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Germ Cell Tumors of the Mediastinum in Children


Mediastinum


  • most common extragonadal location in which germ cell tumors are found
  • extends from the posterior aspect of the sternum to the anterior surface of the vertebral bodies and includes the paravertebral
  • the etiology of germ cell tumors of the mediastinum remains unknown

Germ Cell Tumor

  • Benign germ cell tumors are referred to as benign teratomas or dermoids if they are solid
  • Benign germ cell tumors are referred to as epidermoid or dermoid cysts if they are cystic
  • For malignant germ cell tumors, it is divided into into seminomas and nonseminomatous

Pathophysiology


  • Because of the malleable nature and small size of the pediatric airway and other normal mediastinal structures, benign tumors and cysts can produce local symptoms
  • Compression or obstruction of portions of the airway, the esophagus, or the right heart and great veins by an enlarging tumor or cyst easily can occur and can result in a number of symptoms
  • pproximately 95% of patients with germ cell tumors of the mediastinum have an elevated tumor marker. 
  • Alpha-fetoprotein (AFP) is elevated more often than beta human chorionic gonadotropin (bhCG)

Common Germ Cell Tumors

Ganglioneuroma

  • Ganglioneuromas are the most common neurogenic chest tumors of childhood
  • The tumor cells have their origin from the sympathetic chain which runs down either side of the spine.
  • Because they are well encapsulated, they are easily removed surgically
  •  In rare cases, ganglioneuromas can be a result from a reverse transformation of a malignant tumor neuroblastoma

Neuroblastomas

  • common extracranial solid cancer in childhood and the most common cancer in infancy
  • Neuroblastomas are malignant tumors arising from cells of the sympathetic nerve chain or the adrenal gland
  • Elevated levels of substances in the urine known as catecholamines or their byproducts such as vanillylmandelic acid and homovanillic acid (usually elevated) can suggest the diagnosis
  • euroendocrine tumor, arising from any neural crest element of the sympathetic nervous system
  • on microscopy, the tumor cells are typically described as small, round and blue, and rosette patterns (Homer-Wright pseudo-rosettes) may be seen
  • on chest x-ray: can be dumbbell-shaped and extend into the spinal canal
  • overall survival for children with a mediastinal primary is 80%

Teratoma


  • Teratoma is the third most common mediastinal tumor
  • often have elevated serum α-fetoprotein levels and may have an elevated serum β-human chorionic gonadotropin level
  • Removal of the entire tumor is the strongest predictor of survival
  • often are divided into mature, immature, and teratoma with malignant components

Thymoma

  • Thymomas are tumors of the thymus gland and are extremely rare in children
  • An enlarged thymus in early infancy can look like a tumor and result in breathing difficulties
  • Thymic cortical epithelial cells have abundant cytoplasm, vesicular nucleus with finely divided chromatin and small nucleoli and cytoplasmic filaments contact adjacent cells. 
  • thymic medullary epithelial cells in contrast are spindle shaped with oval dense nucleus

Schwannoma

  • also known as an "neurilemmoma,"
  • a benign nerve sheath tumor composed of Schwann cells
  • Common in patients  between the ages of 20 and 50
  • most commonly arise in the parevertebral sulci, in the posterior mediastinum
  • characteristic features include presence of alternating  Antoni A and Antoni B areas
    • Antoni A area is composed  of spindle shaped Schwann cells arranged in interlacing fascicles.
    • There may be nuclear palisading
    • Antoni  B area consists of loose meshwork of gelatinous and microcystic tissue

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