The histological and radiological spectrum of mediastinal tumors is broad. Thymoma, neurogenic tumors, and benign cysts are the most common lesions in the mediastinum, accounting for 65 percent of patients with mediastinal tumors. 80 percent of pediatric lesions are neurogenic tumors, germ cell neoplasms, and foregut cysts, whereas primary thymic neoplasms, thyroid masses, and lymphomas are the most prevalent in adulthood.
The pleural cavities laterally, the thoracic inlet superiorly, and the diaphragm inferiorly defines the mediastinum. Many anatomists subdivide it further into anterior, middle, and posterior divisions. Thymoma, teratoma, thyroid mass, and lymphoma are all examples of anterior mediastinal tumors, which account for half of all mediastinal tumors. Congenital cysts in the middle mediastinum are common, whereas neurogenic cysts in the posterior mediastinum are common.
Cough, chest pain, fever, and breathlessness are common symptoms at presentation. Local symptoms (respiratory restriction; paralysis of the limbs, diaphragm, and vocal cords; Horner syndrome; superior vena cava syndrome) are caused by tumor invasion, whereas systemic symptoms are caused by the production of excess hormones, antibodies, or cytokines.
Despite their rarity, the exact prevalence of mediastinal masses is unknown due to a lack of consistency in the classification and characterization documented in the medical literature. The majority of them are benign, with only around a quarter of them being cancerous.
The thoracic inlet is on the superior side, the diaphragm is on the inferior side, and the medial pleural reflections of the lungs are on the medial side. The anterior, middle, and posterior mediastinum are the three anatomic divisions that make up the mediastinum.
The anterior mediastinum contains more than half of all mediastinal masses, with the remaining evenly distributed across the middle and posterior mediastinum. They are frequently formed by structures within or passing through the mediastinum. The sternum, pericardium, and brachiocephalic vessels are all included in the anterior mediastinum. Connective tissues, fatty tissues, the thymus gland, the anterior mediastinal lymph nodes, and the internal mammary arteries and veins are all found in this area.
Between the anterior and posterior mediastinum is the middle mediastinum. The heart, vena cava, ascending and transverse aorta, brachiocephalic vessels, phrenic nerves, trachea, principal bronchi, lymph nodes, and pulmonary arteries and veins are all located in the middle mediastinum.
The descending thoracic aorta, esophagus, thoracic duct, paravertebral autonomic chain ganglia, azygos and hemiazygos veins, and posterior mediastinal lymph nodes make up the posterior mediastinum.
Mediastinal Tumors Types
Tumors that originate in the mediastinum are known as mediastinal tumors. They might be malignant (cancerous) or non-cancerous (benign). Because certain mediastinal tumors grow in certain locations of the mediastinum, doctors classify it into three parts:
- Anterior (front)
- Posterior (back)
The most common site for a mediastinal mass is anterior, with approximately 35 percent being thymic malignant tumors, roughly 25% being lymphomas, 15% being thyroid or other endocrine tumors, 10% being benign teratomas, and another 10% being malignant germ cell tumors, with the remaining 5% generally consists of benign thymic masses. In the anterior mediastinum, lipomas, liposarcomas, hemangiomas, fibromas, fibrosarcoma, and Foramen of Morgagni diaphragmatic hernias are less prevalent.
A mass in this area in both males and females over the age of 40 is most probably a thymoma (50 percent). The next most prevalent condition is a substernal thyroid goiter, which affects 10% to 30% of patients, followed by lymphoma, thymic cysts, teratomas, and germ cell tumors.
Lymphoma (either Hodgkin's lymphoma or mediastinal large-cell non-Hodgkin’s lymphoma) is the most prevalent cancer among adult women under the age of 39, followed by thymic tumors and benign teratomas. There is no one mass type that predominates in men under the age of 40.
Lymphadenopathies secondary to metastases or granulomatous diseases, vascular masses, and foregut duplication cysts such as pleuropericardial and bronchogenic cysts account for about 25% of middle mediastinum masses.
Neurogenic tumors (e.g., Schwannomas, Neurofibromas), meningoceles, meningomyelocele, gastroenteric cysts, and esophageal diverticula are the most frequent posterior mediastinal masses. In the posterior mediastinum, Foramen of Bochdalek hernias and paraosseous extramedullary hematopoiesis are less prevalent.
The most prevalent primary tumor of the thymus and the most common tumor of the anterior mediastinum is a thymoma, which is an uncommon tumor. It affects both men and women equally and is most common after the age of 40. It's a type of epithelial neoplasm made up of epithelial cells and mature lymphocytes. About 35% of them are invasive, while the rest are encapsulated. The most common therapy for thymoma is complete surgical resection. An invasive thymoma, a partially resected thymoma, or a disseminated thymoma may be treated with radiotherapy or chemotherapy. The majority of patients with an encapsulated thymoma can be treated with surgery, and many patients with microscopically invasive thymoma can be treated with surgery and radiation therapy. Patients with macroscopic invasion frequently have a long survival with slowly progressing metastatic disease.
Lymphomas are malignancies of the lymphocytes, which are a type of white blood cell. These cells aid in the battle against infections. B and T lymphocytes can both produce lymphomas. T lymphocytes play a crucial role in the immune system's regulation and the fight against viral infections. Antibodies are produced by B lymphocytes, which are critical in the battle against some infections.
Lymphocytes travel throughout the body via the circulation and a network of tubular channels known as lymphatic vessels. Lymph nodes, which hold lymphocyte collections, are dispersed across the lymphatic channel network. Lymphoma cells are malignant lymphocytes that can stay in a single lymph node or move to the bone marrow, blood, spleen, or almost any other organ.
Hodgkin lymphoma (also known as Hodgkin's disease) and Non-Hodgkin lymphoma are the two main types of lymphoma. Hodgkin lymphoma is rarer than non-Hodgkin lymphoma. Non-Hodgkin lymphoma is divided into several subgroups.
Mediastinal Tumors Epidemiology
Mediastinal tumors are uncommon in general. Mediastinal tumors are most commonly identified in people between the ages of 35 and 50, but they can occur at any age and can arise from any tissue that resides in or travels through the thoracic cavity.
Tumors in the mediastinum have different locations depending on the patient's age. Tumors in the posterior (back) mediastinum are prevalent in children. The majority of mediastinal tumors develop in the nerves and are not malignant.
The majority of mediastinal tumors in adults are malignant (cancerous) lymphomas or thymomas that arise in the anterior (front) mediastinum.
Mediastinal Tumors Causes
Mediastinal tumors are frequently caused by unknown factors. Although the exact cause is uncertain, certain types of mediastinal tumors have been linked to other disorders. Thymoma, for example, can be linked to other diseases such as myasthenia gravis, polymyositis, systemic lupus erythematosus, rheumatoid arthritis, and thyroiditis.
Mediastinal Tumors Symptoms
Patients with mediastinal masses are frequently asymptomatic; only about a third of adult patients experience symptoms. The masses are frequently identified on radiographic imaging that is being done for a different cause. Lesions that are malignant are more likely to induce symptoms than benign lesions.
Symptoms can arise as a result of the mass's location and subsequent invasion of local structures, or they can arise as a result of the mass's systemic/paraneoplastic consequences.
Chest discomfort, breathlessness, and orthopnea are all symptoms of anterior masses. As a result of mass compression or invasion, one-third of thymomas are invasive, and patients may develop chest discomfort, cough, or breathlessness. Thirty to fifty percent of people with thymomas also have myasthenia gravis, which can cause symptoms like weakness, tiredness, ptosis, double vision, and dysphagia. Hypogammaglobulinemia affects about 10% of thymoma patients, and pure red blood cell aplasia affects about 6%. Thymomas have been linked to autoimmune diseases such as systemic lupus erythematosus, dermatomyositis, polymyositis, and myocarditis. In the coexistence of goiters and parathyroid adenomas, symptoms of thyrotoxicosis and hypercalcemia might develop.
Lymphoma patients may have peripheral lymphadenopathy as well as the normal constitutional B symptoms of fevers, chills, excessive night sweating, and weight loss. Chest discomfort, cough, superior vena cava syndrome, phrenic or recurrent laryngeal nerve paralysis, cardiac tamponade, pleural and pericardial effusions can all arise if the mediastinum is significantly involved. If these symptoms develop over days to weeks in men under the age of 40, it's most likely a non-seminomatous germ cell tumor or lymphoblastic non-Hodgkin’s lymphoma. Hodgkin's lymphoma and seminoma are more likely if these symptoms appear over weeks to months. This group of males will most likely develop a thymoma or teratoma if the disease progresses in a more indolent or asymptomatic way.
Compression of the blood vessels or airways caused by middle mediastinum tumors might result in superior vena cava syndrome or airway blockage. About 45% of people with bronchogenic cysts experience symptoms such as cough, chest pain, recurring respiratory infections, or breathlessness. Pericardial cysts are seen in the right cardiophrenic angle in about 75% of cases, and these patients can develop right heart failure symptoms.
Dysphagia (difficult swallowing) or odynophagia (painful swallowing) can result from posterior mediastinal tumors putting stress on the esophagus. Cough, hemoptysis, hoarseness, and wheezing are some of the other symptoms that patients may experience. About half of patients with neurogenic tumors are asymptomatic, but the other patients may have backache and compression symptoms as the tumors destroy and deform the ventral spinal bodies to which they are so proximal.
Mediastinal Tumors Diagnosis
Although posteroanterior and lateral chest x-rays are frequently used, the most useful diagnostic for mediastinal tumors is a computed tomography (CT) scan with intravenous (IV) contrast. Although MRI is not frequently performed for mediastinal masses, it is the best way to assess neurogenic masses and their intraspinal expansion. If cystic from solid masses must be distinguished, MRI is the preferred method. It can also distinguish thymic hyperplasia from thymoma. In patients who cannot have IV contrast, non-contrast MRI is a useful option for evaluating mediastinal masses (e.g., renal failure or allergy). In individuals who have had radiotherapy in the past, MRI can help distinguish between scarring and persistent disease. The overall benefit of having suitable imaging is that it can help with surgical planning. If thymoma is detected, however, a brain MRI should be done to check for myasthenia gravis.
After a CT scan confirms the presence of a mass, pathology usually entails a biopsy. Lab tests might be sent while waiting for biopsy findings. Check the complete blood count (CBC) and basic metabolic panel (BMP). Uric acid, lactate dehydrogenase (LDH), erythrocyte sedimentation rate (ESR), and alkaline phosphatase should all be tested if lymphoma is suspected. Check alpha-fetoprotein (AFP) and human chorionic gonadotropin (β-HCG) for teratomas. A considerable increase in serum AFP and/or serum β-HCG is found in almost 90% of individuals suspected of having non-seminomatous germ cell tumors. AFP is usually normal in seminoma patients, with slightly elevated serum β-HCG. Thyroid-stimulating hormone (TSH) levels should be tested to rule out thyroid sources; calcium, phosphate, and parathyroid hormone levels should also be evaluated to rule out the parathyroid underlying cause.
When thymoma is suspected, the anti-acetylcholine receptor antibody concentration in the blood should be measured before surgery to improve preoperative planning and prevent the postoperative myasthenic crisis.
Given their tiny size (typically less than 4 cm), MRI or Technetium nuclear imaging is more useful when evaluating a parathyroid adenoma.
If all of the clinical signs and symptoms, as well as the patient's demographics, corresponding pathognomonic radiological findings, the biopsy is not required, and therapy can begin. Although tissue must be collected for staging and treatment plan when analyzing a lymphoma.
For a final diagnosis, a biopsy, either a core needle biopsy or surgical excision, is needed. Fine needle aspiration is not recommended when lymphoma is being studied since it reduces the amount of tissue available for additional subtyping such as immunohistochemistry and flow cytometry. If a larger sample is needed, mediastinoscopy or video-assisted thoracoscopic surgery (VATS) should be attempted.
Mediastinal Tumors Treatment
The pathophysiology of the mass determines how the mass is treated. Cysts are usually visible unless they are causing a significant level of discomfort. Drainage or thoracic surgery may be required if the tumor is symptomatic or pressing on the heart. Surgical resection is required for teratomas, thymomas, and other benign tumors. Thymomas may potentially be treated with postoperative radiation therapy, according to the grade. Chemotherapy under the supervision of an oncologist is the best treatment for lymphomas, germ cell tumors, and other malignant tumors.
Treatment for a mediastinal tumor is determined by whether the tumor is malignant, its stage, and the patient's overall condition. Following examination of all of these criteria, the surgeon may suggest different plans of treatment.
The doctor divides the sternum by making an incision in the center of the chest (breastbone). The tumor is then located and removed by the doctor.
To obtain access to the required location, the surgeon makes an incision in the side, back, or, in certain situations, between the ribs.
Video-Assisted Thoracoscopic Surgery (VATS)
Video-Assisted Thoracoscopic Surgery (VATS) is a minimally invasive alternative to traditional chest surgery that has a shorter recovery period and less pain. After administering a sedative, the doctor will make small incisions in the chest and install a thoracoscope, a fiber-optic camera, as well as surgical equipment. Images that provide essential information are presented on a video monitor while the surgeon moves the thoracoscope around. VATS is not suitable for all patients; you should examine the options with your doctor before deciding. It is frequently not recommended in persons who have had previous chest surgery because scar tissue might make entering the chest cavity more difficult and dangerous.
Robotic-Assisted Mediastinal Tumors Resection
A computer-controlled device follows the surgeon's movements and moves, adjusts, and manipulates surgical tools. The surgeon is seated at a computer console with a monitor, and the camera produces a three-dimensional image of the heart that is ten times larger than normal vision. The robotic arms are controlled by the surgeon's hands during the procedure.
Chemotherapy is a treatment for cancer that involves the use of a medication or a combination of treatments. Chemotherapy can be taken orally (as a tablet) or intravenously (as an injection). Chemotherapy medications kill cancer cells when they enter the bloodstream. Chemotherapy is especially beneficial for malignancies that have spread or metastasized. Chemotherapy targets all rapidly dividing cells, whether or not they are malignant, and can result in hair loss, mouth ulcers, loss of appetite, nausea and vomiting, diarrhea, and low blood counts, among other adverse effects. Infection, bruising or bleeding, tiredness, and breathlessness are among the risks associated with low blood counts. Chemotherapy side effects are usually transient and disappear once treatment is finished. Chemotherapy treatments differ from one patient to another. They are usually done in rounds, with three to four weeks between each treatment to give injured normal cells a chance to heal. Patients may receive a CT or PET scan after the first two or three rounds of chemotherapy to assess if the drug is effective. If the drug isn't effective, it could be replaced with a new one.
To kill or damage cancer cells, radiation uses specialized equipment to deliver high-energy particles such as x-rays, gamma rays, electron beams, or protons. Radiation (also known as radiotherapy, irradiation, or x-ray therapy) can be administered either internally or externally using linear accelerators (called external beam radiotherapy, or EBRT).
Mediastinal Tumors Follow-up
Cross-sectional imaging modalities provide good visualization of the mediastinum in the assessment of mediastinal diseases. CT scans are commonly used as the initial line of diagnostic imaging. Because of the availability of new MR techniques for mediastinum imaging, MRI is becoming more important in this condition.
The size of the tumor, shape, capsule perimeter, septum, hemorrhage, necrotic or cystic component, homogeneity within the tumor, presence of mediastinal lymphadenopathy, pleural effusion, and great vascular invasion are all examined on CT and MR scanning. In addition, the existence of calcification is determined by CT, and the tumor's signal intensities are determined by MRI.
In the diagnosis, staging, and follow-up of mediastinal tumors, imaging is critical. In many mediastinal tumors, total resection is the standard of care, and the ability to achieve a complete resection seems to be the most critical prognostic factor. CT is currently the most routinely utilized modality for post-treatment follow-up. Follow-up is intended to detect recurrence as soon as possible. CT findings may be used to predict tumor invasiveness, as well as recurrence or metastases after surgery.
Mediastinal Tumors Survival Rate
Patients with malignancies localized in the mediastinum, metastasized to the lungs, or metastasized to distant regions had 5-year overall survival rates of 70 percent, 46 percent, and 0 percent, respectively.
Are Mediastinal Tumors Serious?
Even if they are not malignant, mediastinal tumors that are not managed might create significant problems due to their position. Expanding to the heart, pericardium (the lining around the heart), and major vessels (the aorta and vena cava) are among the issues. The spinal cord can be compressed by tumors in the posterior (back) mediastinum.
Tumors of the mediastinum can cause a wide range of complaints. When narrowing the differential diagnosis, the location and content of a mass are essential. Mediastinal tumors can present with a variety of symptoms, ranging from asymptomatic to compressive. Although many of these tumors have similar imaging characteristics, in many cases, the clinical history, anatomical location, and specific characteristics seen on CT and MRI imaging allow for accurate diagnosis. These tumors are treated with different modalities including surgery, chemotherapy, and radiotherapy.