History
    A 69-year-old male heavy alcoholics presented with swallowing difficulty, which aggravated after endoscopy at private clinic.

Findings
CXR: mediastinal widening
Initial Chest CT: -  entire esophagus, 2 esophageal lumina, low density(30 HU) lesion
Esophagogram: double-barreled esophagus
F/U (3 months) HRCT: 2 esophageal lumina

Discussion
    Duplication of the alimentary tract are rare congenital malformations that may occur at any level from mouth to the anus. The most common site is ileum. Duplication of the esophagus is the second most common duplication of the gastrointestinal tract, consisting 10-15% of those reported. There are 2 types of esophageal duplications: cystic and tubular. Of 44 cases reviewed, only 6 cases were of the tubular variety(1). Although the exact etiology of duplication of the espophagus has not been established, several theories have been proposed such as: bronchopulmonary foregut
malformations, aberrant luminal recanalization theory, abortive twinning theory, split notochord theory, intrauterine vascular accident theory. Most investigators feel that incomplete recanalization of the esophagus during development is the most likely of the proposed theories.(2)
    Three criteria for duplication cysts of the esophagus are (a) attachment to the esophagus, (b) the presence of 2 layers of muscularis propria, and (c) the presence of epithelium representing some level of the gastrointestinal tract. Duplication cysts of the esophagus are usually lined by ciliated epithelium that is most often columnar but may be flat, cuboidal, squamous, or pseudostratified.  Enteric cysts arise from the posterior portion of the foregut and contain incomplete muscular layer on histologic examination. Those cysts which also contain neural tissue are known as neuroenteric cysts.  The latter have connections to the spinal canal and are invariably associated with vertebral anomalies of which the most commonly occurring are segmentation abnormalities.(3) In patients with cystic duplications, the presenting symptoms in early life may be seen when an expanding mediastinal mass compresses structures in the mediastinum: (a) vascular compression with cyanosis and engorgement of head and neck vessels, (b) difficulty in swallowing, regurgitation, and vomiting, (c) dyspnea, obstructive emphysema, and recurrent respiratory infections; (d) mediastinitis due to rupture of the duplication. Tubular duplication may cause recurrent dysphagia and occasional chest pain. When a complication such as rupture occurs, patients present with signs and symptoms of acute mediastinitis. Esophageal duplications are more frequently found in children, but 25% to 30% occur in adults. Men had a 2:1 predominance over women. The location was 60% in the lower third, 17% in the middle third, and 23% in the upper third. In true tubular duplications of the esophagus, esophagography usually shows double-barreled esophagus in which contrast medium can be seen in both lumina. Contrast enhanced CT scan showed a low attenuation (21-34 HU) lesion encircling the esophageal lumen through the entire course of the esophagus. A high-attenuation rim of uniform thickness, presumed to be the muscular layer of the esophagus. True tubular duplications must be differentiated from dissecting intramural hematoma of the esophagus in Boerhaave syndrome with a point of both lumina containing musocal epithelium as well as muscularis propria.(4) Although radiologic and endoscopic examinations may suggest the diagnosis, a definitive preoperative diagnosis is difficult.  The definitive treatment of esophageal duplication is surgical excision and the definitive diagnosis is mainly by the pathologic examination of the lesion after surgical removal. A 69-year-old alcoholic man was diagnosed as  tubular type of esophageal duplication because of double-barreled esophagus on esophagogram, low- and high- attenuation rims at the esophagus on enhanced CT scan, presumed to be the muscular layers of the esophagus. Histologically, both lumina of the esophagus lined by stratified
squamous epithelium and contained muscularis propria.

References
1. Berk JE, Haubrich WS, Kalser MH, Roth JLA, Schaffner F. Bockus Gastroenterology 4th ed. Saunders, Philadelphia, 1985; 680-681
2. Macpherson RI. Gastrointestinal tract duplications: clinical, pathologic, etiologic and radiologic considerations. Radiographics 1993; 13: 1063-1080
3. Silverman FN, Kuhn JP. Caffey's Pediatric X-ray Diagnosis: An integrated imaging approach 9th ed. Mosby, St. Louis 1993; 1008
4. Lee KS, Kim IY, Kim PN. Dissecting intramural hematoma of the esophagus in Boerhaave syndrome: CT findings. AJR 1991; 157: 197-198