Pancreatic mesothelial cyst

Abstract

A 60-year-old woman was investigated for abdominal pain and increasing asthenia. Abdominal CT revealed a 25 mm hypodense cystic lesion in the tail of the pancreas. MRI showed a multiloculated cystic lesion, T1-hypointense and T2-hyperintense lesion, without wall enhancement. Endoscopic ultrasound detected a 25 mm multi-loculated cystic lesion, with regular margin and without pancreatic duct communication. Diagnosis of pancreatic mucinous cystadenoma was discussed and the patient was referred to surgery. She underwent distal pancreatectomy with spleen preservation. Pathological examination revealed the diagnosis of pancreatic mesothelial cyst. Histologically, the cyst was multiloculated, lined by cuboidal epithelium, ovoid nuclei and amphophilic cytoplasm, without mucin deposition or cytological atypia. Immunohistochemistry examination revealed positive staining for cytokeratin 5/6, vimentin and calretinin. At 1-year follow-up, she is in her usual health, without any symptoms.

Background

Pancreatic cystic lesions are being increasingly detected due to enhanced imaging modalities.¹ Mesothelial cyst of the pancreas is a rare benign tumour, with only one case described in the literature.² Its aetiology and pathogenesis are still poorly understood. Diagnosis is challenging with non-specific symptoms and ambiguous imaging findings. Due to its rareness, pancreatic mesothelial cyst is often mistaken for other diagnosis leading to surgery resection. Based on histopathological examination, including immunohistochemical features, diagnosis of pancreatic mesothelial cyst can be confirmed.

Case presentation

A 60-year-old woman presented to the hospital because she felt abdominal pain and increasing asthenia during the last 2 months. She reported nausea without vomiting. The patient had a history of hypertension, diabetes and thyroidectomy. Medications included metformin, vildagliptin, moxonidine, perindopril and levothyrox. On examination, the patient appeared well (81 kg, 168 cm). She did not report a loss of weight. Her vital signs were normal. The abdomen was soft without distension. General examination was unremarkable. However, the patient told us she was unsuccessfully treated at home by paracetamol and codeine drugs during the last weeks. Due to her age, her medical history, increasing asthenia and the failure of the home medical treatment, it was decided to make blood tests and X-ray imaging examinations as first-line examinations.

Investigations

Her white blood cell count was 12.2×10⁹/L, her haemoglobin level was 117 g/L, her platelet count was 337 000/mm³. C reaction protein level was 20 mg/L. The results of renal and liver function, coagulation, blood level of electrolytes, glucose, troponin, total protein, albumin, carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9) tests were normal. Abdominal CT revealed a 25 mm hypodense cystic lesion in the tail of the pancreas (figure 1). MRI showed a multiloculated cystic lesion, 11×18×25 mm, T1-hypointense and T2-hyperintense lesion, without wall-enhancement after injection of gadolinium-based contrast (figure 2). Upper gastrointestinal endoscopy and endoscopic ultrasound (EUS) supported diagnosis of pancreatic mucinous cystadenoma, demonstrating a 25 mm multiloculated cystic lesion, with regular margin and without pancreatic duct communication. Fine-needle aspiration was not done. Following this diagnosis, the patient was referred to surgery.

Figure 1.

Abdominal CT revealing hypodense cystic lesion in the tail of the pancreas.

Figure 2.

MRI showing a multiloculated cystic lesion, without wall enhancement after injection of gadolinium-based contrast.

Treatment

The patient underwent an open distal pancreatectomy with spleen preservation. Abdominal exploration showed a cystic lesion in the tail of the pancreas, without adhesion to adjacent tissues or signs of malignancy (figure 3). Pathological examination revealed the diagnosis of pancreatic mesothelial cyst. Histologically, the cyst was multiloculated, lined by cuboidal epithelium, ovoid nuclei and amphophilic cytoplasm, without cytological atypia (figure 4). Immunohistochemistry examination confirmed the diagnosis showing positive staining for cytokeratin (CK) 5/6, vimentin and calretinin. There was no mucin deposition. The rest of the pancreatic tissue was unremarkable (figure 5).

Figure 3.

Intraoperative picture showing the mesothelial cyst in the tail of the pancreas.

Figure 4.

Pathological findings showing cyst wall lined by cuboidal epithelium, with ovoid nuclei and amphophilic cytoplasm.

Figure 5.

Pathological findings showing multiloculated cyst without mucin deposition or cytological atypia. The rest of the pancreas tissue is unremarkable.

Outcome and follow-up

The patient was allowed to eat and drink at the 3rd day after surgery. Postoperative management included reassessment of pancreatic endocrine function and gastrointestinal transit, analgesic therapy and wound care. Postoperative recovery was uneventful and the patient was discharged on the 7th postoperative day. The patient was seen 5 weeks after operation. At 1-year follow-up, she is in her usual health, without any symptoms.

Discussion

Pancreatic cysts are being increasingly detected due to enhanced imaging modalities, often as an incidental finding.³ Up to 13% of patients undergoing cross-sectional imaging studies for other indications are found to have pancreatic cystic lesions.⁴ It is shown that some pancreatic cystic lesions are a risk factor for pancreatic cancer.⁵ More than half of pancreatic cystic lesions are either malignant or premalignant lesions and therefore cannot be dismissed.⁶ In fact, they comprise a wide range of differing underlying pathologies from completely benign through premalignant to frankly malignant.¹ Diagnostic imaging is limited in differentiating between benign and malignant pancreatic cysts.⁷ Diagnosis requires a multidisciplinary and multimodal approach.⁸ The mainstay of assessment of pancreatic cysts is cross-sectional imaging incorporating CT scan and MRI.¹ EUS complemented by EUS-guided cyst puncture for biochemical and cytological analysis of cyst fluid may provide valuable additional information but can lack sensitivity.^{1 9} Symptomatic cysts, increasing age, multilocular cysts (with a solid component and thick walls), raised cyst aspirate CEA and CA 19-9, mucine content and abnormal cytology are predictors of malignancy.¹ Thus, the exact diagnosis and management pathway of these cysts remain problematic.^{1 10 11} Surgery for diagnostic purposes should be avoided because of its significant morbidity.⁹ Good collaboration between physicians, surgeons, radiologists and endosonographists is necessary for optimal management of pancreatic cysts.⁹ In order of decreasing frequency, the principal entities are: pancreatic pseudocyst (benign lesion), intraductal papillary mucinous neoplasms, mucinous cystic neoplasms, serous cystic tumours and solid pseudopapillary tumours.⁹ Mesothelial cyst of the pancreas is rare and little known.

Mesothelial cysts are rare benign cysts originating in the serous cavities (pleura, pericardium and peritoneum) or in organs closely associated with these mesothelial-lined cavities (mediastinum, mesenterium, spleen, liver ligament, pancreas).^{2 12–15} Cyst size ranges from few centimetres to 40 cm.¹⁶ Mesothelial cyst of the pancreas is anecdotal, with only one case reported in the USA by Nicolas et al.² Authors described a unilocular mesothelial cyst that was clinically and radiologically considered to be a neoplastic cyst necessitating surgical resection. In our case report, we describe for the first time a multilocular mesothelial cyst that was considered to be a pancreatic mucinous cystadenoma. Due to its rareness, pancreatic mesothelial cyst is often mistaken for other diagnosis. What triggers growth of mesothelial cysts is unknown.¹⁷ Some studies have suggested a relationship between sex hormones and mesothelial cysts.¹⁴ Others have reported that development of mesothelial cyst in pancreas may be congenital malformation or related to pancreatitis.² Mesothelial cysts are asymptomatic, except when their important size or location produce non-specific symptoms.¹⁶ Preoperative diagnosis remains challenging. Radiological features based on CT scan, MRI and ultrasound are not specific to determine diagnosis.^{2 18} Cyst fluid analysis for pancreatic mesothelial cyst was not assessed. The diagnosis is based on histopathological examination.¹⁹ The typical microscopic appearance is a single layer of cuboidal cells lining the cyst wall, ovoid nuclei and amphophilic cytoplasm, without cytological atypia.¹⁷ At immunohistochemically examination, epithelial cells stain positively with mesothelial markers: calretinin, thrombomodulin, vimentin, CK 5/6 and Hector Battifora Mesothelial Marker.^{2 20 21} As mesothelial cysts are benign lesions, surgical excision is not essential. However, due to difficulty in identifying mesothelial cyst based on imaging alone and for fear of misdiagnosis (malignant or premalignant lesion), surgery resection is often performed.^{15 19} Laparoscopic resection is an accepted approach, reducing perioperative and postoperative complication.²²

Learning points.

• Optimal management of pancreatic cysts requires multidisciplinary and multimodal approach including collaboration between physicians, surgeons, radiologists, endosonographists and histologists.

• Pancreatic mesothelial cyst is an extremely rare benign tumour.

• Due to its rarity, preoperative diagnosis is challenging based on imaging alone.

• Diagnosis of pancreatic mesothelial cyst requires histopathological analysis.