What is the appropriate management and treatment for a mediastinal mass?

Management and Treatment of Mediastinal Mass

For a newly discovered mediastinal mass, obtain contrast-enhanced CT chest as the initial imaging study, followed by MRI chest (with or without contrast) if CT findings are indeterminate, and proceed to image-guided core needle biopsy when imaging cannot definitively characterize the lesion. 1, 2

Initial Diagnostic Imaging Algorithm

First-Line Imaging

• Contrast-enhanced CT chest is the preferred initial study for suspected mediastinal masses, as it definitively localizes the lesion to the specific mediastinal compartment (prevascular, visceral, or paravertebral) and provides superior tissue characterization compared to chest radiography 1, 2
• CT demonstrates calcium, macroscopic fat, water attenuation fluid, and enhancing cellular components, allowing noninvasive diagnosis of many lesions including mature teratomas 1
• Obtain thin-section imaging (≤5 mm slices) with multiplanar reconstructions to assess relationships to adjacent structures 2
• Pre- and post-contrast imaging is essential to distinguish vascular structures from lymph nodes and identify enhancing components 2

When CT is Indeterminate

• MRI chest (with or without IV contrast) is the next appropriate study when CT findings are indeterminate 1
• MRI provides superior tissue characterization beyond CT by detecting hemorrhagic and proteinaceous fluid, microscopic fat, cartilage, smooth muscle, and fibrous material (though not calcium) 1
• MRI can definitively distinguish cystic from solid lesions, which is diagnostically critical in all mediastinal compartments 1
• MRI can prove the cystic nature of hyperattenuating thymic masses on CT, preventing unnecessary biopsy and thymectomy 1
• Diffusion-weighted imaging (DWI) assists in lesion characterization and can direct biopsy toward areas of higher cellularity 1, 2

Tissue Diagnosis Strategy

Image-Guided Biopsy Indications

• Proceed to image-guided transthoracic needle biopsy when imaging (including MRI) cannot definitively characterize the mass 1
• CT-guided percutaneous core biopsy is safe with good diagnostic yield: 87% for mediastinal masses with mean size 5.3 cm and 77% for masses with mean size 6.9 cm 1, 2
• Core biopsy is more effective than fine-needle aspiration and should be the preferred technique 1

Biopsy Guidance Optimization

• DWI MRI and dynamic contrast-enhanced (DCE) MRI can direct biopsy toward sites of higher cellularity and diagnostic yield, avoiding hemorrhagic necrosis 1, 2
• When the lesion is visible within the sonographic window, transthoracic ultrasound-guided biopsy is feasible with color Doppler providing additional value 1
• PET/CT guidance for biopsy yields no diagnostic advantage over CT guidance 1

Biopsy Yield by Histology

• Biopsy is more frequently diagnostic for thymic epithelial tumors (TETs) than for lymphoma 1
• When distinction between TETs and lymphoma cannot be made by imaging, image-guided biopsy has a definitive role 1

Role of FDG-PET/CT

Limited Primary Diagnostic Value

• FDG-PET/CT offers limited additional value beyond CT and MRI for initial assessment of mediastinal masses, with exceptions for lymphoma staging and surveillance 1
• A negative FDG-PET/CT is helpful in excluding malignancy in prevascular mediastinal masses, but a positive study has little discriminatory value between benign and malignant lesions 1
• Normal and hyperplastic thymus frequently shows FDG-PET/CT avidity, confounding assessment of the prevascular mediastinum 1

Specific Indications

• FDG-PET/CT is the standard for staging and assessment of treatment response for FDG-PET-avid lymphomas at baseline or recurrence 1
• Higher SUVs are more frequently found in high-risk thymoma, thymic carcinoma, and lymphoma than in low-risk thymoma 1
• FDG-PET/CT is more sensitive than CT alone for detection of mediastinal recurrence of thymoma 1

Surveillance Strategy for Indeterminate Masses

When Surveillance is Appropriate

• For indeterminate masses not requiring immediate biopsy, surveillance can be performed at 3-, 6-, or 12-month intervals over 2 or more years, depending on clinical concern 1, 2
• MRI is preferred over CT for surveillance due to greater sensitivity for detecting increased lesion complexity and superior capacity to characterize tissue 1, 2

Assessment of Invasion and Resectability

MRI Superiority for Invasion Assessment

• MRI is superior to CT for detection of invasion across tissue planes, including chest wall, diaphragm, and neurovascular structures, due to higher soft tissue contrast 1, 2
• Dynamic MRI during free-breathing or cinematic cardiac gating can assess movement of the mass relative to adjacent structures and confirm or exclude adherence 1
• Paradoxical diaphragmatic motion or lack of motion indicates phrenic nerve involvement by the mediastinal mass 1

Critical Pitfalls to Avoid

Imaging Errors

• Do not proceed directly to biopsy without MRI evaluation of indeterminate CT findings, as MRI can prevent unnecessary procedures 1, 2
• Do not skip contrast administration unless absolute contraindications exist (severe renal insufficiency or documented severe contrast allergy), as it significantly improves lesion characterization 2
• After cross-sectional imaging has been performed, there is seldom a role for additional chest radiography 1

Biopsy Planning Errors

• Avoid targeting necrotic or hemorrhagic areas during biopsy planning by using imaging guidance (particularly DWI or DCE MRI) to target the most cellular portions 1, 2
• Do not rely on size criteria alone for lymph node assessment, as nodes >1 cm in short axis have limited sensitivity and specificity 2

Anesthetic Considerations

• For large anterior mediastinal masses with >50% airway obstruction at the level of the lower trachea and main bronchi, have femoral vessels cannulated in readiness for cardiopulmonary bypass before induction of general anesthesia 3
• Maintain spontaneous respiration and avoid muscle relaxants during induction for patients with significant mediastinal mass effect 4
• Preoperative thoracic CT is essential to assess degree of airway narrowing and vascular compression 4, 3

Post-Treatment Thymic Hyperplasia

• Be aware of thymic hyperplasia as a common phenomenon in children and young adults after chemotherapy for lymphoma, which can mimic recurrent disease on CT 5
• Mild FDG uptake on PET-CT (typically occurring 3-6 months post-chemotherapy) is consistent with benign thymic hyperplasia rather than recurrence 5
• Avoid unnecessary biopsies when the anterior mediastinal mass demonstrates only mild FDG uptake after successful lymphoma treatment 5