Bullae of the Middle Lobe Ridge Deep in the Interlobar Fissure of Catamenial Pneumothorax Patients

All cases met CP criteria 1 ; the presence of endometrial tissue is not included as a criterion for the diagnosis of CP. Of the 12 patients treated at our institutions, 6 underwent surgical operation and 6 did not ( Supplemental Figure 1 ). Of the 6 who did not undergo surgery, 3 had right middle lobe blebs noted on chest computed tomography (CT). Of the 6 patients who underwent surgery, 5 had blebs in the right middle lobe, and 3 of those 5 patients had endometrial tissue on final pathologic examination. The remaining patient who underwent surgery did not have the middle lobe examined. A 46-year-old woman had repeated right pneumothorax during her menstruation for 3 years and was diagnosed with CP clinically. She had a bulla in the RMLR on CT ( Figure 1 A). Intraoperatively, we found lesions suggestive of endometrial tissue in the diaphragm and a bulla in the RMLR that was resected ( Figure 2 A). No endometrial tissue was found in the resected bulla. Figure 1 Chest computed tomography showing the interlobar fissure intersection. Cases 1, 3, 4, and 5 showed bullae in the middle lobe ridge in the interlobar fissure (arrowhead). Supplemental Figure 2 includes all cases. Figure 2 Interoperative images. Cases 2 ( Video ) and 5 had active leakage during operation. Chest computed tomography showing the interlobar fissure intersection. Cases 1, 3, 4, and 5 showed bullae in the middle lobe ridge in the interlobar fissure (arrowhead). Supplemental Figure 2 includes all cases. Interoperative images. Cases 2 ( Video ) and 5 had active leakage during operation. A 41-year-old woman had a diagnosis of endometriosis. She had repeated right pneumothorax during her menstruation for 3 years. Multiple CT studies, including past examinations, showed no abnormalities without collapse of the lung ( Supplemental Figure 1 ). She underwent drainage for this onset, and surgery was performed for prolonged leakage ( Video ). We found a bulla in the RMLR with active leakage, which was resected and revealed endometrial tissue ( Figure 2 B). The patient, a 43-year-old woman, underwent surgery for right pneumothorax 5 years ago and was diagnosed with CP. She started hormone therapy, but when it was discontinued, she had pneumothorax relapse during menses. Annual medical checkup revealed right pneumothorax, and CT revealed a bulla in the RMLR ( Figure 1 B). Surgery was performed, and the bulla was resected ( Figure 2 C). No endometrial tissue was found in the resected bulla. A 51-year-old woman had asthma. She was diagnosed with right pneumothorax 3 months before and followed up. Pneumothorax improved and exacerbated repeatedly. We performed chest drainage because of progressive lung collapse. She underwent surgery because CT showed a bulla in the RMLR ( Figure 1 C). The bulla was resected and revealed endometrial tissue. A 48-year-old woman had right pneumothorax. Although she had experienced right-sided chest pain in the past regardless of menstruation, she did not seek medical attention. She had a bulla in the RMLR on CT ( Figure 1 D). She underwent drainage, and surgery was performed for prolonged leakage. We found a bulla in the RMLR with active leakage ( Figure 2 D), which was resected and revealed endometrial tissue.

Our findings suggest that bullae associated with ectopic endometriosis are likely to develop in the RMLR of the interlobar fissure in patients with CP. Of the 12 patients with CP treated at both hospitals between January 2011 and December 2022, 5 of the 6 patients who underwent surgical treatment had bullae in the RMLR. Two of them also had obvious air leakage intraoperatively and demonstrated endometrial tissue in the resected specimen. A previous study reported air leakage and ectopic endometrial tissue in resected bullae from patients with catamenial/endometriosis-related pneumothorax. 3 In addition, our report presents novel findings of localization of bullae. The presence of ectopic endometrial tissue observed in resected specimens suggests that there is a relationship with the new formation of bullae as reported in previous studies. 2 , 3 However, a definitive answer for why bullae tend to form in the RMLR of the interlobar fissure remains to be elucidated. We propose that 1 of the causes of ectopic endometriosis is the metastatic hypothesis. 4 As the RMLR in the interlobar fissure has a sharp angle, endometrial tissue may be easily trapped because of the anatomic structure and shedding tissue, which leads to the formation of a new bulla as the ridge is thin and makes a check valve easier. Newly formed bullae not only rupture during menstruation but develop spontaneous pneumothorax characteristics. 3 This is supported by reports that 7.0% to 10.1% of noncatamenial endometriosis-related pneumothorax cases demonstrated thoracic endometriosis. 1 , 5 We also experienced cases 8 and 11, in which patients who were clinically diagnosed with CP gradually began to feel chest pain other than during menstruation. In these cases, CT showed a new bulla at the RMLR. Thus, it is necessary to pay attention to the presence of ectopic endometriosis and bullae in the RMLR in female patients with pneumothorax irrespective of the menstrual cycle. In case 3, only the diaphragm surface and the lung apex were confirmed at the first operation, and pneumothorax repeated after that. CT revealed a bulla in the RMLR, so we performed reoperation and resected the bulla. Similarly, previous studies reported that bullae in the middle lobe were found during reoperation. 6 , 7 Considering that case 2 had no bullae on preoperative CT, bullae in this area could not be confirmed on CT. Therefore, in performing surgical treatment of catamenial/endometriosis-related pneumothorax, it is important to search the RMLR in the interlobar fissure. There were 6 cases without surgery; 4 patients were managed by physicians who opted for hormone therapy without surgery, and 2 patients did not wish to undergo surgery. Among these, CT findings suggestive of bullae in the RMLR were observed in 3 cases. During the surgery of case 6, a patient who was not under the care of the authors, only the diaphragm was observed, and diaphragm resection was performed. However, the patient relapsed after surgery. Although the characteristic diaphragmatic findings may be attractive, the bullae seen in patients with catamenial/endometriosis-related pneumothorax are also the result of ectopic endometriosis. In the case of catamenial/endometriosis-related pneumothorax, we propose that physicians should suspect bullae at the RMLR from the beginning of treatment; and in cases of recurrence despite blind apical wedge resection, adhesion therapy, and hormone therapy, physicians should check for the presence of occult bullae, especially of the RMLR in the interlobar fissure. In conclusion, intrathoracic endometriosis may develop new bullae of the RMLR in the interlobar fissure, which can cause air leakage. In patients with catamenial/endometriosis-related pneumothorax, it is necessary to confirm the RMLR in the interlobar fissure by intraoperative findings and CT.