Adenomyomatosis

Etiology

The cause of adenomyomatosis remains unknown; however, it is often associated with cholelithiasis, and some authors have proposed that it is a response to chronic cholecystitis.[6][7] Although generally considered benign, some forms of gallbladder adenomyomatosis are considered precancerous lesions.

Epidemiology

Adenomyomatosis has been found in 2% to 7.8% percent of cholecystectomy specimens.[1] Although patients are found across a wide age range, they are most frequently diagnosed in the sixth decade of life. Reports vary regarding sex distribution, although it may be slightly more common in women; there is no known racial predilection.[8]

Pathophysiology

Adenomyomatosis is a noninflammatory hyperplasia of the gallbladder wall characterized by Rokitansky-Aschoff sinuses. Gallstones are present in up to 90% of patients with the segmental type and in approximately 50% of patients with diffuse or fundal types.[9] Cholesterol crystals are often seen within the sinuses.

Histopathology

Rokitansky-Aschoff sinuses are intramural diverticula seen on histopathologic examination of adenomyomatosis specimens and appear cystic on ultrasonography. Gallstones or cholesterol crystals may be found in the sinuses. Gallbladder wall thickening results from epithelial hyperplasia and hypertrophy of the muscularis propria.

Thickening of the subserosa is also present, and nerve trunks are often seen in this layer. The surface epithelium may exhibit variable morphology, including reactive epithelial changes, papillary architecture, or metaplasia. Rarely, perineural and intraneural invasion into the subserosa may be present, but the serosa is never involved.[10]

History and Physical

Most patients with gallbladder adenomyomatosis are asymptomatic. Some affected individuals report right upper quadrant abdominal pain. However, this symptom is sometimes observed in cholelithiasis; the relationship between pain and adenomyomatosis remains unclear.

Evaluation

In patients presenting with right upper quadrant abdominal pain, transabdominal ultrasonography should be the primary diagnostic modality. Ultrasonography findings may be characteristic of adenomyomatosis and can aid in diagnosis. When the diagnosis is uncertain on ultrasonography, MRI is preferred as the next diagnostic option.[11] Furthermore, gallbladder wall thickening may be an incidental finding on computed tomography, and transabdominal ultrasonography or MRI may be useful for further characterization. In addition to gallbladder wall thickening, ultrasonography may show small (<10 mm) intramural anechoic cystic spaces or echogenic intramural foci (cholesterol crystals in Rokitansky-Aschoff sinuses) with comet-tail artifact.[1] In most cases, not all characteristic findings are present.[11][12][13]

Of the transabdominal ultrasonography findings described, the echogenic foci with associated V-shaped comet tail artifacts have been described as specific for adenomyomatosis (see Image. Adenomyomatosis). On MRI, adenomyomatosis is demonstrated by thickening of the gallbladder wall and T2-hyperintense intramural cystic spaces. Calculi are seen as signal voids. The T2-hyperintense cystic areas can align in a curvilinear fashion, producing a characteristic pearl necklace sign. On CT imaging, nonspecific thickening and enhancement of the gallbladder wall are sometimes observed. The rosary sign can be present, caused by a thin layer of enhancing epithelium lining the intramural diverticula, surrounded by hypoenhancing, hypertrophied muscularis, which gives the gallbladder wall a rosary-like appearance.[1]

Specific imaging findings can enhance diagnostic confidence and reduce the need for indeterminate radiologic assessments. On transabdominal ultrasonography, true intramural echogenic foci of adenomyomatosis persist and continue to generate a V-shaped comet-tail artifact. In contrast, adherent stones or sludge often shift or layer with changes in patient position. Color Doppler ultrasonography may show a twinkling artifact within intramural foci, supporting the diagnosis of adenomyomatosis. When gallbladder wall thickening is focal and the artifact is equivocal, short cine sweeps at different insonation angles can help reveal the classic appearance.

On MRI, T2-weighted images depict clustered, high-signal intramural cysts that may align to form a pearl-necklace sign, and diffusion-weighted imaging typically shows no convincing restricted diffusion compared with carcinoma. On magnetic resonance cholangiopancreatography, tiny intramural cysts parallel to the normal lumen further support the diagnosis of adenomyomatosis. On computed tomography (CT), gallbladder mural thickening and enhancement are nonspecific, but the cotton ball sign is seen in approximately 75% of cases of adenomyomatosis. This sign is recognized when contrast-enhanced CT demonstrates gray, fuzzy, enhancing dots in the gallbladder wall, or a dotted external border of an inner enhancing layer of the wall.[14]

Treatment / Management

If adenomyomatosis is diagnosed conclusively and is asymptomatic, no treatment is recommended, and follow-up imaging is not required.[15][16]

Cholecystectomy is recommended in the following situations:

• When adenomyomatosis cannot be reliably distinguished from gallbladder cancer
• When associated with an anomalous biliopancreatic junction, a risk factor for gallbladder cancer
• When associated with right upper quadrant pain [15]

Differential Diagnosis

The differential diagnosis for adenomyomatosis of the gallbladder includes the following:

• Gallbladder malignant neoplasms (eg, adenocarcinoma, cholangiocarcinoma, and metastasis)
• Gallbladder polyps
• Benign gallbladder tumors (eg, adenoma)
• Normal variant appearances of the gallbladder, such as gallbladder folds (eg, Phrygian cap)

Prognosis

Adenomyomatosis is a benign condition and carries a good prognosis. Although many patients are asymptomatic, some have right upper quadrant pain. Adenomyomatosis may be detected incidentally on imaging, but a malignant neoplasm can have a similar appearance. Notably, gallbladder carcinoma has a much worse prognosis (less than 5% 5-year survival).[7] Therefore, it is vital to ensure that the imaging diagnosis of adenomyomatosis is conclusive before attributing the finding to a benign process.

Complications

Adenomyomatosis may be associated with gallstones and cholecystitis. Gallbladder cancer may occur in association with segmental or diffuse adenomyomatosis, but has not been reported as a complication of fundal adenomyomatosis.[17] Progressive lesion growth alone is not indicative of a malignant neoplasm.[1]