Prevalence study
The prevalence of gallbladder polyps in our population sample was 1.4% (males, 1.7%; females 1.1%), which corresponds to prevalence data published by Özmen et al. for Great Britain and by Heyder et al, for Germany [7, 9]. Our data were collected as part of a complete survey of a rural population with a response rate of 66.6% [22, 23]. To date, the only available data regarding the prevalence of gallbladder polyps in a representative population sample were published by Jørgensen et al., who reported a prevalence of 4.6% for males and 4.3% for females [8]. Prevalence data from larger, non-surgical patient populations derive from preventive medical studies or from selected populations in Japan and Taiwan, with prevalences in the range of 5.3–9.5% [10–14]. All studies show a predominance of males for the development of gallbladder polyps, compared to a female predominance for the development of gallbladder stones [10–14, 23, 24]. In our study, the peak age for first manifestation of gallbladder polyps lay between 36 and 45 years. In this age group, the respective prevalences for males and females stood at 4.7% and 2.1%, respectively. Segawa and Lin reported the highest prevalence for both sexes in the fourth decade of life [10, 15]. Similarly, Okamoto and Jørgensen found the highest prevalence in males in the fourth decade, but in the fifth and sixth decades in females [8, 10, 11, 15].
Follow-up study
To date, no data on the follow-up of gallbladder polyps derived from studies of representative population samples have been published. Of published studies, the majority used diagnostic ultrasound, while Eelkema et al. analyzed data obtained by cholecystography and Sugiyama et al. examined some of their patients using endosonography. Most subjects were surgical patients, although Collett et al. report on diabetics and healthy controls [9, 13, 14, 17–21]. The average follow-up periods of the available studies range from nine months to 15 years. In most instances, patients were re-examined at intervals of six or 12 months. Similar to the study by Collett et al., we examined our subjects at established follow-up dates of three and seven years [19].
All gallbladder polyps diagnosed at the initial survey were 10 mm or less in diameter. A similar distribution was reported by Moriguchi et al., who reported diameters 5 mm and less in 57%, 6–9 mm in 37% and 10 cm and above in only 6% [13]. Jørgensen et al. and Csendes et al. reported diameters < 5 mm in even higher percentages of subjects, namely 85% and 80%, respectively, and did not, in their respective populations, identify any polyps larger than 10 mm in diameter [8, 17]. The median polyp diameter in our initial survey was 5 mm ± 2.1 mm (range 2–10 mm), which was comparable to data reported by Shinkai et al. at 4.8 mm ± 2.9 mm. In the study reported by Collett et al., the average initial diameter was 3.9 mm. Heyder et al., however, reported larger diameters at 6 mm (range 2–15 mm) [9, 19, 20].
With respect to diameter, the majority of polyps showed no change at either the first (1999) or second (2003) follow-up examination. In 1999, polyp diameter remained constant in 81% (17/21) of subjects, with one person (5%) exhibiting reduction in the size of his polyp and three persons (14%) showing size progression (figure 3). A comparison of size progression between 1999 and 2003 shows that 91% (10/11) of polyps remained constant, one became smaller (1/11; 9%) but none became larger. Over the entire 84-month period 62% (8/13) of polyps showed no change in size, 15% (2/13) became smaller and 23% (3/13) became larger. Thus, our results lie between data published by Moriguchi and Sugiyama on the one hand and those of Csendes on the other [13, 17, 18]. Over an observation period of five years, Moriguchi et al. found an increase in polyp diameter in 11.7% (12/103), while in 84.5% (87/103), polyp size remained constant. Conversely, Csendes et al., who followed subjects for an average 71%, found no change in polyp diameter in 50% of subjects while an increase or decrease in diameter was observed in 25% each (table 1) [13, 17].
At the first follow-up examination, 30 months after the initial survey and with a response rate of 91%, polyps were visualized in only 77% (24/31) of subjects; at the second follow-up examination, 84 months after the initial survey and with a response rate of 65%, polyps were identified in 41.9% (13/31) of subjects. The proportion of polyps that were no longer detected at follow-up examinations was lower in reports by other authors [13, 17–19].
Of the three subjects in our study who exhibited polyps with size progression, two underwent cholecystectomy. The histopathological findings in one patient revealed multiple gallbladder stones in an otherwise unremarkable gallbladder. In all, 19.4% (n = 6) of all structures initially identified as polyps were identified as gallbladder stones at follow-up. Similar results have been reported from surgical series [6, 4, 25, 26].
A possible reason for the false-positive ultrasound findings might be that polyps may form the site of origin in the development of gallbladder stones [6, 27].
The histopathological findings in the second subject who had undergone cholecystectomy due to size progression revealed cholecystitis of moderate severity, which, at the time of the ultrasound examination, may have been polypoid in appearance [27, 28]. A further reason for the failure to demonstrate polyps at histopathological examination could be that polyps may be destroyed by the mechanical action of the gallbladder wall.[8] This may also be an explanation for the observation in our study that the prevalence of gallbladder polyps among women and in advanced age is lower, while, at the same time, in this subsample, the prevalence of gallbladder stones is higher to a statistically significant extent. [23] Neither Sugiyama nor Moriguchi nor Csendes reported the development of gallbladder stones at follow-up [17, 18, 20].
One of the limitations of our study is the small number of only 34 subjects with polyps visualized at ultrasound. One reason may relate to the technically less advanced ultrasound scanners used at the initial survey compared with those used at follow-up. The portable ultrasound scanner used at the second follow-up examination of subjects in their homes may also have limited the strength of the findings and may possible have been the cause of false-negative findings.