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Bronchogenic cysts arise from the abnormal budding of the embryonic foregut during development from the third to seventh weeks of gestation. Rarely, attachments to the foregut persist, forming cysts found in the tracheobronchial tree, most commonly in the mediastinum posterior to the carina and the pulmonary parenchyma. If complete separation occurs, bronchogenic cysts can be found in remote locations, such as the skin, retroperitoneum, subphrenic area, and the esophagus.^1- 2 These benign nonfunctioning cysts contain multiple layers of the foregut while housing a thick proteinaceous material.

Only 38 cases of histopathologically proven subdiaphragmatic bronchogenic cysts have been reported in the English literature.³ Owing to the nature of these exceedingly rare tumors outside the thoracic cavity, almost all are found incidentally by radiographic imaging. However, they may also be the primary source of symptoms that result in abdominal pain (52%), nausea or vomiting (12%), malaise because of secondary infection, or compression of surrounding structures due to mass effect.^4- 5 Bronchogenic cysts lack aberrant laboratory values and tend to be in a precarious location that makes percutaneous tissue diagnosis nearly unobtainable. If a biopsy is obtained, it is rarely diagnostic. Most commonly, the subdiaphragmatic cysts can be found posterior to the stomach in a triangle defined by the splenic vein, midline vertebral body, and the spleen/diaphragm. Although there is no ethnicity or sex discrepancy, interestingly 82% of subdiaphragmatic cysts occur on the left side, as seen in this case.⁵

Radiographic diagnosis of bronchogenic cysts is inherently difficult owing to its variable internal echogenicity and similar radiological properties to others in its differential diagnosis. The cysts appear homogenous in nature and almost inevitably have no noticeable wall. Most bronchogenic cysts appear similar to the attenuation of water (0-20 Hounsfield units), but may appear hyperattenuated with thicker proteinaceous material, hemorrhage, or calcification.⁵ Importantly, a lack of enhancement on computed tomography or magnetic resonance imaging may differentiate it from a vascular lesion.⁶ Magnetic resonance imaging can be a useful adjunct with varying signal intensity in different phases; however, nearly all are misdiagnosed until histopathologic diagnosis is made following surgical excision.

Even if radiological or percutaneous biopsy shows a bronchogenic cyst, surgical management is often pursued owing to a risk of hemorrhage, mass effect, infection, or malignant transformation. Once considered to be lacking malignant potential, 2 cases of malignancy (adenocarcinoma and neuroectodermal) arising from these subdiaphragmatic cysts have been documented.^3,7 Standard surgical practices apply for excision of these masses via an upper midline laparotomy, retroperitoneal, or laparoscopic approach.⁸ Smaller masses may be difficult to palpate owing to its compressibility, but once unroofed, they feel like any cyst-filled cavity and may even harmlessly leak proteinaceous material if the wall is violated. Although often well circumscribed and defined, adjacent organs can be affected, leading to resection of attached stomach (13%) and adrenal glands (5.5%).³ Histopathologic diagnosis of the surgical specimen resembles that of its embryologic foregut derivation and contains respiratory epithelium (pseudostratified ciliated columnar or cuboidal epithelium), cartilage, and interspersed glandular cells.⁹ Immature pleural tissue in conjunction with the previous findings, along with the absence of smooth muscle, must be present to differentiate bronchogenic from other forms of foregut cysts (eg, esophageal). Importantly, surgeons must add bronchogenic cysts to the differential diagnosis of any mass occurring in the retroperitoneum, particularly in the triangle described above.

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Correspondence: Barish H. Edil, MD, Johns Hopkins Hospital, Cancer Research Bldg II, Room 506, 1550 Orleans St, Baltimore, MD 21231 (bedil1@jhmi.edu).

Accepted for Publication: May 21, 2009.

Author Contributions:Study concept and design: Stanwix and Edil. Acquisition of data: Stanwix and Edil. Analysis and interpretation of data: Stanwix and Edil. Drafting of the manuscript: Stanwix and Edil. Critical revision of the manuscript for important intellectual content: Stanwix and Edil. Administrative, technical, and material support: Stanwix and Edil. Study supervision: Edil.

Financial Disclosure: None reported.