Case history: A 56-year-man presented with the chief complaints of pain in the left side of the chest and abdomen on and off since 4 to 5 months. The pain was insidious in onset. It did not radiate and was not associated with consumption of food. There was no history of vomiting, jaundice, fever or other complaints. He denied history of smoking or consumption of alcohol. He is a known case of hypertension and diabetes mellitus since the past 10 years

Physical examination did not reveal any abnormality.

RADIOLOGICAL FINDINGS:

Laboratory investigations including hemogram, liver and renal functions tests revealed high fasting blood sugar but were otherwise within normal limits.

The first imaging study performed was a frontal X-ray of the chest (Fig 1).

Fig. 1

It revealed a 3 x 2 cm well defined fluid density lesion situated in the right cardiophrenic angle. The margin of the cyst adjacent to the heart border was well defined indicating that it was situated in the posterior mediastinum.

CT scan of the chest and upper abdomen. (Fig. 2A and 2B) revealed a large well defined cyst with fluid attenuation in the right inferior mediastinum.

Fig. 2A	Fig. 2B

This cyst was in contact with the esophagus. It did not show enhancement on administration of contrast.

Barium swallow (Fig. 3A and B) showed the esophageal mucosal pattern to be normal.

Fig. 3A	Fig.3B

There was an extrinsic impression on the anterior aspect of the esophagus in the retrocardiac segment. A soft tissue density lesion was seen in the retrocardiac region.

Multiplanar, mutiecho MRI examination of the chest (Fig. 4A, B and C) showed a well-circumscribed hyperintense soft tissue lesion in relation to the lower third of the esophagus in right hemithorax.

Fig. 4A	Fig. 4B	Fig. 4C

It measured approximately 7.5 x 5.5 x 3 cm. The mass extended upto the retrocardiac region. Fat planes between aorta, prevertebral soft tissue and the mass were well preserved; however, the mass was not seen separate from the pericardium. The mass showed hyperintense signal on T1W images.

Correlation of barium and MR findings raised the possibility of a duplication cyst.

Treatment: The patient was operated and the cyst was excised. This led to an improvement in symptoms.

DISCUSSION:

Esophageal duplication cysts are uncommon and constitute only 0.5 - 2.5 % of all esophageal tumors. The true incidence of esophageal cysts is unknown. However, esophageal cysts are rare. Many patients with esophageal cysts are asymptomatic and never diagnosed. Cysts are usually grouped with other benign lesions of the esophagus. Cysts comprise up to 20% of benign esophageal lesions. Up to 80% of cysts are diagnosed in childhood.

Etiology: Embryologic duplication of specific elements of the esophageal wall causes cysts. Esophageal cysts develop from aberrant elements of the esophageal wall. Simple cysts are duplication of the epithelium, whereas true esophageal duplications are duplications of the submucosa and the muscle wall without duplication of the epithelium. Maldevelopment of the posterior division of the primitive foregut is the embryologic defect responsible for esophageal cysts. Esophageal cysts and duplications do not usually communicate with the lumen of the esophagus.

The lining of the cyst can vary and can include squamous, columnar, cuboidal, pseudostratified, ciliated, and gastric mucosa. Hemorrhage can be the presenting symptom if gastric mucosa is present in the cyst. The other types of mucosa are not specifically associated with particular symptoms.

Pathophysiology: Symptoms are caused by compression of surrounding structures. Sixty percent of esophageal cysts occur in the lower third of the esophagus, where difficulty swallowing from compression is the most common symptom; 20% occur in the upper third of the esophagus, where respiratory difficulty from compression of the tracheobronchial tree is the most common symptom; and 20% occur in the middle third of the esophagus, where retrosternal chest pain and difficulty swallowing are the most common symptoms.

Posterior cysts in the lower third of the esophagus can cause cardiac arrhythmias. The larger the cyst, the greater the chance of it causing symptoms.

Clinical features: Many children with esophageal cysts are asymptomatic. Most cysts are diagnosed during childhood. Most adults (67%) with cysts are symptomatic. Chest pain (tightness or fullness) is the most common presentation. Dysphagia may also occur. Hemorrhage can occur if gastric epithelium is present in the cyst. Most esophageal cysts develop in the right posteroinferior mediastinum. Although rare, malignant degeneration can occur.

Embryology: The upper gastrointestinal tract develops from the posterior division of the primitive foregut. During the fourth week of gestation, the primitive foregut develops an anterior diverticulum, which becomes the respiratory bud.

Meanwhile, the posterior division develops into the esophagus and upper gastrointestinal tract. The tracheoesophageal septum separates the primitive esophagus from the primitive trachea. As the esophagus continues to develop, the epithelium eventually obliterates the lumen and later recannalizes. Esophageal duplication cysts probably result from developmental errors occurring at the fifth to eight week of life. Embryologically, esophageal duplication cysts are believed to represent a failure of complete vacuolation of the originally solid esophagus to produce a hollow tube. As expected based on the common embryologic origin, bronchogenic and esophageal cysts can occur together

Imaging studies: All esophageal cysts should be evaluated and, eventually, resected.

Radiographs guided by history and physical examination findings usually confirm the diagnosis. Plain chest radiographs reveal a soft tissue mass within the mediastinum.

Barium swallow studies reveal compression of the esophagus without ulceration. Usually no communication with the cyst is seen.

CT scan reveals a fluid-filled cystic structure originating from the esophagus. Typical CT finding of esophageal duplication cyst is a homogeneous, low-attenuation mass with smooth borders which does not enhance with contrast. Although CT cannot definitely differentiate an esophageal duplication cyst from other benign paraesophageal lesions such as abscess, old hematoma, neurofibroma, lipoma, leiomyoma, or other foregut duplications, it can often suggest a presumptive diagnosis.

Endoscopy demonstrates extrinsic compression with intact mucosa.

Endoscopic ultrasonography reveals a cystic, filled structure in connection with the esophagus.

MRI scans can also help diagnose esophageal cysts.

In children, Technitium-99m scan can help to detect ectopic gastric mucosal in the cyst.

Nearly 75% of patients with esophageal cysts eventually become symptomatic; therefore, cysts should be resected when they are diagnosed.

Differential diagnosis: A double layer of smooth muscle in their walls and absence of cartilage are necessary findings to exclude a diagnosis of bronchial cyst. On CT scan, the differential point with bronchogenic cyst is that the wall of the lesion may be thicker and the mass may assume a more tubular shape with more intimate contact with the esophagus. The commonest differential of a mass in the posterior mediastinum is a neurogenic tumour.

Associations: Esophageal duplication cysts are associated with vertebral anomalies.

Workup: Laboratory studies do not specifically aid in the diagnosis of esophageal cysts. Laboratory evaluation should be guided by the patient's other medical problems. A CT scan should follow chest radiographic findings that suggest a mass in the mediastinum. CT scan is the radiologic modality of choice to aid in diagnosis and operative preparation. Esophagoscopy should be performed to rule out an intrinsic component, which should be biopsied to exclude malignancy. If endoscopic ultrasonography is available, then esophagoscopy should be performed to further delineate the extent of the cyst.

Medical therapy: Medical therapy has no role in the management of esophageal cysts.

Surgical therapy: Simple cysts are enucleated, whereas duplications are excised. Previously, a posterolateral thoracotomy was required to remove the cyst or the duplication; however, minimally invasive thoracoscopy is currently employed to enucleate cysts and resect duplications and is the procedure of choice.