Overview
Mediastinal mesenchymal tumors may remain asymptomatic for years. Over 50% are incidentally detected via imaging, physical exams, or autopsy. Common symptoms include:
- Local symptoms: Chest pain, cough, dyspnea, dysphagia, hoarseness, Horner syndrome, superior vena cava syndrome, or compression of the trachea/heart.
- Systemic symptoms: Fever, night sweats, fatigue, anorexia, or weight loss.
Symptoms correlate with tumor location, size, nature, and growth pattern: - Benign tumors: Often asymptomatic; cystic lesions cause fewer symptoms than solid masses.
- Expansile growth: Causes compression.
- Infiltrative growth: Invades adjacent organs.
Common Mediastinal Mesenchymal Tumors
1. Lipogenic Tumors
(1) Mediastinal Lipoma
- Demographics: Adults, slight male predominance.
- Pathology: Encapsulated, lobulated, yellowish masses with mature adipocytes. May show hemorrhage, necrosis, or calcification.
- Imaging: CT reveals low-density masses (CT ≈ -100 HU) in the anterior mediastinum or cardiophrenic angle.
- Diagnosis: Differentiate from thymolipoma or mediastinal lipomatosis.
- Treatment: Surgical resection; excellent prognosis.
(2) Mediastinal Liposarcoma
- Demographics: Rare, males > females; age 40–60.
- Pathology: Subtypes include well-differentiated, myxoid, round-cell, pleomorphic, and dedifferentiated. Posterior mediastinum common.
- Imaging: MRI superior to CT for assessing tumor extent.
- Treatment: Wide excision + radiotherapy (myxoid subtype is radiosensitive).
- Prognosis: 5-year survival 40%–64%; recurrence rate ~24%.
2. Fibrous Tissue Tumors
(1) Mediastinal Fibromatosis
- Pathology: Non-metastasizing, locally aggressive. Collagen-rich, infiltrative growth around mediastinal structures (e.g., aorta, trachea).
- Symptoms: Superior vena cava syndrome, chest pain, dysphagia.
- Treatment: Complete resection to prevent recurrence.
(2) Mediastinal Fibrosarcoma
- Pathology: High-grade spindle cells with collagen; posterior mediastinum.
- Symptoms: Rapid growth, cough, chest pain, hypoglycemia (insulin-like factor secretion).
- Imaging: Chest X-ray shows well-defined masses; pleural effusion possible.
- Treatment: Radical resection; poor prognosis due to local invasion.
(3) Malignant Fibrous Histiocytoma (MFH)
- Demographics: Most common soft-tissue sarcoma in elderly; rare in mediastinum.
- Pathology: Storiform pattern with fibroblasts, histiocytes, and giant cells. Necrosis/calcification common.
- Imaging: CT/MRI shows heterogeneous masses (posterior/central mediastinum).
- Treatment: Radical surgery; 5-year survival 36%; recurrence rate 40%–55%.
3. Solitary Fibrous Tumor (SFT)
- Pathology: CD34+/STAT6+; 50% malignant. Associated with hypoglycemia (IGF-2 secretion).
- Treatment: Surgery ± adjuvant therapy; poor prognosis in malignant cases.
4. Vascular Tumors
(1) Hemangioma
- Types: Cavernous (90%), capillary, or venous.
- Imaging: CT shows soft-tissue masses ± phleboliths.
- Treatment: Surgical resection.
(2) Hemangioendothelioma
- Pathology: Low-grade malignancy; lung/liver metastases.
- Treatment: Wide excision.
(3) Angiosarcoma
- Pathology: High-grade; infiltrative growth, necrosis.
- Prognosis: Poor; rapid recurrence/metastasis.
(4) Glomus Tumor
- Rarity: Benign; anterior mediastinum.
- Treatment: Surgery; excellent prognosis.
(5) Perivascular Tumors
- Symptoms: Hypoglycemia (renin secretion).
- Imaging: Hypervascular on MRI/angiography.
- Treatment: Preoperative embolization + resection.
5. Lymphatic Tumors
(1) Lymphangioma
- Types: Cystic (most common), capillary, or cavernous.
- Treatment: Challenging resection due to infiltration.
(2) Lymphangioleiomyoma
- Demographics: Females; associated with tuberous sclerosis.
- Complications: Chylothorax.
- Treatment: Surgery; favorable outcomes.
Key Diagnostic Tools
- Imaging: CT/MRI for tumor localization, density, and invasion.
- Biopsy: Histopathology remains gold standard.
- Immunohistochemistry: Essential for subtype classification (e.g., CD34 for SFT).
Management Principles
- Surgery: Primary treatment for resectable tumors.
- Radiotherapy/Chemotherapy: Role varies by subtype (e.g., effective in myxoid liposarcoma).
- Surveillance: Long-term follow-up for recurrence.
Prognosis: Benign tumors generally have excellent outcomes; malignant tumors show high recurrence and mortality.
6. Mediastinal Myogenic Tumors
(1) Mediastinal Rhabdomyoma
This rare tumor can occur in any location, including areas without skeletal muscle. Primary mediastinal rhabdomyoma is exceptionally uncommon. Miller (1978) reported a case originating in the anterior mediastinum, hypothesized to arise from thymic cells. Few cases have been documented in Chinese literature. Surgical resection typically yields a favorable prognosis.
(2) Mediastinal Rhabdomyosarcoma
Rhabdomyosarcoma is a malignant tumor composed of variably differentiated skeletal muscle cells. It is classified into four subtypes based on histology:
- Embryonal (including botryoid variant, the most common),
- Spindle cell,
- Alveolar,
- Pleomorphic.
Epidemiology:
- Alveolar type: Predominantly in adolescents.
- Embryonal type: Common in infants.
- Pleomorphic type: Typically in older adults.
Males are more frequently affected.
Clinical Features:
Often asymptomatic until metastasis occurs. Large tumors may compress adjacent structures. Due to high malignancy, rapid growth, and early metastasis (lymphatic or hematogenous), aggressive treatment is essential.
Treatment:
- Complete surgical resection if localized.
- Combined with radiotherapy and chemotherapy.
Prognosis:
- Botryoid subtype: 5-year survival rate of 95%.
- Spindle cell type: 88%.
- Embryonal type: 66%.
- Alveolar and pleomorphic types: 54%–62%.
7. Other Rare Mediastinal Mesenchymal Tumors
Rare entities include:
- Mesenchymoma,
- Meningioma,
- Synovial sarcoma,
- Extraskeletal osteosarcoma,
- Chondrosarcoma,
- Inflammatory xanthogranuloma (a non-tuberculous granulomatous lesion forming mediastinal masses).
Imaging: Chest X-ray shows smooth-edged, round or lobulated masses protruding into the lung. Surgical resection is recommended for symptomatic large lesions.
Diagnostic Challenges
Due to diverse origins and non-specific symptoms, preoperative diagnosis relies heavily on histopathology. Clinical history, physical examination, and targeted imaging (e.g., CT/MRI) improve diagnostic accuracy.
Staging and Grading of Soft Tissue Sarcomas
Staging and grading are critical for prognosis and treatment planning. Traditional TNM staging is less applicable due to rare lymph node involvement. Simplified systems categorize tumors as low-grade (<15% metastasis risk) or high-grade (≥15%).
ENNEKING Staging System:
- Grade:
- G1: Low-grade (mild atypia, low mitotic activity, minimal necrosis).
- G2: High-grade (marked atypia, high mitotic activity, extensive necrosis).
- Anatomical Extent:
- T1: Intracompartmental (confined to tissue of origin).
- T2: Extracompartmental (invading adjacent structures).
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