Benign multicystic peritoneal Mesothelioma: a case report

We report the case of a patient with a benign multicystic peritoneal mesothelioma and describe its appearance on computed tomography scans and ultrasonography, in correlation with gross clinical and pathological findings.

A 72-year-old Caucasian woman presented to our emergency department with acute abdomen signs and symptoms. A clinical examination revealed a painful palpable mass in her left abdomen. Abdominal ultrasonography and computed tomography demonstrated the presence of a large cystic mass in her left upper abdomen, adjacent to her left hemidiaphragm. The lower border of the mass extended to the upper margin of her pelvis. A complete resection of the lesion was performed. Pathological analysis showed a benign multicystic peritoneal mesothelioma.

Benign multicystic peritoneal mesothelioma is a rare lesion with a non-specific appearance on imaging. Its diagnosis always requires pathological analysis.

Benign multicystic peritoneal mesothelioma is an uncommon lesion arising from the peritoneal mesothelium. It is often diffuse and shows a marked predilection for the surfaces of the pelvic viscera [1-8]. In our case report, the lesion was solitary and situated in the left abdomen. This disease is a rare medical entity and there are challenges in determining its origin, pathogenesis, diagnosis and therapy.

A 72-year-old Caucasian woman was admitted to our surgical department having experienced diffuse abdominal pain and discomfort, nausea and vomiting for the previous two days. Her medical history included diabetes mellitus and arterial hypertension, for which she was on medication. She had no relevant family history and did not smoke or drink alcohol.

On physical examination, she showed signs of acute abdomen and a palpable painful mass in her left abdomen was noted. She was tachycardic and laboratory tests showed a white blood cell count of 13,000 cells per cubic millimeter. Her chest and abdominal radiographs did not reveal any abnormalities.

An ultrasonography (US) examination demonstrated a complex cystic mass with internal septa, without increased vascularity. The source organ could not be identified (Figure 1).

Computed tomography (CT) examination demonstrated a large 18.7 × 13.2 × 22cm, intra-peritoneal hypodense mass in her upper left abdomen, lying between the great curvature of the stomach, the spleen and the tail of the pancreas, and extending caudally to the upper margin of the pelvis, causing pressure over the adjacent organs. The mass demonstrated no internal septa and no enhancement after the intravenous administration of a contrast medium. No abnormal lymphadenopathy was present (Figure 2, Figure 3 and Figure 4).

She underwent an urgent operation and the multicystic mass was found to occupy her entire left abdomen, adherent to the spleen. A complete resection of the lesion and splenectomy were performed. She had an uneventful post-operative recovery and a post-splenectomy prophylaxis was used.

Gross examination of the specimen showed a large gelatinous cystic mass containing multiple smaller cystic spaces. Her immunohistochemical stains were positive for calretinin and cytokeratins, confirming the mesothelial origin of the mass. The final diagnosis was benign multicystic peritoneal mesothelioma. (Figures 5 and 6).

 (Hematoxylin and eosin stain, original magnification × 400).

(Hematoxylin and eosin stain, original magnification × 100).

Six months post-operatively, she had experienced no recurrence and was free of symptoms.

Mesotheliomas are mesenchymal neoplasms originating from the serous lining of the pleural, pericardial or peritoneal space. Multicystic peritoneal mesothelioma involves the peritoneum or extra-peritoneal space, omentum, pelvic or abdominal viscera. It most commonly arises from the pelvic surfaces of the peritoneum and has benign or indolent biologic behavior. Multicystic mesothelioma of the peritoneum was first described in 1979 by Mennemeyer and Smith and since then approximately 130 cases have been described in the literature. It is an intermediate-grade tumor, among the benign adenomatoid tumors of the peritoneum and the more common malignant asbestos-related peritoneal mesothelioma. It is not related to prior asbestos exposure and may recur locally [1-11].

On histological examination, the mesothelial cells lining the cysts may vary from flattened and endothelial-like to cuboidal. The thin-walled cysts may be filled with eosinophilic, serous fluid. Inflammatory cells and fibrous elements may be found within the stroma between the cysts. Foci of mesothelial hyperplasia may also be present [2].

It is usually large at the time of diagnosis (mean diameter, 13 cm). Multifocality, free floating cysts and unilocular cysts have been reported [2].

It commonly occurs in young to middle-aged women (mean age, 37 years). The presenting symptoms are chronic or intermittent lower abdominal or pelvic pain, tenderness, or distension with an abdominal or pelvic mass and, rarely, dyspareunia, constipation and urinary hesitancy and/or frequency. Women with this lesion often have a history of prior pelvic surgery, endometriosis or pelvic inflammatory disease [1-3,5,7-10].

The pathogenesis of benign multicystic peritoneal mesothelioma is unclear and there is some controversy regarding its neoplastic and reactive nature [2,6]. The fact that the great majority of patients are women of reproductive age suggests that a key role is played by female sex hormones in its pathogenesis [5].

US demonstrates multiseptated anechoic cysts. The fluid within the cysts is generally anechoic, but the cysts may contain echoes from debris or hemorrhage. The number and complexity of septations, as well as the size of the cysts, are quite variable. Calcification has not been described in multicystic mesothelioma. CT provides more information about the location and extent of the mass, and demonstrates a well-defined, low-attenuation mass with non-calcified septa. The septa become enhanced following intravenous administration of a contrast material. Magnetic resonance imaging (MRI) provides additional coronal and sagittal planes. The watery serous content has low signal intensity on T1-weighted images and intermediate-to-high signal intensity on T2-weighted images. Septal enhancement has been reported [1,2].

The differential diagnosis includes lymphangioma, other mesenteric and/or omental cysts, cystic teratoma, pseudomyxoma peritonei, cystic smooth muscle tumors, visceral cysts, cystic mucinous neoplasms of the pancreas, non-pancreatic pseudocysts, endometriosis, cystic adenomatoid tumor and cystic mesonephric duct remnants. When multicystic mesothelioma is located solely in the pelvis in women, tubo-ovarian abscess, hydrosalpinx, cystic ovarian neoplasms (ovarian cystadenoma, cystadenocarcinoma) and cystic forms of endosalpingiosis should be considered in the differential diagnosis. Lymphangiomas often occur in younger patients and can be identified if they contain predominantly chylous fluid and microscopically lymphoid aggregates and smooth muscle in their walls. Mesenteric cysts are generally unilocular and contain serous secretions, with no discernible wall or internal septa. Teratomas contain fat and calcification. Pseudomyxoma peritonei can be distinguished when there is co-existing omental caking, soft-tissue peritoneal nodules and scalloping of the serosal margins of the liver or spleen. The cystic component in cystic adenomatoid tumor is usually accompanied by a recognizable solid component. Malignant neoplasms are suggested by ancillary signs such as intramural nodules, ascites, necrosis or peritoneal carcinomatosis, and the source organ can usually be identified [1,5-7,9,10].

Multicystic mesothelioma is seldom diagnosed at pre-operative imaging because it is exceedingly rare; the diagnosis requires histological evaluation.

The treatment of choice is complete surgical excision. Complete removal of the cystic lesion, if possible, is the best treatment and the only hope in avoiding local recurrence. Aggressive surgical approaches including cytoreductive surgery with peritonectomy are recommended [5,6]. Hormonal therapy with anti-estrogens and gonadotrophin-releasing analogues, sclerotherapy with tetracycline, hyperthermic peritoneal perfusion with cisplatin and peritonectomy with intra-peritoneal chemotherapy have also been attempted in individual cases with varied degrees of success. Adjuvant chemotherapy and radiotherapy are not indicated as this tumor has a prevailing benign character [5,6].

About 50 percent of the patients experience a recurrence one to 27 years after the initial diagnosis and malignant transformation has very rarely been reported [1-3]. Thus, routine follow-up imaging is required post-operatively in all patients [4].

The prognosis is excellent and the only death that has ever been reported in the literature occurred in the case of a patient who refused to undergo resection 12 years after diagnosis [5].

Benign multicystic peritoneal mesothelioma is a very rare benign cystic tumor. This lesion has a non-specific appearance on imaging which does not permit differential diagnosis from other cystic lesions and always requires histological evaluation. It has a high recurrence rate after surgical resection but malignant transformation has very rarely been reported. A systematic follow-up of these patients is required and further resection or other therapy may be indicated.

(CT): Computed tomography; (MRI): magnetic resonance imaging; (US): ultrasonography.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

The authors declare that they have no competing interests.

XP performed the chart review and prepared the manuscript. EA, AE and CT carried out the operation. LP was the pathologist who examined the specimen. AP, NS and TC participated in the preparation of the manuscript. All authors read and approved the final manuscript.

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Benign cystic mesothelioma of the plant presentation into a woman: a case report

Benign cystic mesothelioma or peritoneal inclusion cysts are rare benign abdominal tumors usually occurring in females of reproductive age. These cysts present as abdominopelvic pain or masses but are often found on imaging or incidentally at surgery. They are commonly associated with pelvic inflammatory disease, endometriosis, or ovarian cysts. We report what is, to the best of our knowledge, the first case of a benign cystic mesothelioma complicating a presentation of acute appendicitis.

A 19-year-old Irish Caucasian woman presented with abdominal pain. Imaging suggested appendicitis with abscess formation. She was treated with antibiotics and scheduled for interval appendicectomy. At laparoscopy, an unusual cystic mass was found arising from the appendix. Histology revealed benign cystic mesothelioma.

We report what is, to the best of our knowledge, the first case of a benign cystic mesothelioma arising from the appendix and complicating a presentation of acute appendicitis. This is a benign pathology, but recurrences are not uncommon. Benign cystic mesothelioma should be included in the differential when investigating pelvic masses or abscesses associated with either appendicitis or pelvic inflammatory disease in women.

Benign cystic mesothelioma (BCM) or peritoneal inclusion cysts are rare abdominal tumors usually occurring in women of reproductive age. These cysts present as abdominal or pelvic pain or masses but are often found on imaging or incidentally at surgery. There have been many cases described associated with pelvic inflammatory disease, endometriosis, or ovarian cysts. We describe the first case of a benign cystic mesothelioma arising from the appendix and complicating a presentation of acute appendicitis.

A 19-year-old Irish Caucasian woman presented to the hospital with a three-day history of abdominal pain and fever. The pain was gradual in onset and associated with nausea and one episode of vomiting. She had no urinary symptoms, and her last menstrual period had finished the previous day. She had no surgical history, and her medical history was significant only for viral meningitis two years previously. She denied any history of sexually transmitted disease or recent urinary tract infection. She was not taking regular medications and had no allergies. On examination, her vital signs were normal except for mild pyrexia of 37.4 °C. Examination of the abdomen revealed a tender mass in the right iliac fossa.

Laboratory investigations included a white cell count of 10,500 cells/mm, hemoglobin of 13.3 g/dl, and platelets of 212,000/mm. Urea and electrolytes were within normal ranges. Urine analysis was negative for leucocytes and urinary ßHCG was negative.

A computed tomography (CT) scan of the abdomen and pelvis was requested and showed a 10.4 × 4.5 × 3.8 cm loculated cystic mass in the right pelvis that appeared to contain the tip of the appendix (Figure 1). The patient remained febrile. Clinically, we made a working diagnosis of an appendix mass but considered a tubo-ovarian abscess as a differential. The patient was treated with intravenous antibiotics, and radiological drainage of the abscess was arranged. An ultrasound-guided drain was placed in the largest locule via the right iliac fossa. Unusually, 30 ml of serous fluid but no pus was aspirated. The drain was removed after three days with no further output. Drained fluid was sent for culture, and peripheral blood cultures showed no growth after 72 hours of incubation. After five days, intravenous antibiotics the patient was clinically well. She was discharged and readmitted two weeks later for an interval diagnostic laparoscopy, as we were now suspicious of a non-infective pathology based on the drain output. The patient consented to an appendicectomy if no other pathology was found.

At laparoscopy, a multiloculated, thin-walled and translucent cystic mass was seen in the right iliac fossa (Figure 2). Adherent to the cystic mass was a spherical, smooth-walled cyst in continuity with the tip of the appendix. The rest of the appendix, caecum, and large and small bowel appeared grossly normal. Both ovaries and the uterus were visualized and found to be normal. The diagnosis was not clear at this point, but our differential included a mucinous cystadenoma or adenocarcinoma (pseudomyxoma peritonei). The lesion appeared very friable, and we were concerned we would rupture it and contaminate the pelvis with the cyst fluid. We made a decision to convert to an open procedure using a Lanz incision to safely perform an appendicectomy and remove the cystic mass. The incision incorporated the previous drain site.

Operative photograph showing thin-walled cystic mass in the right iliac fossa above the appendix.

Macroscopy showed a 12-cm appendix with an attached 4 × 4 × 3 cm smooth cyst containing clear fluid. Numerous smaller translucent cysts up to 0.7 cm in diameter were loosely attached to and easily separated from the larger cyst (Figure 3). We concluded that the radiological drain had entered one of these cysts. Histological analysis revealed cysts lined with flattened mesothelial cells, and the walls were composed of loose connective tissue with occasional chronic inflammatory cells (Figure 4). These findings were consistent with a histological diagnosis of a multiloculated benign cystic mesothelioma. The appendix showed resolving appendicitis with perforation at the tip. The patient was discharged well on the second postoperative day and was also well at six-week and three-month follow-up.

 Immediately below the 15-cm ruler in the photograph. Membranes of the remainder of the multiloculated cyst after removal from the appendix are seen lying toward the bottom of the photograph. The cyst had ruptured in transit from the operating table to the specimen photography table in the operating room.

 Microscopy showing cysts lined with flattened mesothelial cell and the walls composed of loose connective tissue with occasional chronic inflammatory cells.

Benign cystic mesothelioma or peritoneal inclusion cysts are rare but well-described benign tumors of unknown etiology. First described by Plaut in 1928 (1), they are cystic mesothelial proliferations. They are thought to be due to an inflammatory reaction. They usually occur in the peritoneal cavity in the abdomen or pelvis, and the most common predisposing factors in the clinical history are previous surgery, pelvic inflammatory disease, or endometriosis. These conditions are believed to interfere with peritoneal reabsorption. This would tend to support a hypothesis of BCM being reactive and inflammatory rather than neoplastic (2). These conditions tend to occur in women of reproductive age, but cases have been reported in men (3). The most common sites are the serosal surfaces of the ovary and uterus, but cases outside the abdomen have been described, including the pleural cavity (4). Typical microscopic findings are a single layer of flattened mesothelial cells sometimes described as a hobnail configuration. Squamous metaplasia and papillae may also be seen (3).

The clinical presentation is usually abdominal or pelvic pain, a mass found clinically or radiologically, or an incidental surgical finding (5). BCM is considered to be a benign inflammatory process; however, malignant transformation has been reported (6). Diagnostic modalities include ultrasound and CT, but preoperative diagnosis is often not conclusive and there are no protocols for diagnostic imaging. The main differentials are ovarian cysts, ovarian tumors (benign or malignant), or cystic lymphangioma. When presenting acutely with signs of infection as in the case described here, pelvic inflammatory disease complicated by abscess would be the most common differential as associations with appendicitis are very rare.

Management currently involves surgical resection, but recurrences are well documented. There are no protocols for surgical management, and the literature is based on case reports and small case series. Laparoscopic resections have been described. While laparoscopy is an elegant tool for investigation of masses or pain in women, we believed open surgery to be safer when a malignant process was suspected owing to the possibility of cyst rupture and seeding. Follow-up after surgical resection includes clinical review and ultrasound or CT, but again there are no guidelines.

BCM involving the appendix is very rare. Only four other cases have been reported. Two were in middle-aged women presenting with abdominal pain and suspected appendicitis where cysts were found adjacent to but not involving the appendix (7, 8). In a third case, a BCM was found incidentally beside an otherwise unremarkable appendix at laparotomy for sigmoid diverticular disease (9). The other case involved a 28-year-old man who presented with appendicitis in which a 25-cm separate cystic mass was found (10). Our patient's case is unique in that the BCM was in direct continuity with the tip of the appendix and presented with both clinical signs and histological evidence of acute appendicitis.

BCM is a rare benign tumor, but surgeons should include it in the differential when investigating abdominal masses or pain in women of reproductive age. This is the first reported case of a BCM arising from the appendix which complicated a presentation of acute appendicitis. Surgery is the authors' recommended treatment, but patients should be advised of the possibility of recurrence.

The authors declare that they have no competing interests.

DB O'C drafted and conceived the manuscript, DB assisted in the drafting and editing of the final manuscript, and MA performed critical revisions of the manuscript.

DB O'C and MA performed the operation. All authors read and approved the final manuscript.

The authors have written informed consent from the patient for the publication in a medical journal of the manuscript and images. A copy of this consent can be made available to the editorial team.

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