Thymoma By L.Jamal

The Thymus

The thymus is a specialized organ of the immune system .

It is located in the ant. mediastinum .

Production of T- Lymphocytes .

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 .

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 .

Cortex : contains thymocytes → T- lymphocytes.

Medulla : contains corpuscles (area of maturation) .

Vasculature

Internal mammary , superior and inferior thyroid arteries .

The veins end in the left brachiocephalic vein (innominate vein), and in the thyroid veins .

Mediastinal Masses

Thymoma .

Lymphoma .

Germ cell tumor .

Thyroid an Parathyroid tumors .

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 .

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 .

Epidemiology

Primary tumors of the mediastinum represent 3% of all chest tumors .

Primary anterior mediastinal masses account for 50 % .

45% are thymomas .

F:M → 1 : 1 .

Thymomas in the pediatric age group tend to run an aggressive course .

Clinical Presentation

30 % local symptoms .

30 % abnormal chest radiographs .

30 % Myasthenia Gravis (paraneoplastic syndrome).

Local symptoms :

Dyspnea .

Dyspahgea .

Cough .

SVC obstruction . Thymomas tend to be highly vascular → bleeding

and necrosis .

Paraneoplastic :

MG.

Hypogammaglobulenemia .

Good syndrome .

Oppurtunistic infections .

Work up

Blood :

CBC : Anaemia , thrombocytopenia , agranulocytosis .

Quantitative Ig studies → Panhypogammaobulinenmia .

CD4 T-cell count .

Pre an post vaccination antibody levels .

Radiology :

Chest x ray .

CT or MRI .

Nuclear imaging ( octreotide scan )

Tissue sampling :

Core biopsies .

FNA .

Limited sternotomy

Mediastinoscopy .

Histologic Findings

Mixed epithelial and lymphoid cells .

4 categories : Spindle cell predominant . Lymphocyte predominant . Mixed . Epithelial predominant .

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 .

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

TTT

Surgical and medical .

Thymectomy is curative in the early stages .

It can be challenging .

Thymectomy releaves obstructive symptoms and improves paraneoplastic symptoms .

Hypogammaglobulinemia shows no improvement after thymectomy and requires monthly Ig infusions .

MG patients show a 25 % improvement in mw after thymectomy .

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 .

Prognosis

Adverse predictive factors :

Invasive tumor .

Tracheal compression .

Young age .

Tumor more than 8 cm .

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)

Thymic Hyperplasia

Increase in the size of the gland with normal microscopic arrangement .

Rare intety .

Presentation is similar to a thymoma .

3 subtypes : Massive thymic hyperplasia .

Common in infancy presents with compressive symptoms .

Thymic hyperplasia assocaited with endocrine abnormalities .

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 .

Management :

Close monitoring for 2 years .

If thymic hyperplasia doesn't regress by 2 years , biopsies and resection are warranted .

Thymic rebound hyperplasia in an 11-year-old girl with Hodgkin lymphoma.