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Learn more: PMC Disclaimer | PMC Copyright Notice Front Surg . 2026 Mar 26;13:1790499. doi: 10.3389/fsurg.2026.1790499 Search in PMC Search in PubMed View in NLM Catalog Add to search Discovery and management of accessory hemidiaphragm during video-assisted thoracoscopic segmentectomy for pulmonary nodule: a case report Yijun Fan Yijun Fan 1 West China School of Medicine, Sichuan University, Chengdu, China Visualization, Writing – review & editing, Writing – original draft Find articles by Yijun Fan 1, † , Tingrui Mei Tingrui Mei 2 Department of Thoracic Surgery, West China Hospital, Sichuan University, Chengdu, China 3 Lung Cancer Center / Lung Cancer Institute, West China Hospital, Sichuan University, Chengdu, China Writing – original draft, Writing – review & editing Find articles by Tingrui Mei 2, 3, † , Lei Liu Lei Liu 2 Department of Thoracic Surgery, West China Hospital, Sichuan University, Chengdu, China 3 Lung Cancer Center / Lung Cancer Institute, West China Hospital, Sichuan University, Chengdu, China Writing – review & editing, Writing – original draft Find articles by Lei Liu 2, 3, † , Xiaoling Gu Xiaoling Gu 3 Lung Cancer Center / Lung Cancer Institute, West China Hospital, Sichuan University, Chengdu, China Writing – original draft, Resources Find articles by Xiaoling Gu 3 , Ya Gou Ya Gou 4 West China Medical Technology Transfer Center, Chengdu, Sichuan, China Writing – original draft, Resources Find articles by Ya Gou 4 , Lin Jiang Lin Jiang 4 West China Medical Technology Transfer Center, Chengdu, Sichuan, China Writing – original draft Find articles by Lin Jiang 4 , Jingsi Dong Jingsi Dong 2 Department of Thoracic Surgery, West China Hospital, Sichuan University, Chengdu, China 3 Lung Cancer Center / Lung Cancer Institute, West China Hospital, Sichuan University, Chengdu, China Writing – original draft, Supervision, Conceptualization Find articles by Jingsi Dong 2, 3, * Author information Article notes Copyright and License information 1 West China School of Medicine, Sichuan University, Chengdu, China 2 Department of Thoracic Surgery, West China Hospital, Sichuan University, Chengdu, China 3 Lung Cancer Center / Lung Cancer Institute, West China Hospital, Sichuan University, Chengdu, China 4 West China Medical Technology Transfer Center, Chengdu, Sichuan, China * Correspondence: Jingsi Dong [email protected] † These authors have contributed equally to this work Roles Yijun Fan : Visualization, Writing – review & editing, Writing – original draft Tingrui Mei : Writing – original draft, Writing – review & editing Lei Liu : Writing – review & editing, Writing – original draft Xiaoling Gu : Writing – original draft, Resources Ya Gou : Writing – original draft, Resources Lin Jiang : Writing – original draft Jingsi Dong : Writing – original draft, Supervision, Conceptualization Received 2026 Jan 18; Revised 2026 Feb 27; Accepted 2026 Mar 10; Collection date 2026. © 2026 Fan, Mei, Liu, Gu, Gou, Jiang and Dong. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. PMC Copyright notice PMCID: PMC13063294 PMID: 41971064 Abstract An accessory hemidiaphragm is a rare congenital intrathoracic malformation characterized by a fibromuscular diaphragm located superior to the normal diaphragm, typically featuring a central hiatus through which pulmonary vessels and bronchi traverse. This anomaly is often associated with scimitar syndrome. We present a unique case of an isolated accessory hemidiaphragm—devoid of the characteristic vascular anomalies typical of scimitar syndrome—discovered incidentally during thoracoscopic surgery performed for a pulmonary nodule. This report elaborates the rationale for performing a concurrent partial membranectomy and underscores the necessity of an individualized surgical strategy in such cases. Keywords: accessory hemidiaphragm, case report, membranectomy, segmentectomy, video-assisted thoracoscopic surgery Introduction An accessory hemidiaphragm is an exceptionally rare congenital anomaly, with only about 40 cases reported worldwide. This report details a unique case discovered incidentally during uniportal VATS segmentectomy for a pulmonary nodule. The distinctiveness lies in its isolated presentation—characterized by cardiac dextroposition but without the core anomalous pulmonary venous return of scimitar syndrome—and its proactive surgical management. Unlike conservative approaches, a concurrent total membranectomy was performed. This was a prospective, functionally-driven decision to eliminate the membrane's mechanical barrier, thereby optimizing post-resection lung expansion and thoracic remodeling. This case highlights the necessity of individualized surgical strategies when such anomalies are encountered incidentally. Case presentation A 27-year-old female presented with complaints of “occasional chest tightness and decreased exercise tolerance.” Preoperative computed tomography (CT) revealed a pure ground-glass nodule located in the apical segment of the right upper lobe. Upon follow-up, the nodule had evolved into a mixed ground-glass nodule with a maximum diameter of approximately 1.0 cm ( Figures 1a–c ). The consolidation-to-tumor ratio (CTR) had increased from 0.35 at initial detection to 0.63 on the most recent CT scan prior to surgery ( Figures 1a–c ). One month prior to surgery, a CT scan was repeated following a 7-day course of oral moxifloxacin, which showed persistence of the nodule. The nodule was located adjacent to the pleural surface, posing a potential risk of pleural dissemination if malignant ( 1 ). In addition, the patient experienced significant anxiety and strongly requested surgical resection. Considering that the nodule could be easily localized intraoperatively, the surgical risk was low, and the planned resection would result in minimal loss of pulmonary function, surgical resection was recommended after thorough discussion with the patient. Figure 1. Open in a new tab The diagnostic and therapeutic imaging workflow: preoperative nodule follow-up, identification of accessory hemidiaphragm, and postoperative assessment. (a–c) Serial preoperative follow-up chest CT images of the pulmonary nodule in the right lung. (a) January 2025, CTR=0.35 (b) April 2025, CTR=0.38 (c) October 2025, CTR=0.63. (d, e) Preoperative axial chest CT images illustrating the accessory hemidiaphragm. (d) The black arrow highlights the accessory hemidiaphragm appearing as a continuous linear high-density structure. (e) Detailed view of the hiatus. The black arrowhead indicates the accessory hemidiaphragm. Key structures traversing the hiatus are annotated: black hollow arrowhead, medial basal segmental bronchus (B7); white hollow arrowhead, anterior basal segmental bronchus (B8); black long arrow, posterior basal segmental bronchus (B10); white long arrow, lateral basal segmental bronchus (B9). (f,g) Preoperative CT images with three-dimensional segmentation. (f) Sagittal view. The black arrow traces the accessory hemidiaphragm, showing its anterior attachment to the diaphragmatic pleura and posterior attachment to the pleura at the 6th/7th intercostal space. (g) Axial view. The black arrow indicates the accessory hemidiaphragm. The red area outlines the hypoplastic right lower lobe as segmented by the software. (h, i) Postoperative axial chest CT images at 1-month follow-up. Both images demonstrate well-expanded residual lung tissue, satisfactory thoracic cavity remodeling, and absence of significant atelectasis or inflammatory changes. The patient underwent a uniportal video-assisted thoracoscopic surgery (VATS) with a planned right upper lobe apical segmentectomy. Intraoperative exploration confirmed the presence of the nodule. The most significant finding was an anomalous membrane completely separating the right lower lobe, through which the right lower lobe artery, vein, and bronchus traversed. Furthermore, multiple clusters of micronodular whitish patches were observed in the lung parenchyma adjacent to the membranous attachment, consistent with subpleural fibroplasia induced by chronic mechanical friction ( Figure 2 ). After apical segment resection of the lung, the abnormal membranous tissue was completely resected using an ultrasonic scalpel, fully exposing the right lower lobe. The procedure was completed successfully. Postoperatively, the patient received patient-controlled analgesia (PCA) with hydromorphone hydrochloride combined with ondansetron. The recovery was smooth: the chest drain was removed on postoperative day 2, and the patient was discharged on day 4. Postoperative pathology confirmed the pulmonary lesion to be a chronic inflammatory process, and the accessory membrane was identified as a fibromuscular structure ( Figure 3 ). Figure 2. Open in a new tab Intraoperative findings and surgical management of the accessory hemidiaphragm. (a–c) Before intervention. (a, b) Intraoperative views showing the accessory hemidiaphragm (white arrows). Black arrows indicate clusters of micronodular whitish patches on the adjacent lung parenchyma near the membranous attachment. (c) Dissection of the accessory hemidiaphragm to expose the underlying normal lung tissue, revealing its elastic and resilient membranous nature. (d–f) During resection. (d) Incision of the membrane using surgical instruments; the black arrow marks the cutting edge. (e) The membrane after detachment from one side of its attachment (black arrow). (f) The cut edge of the membrane (black arrow) remains at a distance from the chest wall, minimizing the risk of vascular injury and bleeding. (g–i) After resection. (g) The resection margin of the membrane (white arrow) and adjacent clustered whitish patches (black arrow). (h) View of the resection margin (white arrow). (i) Residual membrane after partial resection (white arrow). The black long arrow indicates the right lower lobe, and the black arrowhead points to the right middle lobe. Figure 3. Open in a new tab Pathological findings of the abnormal membrane and the lung nodule. (a–c) Abnormal membrane: (a) Smooth muscle tissue. (b) Vascular structures within the membrane. (c) Well-arranged fibrous tissue. (d–f) Postoperative pathology of lung nodule, consistent with chronic inflammation: (d) Cholesterol granuloma. The red arrow indicates epithelioid cells; the black arrow indicates infiltrating inflammatory cells; the red triangle marks fibrous tissue. Slit-like cholesterol clefts are present within the lesion. (e) Bronchiole. The red arrow points to ciliated columnar epithelium; the black arrow indicates the circular smooth muscle layer. Inflammatory exudate is visible within the lumen. (f) The boxed area shows congested alveolar septal vessels. The black arrow indicates focal alveolar epithelial hyperplasia. A postoperative review of the preoperative CT images clearly delineated the membrane. In the left sagittal CT view, the membrane was displayed as a complete linear structure extending anteroinferiorly to posterosuperiorly, with its anterior end attaching to the diaphragmatic pleura and its posterior end attaching to the pleura at the level of the 6th/7th intercostal space. Axial CT images demonstrated the vascular structures of the right lower lobe traversing the membrane, and obvious cardiac dextroposition was also noted ( Figures 1d–g ). Discussion The accessory hemidiaphragm typically features a central defect through which vital structures such as the pulmonary artery, pulmonary veins, and bronchi pass ( 2 ). The incidence of accessory hemidiaphragm is extremely low; according to a review by Radhakrishnan et al., approximately 40 confirmed cases were reported globally by 2014, with only 9 cases in adults ( 3 ). The clinical spectrum is broad, ranging from complete absence of symptoms to recurrent respiratory infections and respiratory distress due to lung compression, pulmonary hypoplasia, or associated cardiovascular anomalies (e.g., scimitar syndrome) ( 4 ). Beyond the accessory hemidiaphragm, our patient was also found to have dextroposition of the heart and mild hypoplasia of the right lung; however, they lacked the anomalous pulmonary venous return, aberrant systemic arterial supply, and other core features characteristic of classic scimitar syndrome ( 5 ). Therefore, we classified this case as an “isolated accessory hemidiaphragm”. The distinctive feature of this case lies in the proactive management of the accessory hemidiaphragm during the segmentectomy performed for the pulmonary nodule. Current literature suggests that asymptomatic cases can be observed ( 3 ). Iijima et al., in a case involving pulmonary metastasis, proposed that incision at the membranous hiatus during concurrent thoracic surgery is sufficient to prevent complications such as lung herniation or vascular compression ( 6 ). In our patient, however, the planned right upper lobe apical segmentectomy would lead to upward shift and re-expansion of the remaining middle and lower lobes. Leaving the intact accessory membrane in place would have created a rigid mechanical barrier, severely limiting postoperative lung expansion and thoracic remodeling, thereby increasing the risk of atelectasis and impaired functional recovery. Consequently, we proactively performed a whole membranectomy. This decision was not due to intraoperative obstruction but was a prospective measure to optimize functional outcome ( Figure 4 ). Figure 4. Open in a new tab A management mind map for accessory hemidiaphragm encountered during radical resection of lung cancer. Postoperatively, the patient reported marked alleviation of preoperative chest tightness and exertional dyspnea. Postoperative pulmonary function testing showed a mild decline compared to preoperative values, which was considered acceptable given that the patient was still in the early recovery phase ( Table 1 ). Follow-up imaging confirmed well-expanded residual lung tissue and satisfactory thoracic configuration without significant atelectasis ( Figures 1h, i ). Taken together, the clinical symptoms, imaging findings, and pulmonary function assessment support the functional benefit of the combined procedure. Table 1. Perioperative changes in pulmonary function. Pulmonary function index Preoperative Postoperative (1 month) FVC [L] 2.97 2.83 FEV1 [L] 2.54 2.36 FEV1% 78.3% 74.6% MVV [L/min] 101.6 94.4 MVV% 87.8% 82.8% DLCO [mmol/min/kPa] 9.43 8.15 DLCO% 99.9% 88% Open in a new tab Conclusion We report a rare case of an isolated accessory hemidiaphragm discovered during segmentectomy for a pulmonary nodule. The particularity of this case lies in the proactive partial membranectomy performed to optimize post-resection lung expansion and thoracic remodeling. This case also highlights the diagnostic challenges associated with this anomaly: despite performing three-dimensional reconstruction and multi-planar analysis of CT images, including axial, sagittal, and coronal views, no characteristic radiographic features were identified that could precisely delineate the abnormal membrane. Only subtle findings suggestive of fibrotic thickening of the interlobar fissure were observed. This underscores the difficulty in definitively identifying an accessory hemidiaphragm using current imaging techniques. For patients with an accessory hemidiaphragm found during surgery for other thoracic conditions, surgeons should comprehensively evaluate its mechanical impact on postoperative physiology and formulate an individualized management plan to achieve optimal functional recovery. For accessory hemidiaphragmatic malformation incidentally detected intraoperatively during thoracic surgery, concomitant resection of the accessory hemidiaphragm is recommended to avoid impairing pulmonary re-expansion and secondary remodeling of intrathoracic organs. Funding Statement The author(s) declared that financial support was not received for this work and/or its publication. Footnotes Edited by: Duilio Divisi , University of L'Aquila, Italy Reviewed by: Andrea De Vico , Azienda Usl Teramo, Italy Diego Gavezzoli , Sacro Cuore Don Calabria Hospital (IRCCS), Italy Data availability statement The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author. Ethics statement The studies involving humans were approved by Ethics Committee of West China Hospital, Sichuan University. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article. Author contributions YF: Visualization, Writing – review & editing, Writing – original draft. TM: Writing – original draft, Writing – review & editing. LL: Writing – review & editing, Writing – original draft. XG: Writing – original draft, Resources. YG: Writing – original draft, Resources. LJ: Writing – original draft. JD: Writing – original draft, Supervision, Conceptualization. Conflict of interest The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Generative AI statement The author(s) declared that generative AI was not used in the creation of this manuscript. Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us. Publisher's note All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher. References 1. Jiang L, Liang W, Shen J, Chen X, Shi X, He J, et al. The impact of visceral pleural invasion in node-negative non-small cell lung cancer a systematic review and meta-analysis. Chest. (2015) 148(4):903–11. 10.1378/chest.14-2765 [ DOI ] [ PubMed ] [ Google Scholar ] 2. Al-Yamani M, Kreitmann B, Thambo JB, Roubertie F. Right thoracotomy to repair scimitar syndrome and an accessory hemidiaphragm. Ann Thorac Surg. (2016) 102(4):E317–9. 10.1016/j.athoracsur.2016.03.022 [ DOI ] [ PubMed ] [ Google Scholar ] 3. Radhakrishnan J, Bean J, Piazza DJ, Chin AC. Accessory hemi diaphragm. J Pediatr Surg. 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Data Availability Statement The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author. 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