Thymoma By L.Jamal. The Thymus The thymus is a specialized organ of the immune system. It is located...
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Thymoma By L.Jamal
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The Thymus
The thymus is a specialized organ of the immune system .
It is located in the ant. mediastinum .
Production of T- Lymphocytes .
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The Thymus
A pyramid shaped organ , pinkish grey in colour with a soft and lobulated surface .
5 cm in length , 4 cm in breadth and 6mm in thickness.
Wieghs 20-35 grams during puberty and regresses to 6 gr in adulthood .
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Structure
2 lobes , each lobe is composed of multiple lobules and sorrounded in a capsule .
Each lobule consists of multiple follicle.
Each follicle is divided into a capsule and medulla .
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Cortex : contains thymocytes → T- lymphocytes.
Medulla : contains corpuscles (area of maturation) .
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Vasculature
Internal mammary , superior and inferior thyroid arteries .
The veins end in the left brachiocephalic vein (innominate vein), and in the thyroid veins .
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Mediastinal Masses
Thymoma .
Lymphoma .
Germ cell tumor .
Thyroid an Parathyroid tumors .
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Thymoma
A neoplasm of the Thymic epithelial cells .
Results from dysregualtion of the proliferation and maturation of T- lymphocytes .
This process results in either Autoimmunity or Immune defeciency .
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As a result , thymomas are associated with autoimmune diseases in 70% of the patients during diagnosis .
Thymomas are ussually encapsulated and spread by local extension .
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Epidemiology
Primary tumors of the mediastinum represent 3% of all chest tumors .
Primary anterior mediastinal masses account for 50 % .
45% are thymomas .
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F:M → 1 : 1 .
Thymomas in the pediatric age group tend to run an aggressive course .
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Clinical Presentation
30 % local symptoms .
30 % abnormal chest radiographs .
30 % Myasthenia Gravis (paraneoplastic syndrome).
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Local symptoms :
Dyspnea .
Dyspahgea .
Cough .
SVC obstruction . Thymomas tend to be highly vascular → bleeding
and necrosis .
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Paraneoplastic :
MG.
Hypogammaglobulenemia .
Good syndrome .
Oppurtunistic infections .
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Work up
Blood :
CBC : Anaemia , thrombocytopenia , agranulocytosis .
Quantitative Ig studies → Panhypogammaobulinenmia .
CD4 T-cell count .
Pre an post vaccination antibody levels .
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Radiology :
Chest x ray .
CT or MRI .
Nuclear imaging ( octreotide scan )
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Tissue sampling :
Core biopsies .
FNA .
Limited sternotomy
Mediastinoscopy .
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Histologic Findings
Mixed epithelial and lymphoid cells .
4 categories : Spindle cell predominant . Lymphocyte predominant . Mixed . Epithelial predominant .
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WHO classification :
A : Spindle or Oval cells .
B : dendredtic or epitheloid .
AB: mixed .
C : resembles other organs . Types A , AB → benign . Type B , C → malignant .
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Staging
Masaoka Staging system .
I : Macrospcopically encapsulate , no capsular invasion .
II: Macroscopic invasion to surrounding tissue or microscopic capsular invasion .
III : Macroscopic invasion into neighboring organs.
IVa : Pleural or pericardial dissemination.
IVb : Lymphogenous or hematogenous metastases
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TTT
Surgical and medical .
Thymectomy is curative in the early stages .
It can be challenging .
Thymectomy releaves obstructive symptoms and improves paraneoplastic symptoms .
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Hypogammaglobulinemia shows no improvement after thymectomy and requires monthly Ig infusions .
MG patients show a 25 % improvement in mw after thymectomy .
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Radiotherapy : unresectable tumors & post sugical resection .
Primary radiotherapy for stages III & IVa improved the 5y survival 40-50 % .
Chemotherapy : for stages IV a , b using Cisplatin , Vincristine & Doxyrubicin .
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Prognosis
Adverse predictive factors :
Invasive tumor .
Tracheal compression .
Young age .
Tumor more than 8 cm .
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5 & 10 year survival
Type A - 100% and 95%, respectively Type AB - 93% and 90%, respectively Type B1 - 89% and 85%, respectively Type B2 - 82% and 71%, respectively Type B3 - 71% and 40%, respectively Type C - 23% (5-year survival rate)
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Thymic Hyperplasia
Increase in the size of the gland with normal microscopic arrangement .
Rare intety .
Presentation is similar to a thymoma .
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3 subtypes : Massive thymic hyperplasia .
Common in infancy presents with compressive symptoms .
Thymic hyperplasia assocaited with endocrine abnormalities .
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Rebound thymic hyperplasia :
The thymus gland regresses in size during times of severe stress then enlargres beyond normal .
Seen following , severe burns , pneumonia , tuberculosis and malignancies .
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Management :
Close monitoring for 2 years .
If thymic hyperplasia doesn't regress by 2 years , biopsies and resection are warranted .
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Thymic rebound hyperplasia in an 11-year-old girl with Hodgkin lymphoma.
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