Ciliated foregut cyst (CFC) is an uncommon developmental anomaly, and usually develops above the diaphragm in the form of bronchial and esophageal cysts. Extrahepatic biliary tract cases of lower diaphragm are extremely rare; therefore very few cases have been reported.1 CFC is usually asymptomatic2, 3 and has traditionally been considered lacking any malignant potential. However, recently present published cases observed some risk of carcinoma arising in CFC.4 Therefore, CFC should be regarded as a lesion with a clinical spectrum that is not yet fully defined. We present an extremely rare case of a gallbladder (GB) cyst originating from the foregut remnants in a twenty year-old woman. To our knowledge, only one similar case of foregut cyst in GB lumen has been reported in Korea. We review the clinicopathological aspects of this unusual entity and discuss the usefulness of radiological images and treatment.

This paper reports a case of a twenty year-old woman who presented with intermittent mild right upper quadrant abdominal discomfort and findings of GB abnormality in abdominal ultrasonography. There was no associated jaundice, rigors or weight loss. Apart from minimal right upper quadrant tenderness, other laboratory examinations were unremarkable. Liver function tests were within normal limits (AST 23 IU/L, ALT 21 IU/L) and serum total bilirubin level (0.7 mg/dL). Serology was negative for hepatitis B and hepatitis C. Full blood count and renal function tests and clotting profile were within normal limits. The CA 19-9 serum level was below 2 U/mL (normal 0-37 U/mL). She has taken medicine to treat hyperthyroidism for one year, and all thyroid function tests were normal at time of admission. An abdominal ultrasonography revealed a 2 cm well defined cystic mass with internal echogenic debris attached to the neck of GB wall (Fig. 1), suspicious of a hemorrhagic cyst. CT revealed a similar finding of a 2.0 cm sized low density cystic lesion on the GB neck adjacent to the median segment of liver (Fig. 2), which were not enhanced at the post-contrast phase and appeared to be slightly highly attenuated in the pre-contrast image, suggesting a complicated cyst or hepatic mass mimicking a solitary necrotic nodule. The nature of cyst and exact location was evaluated by MRCP, which revealed a 2.0 cm mass on the GB neck that seemed to be adjacent to the subcapsular area of the left medial segment of liver (S4), presenting high signal intensity at the dependent portion in T1 weighted image without significant enhancement with dynamic scan. It was suspicious of a complicated cyst such as a hemorrhagic cyst (Fig. 3). The communication between the cyst and GB lumen and other abnormality of biliary tract was evaluated by ERCP, which revealed no communication between the GB lumen and cyst and no specific findings of the biliary tract system. Following these studies, we decided to perform laparoscopic cholecystectomy with a view to removing the cyst. The elective operation and subsequent recovery were uneventful. On gross examination, the GB measured 6.5×2.5 cm in dimension.

Fig. 1 Ultrasonography shows about 2.0 cm size cystic mass (white arrow) on the gallbladder neck with internal echogenic debris. Click for larger image

Fig. 2 Contrast enhanced computed tomography shows nonenhancing cystic mass (black arrow) in liver bed. Click for larger image

Fig. 3 Coronal view of MRCP image demonstrating a 2.0 cm cystic lesion (white arrow) adjacent to gallbladder appearing as complicated cyst such as hemorrhage cyst. Click for larger image

The serosal surface showed a protruding cystic mass, measuring 1.6×1.2 cm in dimension (Fig. 4). On section examination, the cyst was filled with some mucin contents and was not hemorrhagically configured. It was clearly separated from the GB mucosa and located just outside the GB wall without luminal communication. The GB mucosa was velvety. Histological examination showed a cyst with fibrous wall lined by ciliated, pseudostratified, columnar epithelium with occasional goblet cells, and revealed underlying smooth muscle layers (Fig. 5).

Fig. 4 The gallbladder was slightly distended (6.5×2.5 cm in dimension) and small protruding cystic mass (black arrow) was attached to the neck region (1.6 ×1.2 cm in dimension). Click for larger image

Fig. 5 Histologic findings (H&E). (A) The cut surface reveals a 1.6×1.2 cm unilocular intramural cyst (asterisk) without communication to the lumen of the gallbladder (×40). (B) The cyst is lined by a pseudostratified ciliated, columnar epithelium with a few goblet cells and underlying smooth muscle layers (×400). Click for larger image

GB cysts were first classified by Wiederman in 1797 as acquired, neoplastic or congenital.5, 6 CFCs are rare congenital cysts, arising from the remnant of embryonic foregut and usually located above the diaphragm, presenting either as a bronchial or esophageal cyst.7 When located below the diaphragm, most are usually found in liver, and were designated ciliated hepatic foregut cysts (CHFC). More than 60 cases of CHFC have been reported.4, 8 Extrahepatic foregut cysts are extremely rare: to our knowledge, only eight cases of GB CFCs have been reported in English literature. Kakitsubata et al.9 in 1995 first described a GB cyst lined by a single layer of ciliated columnar epithelium with a fibro-muscular wall, using the term "epithelial cyst of the gallbladder". They suggested the origin to be from Luschka's duct. Nam et al.7 first used the term "ciliated foregut cyst of the gallbladder" for this rare condition in 2000. They described a cyst lined by pseudostratified ciliated, columnar epithelium (PCCE) and a few goblet cells, and subepithelial structures consisting of fibroelastic tissues and one to two layers of smooth muscles. They also noted that there were no inflammatory changes or bile pigments in the cyst.

The primitive foregut gives rise to organs such as respiratory tract, pharynx, esophagus, stomach, proximal part of duodenum and hepatobiliary system embryologically. In the respiratory ciliated cyst, the PCCE was derived from the caudal-most part of laryngotracheal outgrowth, which remained attached to the portion of the primitive foregut destined to become the foregut cyst. The PCCE was also found in a liver cyst, derived from the primitive foregut10 and CHFC may have arisen as a detached outpouching of the hepatobiliary foregut.

Ultrasound is a useful imaging method for differential diagnosis from other hepatobiliary lesions. Most findings of reported CFC lesions were hypo-anechoic cystic features on ultrasound. However, CFC might be confused with malignant tumors when there are highly echoic areas.11 CT and MRI are also effective diagnostic methods when the mass dimension is larger than 1 cm. CFCs are frequently detected as hyperintense12 in T1 and T2 MR images but are sometimes observed to be iso- or hypointense in the T1 sequences.13 The signal content depends on the viscosity of cyst fluid, mucin density and the presence of calcium or cholesterol crystals. CFCs below the diaphragm are commonly discovered5 on the liver (CHFC), while CFCs of extrahepatic biliary tract such as GB are extremely rare.11

CT axial images of this case were confused with CHFC (Fig. 1) but coronal sequencing images of MRCP allowed diagnosis of CFC of GB (Fig. 2). Surgical findings showed that this cystic lesion was attached to GB neck wall and completely separated from the liver capsule (Fig. 3). Therefore, in this case, high resolution MRCP appears more helpful than CT in indicating the precise origin of the cyst. Congenital GB cysts generally have their own muscle layer and no communication with the lumen, as was true for this case (Fig. 4A). There is a report of CHFC communicating with the cystic duct of GB,14 possibly from a connecting malformation, so awareness of an aberrant connecting duct might be useful when performing hepatobiliary surgery.

Hepatic ciliated foregut cysts can occasionally undergo malignant transformation,15 so one should always bear in mind the possibility of similar changes in GB ciliated cysts. The radiological characteristics of ciliated cysts are not specific and they should be differentiated from biliary, hydatid cyst and hepatobiliary cystadenoma, atypical GB polyp, cholesterolosis, adenomyomatosis and other cysts of malignant nature. The biological behavior of ciliated foregut cyst of the GB is still not understood because of its rarity and the difficulty of fully excluding malignant potential. Muraoka et al.16 recommended either minimally invasive surgery or close observation.

We thought that this cystic lesion was possibly a ciliated foregut cyst of GB, with differential diagnoses including the other cystic masses mentioned above. The patient was very young and the cyst was not small (2.0 cm), so long term observation poses a worrisome risk. Therefore, we decided to perform minimally invasive surgery to remove the cyst. Heo et al.17 also used laparoscopic cholecystectomy in a similar case. If the patient is young or symptoms are present, we recommend minimally invasive surgical intervention for treatment. In conclusion, congenital cysts of GB are extremely rare, with very few ciliated foregut cysts of GB reported. So the biologic behavior of this rare cystic lesion is not yet thoroughly described. Radiologic studies are important to detect cystic structures and examine adjacent organs. Minimally invasive surgical intervention or close follow-up is recommended, because malignant potential cannot be fully excluded.