THYMIC TUMORS
GENERAL THORACIC SURGERY
CHAPTER 167
Thymic tumor
• Almost in the anterior mediastinum.
• Secondary to neurogenic tumor in
mediastinal tumor.
• Rare in children younger than 16 y/o.
Thymic tumor
• Separated into three histologic categories—
Thymoma.
Thymic carcinoma.
Neuroendocrine tumor.
THYMOMA
Location
• 95% in anterior mediastinum.
• Neck.
• Left hilar region.
• Within lung parenchynma.
• Anterior cardiophrenic angle.
Pathology
• All thymoma derive from thymic epithelial
cell.
• Predominantly lymphocytic thymoma
（more than 66% lymphocyte）.
• Predominantly epithelial thymoma （more
than 66% epithelial cell）.
• Mixed lymphoepithelial thymoma.
• Spindle cell tumor.
Pathology
• Most important gross feature — The presence or
absence of encapsulation of tumor and the gross
invasion into adjacent structure.
• The invasion present — The thymoma must be
considered malignant lesion regardless the
microscopic appearance.
• Extensive spread.
• Incidence of distal metastasis is 3%.
• Stage.
Another class
• Cortical.
• Medullary.
• Mixed thymoma.
• Immunohistochemistry.
Clinical presentation
• 50-60 y/o.
• Sex distribution — Equal.
• s/s — chest pain, SOB, cough, SVC
syndrome, paralysis of hemidiaphragm,
hoarseness, weight loss, fatigue, fever, night
sweats.
Parathymic syndrome
• 40% with parathymic syndrome.
• Myasthenia gravis.
• Pure red cell aplasia.
• Immunoglobulin deficiency.
• Systemic lupus erythematosus—infrequently,
2.5%, poor prognosis.
• Nonthymic cancer—17-21%.
• Inappropriate antidiuretic hormone secretion
（SIADH）-- rarely, malignant thymoma and
spindle cell thymoma.
Myasthenia gravis
• Most commonly associated disease.
• 30% of patient with thymoma associate with MG.
• Only 5-15% patient with MG have thymoma.
• 10-15 older than patient with MG without tumor,
younger than patient with thymoma without MG.
• Any type of thymoma except spindle type, marked
associated squamous elements in thymus.
• Little affect on local presention, clinical behavior,
prognosis.
• Better prognosis than patient with thymoma
without MG.
Pure red cell aplasia
• Anemia.
• Suppression erythrogenesis in bone marrow.
• Mechanism--Not clear, IgG antibodies inhibit
erythropoietin or hemoglobin synthesis, cytotoxic
to erythroblast, decrease B cell.
• 50 % patients with red cell aplasia have thymoma,
5% thymoma with red cell aplasia.
• Most （70%）are non-invasive spindle cell.
• 25-33% patient with red cell aplasia benefit from
excision of the thymoma.
Immunoglobulin deficiency
• Spindle cell type.
• Acquired hypogammaglobulinemia.
• Suppressor T-cell inhibiting immunoglobulin
synthesis.
Diagnostic studies
• Standard posteroanterior and lateral chest
radiographies.
• CXR—Smooth or lobulated mas, right side the
silhouette sign present, left side the sign abscent.
• Calcification — 10%.
• CT—Delineate the extent of mass, cannot not
differentiating benign and malignant, assessing
intrathoracic spread of an invasive thymoma.
Surgical biopsy
• Unnecessary for a suspected locally symptomatic
thymoma, because the capsule of tumor may be
violated by invasive procedure.
• Only distinguish the tumor from the other
malignant tumor, or locally symptomatic, clearly
nonresectable, biopsy is to establish the diagnosis
before making decision of therapy.
• Fine needle biopsy by CT or sono-guide.
• Extend substernal mediastinoscopy.
• Anterior mediastinotomy.
• Lateral thoracotomy.
• VATS.
Treatment
• Depend on clinical presentation.
• Surgical resection — thymoma is encapsulated
and free from adjacent structure.
• Radiation — in atage II, III.
• chemotherapy — in locally nonresectable,
presence distal metastasis, neoadjuvant therapy for
initially advanced local diasease or in locally
recurrent disease.
Surgical excision
• All patient with thymoma should undergo as
complete resection as possible.
• Pulmonary lesion should be excised at the same
time.
• Tumor encapsulated — total thymectomy.
• Simple enucleation is avoid except the unusual
condition（excision through lateral thoracotomy
with unknown preoperative diagnosis）.
Surgical excision
• Preferred median sternotomy.
• Posterolateral thoracotomy — for large tumor in
hemithorax or tumor from anterior cardiophrenic
angle.
• Bilateral anterior fourth intercostals incisionwith
transverse section of sternum （clamshell） —
for large midline tumors.
• The use of video-assisted thoracoscopic removal
of thymoma is unacceptable even for stage I tumor.
Surgical excision
• Extend procedure the entire thymus and
adjacent fat should be removed if possible.
• Tumor fixation to nonvital adjacent
structure should be resect（pleura, lung,
pericardium, ）.
Surgical excision
• One phrenic nerve involve could be resected if
patient could tolerate loss of hemidiaphragm
function.
• If both phrenic are involved, only debulking is
performed.
Surgical excision
• The wall of SVC involve — if no SVC
syndrome, lateral wall resection of SVC and
replace graft.
• When the aorta, major pulmonary vessels,
recurrent nerve trachea, are involve, only
debulking.
• Operative mortality 3.1%-7.7%.
Radiation therapy
• For invasive thymoma.
• In stage I is uncertain.
• For resected stage II or completely or
incompletely resected stage III disease.
• 4500-5000 cGy for suspected microscopic residual
disease.
• 6000 cGy for known residual disease.
• Brachytherapy with I-125 seed placed in gross
residual disease at time of operation.
Chemotherapy
• For stage III and IV.
• Cisplatin, doxorubucin, vincristine,
cyclophosphamide, neoadjuvant.
Treatment of recurrent local
disease or distant metastases
• Recurrent I — 0-5%, II — 10%, III — 30%,
IVa — 33%.
• Second resection if possible.
• 5-year survival is 65%.
• For stage III recurrent — irradiation or
chemotherapy.
Survival
• Depend on — stage, tumor size, histology,
extent of resection.
• Better in patient with thymoma associated
with MG.
• Poor in patient with red cell aplasia,
hypogammaglobulinemia, SLE.
Thymic carcinoma
• Low and high grade.
• Malignant cytologic and architectural
feature.
• Staging not standardized.
Squamous cell carcinoma
• Most common.
• Men predominant.
• 60 y/o.
• Partially encapsulated.
• s/s — weight loss, chest pain, cough, hemoptysis.
• Treatment—Surgical resection, sensitive to
radiation, combination chemotherapy.
• Prognosis excellent in well-differentiated
squamous cell carcnoma.
Lymphoepitheliomalike
carcinoma
• Epstein-Barr virus.
• Treatment—irradiation therapy,
chemotherapy.
Tumor of neuroendocrine cell origin
• Thymic carcinoid tumor.
• Small cell carcinoma.
Thymic carcinoid tumor
• Large.
• One-half lesion infiltrative into adjacent structures.
• Associated Cushing’s syndrome.
• 3/4 are men.
• Mean age 42 y/o.
• s/s — asymptomatic, chest pain, cough dyspnea,
SVC syndrome, fatigue fever, night sweat.
Thymic carcinoid tumor
• 1/3 have feature of Cushing sundrome — ectopic
ACTH production.
• 15-18% with multiple endocrine neoplasia（MEN）
syndrome.
• Most MEN I.
• Few MEN II.
• Thymic carcinoid associated with MEN syndrome
is more malignant in behavior.
• 1/3 with bone metastases.
Multiple endocrine neoplasia
（MEN）
• MEN I（Werner syndrome)– Single or
multiple parathyroid adenoma, islet cell
tumor of pancrease, adrenal neoplasm,
thyroid adenoma, multiple lipoma.
• MEN II（Sipple syndrome)—Thyroid
medullary carcinoma, pheochronocytoma,
parathyroid neoplasia.
Thymic carcinoid tumor
• Treatment—complete surgical resction or
debulking tumor, radiation therapy.
• 73% local recurrence or metastases.
• Overall cure rate is low — 13%.
• Mean survival of metastases disease is 3
years.
Small （Oat）cell carcinoma
• Aggressive and metastases extensively,
• Associated with MEN I.
• Treatment—radiation therapy and
chemotherapy.