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Sonographic gallbladder wall thickness in normal adult population in Nigeria.

Introduction

Thickening of the gallbladder wall is a relatively frequent finding in diagnostic imaging studies. (1), (2) Historically, a thick-walled gallbladder has been regarded as proof of primary gallbladder disease, and it is a well-known hallmark feature of acute cholecystitis. (3), (4) The finding itself, however, is non-specific and can be found in a wide range of gallbladder diseases and extracholecystic pathological conditions. (1), (3), (5)

Ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) all allow direct visualisation of the normal and thickened gallbladder wall.5 Traditionally, US is used as the initial imaging technique for evaluating patients with suspected gallbladder disease, because of its high sensitivity in the detection of gallbladder dimensions, real-time character, speed and portability. (6), (7)

To establish our own standards and to contribute to the literature on this subject, we sought to evaluate normal gallbladder wall thickness in healthy adults by means of US.

Materials and methods

This was a prospective cross-sectional study that spanned a 2-year period from June 2005 to May 2007, involving 400 adults aged 16-78 years, carried out at the University of Maiduguri Teaching Hospital (UMTH) at Maiduguri, Borno State, which is in north-eastern Nigeria. The city has a population of slightly over 1.1 million. (8) The study concerned the clinically normal gallbladder in consenting adults aged <16 years. Subjects were recruited consecutively from the neighboring school of nursing and high schools and within the hospital. Excluded from the study were: pregnant women (confirmed by additional pelvic scan because of physiological distension of the gallbladder), volunteers with a past history of gallbladder and liver diseases or chronic alcohol consumption, those who could not fast (such as diabetics and sickle cell patients), and those who were <16 years old. At inclusion, a full history was obtained from each subject, with particular emphasis on demographic characteristics, history of previous jaundice, right hypochondrial pain, and history of upper abdominal surgery or chronic alcohol consumption.

All volunteers gave informed consent but, in addition, a review and authorisation of the study protocols was done by the Ethical Committee of the University of Maiduguri Teaching Hospital. The study subjects were informed of the safety of US. The healthy subjects who voluntarily submitted themselves for routine abdominal US were instructed to fast for 6 - 8 hours prior to the procedure to ensure gallbladder distension and to reduce the amount of gastric and intestinal gas. Subjects were, however, recruited mainly in the afternoon during the Muslim Ramadan period, which assisted in compliance with fasting. The clinical parameters, which included age, sex, height in metres and weight in kilograms, were also recorded for each subject prior to examination.

The examination was performed using a high-resolution real-time Doppler US scanner (Aloka, SSD-3500) equipped with 3.5 MHz and 5.0 MHz curved linear array transducers. A 3.5 MHz curved linear array transducer generally provides optimum resolution while maintaining adequate depth penetration, and is suitable for obese subjects. A 5.0 MHz curved linear array transducer provides greater resolution for slender subjects.

Subjects were scanned in the supine, prone and right anterior oblique positions. The transducer was placed in the right hypochondrial area, in the mid clavicular line and cephalad angled in both longitudinal and transverse planes, to obtain a full view of the gallbladder.

Scanning in the prone position was also adopted as the gallbladder was difficult to visualise otherwise in some of the subjects. For prone scanning, the subjects were placed in the prone position, and then the gallbladder was scanned intercostally or subcostally with the subject positioned prone oblique and right side elevated sufficiently to allow transducer contact at about the midclavicular line. Scanning continued as the subject was rolled slowly into a left lateral decubitus position and then laid supine again. In each separate position, the fluid-filled gallbladder was assessed in the longitudinal scans and sometimes zoomed, to obtain maximum gallbladder wall thickness in millimetres (Fig. 1).

[FIGURE 1 OMITTED]

Data from the structured data collection sheet were entered into a computer to generate a data base for subsequent analysis. For all the observed measurements, the data were initially summarised into frequency distribution tables. From these tables, the percentages of age, sex distributions and mean height and weights were calculated.

Results were expressed as the mean[+ or -]standard deviation (SD). Categorical differences were analysed using the chi-square test of independence. An independent Student's t-test was done to study the group difference for continuous variables. Chi-square and Student's t-tests were applied for univariate analysis. Multivariate regression analysis with logistic regression using the SPSS 11.0 package (SPSS Inc., Chicago, IL, USA) was applied to evaluate the effect of the various factors on gallbladder wall thickness; a p-value <0.05 was considered to be significant.

Results

The sample population comprised 400 healthy subjects made up of 228 (57%) females and 172 (43%) males (ratio of 1.3:1). Their ages ranged from 16 - 78 years, with mean age and SD of 32[+ or -]13.2 years.

One hundred and forty-eight subjects in the sample population were in the age group 16 - 25 years, representing 37% of the population. The age group of 66 - 75 years was the smallest (1.5%) of the population, and had equal numbers of men and women at 3 (0.75%) each (Table I).
Table I. Age distribution of mean gallbladder wall thickness in the
study population

Age group            Wall thickness (mm)
(Years) (N)    Mean          Range        Std

16 - 25 (148)  2.20       1.0 - 3.3       0.56
26 - 35 (142)  2.36       1.0 - 4.0       0.51
36 - 45 (58)   2.37       1.1 - 3.4       0.52
46 - 55 (22)   2.29       1.6 - 2.9       0.38
56 - 65 (16)   2.28       1.7 - 3.0       0.44
66 - 75 (6)    2.57       1.9 - 2.9       0.41
76 - 85 (8)    2.15       1.0 - 3.0       0.71
        400


The highest mean weight (72.14 kg) in the study population was in the age group 46 - 55 years, which correspondingly reflected the highest body mass index (BMI). The lowest body parameters (height 1.60 m, weight 49.13 kg and BMI 19.13) were in the 76 - 85 years age group. Women showed lower mean body parameters than men in the study (p<0.05). However, the mean total BMI was higher for women (23.66) than men (22.99).

Gallbladder wall thickness fond in the study ranged from 1.7 mm - 2.7 mm. There was no correlation between gallbladder wall thickness and subject's age and height (p<0.05) (Table II), although the highest mean wall thickness (2.57[+ or -]0.41 mm) was observed in the 66 - 75 years age group. However, there was a strong positive correlation between gallbladder wall thickness and BMI (r = 0.153, p<0.002)(Table II).
Table II. Correlation between mean gallbladder wall thickness and body
parameters of the population

                Age (years)  Height (m)   Weight (kg)
Wall thickness
(mm)                0.048       0.042      0.168 [dagger]
p value             0.341       0.405      0.001

                   MI

Wall thickness
(mm)             0.153 [dagger]
p value          0.002

[dagger] Correlations were significant at the 0.01 level (2-tailed)
BMI = body mass index


The average gallbladder wall thickness was significantly higher in men than in women (p<0.000), and the differences in body parameter were statistically significant in both sexes (p<0.047) (Table III).
Table III. Comparison of the mean gallbladder wall thickness and body
parameters in the different sexes

Sex (N)       Wall thickness (mm)    Height (m)    Weight (kg)

F (228) Mean              2.196             1.61          60.93
Std               [+ ro -]0.504     [+ ro -]0.07  [+ ro -]14.50
M (172) Mean              2.432             1.72          67.70
Std               [+ ro -]0.524     [+ ro -]0.08  [+ ro -]12.36
p value:                0.000 *          0.047 *        0.000 *

Total Mean                2.298            1.654          63.84
Std               [+ ro -]0.525    [+ ro -]0.925  [+ ro -]14.01

* Significant at p<0.05


Discussion

The study group comprised 228 (57%) women and 172 (43%) men. The female dominance in our study population was probably due to the greater willingness of women to be recruited and, secondly, that most of the volunteers came from a nursing school and therefore were predominanatly female.

The study population's age ranged from 16 - 78 years, with a mean age and SD of 32[+ or -]13.2 years. The age parameter was unevenly distributed with many (37%) of the volunteers falling in the age group of 16 - 25 years, and 35% in the 26 - 35 years group (Table I). The age groups of 66 - 75 years and 76 - 85 years had the least representation (1.5 - 2.0%). The unevenness of our population was a result of the randomised selection process, which unfortunately might affect the accuracy of the age influence on our measurement parameters.

We observed in the study that most of the gallbladder wall thicknesses measured were greater in men than in women. There was also a statistically significant difference between the mean gallbladder wall thickness of women and of men at p<0.001 (Table III), which is in line with the fact that organ sizes in men are generally larger than those in women. This finding is in agreement with Caroli-Bosc et al. (6)

There have been few studies of normal gallbladders in adults, and the resulting dearth of information regarding standard reference measurements can make decisions about the presence or absence of gallbladder disease difficult. In our study, the average gallbladder wall thickness ranged from 1.7 - 2.7 mm, which is lower than figures reported by Wolson et al. (7) and Cooperberg et al., (9) who reported in separate studies that gallbladder wall thickness measured 2 - 3 mm and [less than or equal to]3 mm respectively, though it is known that greater gallbladder wall thickness may be a non-specific finding. (10), (11) However, in adults as well as in children, an increase in thickness may result from a large spectrum of pathological conditions.

In our study, gallbladder wall thickness showed no significant correlation with subjects' age and height (Table II), unlike the observations reported by McGahan et al. (12) in a similar study on children.

Graphing gallbladder wall thickness against age showed a sinusoidal incremental pattern with plateau and peak levels at 26 - 35, 36 - 45 and 66 - 75 years (Fig. 2), which cannot be explained by this study. However, the peak value of gallbladder wall thickness noted in the 66 - 75 years age group could represent the age at which the organ thickness is highest before involution begins to occur.

[FIGURE 2 OMITTED]

Our study also showed a strong positive correlation between gallbladder wall thickness and BMI of subjects (Table II).

The definition of abnormal gallbladder wall thickness measurements of adult subjects has received very little attention. Indeed, the fairly uniform agreement to use 3 mm as the upper limit for normal gallbladder wall thickness also applies to children. (13), (14) We would say that normal gallbladder wall thickness for most adults is [less than or equal to]3 mm. Occasionally, even in normal subjects, the wall cannot be adequately measured, which may simply be due to the superficially located gallbladder being out of the focal zone of the transducer, but this can be corrected by adjusting the focal zone and gain.

Conclusion

US can be used to reliably measure the thickness of the gallbladder wall, as was attested to by this study. In addition, this study enabled the establishing of a population-based US gallbladder wall thickness so that a gallbladder wall >3 mm thick will suggest an abnormality in most patients, whereas a thickness <3 mm will suggest normalcy but cannot be used to rule out gallbladder diseases.

Statistically significant differences between gallbladder wall thickness and height and weight of each sex have been established by the study. The established normogram can be used as both a complementary modality in clinical evaluation as well as a more sensitive means of evaluating patients for gallbladder disorder.

(1.) Middleton WD, Kurtz AB. Ultrasound. The Requisites. 2nd ed. St Louis, USA: Mosby, 1996.

(2.) Cooperberg PL, Burhenne HJ. Real-time ultrasonography. A diagnostic technique of choice in calculus gallbladder disease. N Engl J Med 1980; 302: 277-279.

(3.) Warwick R, Williams PL. Pancreas and liver. In: Warwick R, Williams PL, eds. Gray's Anatomy. 35th ed. Philadelphia: WB Saunders, 1973: 1299-1310.

(4.) Sanders RC. The significance of sonographic gallbladder wall thickening. J Clin Ultrasound 1980; 8: 143- 146.

(5.) Fleischer AC, James AE Jr, Norwalk CT, eds. Real-time sonography. Appleton: Century-Crofts, 1984.

(6.) Caroli-Bosc FX, Pugliese P, Peten EP, et al. Gallbladder volume in adults and its relationship to age, sex, body mass index, body surface area and gallstones. An epidemiologic study in a non selected population in France. Int J Gastroenterol 1999; 60(4): 344-348.

(7.) Wolson AH. Ultrasound measurements of the gall bladder. In: Goldberg BB, Kurtz AB, eds. Atlas of Ultrasound Measurements. Chicago: Year Book Medical Publishers, 1990: 108-109.

(8.) Wikipedia. List of cities proper by population. http://en.wikipedia.org/wiki/Nigeria (accessed 6 April 2009).

(9.) Cooperberg PL, Gibney RG. Imaging of the gallbladder. Radiology 1987; 163: 605-613.

(10.) Callen PW, Filly RA. Ultrasonographic localization of gallbladder. Radiology 1979; 133: 687-691.

(11.) Rall PW, Quinn MF, Juttner HU. Gallbladder wall thickening: Patients without intrinsic gallbladder disease. Am J Roentgenol 1981; 13: 65-68.

(12.) McGahan JP, Phillips HE, Cox KL. Sonography of the normal pediatric gallbladder and biliary tree. Radiology 1982; 144: 873-875.

(13.) Jeong HY, Hyun JK, Myung JL. Sonographic measurements of normal gallbladder sizes in children. J Clin Ultrasound 2003; 31: 80-84.

(14.) Zins M, Boulay CI, Molinie V, et al. Imaging of a thickened-wall gallbladder. J Radiol 2006; 87: 479-493.

S Mohammed, MB BS, FWACS, FMCR

A Tahir, MB BS, FWACS, FMCR

A Ahidjo, MB BS, FWACS, FMCR

Z Mustapha, MB BS, FWACS

O Franza, MSc

Department of Radiology, University of Maiduguri Teaching Hospital, Maiduguri, Borno State, Nigeria

I Okoye, MB BS, FMCR

Department of Radiation Medicine, University of Nigeria Teaching Hospital, Ozalla, Enugu State, Nigeria

A Shugaba, MB BS, MSc, PhD

Department of Anatomy, University of Jos, Jos, Plateau State, Nigeria
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Article Details
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Title Annotation:ORIGINAL ARTICLE
Author:Mohammed, S.; Tahir, A.; Ahidjo, A.; Mustapha, Z.; Franza, O.; Okoye, I.; Shugaba, A.
Publication:South African Journal of Radiology
Article Type:Report
Geographic Code:6NIGR
Date:Dec 1, 2010
Words:2363
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