Pseudocyst of the pancreas is localised fluid collection rich in amylase and other pancreatic enzymes. A mediastinal extension is rare. The frequency of pancreaticpleural fistulas in patients with pancreatitis is estimated to be 0.4 to 4.5%. 80% with fistulas are associated with mediastinal pseudocyst. A posterior mediastinal cyst can be foregut duplication cyst, pancreatic pseudocyst, lymphatic malformation, cystic teratoma and cystic neuroblastoma. Differentiating all these needs prompt clinical examination and diagnostic modalities [1-6].

We report this rare case of mediastinal pseudocyst with the unusual presentation without any ductal communication. The maturation period of pancreatic pseudocyst is reported to be 2 to 6 weeks, during this time 33% of the cyst are expected to spontaneously resolve [7,8,9,10]. Only a few cases were reported in the literature. In our case, a large abdominal thoracic thin-walled pseudocyst with a major thoracic component behind the heart and extending along esophageal hiatus with a smaller component in the lesser sac is seen. Cystic fluid showed elevated levels of amylase and lipase. The histopathology showed thick cyst wall with no definite lining epithelium. It has a collection of chronic inflammatory cells with granulation tissue which was also consistent with a pancreatic pseudocyst. In our patient, due to the lack of abdominal component, the cyst was accessible via a thoracic approach.

A 15-year-old boy presented with progressive worsening of breathlessness and cough for the past 1 month. He had been admitted 5 months ago for similar complaints where chest x-ray did show bilateral pleural effusion for which left side pleural taping was done. Pleural fluid analyses were negative for tuberculosis workup. But, Child was started on empirical ATT, but compliance was poor. CECT thorax done showed bilateral moderate pleural effusion, chronic calcific pancreatitis with pseudocyst extending to the posterior mediastinum. The child was referred to a higher center for further management. On examination, air entry was reduced on bilateral lung field particularly in mid and lower zone regions. Per abdomen examination was normal.

Trauma is the most common cause of pseudocyst in children. Other causes are congenital anomalies, drug-induced. The anomalous pancreatic duct, anomalous pancreaticobiliary junction, pancreatic divisum, annular pancreas causes recurrent pancreatitis. Ectopic pancreatic tissue with the formation of pseudocyst is also reported in the literature.

The usual symptom of pseudocyst will be tense cystic mass in epigastric, umbilical, or in the left hypochondrium. Misleading presentation in case of mediastinal pseudocyst is mainly due to compression or invasion of adjacent structures by pseudocyst i.e. dyspnoea, cough, chest pain, dysphagia, hemoptysis, cardiogenic shock, acute respiratory failure, pseudo achalasia, weight loss [12]. Abdominal symptoms will be rare in the case of the mediastinal cyst.

In the absence of any peripancreatic collection/communication, these cysts are difficult to say as a pseudocyst of the pancreas. A chest X-ray can show pleural effusion.USG/ CT will detect the size, location, and wall thickness of the cyst. MRCP and ERCP will establish fistulous communication between the pancreatic duct and pleura. ERCP leads to diagnosis in 80% of cases, demonstrates a fistulous tract in 59%, and allows stenting. Pleural fluid will high amylase and albumin content (In pancreaticpleural fistula it may exceed 10,000IU/L).Endoscopic ultrasound gives more information about pancreas and duct if any communication. Endoscopic USG guided aspiration of fluid and analysis of fluid will be the definitive diagnostic measure.

Most pseudocyst will resolve spontaneously with supportive care. Spontaneous resolution occurs in about 50% of cases and complications occur in 5 to 40% of cases. Spontaneous regression of pseudocyst is likely with conservative management with bowel rest, total parenteral nutrition and non-operative management are successful, particularly when the pseudocyst is less than 6 cm. If any ductal obstruction or communication with the cyst is there, it should be managed first with ERCP stenting. In cases where the size of pseudocyst exceeds 6cm, conservative management is ineffective thus the choice of treatment includes surgical internal drainage (Cystogastrostomy/Marsupialization, Roux-en-Y cystojejunostomy,), endoscopic drainage procedures and percutaneous catheter drainage methods. For mediatinalpseudocyst, these options are not available.