Posterior Mediastinal Cyst

Clinically: patient presented with low back pain.

No posterior mediastinal symptoms or signs.

MRI DORSAL SPINE shows:

A well-defined unilocular cystic lesion measuring approximately 20 mm in posterior mediastinum adjacent to the dorsal spine at D4 – D5 level at 11 o'clock position on axial sections. No obvious adjacent osseous involvement or intraspinal extension.

Rest of the MRI WHOLE SPINE screening unremarkable.

Imaging diagnosis: 

Appears an incidental non-tumoural posterior mediastinal cyst-like Mullerian cyst.

DDs: 

No associated vertebral anomaly to suggest Neuroenteric cyst. The lesion is not close to trachea or oesophagus to suggest duplication cyst. Rest of the sag T2w screening MRI study of the Whole spine shows no significant abnormality in cord or cauda equina.

Cystic lesions found in the mediastinum are typically included bronchogenic cysts, esophageal duplication cysts and Neuroenteric cysts.

But typical Mullerian cysts of this kind also needs consideration which is often overlooked.

The reason may be Mullerian cysts in locations outside of the female pelvis are rare. Some reported locations include the skin and retroperitoneum. The etiology of Mullerian cysts arising in the mediastinum is unclear. Batt suggested that the lesion is derived directly from the primary Mullerian apparatus.

While only 14 cases of mediastinal cysts with Mullerian differentiation have been described in the literature, it is likely that they are much more common than presumed in older females and often misdiagnosed as either bronchial or oesophagal cysts. 

The fourteen definitive mediastinal cysts with Mullerian differentiation have been identified, have occurred in females 40-60 years old. These patients typically presented with cough or were asymptomatic. All cysts were paravertebral in location, occurring between T3-T8 vertebrae. All of the cysts were positive for either ER or PR. Our report is the first to show expression of PAX8 and WT1, both markers of Mullerian differentiation, in these cysts.

The other DDs for cystic masses of the posterior mediastinum include:

• bronchogenic cyst

• esophageal duplication cyst

• neuroenteric cyst

• meningocele

• lymphangioma

• mediastinal thoracic duct cyst

• mediastinal pancreatic pseudocyst.