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Radical Transsternal Thymectomy

David Park Mason, MD

bnormalities of the thymus comprise more than half of
Athe lesions found in the anterior mediastinal compartment in adults. Greater than 95% of the tumors of the thymus are thymomas that originate from thymic epithelial cells. They generally present as an incidental radiographic finding. They are of surgical importance both as isolated entities as well as in association with myasthenia gravis (MG). Surgical excision is the cornerstone of therapy for thymoma.1 In addition, thymectomy is an integral component of the management of myasthenia gravis.
Ludwig Rehn performed the first thymic operation in 1896, a transcervical exothymopexy for a patient with an enlarged thymus causing episodes of suffocation.2 He pulled the enlarged thymus out of the mediastinum and performed a pexy of the thymic capsule to the posterior aspect of the manubrium. Transcervical thymic surgery was generally the preferred route until the 1930s. In 1936, Dr. Alfred Blalock performed the first successful transsternal thymectomy through an upper median sternotomy in a patient with myasthenia gravis and a large anterior superior mediastinal tumor.3
Radical transsternal resection evolved from this approach and the surgical technique now focuses on the en bloc resection of the entire thymus and pericardial fat pad from the thyroid gland down to the diaphragm and laterally to the phrenic nerves. This is performed through a full sternotomy. Advantages of this approach are direct and safe access to the entire anterior mediastinum. Opening the pleural spaces allows visualization and preservation of the phrenic nerves. Advocates of this approach feel that radical resection is the technique that is most likely to remove all thymic tissue and give the highest likelihood of cure, particularly in the setting of myasthenia gravis.4,5 They point to the fact that even small portions of remnant thymic tissue has been associated with recurrent myasthenic symptoms and that reoperation after transcervical thymectomy has been required for resection of remnant tissue.6 generalized enlargement of the thymic gland caused by diffuse thymocyte proliferation. Thymic hyperplasia is an immunologic condition.10 In children, thymic hyperplasia can be associated with a variety of endocrine disorders including hyperthyroidism. In adults, thymic hyperplasia has been associated with thymoma as well as many immune dysfunction syndromes—the most notable being myasthenia gravis. Removal of the thymus gland, by a variety of surgical approaches, appears to influence the immune dysfunction observed in myasthenia gravis.7 The mechanism of this influence, and the relative benefit of removing all residual or ectopic thymic tissue, is unclear.
The most frequent asymptomatic indication for thymectomy is thymoma. Chest CT scan imaging of the thymus gland is often diagnostic of a thymic mass because the thymus gland is the only anatomic structure anterior to the brachiocephalic vein. Thymomas are not associated with lymphadenopathy. The presence of a separate aortopulmonary window mass or paratracheal adenopathy should raise the possibility of lymphoma. Similarly, Hodgkin’s disease can be associated with thymic enlargement.11
In most cases, the radiographic appearance of thymoma is sufficient to preclude the necessity of a tissue biopsy before surgical resection. Further, tissue biopsy is notoriously inefficient because of the marked heterogeneity within the thymus gland. It is common for a resected thymoma to reflect areas of lymphocyte predominance (stage I) and epithelial predominance (stage III) within the same tumor.8,12 Although the subsequent development of pleural implants is commonly attributable to presurgical biopsy, the supportive data are weak. Pleural implants clearly occur without prior biopsy. Similarly, needle or mediastinotomy biopsy is infrequently associated with localized pleural disease. Local incisional recurrence has rarely been reported.
Thymic carcinomas are rare epithelioid malignancies. Thymic carcinomas are frequently aggressive tumors that spread both within the pleural space (so-called “drop” metastases) as well as hematogenously. In most cases, the diagnosis is suspected on the radiographic studies and confirmed by anterior mediastinotomy. These tumors should be treated with aggressive combination therapy.9 Combined neoadjuvant chemoradiation therapy followed by aggressive radical surgery has had only a limited impact on patient survival.
The three most commonly cited indications for thymectomy are the following: (1) thymic hyperplasia associated with myasthenia gravis7; (2) encapsulated or invasive thymomas8; and (3) thymic carcinomas.9 Thymic hyperplasia is

Cleveland Clinic Foundation, Cleveland, Ohio. Address reprint requests to: David P. Mason, MD, Cleveland Clinic Foundation, Thoracic and Cardiovascular Surgery, 9500 Euclid Avenue, F24, Cleveland, Ohio 44195.E-mail: [email protected].

1522-2942/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.optechstcvs.2005.09.001

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Operative Technique

Figure 1 The thymus gland is derived from the 3rd pharyngeal pouch. The primordia of the thymus gland arises just ventral to the inferior parathyroid gland. The primordial thymic lobes descend caudally and fuse in the midline.13 Ectopic thymus gland can be found along the course of this descent as well as in relation to the parathyroid gland.14 The most common sites of ectopic or variant thymic tissue are (1) indistinct extensions within mediastinal fat (90%)15; (2) extensions lateral to the phrenic nerves (70%)7; (3) extensions into the aortopulmonary window (25%)7; and (4) ectopic thymus in the cervical fat (20%).16,17 Rarely, thymic tissue can be found in a retrothyroid position or posterior to the brachiocephalic vein.7

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Figure 2 For anesthetic management, we recommend placement of a double-lumen endotracheal tube for sequential lung isolation. The skin incision for a radical thymectomy can be cosmetically located in the midline. The length of the incision is typically 8 cm, about half the length of the adult sternum (17 to 18 cm). Before sternotomy, skin flaps are mobilized circumferentially. The full-thickness skin flaps are raised superficial to the pectoralis fascia. Perforating vessels are controlled by electrocautery. The mobility of the skin flaps permit comfortable access to the suprasternal notch and the manubrium with the appropriate retraction.

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Figure 3 Retraction of the skin flaps permits a full sternotomy to be performed. The sternotomy facilitates exposure to the inferior mediastinal and cervical fat. A sternal retractor, initially placed in the midline, is moved to facilitate exposure in the appropriate dissection areas.

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Figure 4 The thymic dissection begins in visible areas of midline pericardium. The dissection is carried cephalad along the pericardium toward the brachiocephalic vein. The dissection is performed with two dental pledgets (cylindrical dental tampon) held by a needle-nosed 11-inch ring handled instrument (Frazier clamp). The cylindrical pledgets facilitate dissection of the pericardial plane while being sensitive to tumor invasion or significant adhesions to the pericardium The dissection is completed at the inferior boarder of the brachiocephalic vein. The intervening tissue is the de facto thymic isthmus and is encircled with an umbilical tape. The capsule of the midline thymus is often indistinct. In addition, the midline is a frequent area of ectopic or discontinuous foci of thymic tissue. For these reasons, the entire anterior mediastinal soft tissue from the anterior pericardium to the retrosternal space is included in the specimen. Dissection of the inferior boarder of the brachiocephalic vein invariably reveals the thymic vein near the midline. This vein is transected between silk ties.

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Figure 5 The right-sided dissection begins at the retrosternal pleura and continues posterior to the superior vena cava and right atrium. The pleura is incised to facilitate visualization of the phrenic nerve. In most cases, the pleura is incorporated into the thymic specimen because of adhesions between the thymic gland. The pleura can be left intact if the mediastinal fat and thymic lobe are readily separable from the gland and mediastinal fat and the phrenic nerves have been identified.

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Figure 6 The cervical extent of the thymic lobe is dissected bluntly using dental pledgets to facilitate the separation of the thymic horn from the surrounding tissue. The cervical extent of the thymic horn lies medial to the carotid artery and deep to the strap muscles. Surrounding fat should be included in the dissection because of the likelihood of ectopic or accessory thymic tissue.16 During the course of this dissection, arterial blood supply from the internal thoracic artery or inferior thyroid artery may be encountered.18 These branches should be clipped and divided.

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Figure 7 The superior horn of the thymus gland is identified above the thoracic inlet. The cephalad extension of the thymus to the level of the thyroid gland likely reflects its embryologic descent. A leash of small vessels, typically from the inferior thyroid artery, is clipped. The clips provide hemostasis as well as a radiographic marker of the extent of the dissection. The cephalad horn of the thymus is marked with a silk tie and a mosquito clamp. The mosquito is useful because the weight of the instrument is sufficient for retraction without disrupting the delicate cervical extension of the lobe. A similar dissection is performed on the left side. There is no attempt to identify retrothyroid thymic tissue.

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Figure 8 The inferior extent of the dissection encompasses mediastinal fat from the retrosternal space to the phrenic nerve. The pleura is rarely involved at this level. If adhesions to the pleura or lung are present, the tissue is resected en bloc. The dissection is extended from phrenic nerve to phrenic nerve. Care is taken to avoid injury to the phrenic nerve. Electrocautery is used sparingly. The arterial blood supply arises from the pericardiacophrenic artery bilaterally.18

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Figure 9 The aortopulmonary (AP) window extension of the thymus is only partially visualized from a median sternotomy. Particularly in AP window thymomas, we commonly use complementary thoracoscopic imaging to facilitate an assessment of hilar involvement. Occasionally, large AP window tumors cannot be adequately resected using a median sternotomy. In these cases, we use a hemi-sternotomy combined with an anterior thoracotomy in the 3rd or 4th intercostal space (hemi-clamshell incision). The AP window thymic neoplasms are the most frequent site of phrenic nerve involvement. Tumor involvement of the phrenic nerve requires division of the nerve. If the phrenic nerve is resected, consideration should be given to immediate plication of the diaphragm to limit discoordinate respiratory movement (pendeluft) in the postoperative period. Plication of the central tendon of the diaphragm is particularly important in patients with compromised preoperative lung function.

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Figure 10 The dotted lines represent the boundaries of the radical, en bloc transsternal resection.

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Figure 11 The incision is drained using two 19 FR Blake drains. One drain is placed in the anterior mediastinum. Occasionally, when a pulmonary resection has been performed as part of the en bloc resection, a separate shortened Blake drain is placed in the pleural space. The sternum is closed using five sternal wires; two wires are placed in the manubrium. A superficial Blake drain is placed beneath the skin flaps to prevent a hematoma from developing in the subcutaneous space. The drains are placed on active suction overnight and usually removed the next morning. Patients are typically discharged from the hospital on postoperative day 3.

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thenia gravis patients: a 20 year review. Ann Thorac Surg 63:853-859, 1996

Conclusion

5. Roth T, Ackermann R, Stein R, et al: Thirteen years follow-up after radical transsternal thymectomy for myasthenia gravis. Do short-term results predict long-term outcome? Eur J Cardiothorac Surg 21:664-670, 2002
6. Masaoka A, Monden Y, Seike Y, et al: Reoperation after transcervical thymectomy for myasthenia gravis. Neurology 32:83-85, 1982
7. Jaretzki A 3rd, Bethea M, Wolff M, et al: A rational approach to total thymectomy in the treatment of myasthenia gravis. Ann Thorac Surg 24:120, 1977

In the absence of lymphadenopathy, mediastinal invasion, or anatomic ambiguity, we recommend transsternal total thymectomy of a thymoma without prior biopsy. The transsternal approach can be performed with a cosmetically acceptable incision. The superficial skin incision of 7 to 8 cm is comparable to the aggregate incision of a thoracoscopic approach and the sternotomy is well tolerated by most patients. More importantly, the transsternal approach provides sufficient incision and exposure to extract the tumor intact for detailed pathologic evaluation of the thymic capsule and to adequately assess for any local invasion. We feel that this approach provides exposure of the neck and anterior mediastinum that is superior to a transcervical approach. We recommend transsternal thymectomy for thymomas that may require a radical resection and for total resection of the observable thymus gland and associated ectopic thymic tissue.

8. Detterbeck FC, Parsons AM: Thymic tumors. Ann Thorac Surg 77:
1860, 2004
9. Greene MA, Malias MA: Aggressive multimodality treatment of invasive thymic carcinoma. J Thorac Cardiovasc Surg 125:434, 2003
10. Beeson, D, Bond AP, Corlett L, et al: Thymus, thymoma, and specific T cells in myasthenia gravis. Ann NY Acad Sci 841:371, 1998
11. Wernecke, K, Vassallo P, Rutsch F, et al: Thymic involvement in Hodgkin disease: CT and sonographic findings. Radiology 181:375, 1991
12. Loehrer PJ Sr, Wick MR: Thymic malignancies. Cancer Treat Res 105:
277, 2001
13. Gilmour JR: Some developmental anomalies of the thymus and parathyroids. J Pathol Bacteriol 52:213, 1941
14. van Dyke JH: On the origin of accessory thymus tissue, thymus IV: The occurrence in man. Anat Rec 79:179, 1941
15. Morin A, Riou RJ, Fischer L: Various aspects of vascularization of the thymus, its vestiges and of the thymic capsule. Arch Anat Pathol (Paris) 21:375, 1973
16. Maisel H, Yoshihara H, Waggoner D: The cervical thymus. Mich Med
74:259, 1975
17. Lewis MR: Persistence of the thymus in the cervical area. J Pediatr
61:887, 1962

References

1. Nakahara K, Ohno K, Hashimoto J, et al: Thymoma: results with surgical resection and adjuvant postoperative irradiation in 141 consecutive patients. J Thorac Cardiovasc Surg 95:1041-1047, 1988
2. Rehn L: Compression from the thymus gland and resultant death.
Excerpts from the transactions of the German Congress of Surgery, April 1906. Ann Surg 44:760-768, 1906
3. Blalock A, Mason MF, Morgan HJ, et al: Myasthenia gravis and tumors of the thymic region. Ann Surg 110:544-561, 1939
4. Masoaka A, Yamakawa Y, Niva H, et al: Extended thymectomy for myas-
18. Bell RH, Knapp BI, Anson BJ, et al: Form, size, blood supply and relations of the adult thymus. Q Bull Northwest Univ Med School 28:156, 1954

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    An Unusual Anatomical Variant of the Left Phrenic Nerve Encircling the Transverse Cervical Artery

    ONLINE FIRST This is a provisional PDF only. Copyedited and fully formatted version will be made available soon. ISSN: 0015-5659 e-ISSN: 1644-3284 An unusual anatomical variant of the left phrenic nerve encircling the transverse cervical artery Authors: J. H. Lee, H. T. Kim, I. J. Choi, Y. R. Heo, Y. W. Jung DOI: 10.5603/FM.a2020.0131 Article type: CASE REPORTS Submitted: 2020-07-24 Accepted: 2020-10-18 Published online: 2020-10-27 This article has been peer reviewed and published immediately upon acceptance. It is an open access article, which means that it can be downloaded, printed, and distributed freely, provided the work is properly cited. Articles in "Folia Morphologica" are listed in PubMed. Powered by TCPDF (www.tcpdf.org) An unusual anatomical variant of the left phrenic nerve encircling the transverse cervical artery Running head: Encircling of the left phrenic nerve around the transverse cervical artery J.-H. Lee1, H.-T. Kim2, I.-J. Choi1, Y.-R. Heo1, Y.-W. Jung3 1Department of Anatomy, School of Medicine, Keimyung University, 1095 Dalgubeol- daero, Daegu, 42601, Republic of Korea 2Department of Anatomy, School of Medicine, Catholic University of Daegu, Daegu, 42472, Republic of Korea 3Department of Anatomy, College of Medicine, Dongguk University, 123 Dongdae-ro, Gyeongju, 368066, Republic of Korea Address for correspondence: Dr. Yong-Wook Jung, Department of Anatomy, College of Medicine, Dongguk University, 123 Dongdae-ro, Gyeongju, 368066, Republic of Korea, tel: +82-54-770-2404, fax: +82-54-770-2402, e-mail: [email protected] Abstract During educational dissection of cadavers, we encountered anatomical variability of the left phrenic nerve.

  • The Contribution of the Left Phrenic Nerve to the Innervation Of

    Clinical Anatomy (2019) ORIGINAL COMMUNICATION The Contribution of the Left Phrenic Nerve to Innervation of the Esophagogastric Junction KATI HAENSSGEN,1 GUDRUN HERRMANN,1 ANNETTE DRAEGER,1 MANFRED ESSIG,2 1 AND VALENTIN DJONOV * 1Institute of Anatomy, University of Bern, Bern, Switzerland 2Department Gastroenterology, Tiefenau Hospital, University of Bern, Bern, Switzerland The contribution of the left phrenic nerve to innervation of the esophagogastric junction. The esophagogastric junction is part of the barrier preventing gastro- esophageal reflux. We have investigated the contribution of the phrenic nerves to innervation of the esophagogastric junction in humans and piglets by dissecting 30 embalmed human specimens and 14 piglets. Samples were microdissected and nerves were stained and examined by light and electron microscopy. In 76.6% of the human specimens, the left phrenic nerve participated in the inner- vation of the esophagogastric junction by forming a neural network together with the celiac plexus (46.6%) or by sending off a distinct phrenic branch, which joined the anterior vagal trunk (20%). Distinct left phrenic branches were always accompanied by small branches of the left inferior phrenic artery. In 10% there were indirect connections with a distinct phrenic nerve branch joining the celiac ganglion, from which celiac plexus branches to the esophagogastric junction emerged. Morphological examination of phrenic branches revealed strong similar- ities to autonomic celiac plexus branches. There was no contribution of the left phrenic nerve or accompanying arteries from the caudal phrenic artery in any of the piglets. The right phrenic nerve made no contribution in any of the human or piglet samples. We conclude that the left phrenic nerve in humans contributes to the innervation of the esophagogastric junction by providing ancillary autonomic nerve fibers.