Lymphoepithelial Cyst of the Pancreas: Serum Markers do not Help

We report a case of lymphoepithelial cyst of the pancreas with non-specific elevation of CA 19.9 and CEA. Pre-operative diagnosis by conventional means proved elusive, and only surgical resection and histopathology revealed the diagnosis. The origin and diagnosis are discussed by literature review.


INTRODUCTION
Cystic lesions of the pancreas are uncommon and can be difficult to diagnose pre-operatively [6,15]. The differential diagnosis of malignancy is ever present and requires assessment. We report a case of a lymphoepithelial cyst of the pancreas which was not correctly diagnosed on serum markers or radiology and laparotomy was necessary to obtain a conclusive diagnosis.

CASE REPORT
The patient is a 47year old male journalist. He presented with a 5 month history of back pain. He had previous multiple episodes of biliary pain but no pain to suggest an episode of acute pancreatitis. There was no history of fevers, jaundice of weight loss. He had a history of heavy alcohol intake and grew up on a sheep farm. Physical examination was normal.
An Abdominal Ultrasound showed a contracted gallbladder with multiple calculi, a hydatid cyst of the liver and a well-defined 46 mm homogenous mass in the head of the pancreas which was reported as a pseudocyst. Computerised tomography (CT) of the abdomen demonstrated a low density, well-defined lesion (measuring 51mm x 35mm) between the head of the pancreas and the vena cava. The rest of the pancreas imaged normally and there was no dilatation of the pancreatic duct or the billiary tree ( Figs. 1 and 2). An endoscopic retrograde cholangiopancreatogram (ERCP) was performed to assess the pancreatic duct. The pancreatic duct was not cannulated successfully.
A CT-guided fine needle biopsy of the pancreatic cyst was undertaken. This also did not contribute towards a pre-operative diagnosis as no cellular material was obtained for assessment and insufficient cyst fluid was aspirated for tumour marker studies.
An upper midline laparotomy was performed.
There was a 5 cm multilobulated soft cystic mass behind the bile duct and pancreatic head. The cyst was easily dissected from the pancreas and the whole specimen was sent for frozen section. This was reported as a squamous lined nonmalignant cyst. A left lateral hepatectomy and cholecystectomy were also performed to deal with the hydatid cyst and gallstones.
Macroscopically, the pancreatic cyst consisted of a slightly lobulated ovoid portion of tissue measuring 65 mm x 50 mm and up to 40 mm in thickness which appeared covered by a thin capsule. On sectioning, the lesion was cystic and contained necrotic soft white material. Microscopically, sections showed a large simple cyst lined by stratified squamous epithelium and containing abundant keratin. The wall of the cyst contained lymphoid tissue with reactive germinal centres and lymphogranulomata. The squamous epithelium was not dysplastic and no appendages were seen. No other epithelial elements were identified. The two other specimens were consistent with a hydatid cyst and chronic cholecystitis. FIGURE CT demonstrating a 51mm x 35mm low density, well-defined lesion between the head of the pancreas and the vena cava.

DISCUSSION
True cysts of the pancreas are uncommon with pseudocysts accounting for upto 90% of all pancreatic cysts [6]. Lymphoepithelial cysts form a rare subset of true pancreatic cysts. Lfichtrath and Schriefers first reported, this lesion in 1985 [16]. Our literature search reveals that only a further 28 cases have been reported [1-5, 7-14, 16-25] (four of these were reported as accessory splenic epidermoids within the pancreas [3,12,19,26]). Truong et al., were the first to give this lesion its current name [22]. With increasing numbers of case reports, characteristics of this rare lesion have become apparent.
The pathogenesis of the lymphoepithelial cyst has not been determined but there are four main current theories [21,23]. Firstly, it may arise from a branchial cyst fused within the pancreas during embryological development (similar to branchial cysts in the neck). Secondly, the cyst may result from squamous metaplasia of an obstructed pancreatic duct which subsequently protrudes into a peripancreatic lymph node. Thirdly, the cyst may arise from accessory splenic tissue within the pancreas. Lastly, benign epithelial inclusion or ectopic pancreatic tissue in a peripancreatic lymph node may be the origin of this lesion. The striking feature of this lesion is its histopathology. All the cysts have been spherical, single, well-circumscribed cysts. The cyst contains a white material which is keratin produced by the mature squamous epithelium which lines the cyst. Surrounding this is a layer of lymphoid tissue. The cyst is then separated from the normal pancreatic tissue by a thin capsule of fibrous tissue [23].
The lymphoepithelial cyst predominantly affects males in their middle to late years. At least 8 cases have been found incidentally either on imaging or at autopsy [5,13,18,20,25]. The rest have presented with non-specific symptoms of abdominal pain, nausea, vomiting, diarrhoea, malaise or weight loss.
Our case has illustrated the difficulty in obtaining a pre-operative diagnosis. There is no blood test specific to this lesion. All the reported cases have shown no consistent pattern in Amylase or tumour markers. Ultrasound, CT and Magnetic Resonance Imaging will all demonstrate a cystic lesion within or near the pancreas. However, none of them are able to differentiate the lymphoepithelial cyst from other cystic lesions of the pancreas. ERCP may help to exclude a pseudocyst, but again does not differentiate between true cystic lesions [9,21,24].