Introduction
Substernal goiter, also referred to as retrosternal goiter or intrathoracic thyroid goiter, is a clinically significant thyroid disorder characterized by the extension of thyroid tissue from the cervical region into the mediastinum. Although often slow-growing and initially asymptomatic, substernal goiter can lead to life-threatening airway and esophageal compression, making early recognition and accurate imaging diagnosis critical.
With increasing longevity of the population and improved cross-sectional imaging, substernal goiter is being diagnosed more frequently, particularly in elderly patients. This article provides a comprehensive, evidence-based review of substernal goiter, integrating pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, diagnosis, treatment, and prognosis, supported by classic and contemporary landmark literature.
All imaging findings discussed below directly correspond to the attached clinical case and figures, making this column particularly useful for radiology trainees and medical licensing exam candidates.
Definition and Classification of Substernal Goiter
A substernal goiter is defined as a thyroid enlargement in which more than 50% of the thyroid mass extends below the thoracic inlet into the mediastinum. Most substernal goiters arise from downward growth of a cervical thyroid gland, rather than from ectopic thyroid tissue.
Classification
Substernal goiters may be classified as:
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Primary substernal goiter (rare): arising from ectopic mediastinal thyroid tissue
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Secondary substernal goiter (common): downward extension of a cervical goiter
Anatomically, they are further divided into:
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Anterior mediastinal goiter (most common)
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Posterior mediastinal goiter (less common, higher surgical risk)
Epidemiology
Substernal goiter accounts for approximately 5–15% of all thyroidectomies. Key epidemiological features include:
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Predominantly affects women
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Peak incidence in the 6th–7th decade of life
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Often associated with long-standing multinodular goiter
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Higher prevalence in regions with iodine deficiency
Importantly, up to 40% of patients may be asymptomatic, and diagnosis is frequently incidental on chest imaging.
Pathophysiology
The development of substernal goiter is driven by several anatomical and physiological factors:
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Gravity and negative intrathoracic pressure promote downward extension
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Thoracic inlet acts as a fixed boundary, directing growth inferiorly
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Chronic thyroid stimulation (iodine deficiency, TSH stimulation)
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Degenerative changes such as hemorrhage, necrosis, and calcification
Despite large size, many patients remain euthyroid, as seen in the presented case, with normal TSH and free thyroxine levels.
Clinical Presentation
Symptoms result from mass effect on mediastinal structures rather than thyroid dysfunction.
Common Symptoms
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Dyspnea (especially supine)
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Dysphagia
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Chronic cough
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Hoarseness
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Wheezing or stridor
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Sensation of chest tightness
Physical Examination
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Cervical thyroid enlargement may be small or deceptively minimal
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Inferior thyroid border often non-palpable
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Pemberton’s sign may be positive in advanced cases
📌 In the presented case, a 67-year-old woman complained of progressive dyspnea and dysphagia over six months, classic for substernal goiter.
Imaging Features of Substernal Goiter
Chest Radiography
Figure 1. Chest P-A
Caption: Chest radiograph demonstrates tracheal deviation (arrow) caused by a superior mediastinal mass consistent with substernal goiter.
Key radiographic findings:
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Widened superior mediastinum
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Tracheal deviation or compression
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Possible calcifications
Computed Tomography (CT)
CT is the imaging modality of choice for substernal goiter.
Figure 2. Coronal CT
Caption: Coronal contrast-enhanced CT shows a large thyroid mass extending from the cervical region into the anterior mediastinum, consistent with substernal goiter.
Figure 3. Axial CT
Caption: Axial CT reveals a heterogeneously enhancing anterior mediastinal mass, containing areas of calcification and necrosis.
Figure 4. Axial CT
Caption: Contrast-enhanced CT demonstrates a strongly enhancing substernal thyroid mass with internal calcifications and necrotic areas, characteristic of multinodular goiter.
Figure 5. Axial CT
Caption: The anterior mediastinal mass (red arrow) causes rightward tracheal displacement (white arrow).
Chest X-ray Review Image
Figure 7. Chest P-A
Caption: Large upper anterior mediastinal mass (white arrow) with marked tracheal deviation to the right (black arrow), classic for substernal goiter.
Differential Diagnosis
Anterior mediastinal masses must be differentiated carefully:
| Condition | Key Imaging Clues |
|---|---|
| Substernal goiter | Continuity with cervical thyroid, intense enhancement |
| Thymoma | Homogeneous soft tissue mass |
| Lymphoma | Lobulated mass, minimal enhancement |
| Teratoma | Fat, calcification, cystic elements |
| Lung cancer | Parenchymal origin, lymphadenopathy |
📌 Tracheal deviation with intense enhancement strongly favors substernal goiter.
Diagnosis
Definitive diagnosis is based on:
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Clinical history
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Imaging (CT/MRI)
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Thyroid function tests
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Occasionally radionuclide scanning
Fine-needle aspiration (FNA) is generally avoided for substernal components due to bleeding risk.
Treatment
Indications for Surgery
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Symptomatic compression (dyspnea, dysphagia)
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Progressive enlargement
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Suspicion of malignancy
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Acute hemorrhage
Surgical Approach
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Cervical thyroidectomy (most cases)
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Sternotomy or thoracotomy (rare, large posterior goiters)
Radioiodine therapy may be considered in poor surgical candidates, though response is limited.
Prognosis
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Excellent prognosis after surgical removal
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Symptom resolution in >90%
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Malignancy rate: 5–15%
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Recurrence is rare with complete resection
Quiz
Question 1. A 67-year-old woman presents with dyspnea and dysphagia. Chest X-ray shows tracheal deviation. CT reveals a strongly enhancing anterior mediastinal mass continuous with the thyroid. What is the most likely diagnosis?
A. Thymoma
B. Lung cancer
C. Pneumothorax
D. Rib fracture
E. Substernal goiter
✅ Answer: E
Explanation: Continuity with cervical thyroid and enhancement pattern are diagnostic.
Question 2. Which imaging modality is most useful in evaluating the extent of substernal goiter?
A. Ultrasound
B. Chest X-ray
C. Contrast-enhanced CT
D. PET scan
E. MRI brain
✅ Answer: C
Question 3. Which complication most commonly necessitates surgery in substernal goiter?
A. Hyperthyroidism
B. Cosmetic deformity
C. Airway compression
D. Hypocalcemia
E. Infection
✅ Answer: C
References
[1] R. L. Newman et al., “Substernal goiter,” N Engl J Med, vol. 357, pp. 222–230, 2007.
[2] D. J. Shaha, “Surgery for substernal goiter,” Head Neck, vol. 35, no. 6, 2013.
[3] J. A. Huins et al., “A new classification system for substernal goiter,” Ann R Coll Surg Engl, 2008.
[4] A. Randolph, Surgery of the Thyroid and Parathyroid Glands, Elsevier, 2020.
[5] S. B. Kim et al., “CT findings of substernal goiter,” Radiographics, 2019.
[6] M. Hegedüs, “Clinical practice: The thyroid nodule,” N Engl J Med, 2004.
[7] A. C. Barbesino, “Evaluation of mediastinal thyroid masses,” Endocrinol Metab Clin North Am, 2021.
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