Clinical History
A 64-year-old man was referred to our institution for an incidentally discovered cystic lesion of the left retroperitoneum. The patient was asymptomatic and physical examination was normal. Routine laboratory tests were unremarkable.
Imaging Findings
Non-enhanced CT scan showed a well-defined hypoattenuating (11 Hounsfield Unit, HU) mass of the left retroperitoneum, measuring 13 x 11 x 12 cm, embedded with the left diaphragmatic cupola. There was no connection to any other structure of the left hypochondrium. This lesion contained a sediment of hyperattenuating material (Fig. 1a) and cystic wall calcification. There was no significant post-contrast-enhancement within this lesion (Fig. 1).
On MRI, the lesion showed high intensity signal on T2-weighted images, confirming its cystic nature, with a thin wall and few thin septations. On T1-weight images, the signal was hyperintense, remaining unchanged after fat suppression, suggesting protein, mucin or methaemoglobin content. Wall and septations were slightly enhanced on post-contrast images with subtraction (Fig. 2).
The patient underwent a left lombotomy and a partial resection was performed.
Pathologic analysis showed a wall composed of loose connective tissue lined by pseudostratified ciliated columnar epithelium (Fig. 3).
Discussion
Bronchogenic cysts (BC's) result from abnormal budding of the ventral foregut between the 26th and 40th days of gestation. [1] BCs commonly occur in the mediastinum or within the lung parenchyma, but ectopic locations exist, depending on the timing of the complete separation from the tracheobronchial tree. Ectopic locations include diaphragm, skin, pleura or neck. Intradiaphragmatic BCs are extremely rare, with only 21 cases reviewed by Mumang et al in 2016. [2]
Intradiaphragmatic BCs are typically asymptomatic, especially when they grow in the large retroperitoneal space. [3] However, patients with large BC may present with abdominal pain or symptoms resulting from compression and/or irritation of adjacent structures.
Intradiaphragmatic BCs have similar imaging characteristics to those of mediastinal locations. On CT, they typically appear as hypoattenuating well-limited spherical lesions, without enhancement after administration of iodinated contrast agents. [1] Spontaneous intracystic high attenuation may result from haemorrhage, mucinous or proteinaceous content. Parietal calcifications or the presence of a milk of calcium also support this diagnosis. On MRI, high intensity signal on T2-weighted images confirms the cystic nature of the lesion. Various spontaneous signal intensities may be observed on T1-weighted images due to the different content of the cyst with increased signal intensity in case of haemorrhage, proteinaceous or mucinous content [3].
The differential diagnosis of retroperitoneal BC arising from the diaphragm include gastrointestinal duplication cyst, cystic teratoma, post-traumatic cyst, hydatid cysts, fibroblast-lined cysts, cystic endometriosis and pancreatic pseudocysts.
Considering the multiple differential diagnoses, in absence of specific clinical history such as pancreatitis, endometriosis, or parasitic disease, the definite diagnosis is difficult to establish prior to histopathological analysis. Furthermore, malignant transformation of diaphragmatic BC, although very rare, has been described. [4] Surgical resection is therefore recommended to confirm this diagnosis, alleviate any symptoms and prevent complications such as haemorrhage, infection, compression of adjacent structures, and malignant transformation. A partial resection was performed in our patient, in order to avoid a complex diaphragmatic reconstruction required by the large embedment in the left hemidiaphragm.
Histologically, BCs are lined by a ciliated pseudostratified columnar epithelium. The fibrovascular connective tissue wall is composed of seromucous glands, hyaline cartilage and/or smooth muscle. [3, 5]
In conclusion, intradiaphragmatic BCs are extremely rare, and this report illustrates the variable imaging findings, particularly highlighting the importance of MRI. These lesions must be considered as a possible differential diagnosis of any unusual retroperitoneal cystic lesion.
Differential Diagnosis List
Intradiaphragmatic bronchogenic cyst with caudal extension towards the retroperitoneum
Gastrointestinal duplication cyst
Cystic teratoma
Post-traumatic cyst
Hydatid cyst
Fibroblast-lined cysts
Pancreatic pseudocysts
Adrenal gland cyst
Final Diagnosis
Intradiaphragmatic bronchogenic cyst with caudal extension towards the retroperitoneum
