Overview
Definition:
Transsternal thymectomy is a surgical procedure involving the removal of the thymus gland through a median sternotomy incision
It is a primary treatment modality for select patients with myasthenia gravis (MG), an autoimmune disorder characterized by fluctuating muscle weakness due to antibodies attacking acetylcholine receptors at the neuromuscular junction.
Epidemiology:
Myasthenia gravis affects approximately 15-20 per 100,000 individuals
Thymectomy is considered in about 70-80% of generalized MG patients, especially those with thymoma (found in 10-15% of MG patients) or early-onset non-thymomatous MG.
Clinical Significance:
Thymectomy offers a potential for remission or significant improvement in muscle strength for many MG patients, potentially reducing the need for long-term immunosuppressive medications
It is a cornerstone of surgical management for thymoma-associated MG and an important consideration for non-thymomatous MG.
Indications
Surgical Indications:
Myasthenia gravis patients with thymoma
generalized myasthenia gravis (especially early-onset, acetylcholine receptor antibody positive, and non-thymomatous) who are refractory to or dependent on anticholinesterase medications
thymic hyperplasia causing symptoms.
Patient Selection:
Selection is based on the presence of thymoma, age (generally younger patients benefit more), disease severity, antibody status (acetylcholine receptor antibodies), and response to medical therapy
A multidisciplinary team approach is crucial.
Contraindications:
Absolute contraindications are rare but include severe comorbid conditions precluding anesthesia and surgery
Relative contraindications include very late-onset MG with no thymic abnormality or extremely long-standing, severe disease with significant muscle atrophy where benefit is less likely.
Preoperative Preparation
Medical Optimization:
Patients are typically optimized medically prior to surgery using anticholinesterase agents (e.g., pyridostigmine) to improve muscle strength
Plasmapheresis or intravenous immunoglobulin (IVIG) may be used to reduce antibody levels in severe cases or to facilitate perioperative management.
Respiratory Assessment:
Pulmonary function tests (PFTs) and arterial blood gases (ABGs) are essential to assess respiratory reserve
Patients with significant respiratory weakness may require prolonged mechanical ventilation postoperatively.
Anesthesia Considerations:
Anesthesiologists must be aware of potential challenges in MG patients, including heightened sensitivity to neuromuscular blocking agents, risk of postoperative respiratory failure, and potential for intraoperative cholinergic crisis
Careful intraoperative fluid management is also important.
Procedure Steps
Surgical Approach:
A median sternotomy is performed, dividing the sternum vertically from the suprasternal notch to the xiphoid process
The pericardium is opened to expose the anterior mediastinum.
Thymus Dissection:
The thymus gland is meticulously dissected from surrounding structures, including the phrenic nerves, mediastinal pleura, and the pericardium
Careful identification and preservation of mediastinal veins, particularly the innominate vein and superior vena cava, are critical.
Thymectomy Technique:
Complete thymectomy, including the thymus gland and any thymic fat in the anterior mediastinum, is the goal
For thymomas, a complete resection of the tumor with adequate margins is paramount
If the tumor invades adjacent structures, en bloc resection is performed.
Closure:
The sternum is approximated and secured with sternal wires
The mediastinal pleura is often not closed to allow drainage
Chest tubes are typically placed for drainage and to re-expand the lungs
The sternal and overlying tissue layers are closed in a standard surgical fashion.
Postoperative Care
Icu Monitoring:
Patients are usually transferred to the intensive care unit (ICU) for close monitoring of respiratory status, hemodynamics, and neurological function
Mechanical ventilation may be required for a variable period.
Pain Management:
Effective pain control is crucial for facilitating deep breathing and mobilization
This is typically achieved with intravenous analgesics, often patient-controlled anesthesia (PCA), and appropriate wound care.
Pulmonary Toilet:
Aggressive pulmonary physiotherapy, including deep breathing exercises, incentive spirometry, and chest physiotherapy, is essential to prevent atelectasis and pneumonia
Early mobilization is encouraged.
Neuromuscular Monitoring:
Ongoing assessment of muscle strength and response to anticholinesterase medications is vital
Weaning from mechanical ventilation is guided by objective respiratory parameters and clinical assessment of muscle strength.
Complications
Early Complications:
Respiratory failure requiring prolonged ventilation
mediastinitis
wound infection
bleeding
chylothorax
phrenic nerve injury
cardiac arrhythmias
thymoma recurrence (if incompletely resected).
Late Complications:
Post-thymectomy syndrome (transient worsening of MG symptoms)
development of other autoimmune diseases
thymic cyst formation
scar-related issues.
Prevention Strategies:
Thorough preoperative optimization
meticulous surgical technique to ensure complete resection and avoid injury to vital structures
aggressive postoperative pulmonary care
judicious use of anticholinesterase agents
prompt management of infections and bleeding.
Prognosis
Factors Affecting Prognosis:
Presence and stage of thymoma
duration and severity of MG symptoms
age at diagnosis and surgery
extent of thymectomy (complete resection is crucial for thymomas)
postoperative management quality.
Outcomes:
A significant percentage of patients with non-thymomatous MG achieve remission or marked improvement within 2-5 years post-thymectomy
Patients with thymoma have a good prognosis with complete resection, but recurrence is possible
Long-term follow-up is essential.
Follow Up:
Regular clinical assessment of muscle strength and neurological status
pulmonary function tests
imaging (e.g., CT scan) for thymoma surveillance
monitoring for the development of other autoimmune conditions
Patients are typically followed by both surgical and neurological teams.
Key Points
Exam Focus:
Transsternal thymectomy is the gold standard for complete thymoma resection and a key treatment for refractory MG
Emphasize indications, complete resection, and potential for remission
Differentiate thymoma stages and management strategies.
Clinical Pearls:
Always consider thymoma in adult-onset MG
Complete thymic resection, including all mediastinal fat, is crucial for optimal outcomes
Intraoperative neuromonitoring can be helpful but needs careful interpretation in MG patients.
Common Mistakes:
Incomplete thymectomy (leaving residual thymic tissue or fat)
failure to adequately optimize medical management preoperatively
delayed recognition and management of postoperative respiratory failure
not considering the possibility of thymoma in MG patients.