Mediastinal masses

Overall - bimodal distribution

Most childhood masses are neurogenic, and found in posterior mediastinum
Most adult masses are thymic/lymphatic, and found in anterior mediastinum

Presentation

Mostly slow-growing and asymptomatic
If symptoms are present, they are usually due to compression or invasion of surrounding structures
Can present with paraneoplastic phenomenon - Cushing syndrome, myasthenia gravis, malignant HTN, hyperparathyroidism

Assessment

Pemberton's sign
Invasion of critical nerves - diaphragm function, hoarse voice, Horner syndrome

Imaging

CT is best initial test
MRI useful for further differentiation
- Good for neurogenic masses in determining whether they involve neural foramen
PET - if thymic carcinoma considered, or when lymphoma considered
Gallium dotatate for NET
Sestamibi for parathyroid adenoma

Bloods

AFP and b-hCG are critical for diagnosis of germ-cell tumours
LDH, uric acid and phosphate should be checked in patients with probable lymphoma - to exclude tumour lysis syndrome
Catecholamine metabolites, VIP, ACTH, considered

Biopsy

Many masses can be diagnosed with imaging alone
However can be very useful if diagnosis may be yielded which needs neoadjuvant therapy
Should be performed when thymic carcinoma or lymphoma are suspected at a minimum
Avoid biopsy for mediastinal duplication cysts
Core biopsy preferred to FNA for diagnoses where architecture is important - thymoma and lymphoma
Surgical biopsy -
- Cervical mediastinoscopy is good for middle mediastinal nodes/structures
- Anterior mediastinum - use anterior mediastinotomy (Chamberlain procedure)
- VATS can be undertaken from either side and provides access to all parts of mediastinum

Aetiology by anatomy

Boundaries
- Thoracic inlet superiorly
- Diaphragm inferiorly
- Paravertebral sulci posteriorly
- Pleural laterally
Compartments - dictates differential
- Anterior (between pericardium and sternum, below innominate vessels)
  - Primary thymic tumours
    - Thymomas
    - Neuroendocrine tumours of thymus (aka thymic carcinoids)
    - These are the most common tumours of anterior mediastinum
    - See separate page
  - Germ-cell tumours
    - Mature teratomas
      - Most common germ cell tumour
      - Seen in men and women of varying ages
      - AFP and bHCG normal
      - Resect to prevent local compression and because there is a small incidence of immature, malignant elements being contained within otherwise mature tumours
      - Seldom recur once resected
    - Primary mediastinal seminomatous germ cell tumours (PMSGCT)
      - Aka seminomas
      - Occurs only in young men
      - Slow-growing, rarely causing symptoms
      - 70% have mets to LNs, bone or lung at presentation
      - Workup:
        Bhcg normal or mildly elevated; AFP normal
        
        Investigate for gonadal primary
        
        Biopsy mediastinal lesion
        
        Comprehensive imaging looking for other sites of disease
      - Treatment:
        Systemic CTX, and sometimes adjuvant RTX
        
        Surgery has a limited role
        
        Good outcomes, survival >85% at 5 years
    - Primary mediastinal nonseminomatous germ cell tumours (PMNSGCT)
      - Occurs only in young men 10-30yo
      - bHCG and AFP elevated
      - Imaging showing heterogenous anterior mediastinal mass with local invasion of surrounding structures
      - If very typical presentation, biopsy needed if bHCG and AFP normal, to differentiate from PMSGCT
      - Histo - yolk sac carcinoma, embryonal carcinoma, or choriocarcinoma
      - Treatment
        CTX followed by surgical extirpation
        
        Re-resection may be considered if looks like local recurrence
      - Patients with no viable tumour in resected mass have a good prognosis
    - Workup
      - Imaging and serologic studies provide much information, but biopsy is usually obtained as well
  - Lymphoma
    - Surgical role is diagnostic - no therapeutic resection options
    - Can be Hodgkin's or non-hodgkin's
    - Core needle biopsy targeted to FDG-avid areas is often sufficient
  - Thyroid and parathyroid
    - Both CAN be found in anterior mediastinum
      - Thyroid goitre with direct extension down - can usually be excised with a low cervical incision
      - Parathyroid glands share an embryological origin with the thymus - can frequently be found in an ectopic location within the anterior mediastinum. Sestamibi scan should be done prior to exploration in all patients looking for a parathyroid adenoma as this location is relatively common.
- Middle/visceral (all structures of pericardium, heart, great vessels, airway, and oesophagus)
  - Mediastinal lymphadenopathy
    - Most common - arising from paratracheal and subcarinal lymph nodes
    - DDx
      - Infectious
        Bacterial
        
        Mycobacterial
        
        Fungal
      - Inflammatory
        sarcoidosis
      - Neoplastic
        Regionally advanced lung cancer
        
        Other met cancer
        
        Lymphoma
      - Diagnosis - biopsy with cervical mediastinoscopy
        Culture, fungal and gram stain, flow cytometry, pathology
      - EBUS or EUS with FNA or core biopsy may be sufficient to diagnose metastatic lung cancer
  - Mediastinal cysts
    - Foregut duplication cysts
      - Bronchogenic
        Most common
      - Oesophageal
      - Workup
        MRI is most diagnostic
        
        Needle biopsy discouraged due to risk of superinfection
      - Treatment
        Indications for resection: local compressive symptoms, or low operative risk (since there is a theoretical risk of malignant transformation)
        
        Minimally invasive resection
    - Pericardial
      - No risk of malignant transformation
      - Resected when symptomatic or enlarging
  - Castleman's disease
    - Aka Angiofollicular hyperplasia
    - Rare lymphoproliferative disease that can occur anywhere but favours locations adjacent to central airways
    - Classically intense enhancement with IV contrast
    - Mostly asymptomatic
    - Mostly young adults
    - Resect if unicentric
    - If multicentric, treat with B-cell targeted immunotherapy and radiation
- Posterior
  - Schwannomas and neurofibromas
    - Commonly benign, but resection indicated to exclude malignant schwannoma or neurofibrosarcoma
  - Ganglion cell tumours
    - Arise from sympathetic ganglia
    - Ganglioneuromas - common in adults, benign
    - Ganglioneuroblastomas and neuroblastomas - common in children, malignant and aggressive
    - Can secrete VIP/catecholamines
    - Should be resected with adjuvant therapy given if malignant features are present
  - Paraganglion cell tumours
    - Mediastinal phaeochromocytomas - arise from paraganglion cells and classically produce malignant hypertension
    - Don't biopsy - can be diagnosed serologically and with imaging
    - Surgical resection, preceded by adrenergic blockade

Surgical approaches

Transcervical - only really good for superior parts of anterior mediastinum
Median sternotomy - gold standard for resecting large or invasive anterior mediastinal structures
Thoracotomy - good for masses in middle and posterior mediastinum
Minimally invasive e.g. VATS - small thymomas, mediastinal cysts, benign posterior mediastinal tumours. Decreased morbidity but not as good for oncologic outcomes.