399 CASE REPORT Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum Copyright (c) 2021 Slovenian Medical Journal. This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum: a case report Videotorakoskopska resekcija Hattorijeve ciste v posteriornem mediastinumu: prikaz primera Matic Domjan,1 Daja Šekoranja,2 Matevž Srpčič1 Abstract First reported by Hattori in 2004, the mediastinal cyst with Mullerian differentiation is a rather new finding. We present a case of a 51-year-old woman with a cystic formation in the left paravertebral space at the level of 4th and 5th thoracic verte- brae, which was discovered on an MRI scan. We have performed a video-assisted thoracosopic (VATS) resection of the cyst. Histological and immunohistochemical staining showed a ciliated cyst with Mullerian differentiation (i.e. Hattori’s cyst). To our knowledge, only 31 cases have been described in the literature so far. Data suggests their prevalence may be higher since they are often found incidentally and are typically asymptomatic. Izvleček Mediastinalna cista z Mullerjevo diferenciacijo, ki jo je odkril Hattori leta 2004, je sorazmerno nova najdba. Predstavljamo primer 51-letne bolnice s cistično formacijo v levem paravertebralnem prostoru na višini 4. in 5. prsnega vretenca, ki je bila odkrita z magnetno-resonančnim slikanjem (MRI). Napravili smo videotorakoskopsko (VATS) resekcijo ciste. Histomorfološko in imunohistokemično so bile spremembe v skladu s cisto z Mullerjevo diferenciacijo (t.i. Hattorijeva cista). Po naših podatkih je bilo v literaturi doslej objavljenih le 31 primerov. Upoštevajoč te podatke je verjetno prevalenca takšnih mediastinalnih cist višja, saj gre za naključno najdbo, ki praviloma ne povzroča simptomov. 1 Department of Thoracic Surgery, Division of Surgery, University Medical Centre Ljubljana, Ljubljana, Slovenia 2 Institute of Pathology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia Correspondence / Korespondenca: Matic Domjan, e: matic.domjan@gmail.com Key words: Hattori; mediastinum; Mullerian cyst; VATS Ključne besede: Hattori; mediastinum; cista z Mullerjevo diferenciacijo; VATS Received / Prispelo: 15. 3. 2020 | Accepted / Sprejeto: 24. 4. 2020 Cite as / Citirajte kot: Domjan M, Šekoranja D, Srpčič M. Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum: a case report. 2021;90(7–8):399–402. DOI: https://doi.org/10.6016/ZdravVestn.3049 eng slo element en article-lang 10.6016/ZdravVestn.3049 doi 15.3.2020 date-received 24.4.2020 date-accepted Cytology, oncology, cancerology Citologija, onkologija, kancerologija discipline Short scientific article Klinični primer article-type Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum: a case report Videotorakoskopska resekcija Hattorijeve ciste v posteriornem mediastinumu: prikaz primera article-title Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum Videotorakoskopska resekcija Hattorijeve ciste v posteriornem mediastinumu alt-title Hattori, mediastinum, Mullerian cyst, VATS Hattori, mediastinum, cista z Mullerjevo diferenci-acijo, VATS kwd-group The authors declare that there are no conflicts of interest present. Avtorji so izjavili, da ne obstajajo nobeni konkurenčni interesi. conflict year volume first month last month first page last page 2021 90 7 8 399 402 name surname aff email Matic Domjan 1 matic.domjan@gmail.com name surname aff Daja Šekoranja 2 Matevž Srpčič 1 eng slo aff-id Department of Thoracic Surgery, Division of Surgery, University Medical Centre Ljubljana, Ljubljana, Slovenia Klinični oddelek za torakalno kirurgijo, Univerzitetni klinični center Ljubljana, Ljubljana, Slovenija 1 Institute of Pathology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia Inštitut za patologijo, Medicinska fakulteta, Univerza v Ljubljani, Ljubljana, Slovenija 2 Slovenian Medical Journallovenian Medical Journal 400 CITOLOGY, ONCOLOGY, CANCEROLOGY Zdrav Vestn | July – August 2021 | Volume 90 | https://doi.org/10.6016/ZdravVestn.3049 1 Introduction A case of a ciliated cyst with Mullerian differentia- tion in the posterior mediastinum was first described by Hattori in 2004. He suggested Mullerian origin due to female preponderance of ciliated cysts as well as their morphological resemblance to fallopian tubes (i.e. cili- ated epithelium with underlying smooth muscle layer) (1). As similar reports of mediastinal cysts with Mulleri- an differentiation followed, it became increasingly clear that they are usually found in female patients aged 40 to 60 years, are often asymptomatic and their true in- cidence is still unknown (2-18). The general treatment recommendation for symptomatic and asymptomatic mediastinal cysts alike is surgical resection (19). 2 Case report We present a case of a 51-year-old woman referred to our outpatient clinic due to a cystic formation in the left paravertebral space, behind the aorta, at the level of 4th and 5th thoracic vertebrae (Figure 1). This well defined lesion was discovered on an MRI scan while running diagnostics for middle back pain. We opted for a vid- eo-assisted thoracoscopic surgery (VATS) resection of the cyst. Two 5 mm ports were made in the 4th intercostal Figure 1: Chest MRI showed a cystic formation in the left paravertebral space at the level of 4th and 5th thoracic vertebrae. space and one 11 mm port in the 5th intercostal space. The lung was retracted anteriorly to obtain good visual- ization of the aorta and the paravertebral cyst. The pa- rietal pleura was opened with a harmonic scalpel and the cyst dissected completely from the chest wall and the aorta. A 20 Fr chest tube was inserted through the incision in the anterior axillary line. The total duration of the procedure (skin to skin) was 32 minutes, there was no blood loss. Postoperative recovery was uneventful. The chest tube was removed on postoperative day one. Histologically, a unilocular cyst was present in the specimen. The cyst was lined by a single layer of non-stratified cuboid to columnar ciliated epithelium that included three different cell types, the ciliated, se- cretory and intercalated. The subepithelial lamina pro- pria was rather scarce, with smooth muscle surrounding the whole of the cyst (Figure 2A). The first morpholog- ical impression of the lesion was rather reminiscent of a fallopian tube. Immunohistochemically, epithelial cells were diffusely positive for WT1, PAX8 and ER (Fig- ure 2B-D), and uniformly negative for calretinin. Due to its histomorphological and immunohistochemical characteristics, the lesion was signed-out as mediastinal cyst with Mullerian differentiation, i.e. Hattori’s cyst. Figure 2: Hattori’s cyst in the posterior mediastinum (A), immunohistochemically positive for (B) PAX8, (C) WT1 and (D) oestrogen receptors (A- 1,25x magnification, B-D 10x magnification). 401 CASE REPORT Video-assisted thoracoscopic resection of a Hattori’s cyst in the posterior mediastinum On follow-up visit, the patient appeared to have no remarkable symptoms other than mild pain following the procedure, whereas the back pain persisted and did not change. 3 Discussion The treatment of choice for mediastinal cysts is complete resection, preferably by VATS. It will provide a definitive diagnosis, exclude the possibility of malig- nancy and prevent the development of symptoms and possible complications. Morbidity, mortality and re- currence rates associated with resection are very low. In patients unfit for surgery, CT-guided percutaneous fine-needle evacuation is a possible less invasive treat- ment modality, although its recurrence rates are higher (19,20). The presence of three types of cells in the cyst ep- ithelium (i.e. ciliated, secretory and intercalated) is typical for a fallopian tube-type epithelium. Mullerian differentiation was demonstrated immunohistochemi- cally with positive WT1, PAX8 and ER stains. In the differential diagnosis of mediastinal cysts one must also consider simple mesothelial cysts, thy- mic cysts and bronchogenic cysts. Simple mesothelial cysts are lined by a single layer of cuboidal, non-cili- ated epithelium, which is imunohistochemically WT1 and calretinin positive, and PAX8 and ER negative. In contrast to Hattori’s cysts, thymic cysts typically pres- ent in the anterior mediastinum and include remnants of thymic tissue in the cyst wall. Bronchogenic cysts are lined by ciliated epithelium, just like Hattori’s cyst, but in contrast to the latter, bronchogenic cyst epithe- lium contains goblet cells as well. Imunohistochemical characteristics differ, too, as bronchogenic cyst lack Mullerian differentiation and are therefore negative for WT1, PAX8 and ER. Reviewing the literature, we have found 31 reports of Hattori’s cysts described so far. Its true incidence is still unclear. Most papers on Hattori’s cysts are case re- ports or small case series with only one larger series reported so far by Thomas-de-Montpréville et al. They published a systematic analysis of 163 mediastinal cysts, nine (5.5%) of which showed Mullerian differen- tiation. Most reported Hattori’s cyst were asymptom- atic and accidental findings, suggesting that a vast ma- jority of these lesions probably go unrecognised and that their true incidence is underestimated (1-18). 4 Conclusion Mediastinal cysts with Mullerian differentiation are a rather newly described entity. Data suggests their prevalence may be higher since they are often space and one 11 mm port in the 5th intercostal space. The lung was retracted anteriorly to obtain good visual- ization of the aorta and the paravertebral cyst. The pa- rietal pleura was opened with a harmonic scalpel and the cyst dissected completely from the chest wall and the aorta. A 20 Fr chest tube was inserted through the incision in the anterior axillary line. The total duration of the procedure (skin to skin) was 32 minutes, there was no blood loss. Postoperative recovery was uneventful. The chest tube was removed on postoperative day one. Histologically, a unilocular cyst was present in the specimen. The cyst was lined by a single layer of non-stratified cuboid to columnar ciliated epithelium that included three different cell types, the ciliated, se- cretory and intercalated. The subepithelial lamina pro- pria was rather scarce, with smooth muscle surrounding the whole of the cyst (Figure 2A). The first morpholog- ical impression of the lesion was rather reminiscent of a fallopian tube. Immunohistochemically, epithelial cells were diffusely positive for WT1, PAX8 and ER (Fig- ure 2B-D), and uniformly negative for calretinin. Due to its histomorphological and immunohistochemical characteristics, the lesion was signed-out as mediastinal cyst with Mullerian differentiation, i.e. Hattori’s cyst. Figure 2: Hattori’s cyst in the posterior mediastinum (A), immunohistochemically positive for (B) PAX8, (C) WT1 and (D) oestrogen receptors (A- 1,25x magnification, B-D 10x magnification). 402 CITOLOGY, ONCOLOGY, CANCEROLOGY Zdrav Vestn | July – August 2021 | Volume 90 | https://doi.org/10.6016/ZdravVestn.3049 References 1. Hattori H. Ciliated cyst of probable mullerian origin arising in the posterior mediastinum. Virchows Arch. 2005;446(1):82-4. DOI: 10.1007/s00428-004- 1087-0 PMID: 15480767 2. Hattori H. High prevalence of estrogen and progesterone receptor expression in mediastinal cysts situated in the posterior mediastinum. Chest. 2005;128(5):3388-90. 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With the widespread use of minimal- ly invasive techniques, complete resection is the most sensible treatment of posterior mediastinal cysts since it provides a definitive histological diagnosis and pre- vents possible symptoms and complications. Conflict of interest None declared. Informed consent of the patient Written informed consent for publication was ob- tained from the patient.