In-Ho Kang; Jae-Yoon Chung; Kyung Nyeo Jeon; Hyo Jung An; Kyungsoo Bae

doi:10.12701/jyms.2025.42.44

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Posterior mediastinal Müllerian cyst: a rare but distinctive lesion: In-Ho Kang^1,*, Jae-Yoon Chung^1,*, Kyung Nyeo Jeon^2,3, Hyo Jung An⁴, Kyungsoo Bae^2,3; Journal of Yeungnam Medical Science 2025;42:44.
DOI: https://doi.org/10.12701/jyms.2025.42.44
Published online: August 15, 2025

¹Gyeongsang National University School of Medicine, Jinju, Korea

²Department of Radiology, Institute of Medical Science, Gyeongsang National University School of Medicine, Jinju, Korea

³Department of Radiology, Gyeongsang National University Changwon Hospital, Changwon, Korea

⁴Department of Pathology, Gyeongsang National University Changwon Hospital, Gyeongsang National University School of Medicine, Changwon, Korea

Corresponding author: Kyung Nyeo Jeon, MD, PhD Department of Radiology, Gyeongsang National University Changwon Hospital, Gyeongsang National University School of Medicine, 11 Samjeongja-ro, Seongsan-gu, Changwon 51472, Korea Tel: +82-55-214-3895 • Fax: +82-55-214-3134 • E-mail: knjeon@gnu.ac.kr

*These authors contributed equally to this work.

• Received: July 31, 2025 • Revised: August 10, 2025 • Accepted: August 13, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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A 52-year-old female presented with an incidental posterior mediastinal mass detected on routine chest radiography (Fig. 1A). She had no history of trauma or surgery and was in the early postmenopausal period without hormonal therapy. She was 161 cm tall, weighed 78 kg, and had a body mass index of 30.1 kg/m². Chest computed tomography (CT) revealed an approximately 4.3 cm low-density lesion in the right paravertebral region from T4 to T5 (Fig. 1B). Magnetic resonance imaging (MRI) confirmed a thin-walled cystic lesion (Fig. 1C, 1D). Differential diagnoses included a foregut cyst, neurogenic tumor with cystic degeneration, and mesothelial cyst based on the cystic nature and location of the lesion.

The patient underwent video-assisted thoracoscopic surgery. The lesion was located beneath the carina, adjacent to the azygos vein, and was firmly adherent to the spine (Fig. 2A). Clear serous fluid was released during the resection. Histopathological examination revealed a benign cyst lined with ciliated, non-mucinous, pseudostratified columnar epithelium. Immunohistochemical staining revealed estrogen receptor positivity, confirming the diagnosis of a mediastinal Müllerian cyst (Fig. 2B, 2C). The patient was discharged without complications, and no recurrence was observed during 2 years of follow‑up.

Although Müllerian cysts are typically found in the abdominopelvic region, they occasionally occur at atypical sites. Hattori proposed that Müllerian cysts may develop in the posterior mediastinum, establishing them as a distinct entity [1]. A plausible explanation is the aberrant migration or persistence of immature Müllerian duct cells in the mediastinum during fetal development [2]. In stage-16 embryos, a focally thickened coelomic epithelium, later forming the paramesonephric (Müllerian) bud, emerges at the cranial end of the mesonephric fold (Fig. 2D). This bud gives rise to the initial segment of the Müllerian duct, which eventually forms the fallopian tubes. This process occurs along the dorsal wall at approximately the third to fifth thoracic vertebral blastema, after which the duct elongates caudally toward the pelvis (Fig. 2E). The failure of these remnants to regress or migrate properly can lead to their persistence at ectopic locations [2,3]. Mediastinal Müllerian cysts are often found at the T3 to T5 level, which is consistent with their embryological origin. Radiologically, mediastinal Müllerian cysts are distinguished from more common foregut cysts by the former’s close contact with vertebrae, lower minimum-to-maximum diameter ratios, lower CT attenuation due to serous content, and reduced cyst-to-spinal cord signal intensity ratios on MRI [4].

Most mediastinal Müllerian cysts occur in women who are perimenopausal (mean age, 47–50 years). Estrogen is thought to contribute to cyst development, with associated risk factors including obesity and gynecologic history, such as hormone replacement therapy [3]. In women who are obese, elevated estrogen levels are attributed to increased aromatase activity in adipose tissue.

Histopathologically, a cyst lined by non-stratified, non-mucinous, ciliated cuboidal or columnar epithelium resembling fallopian tubes is a key diagnostic feature [4]. This diagnosis can be further confirmed by positive immunohistochemical staining for estrogen and progesterone receptors [5]. Surgical excision is generally recommended to confirm the diagnosis and mitigate the potential, albeit theoretical, risk of malignant transformation [3,5].

Due to their rarity, mediastinal Müllerian cysts are frequently overlooked in the differential diagnosis of mediastinal masses. They should, however, be considered among posterior mediastinal cystic masses, particularly in women who are perimenopausal or obese.

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Ethics statement

This study was approved by the Institutional Review Board (IRB) of the Gyeongsang National University Changwon Hospital (IRB No: 2025-07-019). The requirement for informed consent was waived because of the retrospective nature of the study and the use of anonymized data.

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Author contributions

Conceptualization: KNJ, HJA, KB; Formal analysis: all authors; Validation: KNJ; Investigation, Supervision, Visualization: KB; Methodology: IK, JYC, HJA; Resources: KNJ, HJA; Writing-original draft: IK, JYC; Writing-review & editing: KNJ, HJA, KB.

Fig. 1.

(A) Chest radiograph shows a well-circumscribed mass (arrow) in the posterior mediastinum. (B) Axial chest computed tomography image reveals an approximately 4.3 cm low-attenuation (~10 Hounsfield units) lesion in the right paravertebral region. (C) Coronal T2-weighted magnetic resonance image demonstrates a hyperintense cystic lesion extending from T4 to T5. (D) Axial post-contrast T1-weighted image with fat saturation shows no enhancement (arrow).

Fig. 2.

(A) Thoracoscopic view shows a cystic lesion located beneath the carina, adjacent to the azygos vein, and firmly adherent to the spine. (B) Histopathologic examination reveals a benign cyst lined by ciliated, non‑mucinous, pseudostratified columnar epithelium (hematoxylin and eosin stain, x200). (C) Immunohistochemical staining demonstrates estrogen receptor positivity in the epithelial lining, confirming the diagnosis of a Müllerian cyst. (D, E) Schematic illustration of Müllerian duct development. (D) In stage 16 embryos, a focal thickening of the coelomic epithelium appears at the cranial end of the mesonephric fold, forming the Müllerian bud. (E) This occurs along the dorsal wall at the third to fifth thoracic vertebral blastema, after which the duct elongates caudally toward the pelvis.

References

1. Hattori H. Ciliated cyst of probable mullerian origin arising in the posterior mediastinum. Virchows Arch 2005;446:82–4.Article PubMed PDF
2. Batt RE, Mhawech-Fauceglia P, Odunsi K, Yeh J. Pathogenesis of mediastinal paravertebral müllerian cysts of Hattori: developmental endosalpingiosis-müllerianosis. Int J Gynecol Pathol 2010;29:546–51.Article PubMed
3. Domedel Puig N, Cufí Quintana M, Escobedo Rodriguez V, Iglesias Sentís M, Gallego M. Bilateral mediastinal cysts with müllerian differentiation. Thorax 2024;79:796–7.Article PubMed
4. Kawaguchi M, Kato H, Hara A, Suzui N, Tomita H, Miyazaki T, et al. CT and MRI characteristics for differentiating mediastinal Müllerian cysts from bronchogenic cysts. Clin Radiol 2019;74:976.e19–25.Article PubMed
5. Saad Abdalla Al-Zawi A, Idaewor P, Asaad A, Harsten R, Salih V, English J, et al. Posterior mediastinal paravertebral Müllerian cyst (cyst of Hattori): literature review. Adv Respir Med 2020;88:134–41.Article PubMed

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Figure

Posterior mediastinal Müllerian cyst: a rare but distinctive lesion

Fig. 1. (A) Chest radiograph shows a well-circumscribed mass (arrow) in the posterior mediastinum. (B) Axial chest computed tomography image reveals an approximately 4.3 cm low-attenuation (~10 Hounsfield units) lesion in the right paravertebral region. (C) Coronal T2-weighted magnetic resonance image demonstrates a hyperintense cystic lesion extending from T4 to T5. (D) Axial post-contrast T1-weighted image with fat saturation shows no enhancement (arrow).

Fig. 2. (A) Thoracoscopic view shows a cystic lesion located beneath the carina, adjacent to the azygos vein, and firmly adherent to the spine. (B) Histopathologic examination reveals a benign cyst lined by ciliated, non‑mucinous, pseudostratified columnar epithelium (hematoxylin and eosin stain, x200). (C) Immunohistochemical staining demonstrates estrogen receptor positivity in the epithelial lining, confirming the diagnosis of a Müllerian cyst. (D, E) Schematic illustration of Müllerian duct development. (D) In stage 16 embryos, a focal thickening of the coelomic epithelium appears at the cranial end of the mesonephric fold, forming the Müllerian bud. (E) This occurs along the dorsal wall at the third to fifth thoracic vertebral blastema, after which the duct elongates caudally toward the pelvis.

Fig. 1.

Fig. 2.

Posterior mediastinal Müllerian cyst: a rare but distinctive lesion