Types of Retrosternal Extension of Thyroid
Retrosternal goiter can be classified into four distinct types based on anatomical shape, size, and location, which helps in surgical planning and predicting the difficulty of thyroid removal.
Classification of Retrosternal Goiters
Type A: Cone or pyramid-shaped goiters with the apex pointing downward into the mediastinum. These can typically be removed through a cervical approach alone 1.
Type B: Pyramid-shaped goiters with the apex pointing upward. These may require a cervical approach with possible additional manubriotomy or sternotomy depending on the extent 1.
Type C: Thyroid enlargements in the mediastinum connected by a pedicle to the cervical thyroid. These often require a combined cervical approach with manubriotomy, sternotomy, or thoracotomy 1.
Type D: True intrathoracic or "forgotten" goiters without significant connection to the cervical thyroid. These typically require sternotomy for anterior mediastinal goiters or thoracotomy for posterior mediastinal goiters 1.
Anatomical Considerations
Retrosternal goiter is defined as any goiter in which at least 50% of the thyroid tissue extends below the thoracic inlet into the mediastinum 2.
The majority of retrosternal goiters (85-90%) are located in the anterior mediastinum, while posterior mediastinal goiters comprise only 10-15% of all mediastinal goiters 3.
Distortion and elongation of the recurrent laryngeal nerve caused by large goiters with retrosternal extension should be considered as an important risk condition during surgery 4.
Clinical Significance
Retrosternal extension increases surgical complexity and potential complications, with the main goal of management being prevention or treatment of compression of vital structures 5.
Patients with retrosternal goiters may experience compressive symptoms including dyspnea, orthopnea, obstructive sleep apnea, dysphagia, and dysphonia due to mass effect on the trachea or esophagus 5.
Severe cases can present with superior vena cava syndrome due to vascular compression 6.
Diagnostic Evaluation
CT imaging is essential for surgical planning and is superior to ultrasound for evaluating substernal extension and defining the degree of tracheal compression 5.
CT scan with cross-sectional reconstruction should be analyzed before operation to determine the appropriate surgical approach based on the goiter's anatomical characteristics 1.
MRI is an alternative to CT but has more respiratory motion artifact, making CT the preferred imaging modality 7.
Surgical Approach Considerations
The surgical approach depends on the type of retrosternal extension, with most (approximately 85%) being manageable through a cervical approach alone 8.
Goiters extending beyond the aortic arch into the posterior mediastinum generally require sternotomy or lateral thoracotomy 3.
Preoperative CT imaging is crucial to determine whether 50% of tumor volume is located above the thoracic inlet, which would favor a cervical approach 8.
Retrosternal goiter surgery carries risks including recurrent laryngeal nerve palsy, transient hypocalcemia, and hypoparathyroidism, though permanent complications are rare with proper surgical technique 8.
Understanding the type of retrosternal extension is essential for proper surgical planning and minimizing complications in patients with goiters extending beyond the thoracic inlet.