Mediastinal Disorders

Fig. 5.1.
Medial view of the left hemithorax. Used with permission from the McGill University Health Centre Patient Education Office.
A325685_1_En_5_Fig2_HTML.gif
Fig. 5.2.
Medial view of the right hemithorax. Used with permission from the McGill University Health Centre Patient Education Office.
Table 5.1.
Differential diagnosis of a mediastinal mass based on compartment.
Anterosuperior compartment
Middle compartment
Thymus
Thymic hyperplasia
Lymph node
See anterosuperior compartment
Thymoma
Cyst
Bronchial cyst
Thymic carcinoma
  
Pericardial cyst
Carcinoid tumor
  
Enteric (duplication) cyst
Small-cell carcinoma
Esophagus
See posterior compartment
Thymolipoma
Posterior compartment
Thymic cyst
Neurogenic
Schwannoma
Germ cell
Teratoma
  
Neurofibroma
Dermoid cyst
  
Ganglioneuroma
Seminoma
  
Ganglioneuroblastoma
Choriocarcinoma
  
Neuroblastoma
Embryonal cell carcinoma
Esophagus
Duplication cyst
Yolk sac tumor
  
Diverticulum
Lymph node
Inflammatory
  
Benign tumor
Infectious
  
Malignant tumor
Malignant (metastasis)
Other
Meningocele
Lymphoproliferative disorder
  
Paraganglioma
(e.g., lymphoma)
    
Mesenchymal
Fibroma/fibrosarcoma
    
Lipoma/liposarcoma
    
Lymphangioma
    
Hemangioma
    
Endocrine
Thyroid
    
Parathyroid
    
Vascular
Aneurysm
    
  • Anterior Compartment: anterior to pericardium and reflection over the great vessels.
    • Includes: thymus gland, lymph nodes, fat
    • In adults, approximately 50 % of mediastinal masses are located in the anterosuperior compartment
    • >90 % consist of thymomas, ectopic thyroid tissue, germ cell tumors, or lymphomas
  • Middle Compartment: bound by anterior and posterior edges of the pericardium
    • Includes: heart, pericardium, ascending and transverse aorta, brachiocephalic vessels, vena cavae, pulmonary arteries and veins, phrenic and vagus nerves, trachea, bronchi, and lymph nodes
  • Posterior Compartment: posterior to pericardium, heart, and trachea and extends to the thoracic vertebral column and paravertebral gutters
    • Includes: esophagus, descending aorta, azygos and hemiazygos veins, thoracic duct, sympathetic chain, and lymph nodes
      Clinical Presentation (Table 5.2):
      Table 5.2.
      Clinical presentation of a patient with a mediastinal mass.
      Locoregional symptoms
      Systemic symptoms
      Somatic
      Chest pain
      Constitutional Symptoms
      Night sweats
      Pulmonary
      Cough
      		  
      Fatigue
      Wheezing
      		  
      Weight loss
      Stridor
      		  
      Pel–Ebstein fevers
      Dyspnea
      Systemic
      Thyrotoxicosis
      Hemoptysis
      Syndromes
      Hypercalcemia
      Post-obstructive pneumonitis
      		  
      Hypoglycemia
      Recurrent pneumonia
      		  
      Osteoarthropathy
      Cardiovascular
      Superior vena cava syndrome
      		  
      Autoimmune syndrome
      Pericardial tamponade
      		  
      Paraneoplastic syndrome
      Congestive heart failure
      		  
      Yolk sac (endodermal cell) tumor
      Neurogenic
      Hoarseness
      		    
      Horner’s syndrome
      		    
      Phrenic nerve paralysis
      		    
      Brachial plexopathy
      		    
      • Majority are asymptomatic and discovered incidentally (especially benign lesions)
      • Symptomatology related to local mass effect, invasion of surrounding structures, and immunologic and hormonal factors related to the lesion. Systemic symptoms (e.g., Type B symptoms) are also seen in lymphoma.
      • Physical examination: a full head-to-toe examination, including peripheral lymph nodes and testes in men.
      • Diagnosis made by considering the patient’s age, location of the mass, presence or absence of locoregional and distant clinical manifestations:
      Workup
      • Laboratory: full blood panel, including thyroid function tests, tumor markers (α-fetoprotein (AFP), β-human Chorionic Gonadotropin (βhCG)), cardiac enzymes for chest pain, and autoantibody assays for suspected autoimmune syndromes.
      • Imaging:
        • Contrast enhanced CT is the modality of choice for detailed characterization of the mass (Fig. 5.3).
          A325685_1_En_5_Fig3_HTML.jpg
          Fig. 5.3.
          Axial cuts from contrast enhanced CT scan of thymoma in the anterior compartment of the mediastinum.
        • MRI used as an adjunct to provide additional information about the tissue planes and margins, as well as to differentiate between tumor compression and invasion of surrounding structures.
        • FDG-PET:
          • High uptake more likely to correlate with invasiveness and is seen in thymic carcinoma and invasive thymoma [1, 2].
          • Comparable sensitivity and specificity to CT scan.
          • Significantly higher sensitivity compared with gallium-67 scintigraphy for non-Hodgkin’s lymphoma and Hodgkin’s lymphoma [3, 4].
      • Tissue diagnosis:
        • Routine needle biopsy (FNA and core-needle) is typically avoided and the choice of resection or biopsy is made according to the most likely diagnosis based on workup.
          • If lymphoma is suspected, biopsy is required.
          • Well-encapsulated lesions unlikely to be lymphoma can be directly resected.
          • Locally invasive and unresectable lesions (other than lymphoma) are typically biopsied and evaluated for possible neoadjuvant therapy (e.g., thymic carcinoma).
        • Complications of biopsy include: pneumothorax (20–25 %), hemoptysis (5–10 %), significant hemorrhage (rare), and tumor seeding along needle tract (extremely rare).
        • Incisional and excisional biopsies may also be performed under general anesthesia. This may not be possible for patients with high risk of cardiopulmonary compromise (e.g., posture-related dyspnea, SVC syndrome). Options include:
          • Mediastinoscopic biopsy
          • 2nd/3rd intercostal space parasternal mediastinotomy (Chamberlain procedure)
          • Transcervical approach
          • VATS

      Thymoma

      Overview
      • Most common neoplasm of the anterosuperior compartment in adults.
        • Incidence: 0.15 per 100,000 person-years in the USA; M = F [5]
        • Rare in the first 2 decades of life
        • Incidence peaks at ages 30–40 (with associated myasthenia gravis (MG)) and 60–70 (without MG) [6]
      • Slow-growing epithelial tumor that spreads by local invasion. Extra-thoracic metastases are uncommon [7]
      Pathology
      • Controversial distinction between thymomas and thymic carcinomas (Table 5.3).
        Table 5.3.
        Classification of mediastinal masses originating from the thymus.
        Thymus hyperplasia
        		  
        Epithelial neoplasms
        Thymoma
        Thymic carcinoma
        Thymic neuroendocrine tumors
        –  Carcinoid tumor
        –  Small-cell carcinoma
        Thymolipoma
        		  
        Thymic cyst
        		  
        • WHO Classification (Table 5.4) stratifies them along a continuum [8].
          Table 5.4.
          WHO classification of thymomas and thymic carcinomas [8].
          WHO classification
          Epithelial cell shape
          Epithelial cell atypia
          Lymphocyte
          Organotypic “(Thymus-like)”
          Incidence (%) [29]
          A
          Spindle
          Minimal
          Poor
          Yes
           9
          AB
          Spindle/polygonal
          Minimal
          Moderate
          Yes
          24
          B1
          Polygonal
          Minimal
          Abundant
          Yes

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          Sep 23, 2016 | Posted by in CARDIOLOGY | Comments Off on Mediastinal Disorders

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