Read first the text book: Computed Tomography and Magnetic resonance of the Thorax by Nadich et all

Then go through this exercise to assess your comprehension

Review of anterior Mediastinal masses

Q: What are the boundaries of anterior mediastinum?

• Sternum anteriorly
• Suprasternal notch superiorly
• Heart , Aorta and Brachiocephalic vessels posteriorly
• Lungs on either side

Q: What are the normal structures in anterior mediastinum?

• Thymus
• Lymph nodes
• Mesenchymal tissue

Q: What are the common anterior medistinal masses?

• Thymic lesions
• Teratoma
• Thyroid (Intrathoracic goiter)
• Terrible Lymphoma
• Testicular tumor metastasis
• Mesenchymal neoplasms

Q: What is the normal size of Thymus?

• There is a wide variation in size under 25 years old
• Thymus increases in size from birth to puberty to a maximum size
• Rapid involution starting from puberty over a period of 5-15 years.
• Replaced by fat.
• Negligible after 60 years

Q: Describe normal Thymus location and configuration

• Thymic morphology changes with age . 
• Bilobed fused at apex near thyroid gland.
• Smoothly molded to the anterior aspect of great vessels
• Located in anterior mediastinum

Thymic morphology changes with age . 

Q: Describe normal Thymus location and configuration "birth to puberty" .

• Thymus entirely fills the anterior mediastinum
• Equal to higher than muscle density
• Borders are convex
• Triangular
• Lacks fat

Q8: Describe Thymus "Puberty to 25 years"

• Fat appears
• Distinct triangular bilobed structure
• Flat and concave laterally
• Density less than muscle

Q9: Describe Thymus over 25 years

• No definable structure
• Anterior mediastinum fatty

Q: List conditions where there is Thymic enlargement

Normal 1.8 cm thickness before age 20

• Hyperthyroidism
• Acromegaly
• Addisons

Q: What is Thymic hyperplasia

• Germinal or lymphoid follicular hyperplasia
• Cannot diagnose by CT
• purely a histological diagnosis

Q: Describe CT appearanace of Thymoma

• Lobular contour
• Homogenous soft tissue density; oval or round or lobulated mass
• Sharply demarcated
• Enhances homogeneously
• May contain calcium
• Asymmetric

Q: What are the  malignant characteristics of  Thymoma

• Invasive Thymomas are slow growing
• Malignant Thymomas infiltrate adjacent  mediastinal structures pleura and pericardium
• Rarely metastasizes outside thorax
• Invasive Thymoma grow along pleural surfaces can reach posterior mediastinum along aorta to involve the crus of the diaphragm and the retroperitineum

Q: Should we rely on histology or Radiology to determine whether Thymoma is malignant?

It is difficult to judge maligancy from Hitological exam 

More reliable criteria is from gross characteristics of local; invasion or complete encapsulation.

Q: Why should Thymoma be resected routinely?

• Surgical resection of all Thymomas are indicated because 30% of cases are invasive
• 30% of Thymomas are malignant

Q: Describe the relationship between Thymoma and Myasthenia gravis

• Thymoma occurs in 15% of patients with Myasthenia gravis
• 65% of patients with Myasthenia have thymic hyperplasia
• Thymectomy (normal or abnormal) is indicated only when not controlled medically
• Cures and remissions following Thymectomy (normal or with Thymoma) has been observed

Q: What are other Thymic tumors besides Thymoma

• Hodgkin's
• Thymic cyst
• Thymolipoma

Q: What is the common age at which Thymoma is encountered?

Thymomas are rare below the age of 25

Q: What is Thymic rebound

• Involutes during periods of stress (Burns, Chemotherapy)
• Rebounds in size following resolution of stress

Thyroid

Q: What is the incidence of intra-thoracic goiter? 

• Intra-thoracic extension is common

• 10% of mediastinal masses

Q: What is the normal location  of intra-thoracic goiter? 

• Arise from lower pole or the isthmus of thyroid and extend into anterior mediastinum in front of trachea

• In thyro-pericardiac space in anterior mediastinum in front of subclavian and innominate vessels

• Posterior mediastinal goiter in 20% of cases Usually on right side Arising from posterior aspect of thyroid and extends behind trachea, innominate vein and artery.

Q: What are the CT characteristics of intra-thoracic goiter.

• Represents direct contiguous growth of goiter into the mediastinum. Demonstration of communication with the cervical portion of thyroid gland

• Easily identifiable because of increased density due to its high iodine content

• Inhomogeneous densities with small cystic areas, and curvilinear, punctate or ring like calcification

• No fat (Differential from Teratoma)

• Marked enhancement with contrast

• Prolonged enhancement of the gland (Active trapping of iodine contained in the contrast medium)

Q: What are the CT findings suggesting potential malignancy of intra-thoracic goiter?

• Marked irregularity of contour

• Loss of distinct facial planes

• Presence of cervical or mediastinal adenopathy

Q; Clinical manifestations

• Asymtomatic mostly

• Tracheal compression (stridor, respiratory distress, hoarseness worsened by movements of neck

• Goiter in neck extending to mediastinum. Cannot feel the lower margin.

• Rarely can cause superior vena caval obstruction

Q: What are the indications for surgical resection of intra-thoracic goiter?

• To relieve symptoms

• Acute hemorrhage

• Inflammation

Surgical approach depends on precise location

Q: Germinal cell tumors

• Benign Dermoid cysts
• Benign and malignant Teratoma
• Endodermal sinus tumors
• Seminoma
• Choriocarcinoma
• Embtyonal carcinomas

Arise from primitive germ cell rests 

Dermoid cysts and Teratoma

• Solid or cystic
• Dermoid: Tumor consists only of epidermis and appendages
• Teratoma: Ectodermal, mesodermal and endodermal derivatives
• Cystic lesions are usually benign benign lesions are round or oval with smoot contour.
• Solid lesions are usually malignan and tend to be lobulated
• Located close to heart and great vessels in the anterior mediastinum
• Dermoid Bone or tooth inside
• Teratoma: Fat, bone, teeth, globular calcification
• Trochoptysis; Coughing up hair from ruprured dermoid into trachea.

Seminoma: Rare

Primary Choriocarcinoma: Rare

Lymphoma is primary neoplasm of the lympho-reticular system

Q: How do you classify Lymphoma?

Answer

Q: How do you classify Lymphoma?

• Hodgkin's Lymphoma
• Non-Hodgkin's lymphoma

Q: What is the incidence of Mediastinal involvement in Lymphoma?

Answer

Q: What is the incidence of Mediastinal involvement in Lymphoma?

• Hodgkin's more common in mediastinum
• 50-80 % of HD present with mediastinal adenopathy
• Less than 20% of NHL present with mediastinal adenopathy

Lymphomatous nodes is not distinctive and can range from well-defined nodes to diffuse extensive involvement

Hilar adenopathy in the absence of mediastinal adenopathy is unusual

Q: What are the characteristics of mediastinal lymph node involvement in HD and NH Lymphoma?

Answer

Q: What are the characteristics of mediastinal lymph node involvement in HD and NH Lymphoma?

• Anterior mediastinal, Para-tracheal and hilar nodes is 3-4 times more common in HD than with NHL
• Para-cardiac and posterior mediastinal nodes is almost exclusively seen in NHL
• Internal mammary node is 10 times more common in HD than in NHL

Q: What is the mode of spread in HD and NH Lymphoma?

Answer

Q: What is the mode of spread in HD and NH Lymphoma?

• HRD is unifocal and spreads by contiguity to involve adjacent lymph node groups
  • Skipped areas are unlikely
• IN NHL the disease can be generalized  And non-contiguous spread is common.

Q: What is the role of CT in evaluating residual mass in Lymphoma?

Answer

Q: What is the role of CT in evaluating residual mass in Lymphoma?

• CT has a major role for monitoring size of nodes during therapy
• In some cases residual masses consist of fibrotic residual tissue "sterilized" lymphoma
• Sterilized mass cannot be distinguished from mass containing residual lymphoma

Q; Mesenchymal neoplasms

• Lipoma

• Fibroma

• Hemangioma

• Lymphangioma

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