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Cholesterolosis is an acquired histologic abnormality of the gallbladder epithelium that results in an excessive accumulation of cholesterol esters within epithelial macrophages [60] Clinicians generally encounter the lesion only as an incidental pathologic finding after surgical resection of the gallbladder, although, in certain patients, the diagnosis may be suspected before surgery.
Cholesterolosis,
as well as adenomyomatosis of the gallbladder, has been classified as one of
the hyperplastic cholecystoses, a term introduced in 1960 to describe
several diseases of the gallbladder thought to share the common features of
mucosal hyperplasia, hyperconcentration and hyperexcretion of dye on
cholecystography, and absence of inflammation.[61] The proponents of
this concept believed that biliary colic, in the absence of gallstones, could
often be explained by the presence of one of the hyperplastic cholecystoses,
whereas other investigators, citing the lack of a common etiology and the
nonspecificity of the clinical features, have recommended that the term
hyperplastic cholecystoses be abandoned.
Although recognized as a distinct pathologic entity for almost a century, the actual prevalence of cholesterolosis remains a matter of some dispute. Depending on whether gross or microscopic criteria were used for diagnosis, the prevalence of cholesterolosis in necropsy specimens has ranged from 5% to 40%. A large autopsy series involving more than 1300 cases in which each gallbladder was examined microscopically found the prevalence of cholesterolosis to be 12%.[62] When surgically resected gallbladders were examined, the prevalence was, not surprisingly, about 50% higher (18%) than that found in necropsy material. [63] The incidence of cholesterolosis has not been calculated, because the entity is usually only an incidental pathologic finding, and the onset is rarely known.
The epidemiology of cholesterolosis is analogous to that of cholesterol gallstone disease[64] in that similar groups of persons are predisposed; however, the two lesions occur independently and do not usually coexist in the same individual. Like gallstone disease, cholesterolosis is uncommon in children (the youngest reported patient was a 13-year-old girl) and shows a marked predilection for women as old as 60 years of age. After that, the sex differences are less pronounced. No racial, ethnic, or geographic differences in prevalence have been described, although if the analogy with
cholesterol gallstone disease is extended, the prevalence would be expected to be higher in Western than non-Western societies.
Cholesterolosis is defined pathologically by the accumulation of lipid (cholesterol esters and triglyceride) within the gallbladder mucosa. The following are four patterns of lipid deposition[60] :
When the gallbladder is visually inspected at the time of laparotomy (or laparoscopy), a diagnosis of cholesterolosis can be made in one fifth of the cases on the basis of the gross appearance of the gallbladder mucosa as seen through the translucent serosal surface. When the gallbladder is opened, the mucosa characteristically has pale, yellow linear streaks running longitudinally, giving rise to the term strawberry gallbladder (although the mucosa is usually bile stained rather than red). When cholesterolosis is diagnosed at the time of surgical resection of the gallbladder, gallstones are also present in one half of cases. If the diagnosis is made at autopsy, stones are present in only 10%,[62] demonstrating that the two disease processes are independent of each other.
Hyperplasia of the mucosa is invariably present and is described as marked in one half of cases. Usually, the hyperplasia is of the villous type. The most prominent feature is an abundance of macrophages within the elongated villi. Each macrophage is stuffed with lipid droplets and has a characteristic appearance of a "foam cell" .In milder cases, the foam cells are limited to the tips of the villi (accounting for the linear streaks seen grossly); with more severe involvement, the foam cells may fill the entire villi and spill over into the underlying submucosa. Although extracellular deposits of lipid are rare, small yellow particles ("lipoidic corpuscles") representing detached masses of foam cells are occasionally seen floating in the bile.
The cause of the accumulation of cholesterol esters and triglyceride[65] in cholesterolosis remains obscure. Several hypotheses have been put forth suggesting that the cholesterol is derived from the blood[66] or that mechanical factors that impede emptying of the gallbladder lead to the deposition of lipid.[67] More recent data have unequivocally shown that the gallbladder epithelium is capable of absorbing cholesterol from the bile, as might be expected in epithelium that is embryologically and histologically similar to intestinal absorptive cells.[68] [69] Moreover, the cholesterol in gallbladder bile is already in the ideal physical state for absorption (i.e., a mixed micelle). The question remains as to why, in some patients, resorbed biliary cholesterol is esterified and then stored in foamy macrophages as cholesterolosis.[70] The lesion is frequently, but not always, found in gallbladders exposed to bile that is supersaturated with cholesterol,[71] just as cholesterol stones frequently, but not always, form under the same circumstances. These two disorders, both of which lead to the ectopic accumulation of cholesterol, probably share common pathogenic mechanisms (such as the secretion of an abnormal bile) but progress independently in a given patient, depending on other factors such as the presence of nucleating proteins in bile and the rate of mucosal esterification. [72]
Cholesterolosis usually does not cause symptoms, as demonstrated by autopsy specimens that show the lesion in patients who never had biliary symptoms. On occasion, however, individual patients may have dull, vague, right upper quadrant or epigastric pain that resembles biliary colic, and, at the time of cholecystectomy, they are found to have no stones, no gallbladder inflammation, and only incidental cholesterolosis. In those patients who undergo cholecystectomy for the syndrome of acalculous biliary pain and have incidental cholesterolosis on pathologic examination of the gallbladder, the prognosis is better in terms of resolution of pain than if cholesterolosis is not found.[73]
A retrospective surgical series looking at almost 4000 gallbladders removed by cholecystectomy identified 55 patients with acalculous cholesterolosis. The investigators
found that almost one half of these patients had presented with recurrent pancreatitis of unknown etiology and speculated that small cholesterol polyps had detached from the gallbladder wall and transiently obstructed the sphincter of Oddi, thereby provoking the acute pancreatitis. After 5 years of follow-up, the pancreatitis did not recur. These authors and others[ have suggested that cholesterolosis (or more specifically, cholesterol polyps) should be considered in the differential diagnosis of idiopathic pancreatitis.
Diffuse cholesterolosis (which, as noted earlier, constitutes 80% of cases) is only rarely detectable by either ultrasonography or oral cholecystography. However, in the polypoid form, if the polyps are of sufficient size, there is a characteristic appearance on ultrasonography of single or multiple nonshadowing, fixed echoes projecting into the lumen of the gallbladder.[77] Most of the polyps are small (2 to 10 mm). On oral cholecystography, the polyps appear as small, round radiolucencies in the lumen of the opacified gallbladder and are best demonstrated after the gallbladder has been partially emptied and compression has been applied.
Because cholesterolosis is only rarely diagnosed before resection of the gallbladder, the issue of treatment is usually irrelevant. In the rare case of polypoid cholesterolosis diagnosed by ultrasonography or cholecystography, the absence of biliary tract symptoms argues against any intervention. If the patient has symptoms consistent with biliary colic or pancreatitis,[74] a cholecystectomy is indicated. There is no medical therapy for cholesterolosis.
Adenomyomatosis (an unwieldy term that obscures its meaning) is defined as an acquired, hyperplastic lesion of the gallbladder characterized by excessive proliferation of surface epithelium with invaginations into the thickened muscularis or beyond.[78] Despite the prefix adeno-, the lesion is entirely benign and unrelated to adenomatous epithelia elsewhere in the gastrointestinal tract. Adenomyomatosis is not thought to have potential for malignant transformation.
The literature on this obscure topic is made all the more difficult to understand by the proliferation of different terms used to describe the same condition. One author[79] notes that adenomyomatosis has been described by at least 18 different names, the more common of which include adenomyoma (used when the lesion is localized to the gallbladder fundus), diverticulosis of the gallbladder (ignores the hyperplasia), cholecystitis glandularis proliferans (overemphasizes the role of inflammation), Rokitansky-Aschoff sinuses (familiar but anatomically incorrect), adenomyosis, and adenomyomatous hyperplasia. Some terms are used in the radiologic literature, whereas others are used exclusively by pathologists; none are familiar to most gastroenterologists.
The prevalence of adenomyomatosis of the gallbladder varies greatly depending on the criteria used for diagnosis and whether resected gallbladders or necropsy specimens were examined. In a large series of more than 10,000 cholecystectomy specimens, Shepard and associates[80] found only 103 cases of adenomyomatosis, for a prevalence of about 1%. The lesion is more common in women than men, by a 3:1 ratio, and the prevalence increases with age. Neither ethnic nor geographic differences in prevalence have been described.
To understand the pathology of adenomyomatosis, it is useful to consider briefly the normal histologic architecture of the gallbladder as well as the entity of Rokitansky-Aschoff sinuses Unlike the small intestine, the gallbladder has no muscularis mucosa; thus, the lamina propria abuts directly on the muscular layer. In childhood, the epithelial layer is cast up into folds and supported by the lamina propria. As the gallbladder ages, the valleys of the epithelial layer may deepen so that they penetrate into the muscular layer and form Rokitansky-Aschoff sinuses. These sinuses are acquired lesions and are present in about 90% of resected gallbladders. If the Rokitansky-Aschoff sinuses are
deep and branching and accompanied by thickening (hyperplasia) of the muscular layer, then a diagnosis of adenomyomatosis can be made.[
Adenomyomatosis may involve the entire gallbladder (generalized adenomyomatosis) or, more commonly, may be localized to the gallbladder fundus, in which case the lesion is often termed an adenomyoma. On rare occasion, the process may be limited to only an annular segment of the gallbladder wall and give rise to a luminal narrowing and a "dumbbell-shaped" gallbladder In any case, the involved portion of the gallbladder wall is thickened to 10 mm or more, and the muscle layer is three to five times its normal depth. On cut sections, cystic dilations of the Rokitansky-Aschoff sinuses are evident and may be filled with pigmented debris or calculi.
Hyperplasia of the muscle layer is invariably present, and the epithelial lining occasionally undergoes intestinal metaplasia. Mild chronic inflammation is often present.
The pathogenesis of adenomyomatosis is unknown. Increased intraluminal pressure from mechanical obstruction (e.g., from an obstructing calculus, kink in the cystic duct, or congenital septum) has been postulated to result in cystic dilation of the Rokitansky-Aschoff sinuses, subsequent hyperplasia of the muscle layer, and adenomyomatosis.[78] Like pressure-related colonic diverticula, Rokitansky-Aschoff sinuses are most likely to be found where the muscle layer is weakest (at the site of a penetrating blood vessel). However, evidence for outflow obstruction is not always found; for example, calculi are present in only about 60% of the cases of adenomyomatosis.[80] Although some investigators have proposed that adenomyomatosis is a consequence of chronic inflammation, inflammation is not always present, particularly when the lesion is localized to the fundus.[81] Finally, several investigators have noted an association between adenomyomatosis and anomalous pancreaticobiliary ductal union. In one study,[82] one half of patients with adenomyomatosis had anomalous pancreaticobiliary ductal union, and, in another study,[83] one third of patients with anomalous pancreaticobiliary ductal union had adenomyomatosis. The pathogenic link between these two peculiar entities is unclear.
Adenomyomatosis, like cholesterolosis, usually causes no symptoms but is rather an incidental finding at autopsy or surgical resection. As noted earlier,[80] gallstones are present in more than one half of the resected gallbladders that are found to have adenomyomatosis, in which case the symptoms can be ascribed to the stones. The symptoms that have been ascribed to acalculous adenomyomatosis are indistinguishable from biliary colic caused by cholelithiasis.
On rare occasions, adenocarcinoma of the gallbladder has been found in association with adenomyomatosis[84] ; however, the malignancy is often far removed from the localized area of adenomyomatosis, and the association has been thought to be coincidental rather than causal. Nonetheless, several recent reports[85] [86] of adenocarcinoma occurring in an area of gallbladder wall involved with adenomyomatosis have created diagnostic uncertainty on ultrasonography or cholecystography. In particular, a retrospective review[87] of more than 3000 resected gallbladders revealed a significantly higher frequency (6.4%) of gallbladder cancer in gallbladders with the segmental form of adenomyomatosis than would have been expected by chance alone, and the investigators proposed that segmental adenomyomatosis should be considered a potentially premalignant lesion.
When simple adenomyomatosis of the gallbladder is discovered incidentally, the lesion is likely to be benign. However, if there is any suspicion of an associated mass lesion, particularly one greater than 10 mm in size, or if segmental adenomyomatosis is found, then a thorough radiologic evaluation of the gallbladder is warranted.
As noted previously, adenomyomatosis is frequently not diagnosed before resection and direct examination of the gallbladder. However, there are several specific radiologic and ultrasonographic findings that may, if present, allow a diagnosis to be made preoperatively.
On oral cholecystography, the mural diverticula constituting the Rokitansky-Aschoff sinuses may fill with contrast material and produce characteristic radiopaque dots paralleling the margin of the gallbladder lumen.[88] Any portion of the gallbladder wall may be involved ( Fig. 58-6 ). Localized, fundal adenomyomatosis (adenomyoma) may present as a filling defect in the fundus, whereas segmental adenomyomatosis may present as a circumferential narrowing of the gallbladder lumen. As is the case with cholesterolosis, the radiologic findings of adenomyomatosis are best appreciated when the gallbladder has partially emptied of contrast material and pressure has been applied during radiography.[88]
Although ultrasonography has largely replaced oral cholecystography in the evaluation of the gallbladder, the ultrasonographic findings of adenomyomatosis are less specific than the radiographic findings.[89] A thickened gallbladder wall (>4 mm) is not specific for gallbladder disease and is seen in many other conditions, particularly liver diseases resulting in hypoalbuminemia or ascites.[90] Carefully done studies in which radiologic and ultrasonographic findings of adenomyomatosis were correlated with pathologic findings have determined that diffuse or segmental thickening of the gallbladder wall in association with intramural diverticula (seen as round anechoic foci) accurately predicts adenomyomatosis.[91] If the intramural diverticula (dilated Rokitansky-Aschoff sinuses) are filled with sludge or small calculi, then the lesions may appear echogenic with acoustic shadowing or a reverberation artifact.[92]
Finally, CT and magnetic resonance findings of adenomyomatosis have been described[93] and include differential enhancement of gallbladder wall layers, detection of Rokitansky-Aschoff sinuses within a thickened wall,[94] and subserosal fatty proliferation.[
In the absence of biliary tract symptoms, adenomyomatosis requires no treatment. If the patient has biliary colic and radiographic or ultrasonographic evidence of adenomyomatosis with calculi, then a cholecystectomy is indicated. A more difficult clinical problem arises when a patient is symptomatic with suspected adenomyomatosis but no stones. [85] In such cases, the more extensive or severe the adenomyomatosis appears to be, the more confident the clinician can be that the symptoms are related to the lesion and the more likely the patient will be to benefit from cholecystectomy. Fear of malignant transformation is not a reason to operate, [96] unless an ultrasonographic or radiologic image is worrisome for a mass or perhaps the segmental form of adenomyomatosis.
Adenomyomatosis of the gallbladder that is localized to the fundus may produce a hemispheric projection into the lumen that resembles a polyp. Such a lesion has come to be known as an adenomyoma, although it is not neoplastic in origin. The pathogenesis of an adenomyoma is discussed in the section on adenomyomatosis (see earlier). The lesions are usually approximately 15 mm in size, and the bulk of the adenomyoma is confined to the muscular wall of the gallbladder.[
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