults ranges from 20 to 33% [13]. AFLD is induced by consumption of excessive alcohol. It has been reported that 30 gram of alcohol intake per day can induce liver damage [14]. AFLD

Aim
Determination of the range of CTHFN in different categories of FLD by USG.

Material and Methods
The rules and regulations set by the ethical committee of

Computed tomography
Siemens 64 slice dual source at both centers was used to scan patients. Patients were scanned in supine position.

Results
In this study 227 patients of FLD was taken. The mean age of population was 49.88 ± 14.52 years and range was 20-80 years as shown in Table 1 and Figure 3. The mean Values of CTHFN of liver was 36.16 ± 12.84 HU and range was -11.83-53.20 HU with significant p value as shown in Table   2 and Figure 4A. The frequency of male population was 141(62.11%) and female was 86 (37.89%) as shown in Figure 4B. The mild, moderate and severe FLD was found in 159 (70.04%), 50(22.03%) and 18(7.93%) patients respectively as shown in Figure 4C.  Table   3 and Figure 5.       Table 4.

Discussion
The FLD occurs worldwide in obese and excessive alcohol consumers [26]. FLD also occurs in metabolic disorder and several conditions that effect fatty acid metabolism [27].
The diagnosis of FLD is made when lipid content in the liver exceeds 5-10% by weight [15]. . If the cause persist, FLD invariably progresses to steatohepatitis, cirrhosis and liver cancer [28]. In 2016 Wolff L et.al. reported severe FLD is associated with excessive pericardial fat and suggested it as a marker for vascular disease [29]. FLD is a precursor or it may signal the development of hypertension, cardiovascular diseases and type II diabetes mellitus which is associated with high rates of mortality [30].
Ultrasonography is suggested as a first choice for the diagnosis of FLD, considering its wide availability, low cost and absence of side effects or risks to the patient, furthermore liver enzymes are not a good parameter for detection of FLD [31]. The prevalence of FLD in routine Sonography is much higher as compared to laboratory findings [32]. Utilizing USG the prevalence of FLD ranges from 20-40% in industrialized countries [33]. The most common criteria for grading of FLD by USG takes into account the echogenicity of liver and its comparison with echogenicity of right kidney. The grading is defined as: G 0-normal echogenicity, Liver appears slightly echogenic or isoechoic to right kidney cortex). G I-mild increase in echogenicity, Liver appears bright than right renal cortex with normal appearance of intrahepatic vessels and diaphragm; G II-Moderate increase in echogenicity with slightly blurred visualization of intrahepatic vessels and diaphragm; G III-Severe increase in echogenicity with poor or no visualization of intrahepatic vessels and diaphragm [34].
In 2011 Hernaez R et.al. [35] conducted a met-analysis on  [38]. Unenhanced CT has sensitivity of 43-95% and specificity of 90-100% for detection of Liver Steatosis [39]. CT has been proved to be a sensitive modality for quantitative measurement of moderate to severe FLD but its performance for mild FLD is limited [40]. The most common diagnostic criteria for diagnosis of FLD on CT is liver CTHFN less than 40 HU or liver CTHFN less than 10HU as compared to Spleen CTHFN which correlates with pathologic fat content of 30% or more [41]. However this diagnostic criteria excludes mild FLD decreasing overall prevalence as much as 40% as compared to other CT criteria [42].
CT provides fast, objective and reproducible assessment of liver fat having a good correlation with pathologic findings obviating the need of biopsy in most of the cases [43]. But to date there has been no standard criteria for grading of FLD on CT. The first study correlating USG grading of FLD with CT was published in 1985 by John CS et al. [44] to evaluate accuracy of USG for diagnosis of FLD. They reported the overall accuracy of USG for detection of FLD 85%, with 100% sensitivity and 56% specificity. The USG/CT correlation was found particularly well for the diagnosis of grade I and II FLD.

Conclusion
In best of our knowledge to date this is third study comparing USG grades of FLD with CTHFN to determine CTHFN for each Ultrasonographic category of FLD. We found significant p values of CTHFN for all grades of FLD by USG. CTHFN decreased with severity of FLD. Hence we can conclude that USG is a reliable and sensitive modality for the grading of FLD.