Aberrant malignant invasive thymoma presenting as isolated left internal jugular vein thrombosis.and resected by VATS thymectomy: a case report

Introduction

Thymomas often present as incidental anterior mediastinal masses or with local compressive symptoms or paraneoplastic syndromes. This case report describes a rare occurrence of isolated internal jugular vein thrombosis caused by venous compression from an anomalous left lobe thymoma arising behind the innominate vein. Though superior vena cava (SVC) thrombosis has been frequently reported previously, this is the first reported case of isolated jugular vein thrombosis due to compression by an aberrant thymoma arising from an anomalous accessory thymus located behind the innominate vein. This article is presented in accordance with the CARE reporting checklist (available at https://med.amegroups.com/article/view/10.21037/med-2025-1-62/rc).

Case presentation

This is a case report of an unusual presentation of malignant thymoma. Patient is a 51-year-old male who noticed prominent left neck veins during shaving in front of a mirror for 1 month duration. Ultrasound of neck veins revealed left internal jugular vein thrombosis. CT scan of the neck and thorax showed a 5 cm anterior mediastinal thymoma compressing the posterior wall of the left innominate vein and internal jugular subclavian vein junction (Video 1). Patient was started on oral anticoagulant with resolution of venous thrombosis within a week. Clinically, the patient had no associated myasthenia gravis (MG) or paraneoplastic syndromes. Patient underwent a left video-assisted thoracoscopic surgery (VATS) radical thymectomy. As the tumour was abutting the left innominate vein informed consent was obtained preoperatively for possible conversion to median sternotomy in the event of intraoperative venous injury.

The author’s VATS “no-touch, tumour last” oncological technique for thymomas has previously been reported (1). General anaesthesia was induced and lung isolation obtained using a left-sided double-lumen endotracheal tube supplemented with carbon dioxide insufflation (5–8 mmHg pressure at 4 L/min flow rate). This helps with rapid deflation of the lung and opening of mediastinal tissue planes, especially to the horns in the neck. The patient was positioned at 30 degrees in a semi-supine position with a roll placed under the shoulder with the left arm abducted over a padded L-screen for exposure of the axilla. As the tumour was compressing and near the left innominate, internal vein junction, this approach facilitated quick conversion to median sternotomy in the event of intraoperative bleeding

A 3-port VATS technique was used (Figure 1). Intraoperative findings were those of a locally invasive malignant thymoma arising from the left lobe and horn of the thymus, located anomalously behind the left innominate vein. The whole left lobe and left superior horn were arising completely behind the innominate vein with no accessory extension above the vein. The right superior horn and lobe, as usual, was traversing the superior aspect of the left innominate vein. The malignant thymoma arising from the left lobe behind the vein was causing mechanical compression of the innominate and internal jugular vein junction at the left thoracic inlet, causing thrombosis of the internal jugular vein. There was no local invasion of the vein. Tumour was also noted to have invaded the left phrenic nerve and abutted the left vagus and recurrent laryngeal nerves (RLNs). A radical en bloc removal of the tumour together with the surrounding normal thymus, perithymic fat and left phrenic nerve was done. No intraoperative reconstruction of the phrenic nerve was done. The left vagus and recurrent nerves were identified and preserved with careful dissection (Figure 1, Video 2).

Figure 1 Port placements for right VATS thymectomy. VATS, video-assisted thoracoscopic surgery.

Post op recovery was uneventful. Final histology showed an 11 cm × 5.1 cm × 2.3 cm thymic specimen with a 5.5 cm × 3.9 cm × 2.1 cm stage 2 World Health Organisation (WHO) Type B2 thymoma (Figure 1). Mediastinal radiotherapy was given postoperatively. One-year post-surgery surveillance CT scan of the thorax showed no tumour recurrence except mild elevation of the left hemidiaphragm. As the patient was well and asymptomatic, diaphragmatic plication was not recommended presently.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report, accompany images and videos. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Up to 30% of thymomas are asymptomatic and detected incidentally on chest X-ray or CT scan. Another 30% presents as paraneoplastic syndrome with the rest presenting, with local compressive symptoms like cough, chest pain, palpitations, SVC syndrome, dysphagia, and hoarseness (2). Though SVC syndrome from local invasion is well described in the literature, thrombosis from local limited obstruction of the internal jugular vein has not been reported previously. In our patient, as the thymoma was arising from an anomalous left thymic lobe behind the innominate vein, it was causing obstruction with thrombosis of the internal jugular at the thoracic inlet.

Anatomically, a normal thymus is classically a bilobed H or butterfly-shaped gland with 2 superior and inferior horns, with the superior horns traversing the superior aspect of the left innominate vein. The foetal thymus develops in the neck from the 3^rd pharyngeal pouch together with the inferior parathyroid gland as the thymopharyngeal duct. It progressively reaches the mediastinum by birth, undergoing involution after puberty, and is completely replaced by fat in adults (3). Due to these embryological and age-related changes, the thymus can have important surgical variations in the neck, mediastinum, or both in up to 82% of patients. These anatomical variations can be ectopic, aberrant, or accessory (3-7).

Ectopic thymic tissue can be found in up to 40% to 70% of patients (4). It is due to the implantation of disrupted, persistent, and undescended thymic tissue islets separated from the main gland during its foetal descent, from the angle of the mandible to the upper mediastinum (5). It is commonly found in the adipose tissue of the cervical pretracheal area below the thyroid, anterior mediastinum, perithymic fat lateral to the phrenic nerves, retroinnominate vein, bilateral pericardial fat pads, aortocaval groove, aortopulmonary window and rarely intrathyroidal. or above the thyroid notch (4-10).

Aberrant variations are due to the anomalous location of the thymic lobes or horns. Commonest is cervical extension of the thymus extending anywhere from the thyroid gland to the suprasternal notch (50%). Very rarely, it can extend above the thyroid notch (3). Other aberrant variations are the anomalous location of the thymus lobe and superior horns behind the innominate vein, fibrous connection to the thyroid gland and extension of the lobe to the diaphragm. Rarely, the superior horn may retain its thymopharyngeal duct connection extending up to above the suparathyroid notch (3,8-10).

Accessory variations are due to additional accessory lobes or horns (3-5,10). The thymus can be bilobed (74%) or multilobed (3 to 5 lobes) in 26% and very rarely unilobed. Accessory cervical thymic lobe can present as a neck extension of the main gland. The thymus may appear unilobed when one lobe is arising behind the innominate vein due to partial coverage of the overlying lobe (3,5,10). Accessory horns, when present, are typically found under the innominate vein and may extend laterally to the phrenic nerves (Video 3).

Awareness of these variations and anomalies is important when performing radical thymectomy for MG, as incomplete surgery will affect long-term neurological outcomes (4,7,11-13). Many of these anatomical thymic variations are difficult to diagnose preoperatively by current radiological modalities. In this patient, contrast-enhanced CT scan of the thorax made it possible to diagnose preoperatively the anomalous posterior origin of the thymoma arising behind the left innominate vein with compression rather than invasion of the venous wall. This information helped in planning and adopting a minimally invasive approach (Video 1).

In the absence of MG, some advocate removal of only the thymoma (thymomectomy) without the rest of the normal thymus. Though this may make the technical removal of thymoma by a minimally invasive approach easier, it may not be oncologically optimal (11,13). Optimal surgery in all thymomas, irrespective of MG status, should be a radical thymectomy. The radical en bloc removal of the whole thymus and perithymic fat together with the tumour ensures an oncologically complete R0 resection with clear surgical margins and a concomitant mediastinal nodal dissection of the N1 anterior thymic lymph nodes. It reduces the 5% risk of developing recurrence in the remnant thymus from multifocal thymomas. It also avoids the need for repeat remnant thymectomy in the 10% of thymoma patients who develop MG postoperatively (1,13-16).

Unlike in VATS thymectomy for non-thymomatous MG, when performing VATS for thymomas, it is important to do a ‘no touch’ oncological technique with minimal handling of the thymoma to reduce risks of capsular injury and tumor seeding (1,14-17). In this technique, the side of the surgical approach should be from the same side as the main tumour to allow for safe dissection of the main tumour under direct vision (1). The non-tumour part of the thymus and surrounding perithymic fat should routinely be dissected first, leaving the dissection of the tumour last. This allows the initial circumferentially dissected normal thymus and perithymic tissue to be used for traction and grasping during dissection of the main tumour, thus minimising the risk of tumour capsular injury. If the tumour is dissected first, the weight of the tumour under gravity, especially if bulky, would obstruct the surgical field of vision and make subsequent dissection of the rest of the gland difficult and oncologically hazardous (1). Extreme caution should be exercised when resecting cystic thymomas by VATS due to the high risk of possible rupture of these thin-walled tumours.

Early dissection and caudal traction of the main thymus and its perithymic tissue from the innominate vein, pericardium, and mediastinum helps in the delivery of the superior horns and cervical thymic lobes, especially when they are hyperplastic and extend deep into the neck. All specimens should be removed via an Endo bag by appropriate enlargement of the utility incision to prevent tumour seedling When associated with MG. Intraoperative completeness of thymectomy should be done routinely by anatomical examination of the resected specimen and inspection of the surgical bed for remnant ectopic and perithymic tissue (Figures 1,2). Adopting the principles of this technique in this patient allowed the thymoma to be dissected from under the vein safely without resorting to a sternotomy (Video 2) (1,14-17).

Figure 2 Resected thymus specimen.

Injury to phrenic nerves can be avoided by routine identification of both nerves by opening the contralateral pleura and dissecting them under direct vision, avoiding thermal injury from electrocautery (17). If one phrenic nerve is involved by cancer, it can be sacrificed safely with possible prophylactic concomitant diaphragmatic plication. If prophylactic diaphragmatic plication is planned pre-operatively, it is best to do thymectomy in a lateral decubitus position, as plication can be technically difficult in the supine position (1).

Conclusions

Anomalous thymomas arising from the aberrant left lobe below the innominate vein, though rare, may present as localised internal jugular vein thrombosis. In the absence of direct venous invasion, they are amenable to be removed by VATS using the “no touch, tumour last” oncological technique.

Acknowledgments

None.

Footnote

Reporting Checklist: The author has completed the CARE reporting checklist. Available at https://med.amegroups.com/article/view/10.21037/med-2025-1-62/rc

Peer Review File: Available at https://med.amegroups.com/article/view/10.21037/med-2025-1-62/prf

Funding: None.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at https://med.amegroups.com/article/view/10.21037/med-2025-1-62/coif). The author has no conflicts of interest to declare.

Ethical Statement: The author is accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report, accompany images and videos. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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