Mediastinal Masses & Lung Resection Evaluation

Localizing a mediastinal mass

Three compartments. The anterior (prevascular) compartment lies in front of the pericardium and great vessels; the middle (visceral) compartment holds the heart, trachea, main bronchi, and their nodes; the posterior (paravertebral) compartment runs along the spine. Location sets the differential; age, sex, symptoms, and serum markers narrow it.

Imaging. A mass seen on chest radiograph is characterized next with contrast-enhanced chest CT (fat, fluid, calcification, invasion). MRI best proves a simple cyst (bright on T2) and shows posterior tumors extending into the spinal canal.

Anterior mediastinum: the 4 T's

Thymoma. The most common primary anterior mediastinal tumor in adults, usually at age 40–60. About 30–50% of patients with thymoma have myasthenia gravis, but only 10–15% of patients with myasthenia have a thymoma; every new myasthenia diagnosis still gets a chest CT. Other associations are pure red cell aplasia (isolated anemia with near-zero reticulocytes) and hypogammaglobulinemia with sinopulmonary infections (Good syndrome).

Thymoma management. An encapsulated mass with a typical appearance undergoes en bloc resection with total thymectomy, without preoperative needle biopsy, which can breach the capsule and seed the pleura; biopsy is reserved for masses that look unresectable. Check anti-acetylcholine receptor antibodies first so occult myasthenia is controlled before anesthesia. Radiation is added for invasive or incompletely resected tumors. Thymectomy also benefits generalized AChR-positive myasthenia without a thymoma.

Germ cell tumors. The mediastinum is the most common extragonadal site. Malignant types occur almost entirely in men aged 20–40, who need AFP, β-hCG, and LDH plus a testicular exam and scrotal ultrasound to exclude a gonadal primary. Mediastinal nonseminomatous tumors are associated with Klinefelter syndrome.

Retrosternal goiter. A multinodular goiter extending below the thoracic inlet stays continuous with the cervical thyroid on CT and can compress the trachea, esophagus, or SVC (dyspnea, stridor, dysphagia). Raising both arms may cause facial plethora and neck-vein distension (Pemberton sign). Check TSH; symptomatic goiters are removed by thyroidectomy, almost always through a cervical incision.

Lymphoma. Nodular sclerosis Hodgkin lymphoma affects young adults; T-lymphoblastic lymphoma affects adolescent and young men and can cause SVC syndrome, airway compression, and effusions within weeks. B symptoms: fever >38 °C, drenching night sweats, >10% weight loss over 6 months. Treatment is chemotherapy with or without radiation; surgery only supplies tissue.

Getting tissue safely

A large anterior mass, especially with orthopnea, stridor, or tracheal narrowing on CT, can cause airway obstruction or cardiovascular collapse at induction: paralysis and positive-pressure ventilation remove the chest-wall tone and negative intrathoracic pressure that were holding the airway and heart open.

Local anesthesia first. Obtain tissue with spontaneous breathing preserved: excision of a peripheral (e.g., supraclavicular) node, CT-guided core biopsy, or cytology and flow cytometry of pleural fluid. Fine-needle aspiration alone is inadequate for lymphoma. Empiric glucocorticoids before biopsy can leave the specimen nondiagnostic, so they are reserved for impending airway failure.

Middle and posterior mediastinum

Cysts. Bronchogenic cysts are foregut remnants near the carina or trachea; because they compress airways or become infected, they are usually excised. Pericardial ("spring water") cysts sit at the right cardiophrenic angle and are observed when asymptomatic. Both show water attenuation without enhancement on CT.

Lymphadenopathy. Hilar, paratracheal, or subcarinal nodes suggest sarcoidosis (noncaseating granulomas), lymphoma, TB or histoplasmosis, or metastases. EBUS-guided transbronchial needle aspiration is the least invasive sampling route; mediastinoscopy follows if it is nondiagnostic.

Neurogenic tumors. The most common posterior masses. Adults have nerve sheath tumors, mostly benign (schwannoma most often; neurofibroma in NF1). Children have sympathetic-chain tumors: neuroblastoma (often calcified, elevated urine VMA and HVA), ganglioneuroblastoma, and ganglioneuroma. MRI before resection detects "dumbbell" extension through the neural foramen.

Other posterior lesions. Extramedullary hematopoiesis causes smooth, often bilateral lower-thoracic paravertebral masses in β-thalassemia, sickle cell disease, hereditary spherocytosis, or myelofibrosis. Esophageal cancer, leiomyoma, duplication cysts, and diverticula occupy the retrocardiac space.

Physiologic evaluation before lung resection

FEV1 and DLCO for everyone. A low DLCO predicts complications even when FEV1 is normal. Each value is converted to a predicted postoperative (ppo) value: preoperative % predicted × (1 − segments removed ÷ 19). The right lung has 10 segments (upper 3, middle 2, lower 5) and the left 9 (upper 3 plus lingula 2, lower 4); pneumonectomy estimates use a quantitative perfusion scan.