8 February 2017 - Case of the Week #416

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Case of the Week #416

Clinical history:
A 45 year old woman presented with a 5.3 cm posterior mediastinal cyst, which was excised.


Micro images:

H&E




What is your diagnosis?





























Diagnosis:
Posterior mediastinal Mullerian cyst (Hattori cyst)


Special Stains:

PAX8



Test Question (answer at the end):
Which of the following is NOT a feature of mediastinal Mullerian cysts?

A. Have been described in the posterior mediastinum
B. Occur primarily in peri-menopausal females
C. Have a ciliated epithelium similar to normal fallopian tube epithelium
D. Have a thin wall containing smooth muscle and cartilage
E. Epithelium stains positive with the same markers as normal fallopian tube epithelium

Discussion:

Mullerian cysts are rare outside of the genital tract, but they can arise in the retroperitoneum and posterior mediastinum, and similar appearing ciliated cysts can arise in the skin and subcutis (Virchows Arch 2005;446:82, Case Rep Med 2016;2016:2487820). Their origin may be remnant Mullerian tissue, endosalpingiosis or metaplasia of other tissue types. Of interest, but perhaps coincidental, is a reported mediastinal Mullerian cyst in a woman with a prior mediastinal teratoma (Ann Thorac Cardiovasc Surg 2011;18:39).

In a French study, mediastinal cysts with Mullerian differentiation represented 5.5% (9/163) of non-neoplastic mediastinal cysts collected over 23 years. Mediastinal Mullerian cysts are found only in women, who are usually peri-menopausal. The cysts are typically paravertebral and are often mistaken for neurogenic tumors clinically. They may be asymptomatic or cause chest pain, cough and dysphagia (Ann Diagn Pathol 2007;11:417). Typically there is only one cyst, but a case with multiple, bilateral cysts has been reported (Ann Thorac Surg 2015;100:1898).

Mullerian cysts are thin walled and serous, with lining cells that resemble normal fallopian tube – ciliated cells with interspersed secretory cells and intercalated (peg) cells. Areas with small cuboidal lining cells can also be seen. Within the wall is a circumferential layer of smooth muscle. Goblet cells, cartilage and glandular structures are not present, which helps to differentiate them from bronchogenic cysts, their main differential diagnosis. Immunohistochemistry can also help in the distinction, as the Mullerian epithelium is positive for ER and PR. The smooth muscle cells in the wall can also stain positive for ER and PR. Bronchogenic cysts, on the other hand, will be negative for ER and PR (Virchows Arch 2005;446:82, Ann Diagn Pathol 2007;11:417). Other markers that are positive in Mullerian epithelium, such as PAX8 and WT1, are also positive in cysts with Mullerian differentiation (Case Rep Med 2016;2016:2487820, J Thorac Dis 2013;5:E8). Stains that have been reported negative in mediastinal Mullerian cysts include CK5/6, calretinin, CK20, CEA and CD10 (Virchows Arch 2005;446:82, Ann Diagn Pathol 2007;11:417). For the current case, both PAX8 (see image) and ER were positive.

Mediastinal Mullerian cysts are benign and there are no reports of recurrence after excision (usually performed thorascopically).

Test Question Answer:
D. Mullerian cysts should not have cartilage in the cyst wall.