Bronchogenic cysts are caused by abnormal development of lung buds and occur in the mediastinum in about 90% of cases, while those occurring in the retroperitoneum are rare. 2 cases were admitted to our clinic between August 2001 and December 2009, and the diagnosis was confirmed pathologically and is reported as follows. Case report: Case 1, female, 55 years old. She was admitted to the hospital on November 25, 2009, because of a left adrenal cyst that had been present for 3 years and left lumbar pain for 10 days. Physical examination: BP 140-80 mmHg (1 mmHg=0.133 Kpa), left renal tenderness. Urine routine (-), blood cortisol and aldosterone were normal.Ultrasound: a cystic solid mass was seen in the splenic hilar region equivalent to the tail of the pancreas, with a diameter of about 3.9 cm, not rich in blood supply, with a thin and smooth wall, and with an enhancement effect on the posterior wall and posterior aspect.CT examination showed a rounded low-density shadow of about 4 cm × 4 cm in the left adrenal region, with smooth edges and intact peripheral membrane, and the CT value of 10 Hu, and the enhancement of enhancement was not obvious, and the CT value of 20 Hu. The CT value was 10 Hu, and the enhancement was not obvious, with a CT value of 20 Hu (Figure 1). The left adrenal gland adenoma was diagnosed. Under epidural anesthesia, left adrenalectomy was performed. Intraoperatively, a 4cm × 4cm × 3cm mass was seen between the diaphragm and the upper pole of the left kidney, which was smooth and connected to the left adrenal gland with its tip, and the peripheral membrane was intact, so the mass and the adrenal gland were completely removed. There was a viscous yellowish jelly-like fluid coming out of the incised mass. Pathology report: gray-white tissue, cystic in section, the wall of the capsule was fibrous connective tissue, most of it was lined with pseudociliated columnar epithelium, with cup-shaped cells in between, and there was basement membrane under the epithelium. Adrenal cortical tissue was hyperplastic and no tumor tissue was seen. Pathologic diagnosis: bronchogenic cyst with adrenocortical hyperplasia. Postoperative follow-up was 9 months without recurrence. Case 2, male, 17 years old. He was admitted to the hospital on October 9, 2001 for 3 weeks of hematuria after strenuous activity. There was no urinary frequency, urgency, pain or difficulty in urination. Physical examination: abdomen was flat and soft, no pressure and rebound pain, no percussion pain in both renal regions, no elevation and no pressure pain in the bladder region, a cystic mass of about 7 cm was palpable on rectal palpation on the left wall, soft, smooth surface, unclear boundary, no tenderness. Urine routine: RBC (++++), WBC (-). ultrasound showed a well-filled bladder, smooth mucosa, 8.4 cm × 7.7 cm × 9.0 cm rounded echo-like dark area in the posterior part of the bladder, and no blood flow signal was detected. CT examination showed an elliptical cystic lesion below the anterior part of the sacral bone, about 9.0 cm × 7.2 cm × 9.0 cm, with a thin wall, a continuous and smooth wall of the bladder, and a uniform density at the center, with a CT value of 8Hu. There was no abnormality in the upper urinary tract of IVU; after the bladder was filled, the top of the bladder could be seen as a right-high and left-low flat compression trace, and the lower edge was semicircular. The diagnosis was presacral cyst. Pre-sacral cyst excision was performed under epidural anesthesia. The cyst was located in the lower part of the anterior sacrum, about 8.0 cm × 8.0 cm × 9.0 cm in size, adjacent to the bladder, pushing the rectum to the right anteriorly, with soft texture and smooth surface. The wall was thin and uniform, and the adhesion with the sacrum was relatively tight. After complete excision of the cyst, the cyst wall was opened, and about 350 ml of yellowish thin pus-like fluid was aspirated.Pathology report: the tissue was sent for examination as a cystic cavity of unequal sizes, with fibrous cystic wall tissues lined with pseudo-complex ciliated columnar epithelium, with cupular cells visible in the epithelium, and basement membranes were present in the subepithelium. Mixed glandular structures, a small amount of cartilage tissue and muscle tissue were seen in the fibrous tissue (Figure 2). Pathologic diagnosis: bronchogenic cyst. The patient was followed up for 2 years after surgery and no recurrence was observed. DISCUSSION Bronchogenic cysts are congenital disorders that arise from developmental abnormalities of the primitive foregut and consist of one or more tissues of the respiratory system, including respiratory epithelium, smooth muscle, hyaline cartilage, and plasma or mucous glands. The cause is not completely clear. Sumiyoshi et al [1] proposed the hypothesis of germ detachment and migration, suggesting that in the third to sixth week of embryonic development, the thoracic and abdominal cavities are one and the same, and the primitive foregut splits ventrally into the trachea and the bronchial tree, and then the abnormal germ and the bronchial tree detach and migrate with the development, and the bronchial cysts may occur in the subcutaneous area, the abdominal area, and the intraspinal canal, and so on. About 90% of retroperitoneal bronchogenic cysts occur on the left side, which may be related to the counterclockwise transposition of the caudal primitive foregut and midgut from the left to the right during embryonic development, and the dislodged germs do not follow the transposition and remain on the left side. In our case 1, the bronchogenic cyst occurred in the left retroperitoneum, which is consistent with the above pattern. The cystic walls of bronchogenic cysts contain glands, cartilage, and smooth muscle lined with respiratory epithelium [2], and bronchogenic cysts occasionally lack cartilage; therefore, cystic lesions without cartilage in the cystic wall should not be excluded from this diagnosis [3], and the diagnosis of case 1 in our group, in which no cartilaginous tissue was found, can be confirmed by the typical mixed glandularity. This disease is easily confused with other cystic diseases, cystic teratoma has endoderm derived mesoderm and ectoderm bronchi and other structures, bronchial cysts may also show ectodermal differentiation, and it is difficult to identify with cystic teratomas [4],, combined with immunohistochemical indexes EM A ( + ), CK ( + ) , GFAP ( – ) can be clear that the cystic tissue is of bronchial origin. Bronchogenic cysts have a low incidence and can occur at any age, with a male to female ratio of approximately 1:1, and are most commonly found in the mediastinum, with approximately 5% located in the retroperitoneum. Retroperitoneal bronchial cysts are found in the pancreatic region and in the left adrenal region. These cysts are usually less than 6 cm in diameter and develop slowly, and in our case 1, the cyst had only increased in diameter by about 0.5 cm in 3 years of preoperative observation.The disease is usually asymptomatic, but when combined with infection or compression of the surrounding organs, it may manifest as abdominal or back pain, and the cysts of the lower abdomen may compress the bladder and urethra and present as hematuria, and in case 2, the patient was found to have presacral cysts at the consultation because of hematuria. Symptomatic cysts are generally 7 cm in diameter, with a maximum diameter of 18 cm reported in the literature [5]. In a few patients, the clinical presentation is similar to that of a functional adrenal tumor. Dogget et al [6] reported a case with symptoms similar to those of a pheochromocytoma, which may be related to the excessive release of catecholamines from the adrenal glands due to compression of the cyst. Because of the lack of specificity in clinical manifestations, it is often necessary to distinguish it from other cystic lesions in the retroperitoneum, such as pancreatic cysts, caecal cysts, Müllerian cysts, cystic teratomas, and urethral epithelial cysts, etc. [7], and it is easy to misdiagnose it as adrenal adenoma when it occurs with high density in adrenal gland area [8]. In our case 1, the preoperative CT examination showed that the mass was a cystic predominantly mixed lesion, and the diagnosis was adrenal tumor, and the reason for the misdiagnosis might be related to the elevated CT value caused by more endocrine proteins in the cyst. Typical bronchogenic cysts appear as round, well-bordered hypodense foci on CT, with no enhancement on enhancement scans. Retroperitoneal bronchial cysts are most valuable on CT and MRI [9]. The lesions can be hyperdense due to the protein content and are easily misdiagnosed as solid masses. Very few cysts may be calcified [10].MRI is valuable in the diagnosis of bronchogenic cysts because of its high soft tissue resolution and its ability to perform multiplanar and multiparametric imaging. Bronchogenic cysts are characterized by high signal in T1WI, shorter T1-weighted relaxation time, and long T2-weighting due to their high protein content [11-12]. It is controversial whether asymptomatic retroperitoneal bronchogenic cysts should be surgically resected, but most scholars believe that they should be operated. For symptomatic retroperitoneal bronchogenic cysts, surgical resection is the best option to relieve symptoms and prevent secondary infection and malignancy. Because the disease is difficult to diagnose preoperatively and cancerous transformation of retroperitoneal bronchogenic cysts has been reported [13], surgical excision can reduce the risk of malignancy. Residual cystic epithelial tissue can cause recurrence, and the cyst needs to be removed completely. The surgical approach depends on the characteristics of the lesion, and laparoscopic surgical resection may be the first approach for lesions that are confined and have clear boundaries with the surrounding tissues [14-15]. Larger lesions or invasion of surrounding adjacent tissues require open surgical treatment. Postoperative prognosis of retroperitoneal bronchogenic cysts is good, and no recurrence has been reported.