1. CYSTIC MESOTHELIOMA OF GALLBLADDER LODGE: AN EXCEPTIONAL LOCATION H. MHALLA(1), S. MEZGHANI(1), L.BOUALLEGUE(2), S.GHARBI DHAOUADI (1), F. CHEBBI(3), I CHELLY(4), S. HAOUET(4) (1) Radiology department, Ben Arous Regional Hospital, Ben Arous, Tunisia (2) Gastro-enterolgy department, Ben Arous Regional Hospital, Ben Arous, Tunisia (3) Surgery department, The Rabta Hospital, Tunis, Tunisia (4) Cytology and pathology department, The Rabta Hospital, Tunis, Tunisia

2. INTRODUCTION Cystic peritoneal mesothelioma (CPM) is a rare benign neoplasm arising from the mesothelial cells of the peritoneum. It occurs predominantly in young and middle-aged women with a reported mean age at presentation of 37 years (1). The natural history and pathogenesis of this condition remains poorly defined in the limited information available. There is no association with asbestos exposure. It has been suggested that chronic peritoneal irritation and possibly previous laparotomy may be involved in the pathogenesis of CPM (2).

3. OBJECTIVES: The aim of this study is to report the first case of a benign cystic mesothelioma of the gallbladder lodge, to describe imaging features and to propose differential diagnosis.

4. MATERIALS AND METHODS: Woman aged 53 years old presented with gallstone colic. Liver Test and Fibroscopy were done. Ultrasound exam and Bili MRI were performed. Abdominal laparoscopy was performed and anathomopathologic exam confirmed the diagnosis.

5. RESULTS: Clinical symptoms The patient suffers from gallstone colic beginning several years ago. During this period, she saw a gastroenterologist. A liver test did not indicated abnormal patterns. The fibroscopy was normal.

6. Ultrasound exam (US) showed two adjacent cystic structures in the gallbladder fossa with regular thin walls and homogeneous contents. Repeat non fasting sonogram, showed that the lateral smaller cystic structure had undergone a contraction similar to that seen in normal gallbladder but no changes were observed concerning the volume and the shape of the medial larger cystic structure. These findings suggested a pericholecystic cystic mass, the diagnosis of gallbladder duplicity was less likely.

7. Cystic peritoneal mesothelioma Gallbladder Figure 1: An anechoic homogeneous well-defined mass with regular fine margins on gallbladder lodge is described in ultrasonography exam.

8. Bili MRI exam confirmed that the lateral cystic structure correspond to the gallbladder. Infact her body is followed by the cystic duct entering the common hepatic duct. On the medial side of gallbladder, Bili-MRI showed a homogeneous unilocular and well defined fine walled cystic mass that did not communicate with the biliary ducts Figure 2:A

9. Cystic peritoneal mesothelioma Gallbladder Figure 2:B

10. Figure 2: a; MRI coronal T2 slice, b; MRI axial T2 slice sagital (2c) and frontal (2d) Cholangio- MR T2 Weighted images showing a thin wall homogeneous cystic mass adjacent to the gallbladder (arrow) which its cystic duct is well identified (arrow head) showing a fine- walled cystic mass well defined with high T2 signal projecting into medial side of gallbladder region. Gallbladder Cystic peritoneal mesothelioma

11. Abdominal laparoscopy found a cystic mass developed on gallbladder wall. Cystic peritoneal mesothelioma Gallbladder Figure 3: A preoperative photograph of a cystic peritoneum mesothelioma developed on the posterior side of gallbladder lodge

12. Anatomopathologic exam confirmed the diagnosis of a benign cystic peritoneal mesothelioma associated to chronic cholecyst. Figure 4: Fibrous wall lined by a single layer of regular benign cubic mesothelial cells without specific or malignant signs. Cystic peritoneal mesothelioma

13. DISCUSSION Cystic peritoneal mesothelioma (CPM) is a rare benign neoplasm arising from the mesothelial cells of the peritoneum. It occurs predominantly in young and middle-aged women with a reported mean age at presentation of 37 years (1). The natural history and pathogenesis of this condition remains poorly defined in the limited information available. There is no association with asbestos exposure. It has been suggested that chronic peritoneal irritation and possibly previous laparotomy may be involved in the pathogenesis of CPM (2).

14. In our case, proliferative reaction within the peritoneal tissue appeared to be related to the chronic gallbladder inflammatory process as well, as has been suggested with a 43-year old man with a benign chronic cholecyst accompanied by multiple peritoneal cystic mesothelioma (3). Involvement of the pelvic region is characteristic. Common features include abdominal pain and distension, usually associated with a pelvic or abdominal mass. Furthermore, abdominal presentation of the neoplasm is thought to be secondary to extension from the pelvis (1).

15. Although CPM is most frequently seen in the pelvis, it may affect any peritoneal or omental surface. We report here the first case of benign cystic mesothelioma of the gallbladder lodge. Indeed no findings were described in the literature concerning the gallbladder lodge location, but this structure can theoretically be affected because of its fundic and posterior peritoneal surface. US is useful in defining the mass and typical appearance of CPM is a non-specific multiloculated anechoic cystic mass, but there is often no clear distinction between a hepatic lesion and a pericholecystic one.

16. CT features vary according to the gross morphologic appearance of this tumor, which appears as a multiloculated cystic mass, multiple unilocular thin-walled cysts or a unilocular cystic mass. MRI was very helpful here. In fact, it clearly defined the mass and its relation to the gallbladder. It is also interesting to use specific magnetic contrast products such as Mangafodipir Trisodium (Mn DPDP) which allow the study of biliary ducts. Indeed, it allows us to establish wether a cystic mass communicates or not with the biliary duct.

17. The differential diagnosis of cystic peritoneal mesothelioma includes malignant peritoneal mesothelioma, abdominal lymphangioma, pseudomyxoma peritonea and tuberculosis peritonitis (5). Malignant peritoneal mesothelioma presents as a nodular thickening of the peritoneum, associated with abdominal soft tissue masses and an invasion of the intestinal wall. A cystic appearance is not expected. Abdominal lymphangioma occurs in children and young adults, with retroperitoneal, mesenteric or omental location. Pelvic involvement is uncommon. Evidence of fat tissue within the neoplasm may help in diagnosing lymphangioma.

18. Pseudomyxoma peritoneum appears to be a complication of a mucin- producing neoplasm, appearing as a solid component mass producing peritoneal implants with visceral parenchymatous involvement. Some differential diagnosis of cystic mass of gallbladder lodge may be proposed such as simple intrahepatic cysts but they are characterized by their several intrahepatic locations and their association with other hepatic sicknesses, ductal ectasia, type V choledochus cyst, pericholecystic cystic tumors, edema…

19. Treatment of CPM requires surgical excision. Radiotherapy and chemotherapy are of no use (are useless) in this neoplasm (6). The prognosis of cystic mesothelioma is good. However, further resection is usually required because of the high rate of recurrence of this tumor (in 27-50% of cases) (7). Invasion of abdominal structures has not been reported and cystic mesothelioma does not have any metastatic potential. However, although, researchers generally agree that cystic mesothelioma is benign and has no metastatic potential, malignant transformation of cystic mesothelioma has been documented (8).

20. CONCLUSION: Benign cystic mesothelioma is a rare neoplasm and gallbladder lodge is an exceptional location. To our knowledge, no cases have been published previously in the medical literature. Imaging features are not specific but ultrasound exam and Bili MRI are very helpful; they can provide more details about relationship between the mass and the biliary ducts. Differential diagnosis such as other rare gallbladder cystic mass as lymphangioma can only be defined histologically.

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