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Q1: What does the chest radiograph show and what would be your next investigation?
The chest radiograph (see p 436) shows an abnormal cardiac shadow, which gives the appearance of a dextrocardia. Closer examination, shows a mass on the right side, which represents the right atrium being compressed forward by a posterior lesion. There is also a double left cardiac border, the medial border being the true one. The lateral border represents a posterior mediastinal cyst. Bilateral pleural effusions are also noted, more marked on the right, and so the differential diagnosis should also cover other causes of bilateral pleural effusions. These include hypoproteinaemia secondary to nephrotic syndrome or chronic liver disease and in addition, given that there are absent breast shadows, in a women of this age a possible diagnosis of metastatic breast carcinoma with previous mastectomies should also be considered. As a next investigation, contrast enhanced computed tomography of the abdomen would offer useful diagnostic information see figs 1 and 2(below).
Q2: What is the diagnosis and how would you manage this patient?
The diagnosis is mediastinal pancreatic pseudocyst.
The patient was then referred to a pancreatic surgeon and the diagnosis was confirmed at laparotomy. The mediastinal cyst was drained by a tube passing through the diaphragm, across the abdominal cavity to the exterior, and the abdominal pseudocyst was drained by cyst gastrostomy.
Discussion of further management
Mediastinal pseudocyst is a rare complication of pancreatitis, with fewer than 60 cases reported in the English language.1 The pseudocyst is inflammatory in origin and the lesion lacks a true epithelial lining. As a consequence, extrapancreatic fluid collections, rich in proteolytic enzymes, fat, and necrotic debris accumulate outside the boundary of the gland surrounded by a thick fibrous capsule. While spontaneous resolution of pseudocysts has been reported,2 this is unlikely if there is evidence of chronic pancreatitis, pancreatic duct abnormalities exist, or if ultrasound imaging suggests a thick walled lesion.3
The pathogenesis and natural history of pseudocysts in acute and chronic pancreatitis are different.4 Both lesions may lead to extension of the pseudocyst along fascial planes which offer least resistance and may result in mediastinal pseudocyst formation. Entry to the thorax is most commonly seen via the oesophageal hiatus, aortic hiatus, or by direct erosion through the diaphragm.5
The review of mediastinal pseudocyst case reports by Beauchampet al suggests that they are more commonly seen in men, have a median age of distribution of 45 years and most commonly present with dyspnoea, chest and abdominal pain, and weight loss. Dysphagia may be present if there is oesophageal displacement by the extending pseudocyst. Recurrent hospital admissions for alcohol associated pancreatitis was a feature in most reported cases.
Radiography findings and the role of radiography
Radiographically non-specific findings of pleural effusion, pulmonary oedema, atelectasis, and cardiac enlargement may be accompanied by more specific findings of mediastinal inflammation or abscess and mediastinal pseudocyst.6-8 Kirchner identified that when present, pleural effusions were most commonly left sided and the location of the thoracic mass was in the posterior mediastinum. Magnetic resonance imaging and endoscopic retrograde cholangiopancreatography have proved useful in diagnosis and planning treatment strategies.
External drainage of the mediastinal pseudocyst represents the simplest surgical approach but is associated with the highest mortality and greatest recurrence rate.9 10 Erb and Grimes highlight a greater recurrence of mediastinal pseudocyst with external drainage when compared with intra-abdominal drainage. Thus, while the thoracic symptoms often give the greatest concern, mediastinal pseudocysts are best managed by laparotomy rather than thoracotomy. Thoracic drainage may be useful preoperatively if the cyst is infected. The formation of a controlled fistula into the gastrointestinal tract by cyst intestinal anastomosis, represents the treatment of choice for non-complicated mature pseudocysts and is associated with lowest mortality and recurrence rates. Internal decompression of the pseudocyst may be either with cyst gastrostomy or more commonly with cystojejunostomy Roux on Y.
This case highlights a rare complication of pancreatic disease, manifesting with symptoms outside the gastrointestinal tract. Mediastinal pseudocyst should be considered in the differential diagnosis when a patient with previous pancreatic disease presents with shortness of breath and unexplained thoracic radiographic findings. Radiological techniques offer invaluable diagnostic information and may have a role in treatment. Currently, surgical intervention with internal abdominal drainage of the lesion close to the pancreas, and external transdiaphragmatic drainage of the intrathoracic component offers the best therapeutic outcome.
Mediastinal pancreatic pseudocyst.
The authors thank Dr Simon Jackson, Consultant Radiologist, at Derriford Hospital, Plymouth.
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