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  Volume 94
Numero 1
gennaio-febbraio 2008 		I documenti sono in formato PDF, consultabili utilizzando Acrobat Reader
 
Thin-walled cysts as a pathognomonic CT finding in cystic mesothelioma
Paul Sugarbaker, Tristan Yan, Luis Zappa, Namik Haveric, Erwin Brun
1Washington Cancer Institute, 2Department of Radiology, and 3Department of Pathology, Washington Hospital Center, Washington, DC, USA

Key words: mesothelioma, cystic mesothelioma, intraperitoneal chemo­therapy, cytoreductive surgery, radiologic diagnosis



abstract
Aim. Cystic mesothelioma is a rare disease that results in abdominal distention and poorly defined abdominal pain. Diagnosis has always been made by tissue biopsy rather than by radiologic studies.
Materials and methods. Our experience with 7 patients with cystic mesothelioma includes 4 patients who had not had prior surgery before the performance of a high resolution CT scan. A special review of the radiology of these cases was performed in order to identify any pathognomonic signs of this disease.
Results. In all patients who did not have a distortion of the radiologic images (as a result of surgical interventions) prior to the performance of a high resolution CT scan at our institution, a pathognomonic thin-wall cystic structure located within the gelatinous appearing mass was observed. These thin-walled cysts were of variable size and preferentially located within the greater omentum, pelvis and beneath the right hemidiaphragm.
Conclusion. Cystic mesothelioma can be diagnosed preoperatively by a high resolution abdominal and pelvic CT. The thin-walled cysts with great variation in size are located beneath the right hemidiaphragm, within the greater omentum and in the pelvis. No other disease with these radiologic findings has been identified.
Introduction
Cystic peritoneal mesothelioma is a rare disease with less than 100 cases reported in the literature. It occurs in females approximately 80% of the time. New treatment strategies for peritoneal surface malignancy that are capable of complete disease eradication are now available1,2. These new treatment options have stimulated renewed interest in tumors that show peritoneal dissemination as a major component of the disease process. An optimal choice of a definitive management plan that properly balances the risks and benefits of the disease and its treatment options is necessary3,4.
In this manuscript a description of characteristic radiologic findings in cystic mesothelioma patients is presented. A definitive preoperative diagnosis in the absence of invasive tests was thought to facilitate the management of patients with this disease.
Materials and methods
Technique for Computed Tomographic Scans
CT scans were performed with a GE 9800 Hilight CT scanner (General Electric, Milwaukee, WI) using 1-cm continuous slice thickness. The radiologic studies were performed following the administration of oral and intravenous contrast media in all patients. These were 2-second scan times with a 3- to 4-second interscan delay for breathing. Some patients had three to five slices obtained between consecutive breath holds. All CT scans were performed following andiodynamic bolus at a rate of 1 to 2 ml/second, for a total of 150 to 180 ml of iothalamate meglumine 60% (Conray 60®, Mallinckrodt, St. Louis, MO) or iohexol 240 (Omnipaque®, Sanofi Winthrop, New York, NY). A 30- to 60-second delay occurred between the initiation of contrast administration and the start of CT scanning. Precontrast bowel preparation included a total of 900 to 1,200 ml of barium ingested at least six hours before CT and rectal barium contrast administered immediately before CT. For clinical use, the CT scans were read by a staff radiologist.
For clinical research study, all CT scans were reread in order to score abdominal and pelvic tumor deposits in a standardized manner. The radiologist was aware that all patients in the study had clinical evidence of cystic peritoneal mesothelioma but was masked to the findings at surgery.
Radiologic assessment of these images was performed in a standardized manner. The distribution and volume of tumor was scored by the peritoneal cancer index. Nine abdominopelvic regions were defined by two horizontal lines through the costal margin and anterior superior iliac spines and two vertical lines defined by the mid-clavicle. Tumor volume was scored by a lesion size (LS) score. LS-0 indicated an absence of tumor, LS-1 indicated tumor masses less than 0.5 cm, LS-2 indicated tumor masses more than 0.5 but less than 5.0 cm. and LS-3 indicated tumor masses greater than 5 cm or a layering of tumor at any site. The small bowel regions were scored by an interpretative classification into four groups. Group 0 CT scans showed no tumor in the region of the small bowel. The jejunal and ilial vessels appeared as round and curvilinear densities within the mesenteric fat. Second, Group II CT scans showed intraperitoneal ascites fluid only. The mesentery was stranded and stratified as the fluid accumulation outlined the small bowel mesentery. The small bowel vessels are identified easily within the mesenteric fat. Third, Group II CT scans showed tumor involvement of the small bowel and/or it mesentery. The peritoneal surface was thickened and enhanced due to the presence of tumor nodules (usually half-spherical bodies) or plaques (flat implants whose diameter was greater than thickness). Because of an increased amount of solid tumor or ascitic fluid, the mesentery may appear to be stellate or pleated. The small bowel mesenteric vessels were still identifiable. Fourth, Group III CT scans showed increased solid tumor involvement and adjacent small bowel loops are matted together in some cuts. The configuration of the small bowel and its mesentery was distorted and thickened. Segmental small bowel obstruction may be present. Intraperitoneal fluid may be loculated. The small bowel mesenteric vessels were difficult to define on some cuts due to obliteration of mesenteric fat.
Results
Four patients with cystic mesothelioma had CT prior to any surgical intervention. In all four of these patients a review of the CT images revealed thin-walled cysts within the ascites fluid. In our most recent case the radiologic findings permitted definitive diagnosis in the absence of a preoperative biopsy.
Case report
A 44 year old woman was referred with a diagnosis of “pseudomyxoma peritonei.” Two months prior to presentation this patient began developing abdominal discomfort. She also noted some increase in her abdominal girth which she attributed to an increase in her normal abdominal fat. Her doctors performed a CT scan which was given a radiologic diagnosis of pseudomyxoma peritonei. Her physical examination except for the distended abdomen was otherwise normal. There were no masses on pelvic or rectal examination.
The CT was reviewed at our institution; it showed cystic masses between the liver and the undersurface of the right hemidiaphragm, within the greater omentum and within the pelvis (Figures 1-3). The thin-walled cystic masses of variable size were noted to be an integral part of the gelatinous masses within the abdomen and pelvis.






On the basis of the characteristic location of the gelatinous masses, the presence of the thin-walled cysts and the variable size of these cysts a preoperative diagnosis of cystic mesothelioma was made in the absence of biopsy.






Subsequently, the patient was explored and had cytoreductive surgery. Multiple delicate cysts with great variation in size were resected from beneath the right hemidiaphragm (Figure 4). A greater omentectomy was used to resect the disease from the mid-abdomen (Figure 5). Thin walled cysts free floating within ascites fluid were present in the mid-abdomen (Figure 6).






Because of the non-invasive character of the disease and its lack of small bowel involvement, all visible evidence of the disease was removed1. The patient had an intraperitoneal chemotherapy washing with hyperthermic cisplatin and doxorubicin in an attempt to prophylax against the recurrence of this disease process. Characteristic histopathologic findings confirmed the diagnosis of cystic mesothelioma (Figure 7).



A summary of the radiologic findings in the four patients who had no surgery prior to our radiologic evaluation is given in Table 1. All four patients had thin walled cysts clearly seen by CT. These cystic structures were most prominent in the mid-abdomen/omental cake region. All patients had massive tumor accumulations in the absence of small bowel dysfunction. Although small and large bowel were markedly displaced no dilatation was present.

Table 1 - Radiologic findings in four patients with cystic mesothelioma whose abdominal and pelvic CT was performed prior to a surgical intervention. Tumor was scored as present (+) versus absent (-)

Patient

Thin walled

Small bowel

Small bowel

Mid-abdominal-

Right upper

Left upper

Pelvic

 

cysts

displacement

dysfunction

omental

quadrant

quadrant

 

 

 

 

 

region

region

region

 

 

 

 

 

 

 

 

 

1

+

+

-

+

+

O

+

2

+

+

-

+

+

+

+

3

+

+

-

+

O

O

+

4

+

+

-

+

O

O

+


Discussion
Multiple case reports are present in the oncology and radiology literature describing cystic mesothelioma of the peritoneum. Stoutis et al. called attention to the “hyaline globules” of variable size present on abdominal and pelvic CT5. Pandolfo called attention to the characteristic location at 3 sites within the abdomen: Beneath the right hemidiaphragm, associated with the greater omentum, and filling the pelvis6. Our report identifies these cysts within large volume ascites as a pathognomonic radiologic finding with this disease.
At this point in time the clinical features of this disease have been well-characterized. The gross pathology shows the multiple thin-walled cysts of variable size that can be punctured with even the slightest rough handling or trauma7. Also, a characteristic pathology with a hobnail epithelium lining these cysts has been described8.
Despite the definitive clinical description of cystic mesothelioma, there is not agreement regarding the nature of the process. Ross and colleagues concluded from their study of 25 cases that cystic mesothelioma was a non-neoplastic reactive mesothelial proliferation9. In contrast, Weiss and colleagues concluded that this was a neoplastic rather than a reactive process10. Clearly, mortality has occurred associated with this disease process. Also, approximately 50% of the patients followed in the literature have shown recurrence after debulking surgery11. In one of seven patients treated at our institution a transition to invasive mesothelioma occurred over a ten year time period12. This patient died of disease. For this reason our group has advocated treatment of this disease with a complete cytoreduction followed by warm intraperitoneal chemotherapy washing. According to Cerruto and colleagues careful histopathologic study of this disease from numerous anatomic sites will reveal areas of peritoneal invasion13. Hutchinson and colleagues suggested that the term “benign cystic mesothelioma” be abandoned and that the disease be called diffuse malignant peritoneal mesothelioma, multicystic type14.
If this disease is a neoplastic process and is considered a less aggressive manifestation of diffuse malignant peritoneal mesothelioma, exploratory laparotomy, laparoscopy, and even CT-guided biopsy of the process should be avoided in establishing the diagnosis. Implantation of neoplastic cells in puncture sites or abdominal incisions is a prominent part of the disease process15. If the diagnosis can be established radiologically the possibility of complete intraperitoneal eradication without recurrence in the abdominal wall should be possible14. In our most recent patient the diagnosis of this disease by CT preoperatively allowed for its removal without preliminary biopsy. The pathognomonic appearance of the disease in the operating room allowed its gross anatomic diagnosis. This gross diagnosis was confirmed by histologic study at a later time.    
From a radiologic perspective, the most impressive characteristic of CT in cystic mesothelioma was the thin walled cysts located throughout the massive tumor accumulation within the abdomen and pelvis. However, from a clinical perspective the most impressive characteristic was the complete preservation of bowel function concomitant with a massive tumor accumulation that filled the abdomen and pelvis. None of these patients showed any small or large bowel dilatation, gastric outlet obstruction, or pelvic outlet obstruction. Also, radiologic involvement of the epigastric region did not occur. This lack of involvement of the lesser omentum and omental bursa indicated that no major surgical interventions on the stomach was necessary and contributed to the complete surgical extirpation of tumor that occurred in all 4 of these patients.
Cystic mesothelioma can be distinguished from pseudomyxoma peritonei in that there is an absence of disease in the epigastric region, an absence of mucinous tumor infiltrating between small bowel loops, and well-defined spherical cysts as compared to mucin globules that contain no wall that is visible on radiologic examination.
Cystic mesothelioma cannot be distinguished from multilocular peritoneal inclusion cysts; most pathologists consider these two pathologic diagnoses describe the same clinical entity16. Generally, multilocular peritoneal inclusion cysts is a terminology used in young to middle aged premenopausal women who have had prior surgery and present with multiple pelvic cysts. The cysts are not as extensive as in multicystic mesothelioma. Over time in an individual patient, the multilocular inclusion cysts may progress to become multicystic mesothelioma. A transition from multicystic mesothelioma to diffuse malignant peritoneal mesothelioma must be considered a possibility13,14,16.
References
 1. Sugarbaker PH: Management of peritoneal surface malignancy. The surgeon’s role. Langenbeck’s Arch Surg, 384: 576-584, 1999.
 2. Sugarbaker PH, Welch L, Mohamed F, Glehen O: A review of peritoneal mesothelioma at the Washington Cancer Institute. Surg Oncol Clin N Am, 12: 605-621, 2003.
 3. Esquivel J, Sugarbaker PH: Elective surgery in recurrent colon cancer with peritoneal seeding: When to and when not to proceed. (Editorial) Cancer Therapeutics, 1: 321-325, 1998.
 4. Yan TD, Edwards G, Alderman R, Marquardt CE, Sugarbaker PH: Morbidity and mortality assessment of cytoreductive surgery and perioperative intraperitoneal chemotherapy for diffuse malignant peritoneal mesothelioma. A prospective study of 70 consecutive cases. Ann Surg Oncol, 14: 515-525, 2007.
 5. Stoupis C, Ros PR, Abbitt PL, Burton SS, Gauger J: Bubbles in the belly: imaging of cystic mesenteric or omental masses. Radiographics, 14: 729-737, 1994.
 6. Pandolfo I, Blandino A, Zimbaro G, Faranda C, Gaeta M, Albanese V, Gulino FM: CT findings in a benign cystic mesothelioma of the greater omentum. A case report. Rays, 11: 63-65, 1986.
 7. Lamovec J, Sinkovec J: Multilocular peritoneal inclusion cyst (multicystic mesothelioma) with hyaline globules. Histopathology, 28: 466-469, 1996.
 8. Sethna K, Mohamed F, Marchettini P, Elias D, Sugarbaker PH: Peritoneal cystic mesothelioma: A case series. Tumori, 89: 31-35, 2003.
 9. Ross MJ, Welch WR, Scully RE: Multilocular peritoneal inclusion cysts (so-called cystic mesotheliomas). Cancer, 64: 1336-1346, 1989.
10. Weiss SW, Tavassoli FA: Multicystic mesothelioma. An analysis of pathologic findings and biologic behavior in 37 cases. Am J Surg Pathol, 12: 737-746, 1988.
11. van Ruth S, Bronkhorst MWGA, van Coevorden F, Zoetmulder FAN: Peritoneal benign cystic mesothelioma: A case report and review of literature. Eur J Surg Oncol, 10: 192-195, 2000.
12. Gonzalez-Moreno S, Yan H, Alcorn KW, Sugarbaker PH: Malignant transformation of “benign” cystic mesothelioma of the peritoneum. J Surg Oncol, 79: 243-251, 2002.
13. Cerruto CA, Brun EA, Chang D, Sugarbaker PH: Prognostic significance of histomorphologic parameters in diffuse malignant peritoneal mesothelioma. Arch Pathol Lab Med, 130: 1654-1661, 2006.
14. Hutchinson R, Sokhi GS: Multicystic peritoneal mesothelioma: Not a benign condition. Eur J Surg, 158: 451-453, 1992.
15. Jacquet P, Sugarbaker PH: Wound recurrence after laparoscopic colectomy for cancer: New rationale for intraoperative intraperitoneal chemotherapy. Surg Endosc, 10: 295-296, 1996.
16. Churg A, Cagle PT, Roggli VL: Tumors of the Serosal Membranes. AFIP Atlas of Tumor Pathology, Fourth Series, Fascicle 3. American Registry of Pathology: Washington, DC, 2006.
 
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