Mediastinal Masses — Diagnosis and Management

Mass effect and compression mechanisms

• Direct encroachment on cardiac chambers, pericardium, and great vessels produces elevated intrapericardial pressures, restricting ventricular filling (diastolic dysfunction), reducing stroke volume, and precipitating pulsus paradoxus (>10 mmHg systolic variation with respiration)
• Compression of the superior vena cava increases venous hydrostatic pressure upstream, causing facial plethora, upper extremity edema, and subcutaneous venous collaterals; the azygos system partially decompresses but becomes inadequate with rapid mass growth
• Tracheal and bronchial compression narrows the airway lumen by >50%, increasing airflow resistance (inversely proportional to radius to the fourth power), causing stridor at rest and dyspnea during exertion or recumbency

Pericardial involvement and tamponade physiology

• Infiltration or direct extension into the pericardium prevents normal visceral-parietal sliding, increasing friction and triggering pericarditis (chest pain, friction rub)
• Malignant pericardial effusions accumulate slowly in some cases (allowing pericardial stretch and accommodation) or rapidly (precipitating acute tamponade); the critical pressure at which cardiac filling ceases depends on pericardial compliance, not absolute fluid volume
• Equalization of diastolic pressures (right atrial = right ventricular = pulmonary arterial pressures) occurs once intrapericardial pressure exceeds ventricular compliance, halting diastolic filling and precipitating shock

Esophageal and neural involvement

• Posterior mediastinal masses compress the esophagus, disrupting peristalsis and causing dysphagia (food > liquids) and aspiration risk
• Invasion of the left recurrent laryngeal nerve (running lateral to aortic arch) produces vocal cord paralysis with hoarseness, weak cough, and aspiration
• Sympathetic and parasympathetic plexus involvement may cause Horner syndrome (miosis, ptosis, anhidrosis) or cardiac arrhythmias

Anterior mediastinal masses (40-50% of mediastinal pathology)

• Lymphomas (Hodgkin and non-Hodgkin): Most common anterior mass; often presents as widened mediastinum on CXR in young adults
• Thymoma and thymic hyperplasia: Peak incidence 40-60 years; association with myasthenia gravis (30-50% of thymoma patients); WHO classification (A, AB, B1, B2, B3) predicts invasiveness
• Germ cell tumors (teratoma, seminoma, yolk sac tumor, choriocarcinoma): Peak incidence 20-40 years; elevated α-fetoprotein (AFP) or β-human chorionic gonadotropin (β-hCG) are diagnostic and prognostic markers
• Thyroid masses: Ectopic or retrosternal thyroid extension; iodine-123 or technetium-99m uptake confirms diagnosis

Middle mediastinal masses (pericardial, hilar)

• Pericardial cysts: Benign, asymptomatic unless large; water-density on CT, no enhancement
• Bronchogenic cysts: Developmental foregut anomalies; low-density, non-enhancing on CT
• Lymphadenopathy: Sarcoidosis, tuberculosis, metastatic carcinoma, lymphoma

Posterior mediastinal masses (30-40% of mediastinal pathology)

• Neurogenic tumors (most common posterior mass in children and adolescents): Schwannoma, neurofibroma, ganglioneuroma; associated with neurofibromatosis type 1 (NF1)
• Paravertebral masses: Meningiomas (rare), extradural spinal extension of lymphomas
• Esophageal pathology: Achalasia, megaesophagus, esophageal carcinoma

Risk factors across compartments

• Malignancy history (lymphoma, lung cancer with mediastinal involvement)
• Immunosuppression (HIV/AIDS): Increased risk of lymphomas and infections
• Autoimmune conditions: Sarcoidosis, systemic lupus erythematosus (SLE)
• Genetic syndromes: NF1, Li-Fraumeni syndrome (TP53 mutations increase germ cell tumor risk)
• Tobacco and asbestos exposure (associated with primary lung cancers extending into mediastinum)

Asymptomatic presentations (30-50% of cases)

• Incidental finding on chest X-ray performed for unrelated indication
• Widened mediastinum or abnormal silhouette without patient complaints
• Commonly identified in anterior mediastinal thymomas and benign cysts

Obstructive symptoms

• Dyspnea: Progressive, worsened by exertion or when supine (orthopnea); stridor indicates tracheal involvement; dyspnea at rest suggests significant airway compromise (>50% narrowing)
• Chest pain: Pleuritic or constant; suggests pericardial involvement, pleural invasion, or rib involvement
• Dysphagia and odynophagia: Esophageal compression (posterior masses); food impaction precedes liquids
• Cough: Often dry; may indicate bronchial compression

Compressive symptoms related to SVC syndrome

• Facial flushing and plethora: Venous congestion in upper face
• Upper extremity edema and venous distension: Pitting edema progresses from hands to forearms to shoulders
• Neck and chest wall venous collaterals: Visible, prominent vessels bypassing SVC obstruction
• Stridor: Laryngeal edema from venous congestion contributes to airway obstruction

Tamponade presentation (hemodynamic compromise)

• Hypotension (systolic <90 mmHg in acute tamponade, gradual decline in chronic)
• Pulsus paradoxus: Systolic BP drop >10 mmHg during inspiration (normal <10 mmHg); best detected by palpating radial pulse during slow blood pressure deflation or auscultating Korotkoff sounds
• Jugular venous distension (JVD): Elevated central venous pressure from impaired venous return
• Cool extremities, altered mental status, oliguria: Signs of cardiogenic shock from severely reduced cardiac output
• Muffled heart sounds: Fluid damping, though may be inaudible given chest wall edema

Neurologic symptoms

• Hoarseness: Recurrent laryngeal nerve involvement (left side more common)
• Horner syndrome: Ptosis, miosis, anhidrosis, and facial flushing (right side more common with superior sympathetic chain involvement)
• Arm/leg weakness or paresthesias: Spinal cord compression from posterior masses extending into neural foramen
• Diaphragmatic paralysis: Phrenic nerve involvement (presents as elevated hemidiaphragm on CXR)

Systemic and paraneoplastic symptoms

• Constitutional symptoms: Fever, night sweats, weight loss (suggests lymphoma or aggressive malignancy)
• Myasthenic symptoms: Ptosis, diplopia, bulbar weakness; pathognomonic association with thymoma
• Hypercalcemia: Paraneoplastic syndrome with lymphomas producing calcitriol
• Ectopic hormone production: ACTH secretion (small cell lung cancer extending into mediastinum), inappropriate antidiuretic hormone (SIADH)

Imaging hierarchy and interpretation

Laboratory studies

• Tumor markers (drawn before biopsy):
• AFP and β-hCG: Diagnostic for germ cell tumors; AFP >400 ng/mL or β-hCG >5 mIU/mL highly specific; normal levels do not exclude histology
• Lactate dehydrogenase (LDH): Elevated in lymphomas and germ cell tumors; prognostic significance in lymphoma (international prognostic index)
• Thyroglobulin: Elevated if thyroid origin

• CBC and CMP:
• Leukocytosis, lymphocytosis, or blasts (hematologic malignancy)
• Hypercalcemia (lymphoma, rare in other histologies)
• Renal dysfunction (paraneoplastic, treatment-related)

• Pericardial fluid analysis (if effusion present):
• Cytology: Malignant cells diagnostic of metastatic disease
• Adenosine deaminase (ADA): >10 U/L suggests tuberculosis
• LDH, glucose, protein: Exudative pattern (LDH >200 U/L, protein >3 g/dL) supports malignancy

Biopsy and tissue diagnosis

• CT or ultrasound-guided needle biopsy (18-20 gauge core needle): Preferred approach; 80-95% sensitivity for lymphoma and carcinomas; low morbidity
• Mediastinoscopy: Gold standard for anterior/middle compartment masses; allows direct visualization and multiple sampling; requires general anesthesia
• EBUS-TBNA (Endobronchial ultrasound with transbronchial needle aspiration): Excellent for hilar/middle mediastinal lymph nodes; minimally invasive
• Anterior mediastinotomy (Chamberlain procedure): Utilized when needle/endoscopic approaches non-diagnostic; allows visualization and direct biopsy
• Surgical biopsy: Reserved for cases where imaging or needle biopsy non-diagnostic and diagnosis essential before therapy (e.g., thymoma vs. lymphoma)

Staging and functional assessment

• Masaoka-Koga staging (thymomas): Stage I (encapsulated, no invasion), IIA (microscopic invasion), IIB (macroscopic invasion into neighboring organs), III (invasion of pleura/pericardium/lung), IV (hematogenous/lymphatic metastases, IVa pleural; IVb distant)
• Nottingham histologic classification (thymomas): A (spindle/oval epithelial cells), AB (mixed A + lymphocyte-rich), B1 (lymphocyte-rich, medullary-like), B2 (lymphocyte-rich with increased epithelial cells), B3 (epithelial-predominant with atypia); B3 and IV most aggressive
• PFTs and arterial blood gas: Assess respiratory reserve if airway compromise suspected; <50% FEV1 may preclude general anesthesia for biopsy/surgery
• Cardiac stress testing or preoperative echocardiography: Evaluates cardiac reserve and identifies pre-existing dysfunction complicating tamponade management

Emergency management (SVC syndrome, tamponade, airway obstruction)

• Pericardiocentesis (18-22 gauge catheter, ultrasound or fluoroscopic guidance): Immediate intervention for hemodynamic tamponade; removes as little as 50-100 mL to restore cardiac output (does not require complete drainage); recurrent effusions warrant pericardial window (surgical drainage creating communication between pericardium and pleural space) or pericardial catheter drainage (pigtail catheter left in situ 5-7 days)
• Oxygen supplementation and head-of-bed elevation: Reduces airway edema; maintains SaO2 >90%
• Avoid sedation/general anesthesia until airway compromise addressed: Spontaneous ventilation critical; induction agents and positive-pressure ventilation may precipitate complete airway obstruction (consider awake fiberoptic intubation if intubation required)
• Diuretics (IV furosemide 40-80 mg): Reduces total body fluid in SVC syndrome; monitor electrolytes given risk of dehydration
• Corticosteroids (dexamethasone 4 mg IV q6h or prednisone 1-2 mg/kg/day): Reduces airway edema and venous inflammation; taper over 1-2 weeks
• Superior vena cava stenting: Emergency intervention when airway obstruction or severe hemodynamic compromise unresponsive to above measures; expandable metal stents restore flow within hours; reserved for malignant obstruction (benign thrombosis usually treated medically or with anticoagulation)

Definitive treatment by histology

Thymoma

• Surgical resection (thymectomy) with en bloc resection of invaded structures: First-line definitive therapy; complete resection (R0) improves 5-year survival to 90%+ vs. 50-60% with incomplete resection (R1/R2)
• Neoadjuvant chemotherapy (cisplatin-based: cisplatin + doxorubicin + cyclophosphamide [CAP] or cisplatin + etoposide): Considered for Stage III-IV or locally advanced disease; shrinks mass to facilitate complete resection
• Adjuvant radiation therapy (50-54 Gy): Administered for Stage II-IV or incomplete resection; improves local control and 5-year survival (50-70%)
• Chemotherapy monotherapy (CAP or cisplatin/etoposide): Palliative for metastatic or unresectable disease; response rates 60-80%; median survival 3-5 years with treatment
• Myasthenia gravis management: Concurrent acetylcholinesterase inhibitors (pyridostigmine 60 mg PO q4-6h) and immunosuppression (prednisone, azathioprine) during perioperative period; 30% of thymoma patients achieve myasthenic remission post-thymectomy

Airway and hemodynamic emergencies

• Mediastinal mass syndrome (anesthetic catastrophe): loss of spontaneous negative intrathoracic pressure with induction or deep sedation abolishes the tethering that holds a compressed trachea/main bronchus open, and muscle relaxation removes diaphragmatic descent — the result is total airway collapse or pulmonary artery/right atrial compression that is unrelieved by intubation. Signals: orthopnea, stridor, syncope with recumbency, >50% tracheal narrowing or pericardial effusion on CT. Consistent with ASA difficult-airway principles, maintain spontaneous ventilation, biopsy under local anesthesia when possible, position lateral or semi-upright, and have rigid bronchoscopy and cardiopulmonary bypass/ECMO capability standing by. True emergency.
• Cardiac tamponade: Beck triad (hypotension, JVD, muffled sounds) with echocardiographic right atrial systolic and RV diastolic collapse and exaggerated respirophasic inflow variation. Emergency — drain, do not volume-load indefinitely.
• Malignant SVC obstruction with laryngeal or cerebral edema: stridor, obtundation, or seizure converts SVC syndrome from an urgency into an emergency warranting endovascular stenting before tissue diagnosis.
• Spinal cord compression from a dumbbell neurogenic tumor extending through the neural foramen: back pain, sensory level, urinary retention. Emergency — corticosteroids plus urgent MRI of the whole spine.

Treatment-related complications

• Tumor lysis syndrome: bulky lymphoblastic or Burkitt-type disease lysing after steroids or chemotherapy releases potassium, phosphate, and urate; hyperkalemia, hypocalcemia, and AKI. NCCN supportive-care guidance favors aggressive hydration with rasburicase for high-risk disease.
• Empiric steroids before biopsy: lympholysis can render tissue nondiagnostic — reserve for airway or cord emergencies.
• Post-thymectomy myasthenic crisis: perioperative stress and cholinesterase-inhibitor withdrawal precipitate bulbar/respiratory failure; falling vital capacity and negative inspiratory force precede desaturation. Managed with plasma exchange or IVIG per international MG consensus guidance.
• Pericardiocentesis injury: RV laceration, pneumothorax, arrhythmia, or post-decompression pulmonary edema.
• Late thoracic radiation and anthracycline toxicity: constrictive pericarditis, premature coronary and valvular disease, cardiomyopathy, and secondary breast cancer after mantle-field radiation — the basis for survivorship cardiac and breast surveillance in NCCN survivorship guidelines.

• The 4 T's of the anterior mediastinum: Thymoma, Teratoma (and other germ cell tumors), Terrible lymphoma, Thyroid (retrosternal goiter). Compartment plus patient age narrows the differential faster than any lab.
• Young man + anterior mediastinal mass + elevated AFP = nonseminomatous germ cell tumor. Pure seminoma does not make AFP; a raised AFP overrides a "seminoma" biopsy read. Draw AFP, β-hCG, and LDH before biopsy, and remember the Klinefelter syndrome association.
• Thymoma is the paraneoplastic magnet: myasthenia gravis (anti-AChR antibodies) most often, plus pure red cell aplasia and hypogammaglobulinemia (Good syndrome, presenting as recurrent sinopulmonary infection). This is the single association examiners test most.
• Single best next step with orthopnea, stridor, or syncope when supine: contrast CT and echocardiography before any sedation, with tissue obtained under local anesthesia in a semi-upright or lateral position. Choosing "general anesthesia for mediastinoscopy" in that stem is the trap — positive-pressure ventilation can produce irreversible airway or vascular collapse.
• Do not give empiric corticosteroids before biopsy in suspected lymphoma unless there is airway compromise, cerebral edema, or cord compression; steroid-induced lympholysis destroys diagnostic architecture.
• SVC syndrome is usually an urgency, not an emergency: obtain a histologic diagnosis first; escalate to endovascular stenting only for stridor, altered mental status, or hemodynamic instability.
• Posterior mediastinal mass in a child or adolescent is neurogenic until proven otherwise (neuroblastoma, ganglioneuroma, schwannoma; NF1 link) — get MRI to exclude intraspinal dumbbell extension before resection.
• Distractor to avoid: Kussmaul sign points to constrictive pericarditis, not tamponade, where it is characteristically absent; pulsus paradoxus is the tamponade finding. Likewise, calcification with fat or a tooth on CT means mature teratoma, not thymoma.