| disease | Primary Mediastinal Infection |
| alias | Idiopathic Fibrous Mediastinal Infection, Idiopathic Fibrosing Mediastinitis |
Primary mediastinal infection is a clinically imprecise diagnosis, with a few cases developing from inadequately treated acute mediastinal infections. Primary mediastinal infections can be caused by fungi, histoplasmosis, actinomycosis, subcutaneous nodules, and other diseases. Mediastinal lymph node subcutaneous nodules were once considered a specific disease cause, clinically presenting as lymphadenopathy. After acute inflammation subsides, the lymph nodes undergo fibrosis and contraction, transitioning into a chronic infectious state. The so-called primary mediastinal fibrous tissue infection often refers to an idiopathic, nonspecific, diffuse dense connective tissue fibrotic process, also known as idiopathic fibrosing mediastinitis. It can involve the entire mediastinum or a portion of it. Fibrotic tissue in the mediastinum causing tracheal stenosis is one piece of evidence for lymphatic infection.
bubble_chart Pathogenesis
Primary mediastinal infection can be divided into three types:
(1) Granulomatous form: Mainly caused by histoplasmosis and subcutaneous node, characterized by caseous necrosis and abscess formation in lymph nodes, which then spread to the mediastinum. The infection is confined to the invaded lymph nodes within the connective tissue but may also erode adjacent structures. When the infection is localized to the right paratracheal or tracheobronchial lymph nodes, it can cause superior vena cava obstruction. Involvement of the subcarinal lymph nodes may affect the anterior wall of the esophagus. If the lymph nodes perforate into the esophagus, it can lead to traction diverticulum. Granulomatous erosion of the esophageal ring may result in stenosis. If the infection spreads along the bronchi, it can cause bronchiectasis. Isolated erosion of the trachea is rare, though in children, subcutaneous node-related lymph nodes may perforate into the trachea, causing obstruction.
(2) Localized fibrous form: This type shows no obvious granulomatous masses and represents an advanced stage of granulomatous lesions. Most cases are caused by histoplasmosis and subcutaneous node, though some have unclear causes. This form often leads to superior vena cava obstruction and tracheal deformation or stenosis. It may also complicate pulmonary stirred pulse or pulmonary vein stenosis, as well as constrictive pericarditis.
Normally, the main stirred pulse, left main bronchus, and surrounding esophagus are separated by loose connective tissue, allowing independent movement. However, in fibrosing mediastinitis, these tissues become adherent. During a barium swallow examination, the aortic arch and trachea may elevate together, a phenomenon known as the "aortic swallowing sign." Localized fibrous mediastinitis, with adhesions and constrictive pericarditis, often has unclear causes beyond conditions like subcutaneous node. Bronchial stenosis is also a common complication of this type of mediastinal infection.
(3) Chronic mediastinal abscess: Chronic mediastinal abscesses result from chronic mediastinal lymph node infections, inadequate drainage of acute mediastinal abscesses, bronchial fistulas, or esophageal fistulas. Chronic abscesses originating from lymph nodes or the spine are often due to subcutaneous node. Bronchial or esophageal fistulas are usually surgical complications and belong to secondary mediastinal infections.
Chronic mediastinal abscesses are almost indistinguishable from localized granulomatous or fibrous mediastinitis unless they communicate with the esophagus or bronchi. The presence of an air-fluid level in the mediastinum or evidence of communication with the esophagus suggests the abscess is caused by esophageal rupture, though it could also indicate abscess perforation into the esophagus.bubble_chart Clinical Manifestations
Primary mediastinal infection causes mediastinal contraction, so X-ray films may not reveal abnormalities. The most severe mediastinal fibrosis can involve the superior vena cava, leading to superior vena cava obstruction. If a chronic abscess is present, it can produce a variety of symptoms depending on the location and extent of the lesion, such as pain, fever, dysphagia, anemia, persistent leukocytosis, weight loss, or even cachexia. Chronic dry cough may also be a symptom caused by the spread of mediastinal lesions to the lungs. The patient may remain in a chronic state of infection for a long time, with abscess compression and tissue fibrosis causing pressure and damage to mediastinal organs, resulting in corresponding symptoms.
Early diagnosis of primary mediastinal infection is relatively difficult. Common symptoms include chest pain, low-grade fever, general weakness, weight loss, and cough, presenting as chronic sexually transmitted disease-like symptoms, and may even progress to cachexia. Laboratory tests may reveal decreased hemoglobin and persistently elevated white blood cell counts, while early X-ray films may show no abnormalities. When localized granulomatous mediastinal infection is detected, X-ray films may show localized widening of the mediastinal shadow. The most common X-ray finding is a protruding mass in the right paratracheal region, with increased density in the retrosternal space, consisting of a mixture of granulomatous masses, inflammatory lymph nodes, and fibrous tissue. Similar masses in the subcarinal region are most easily observed on lateral and oblique views. If the infection erodes the posterior mediastinal space and invades the esophageal margin, esophagography may reveal localized irregular edges. On posteroanterior chest X-rays, subcarinal masses appear only as increased density in the upper part of the cardiac shadow. Large masses may displace both main bronchi, widen the carinal angle, and have indistinct contours. If the center of the mass undergoes necrosis or caseous degeneration, calcification is likely to occur. Calcifications often have irregular outlines, which can be visualized by tomography (CT). For localized fibrotic types, X-ray diagnosis is characterized by prominent imaging of a specific mediastinal organ, most commonly the superior vena cava syndrome with widening of the right upper mediastinal shadow. If the obstruction is below the superior vena cava entrance, the superior vena cava becomes the main collateral pathway and dilates, showing localized dilation at the right bronchial angle. Pulmonary artery stenosis manifests as reduced pulmonary blood supply and right ventricular hypertrophy. Pulmonary vein stenosis leads to pulmonary congestion due to impaired venous return. In extensive fibrotic mediastinal infection, the mediastinum becomes rigid, with sharp edges, loss of normal curvature, and bilateral mediastinal shadows appearing stiff and rough. If chronic mediastinal abscesses are secondary to vertebral infections, the mass may bulge bilaterally into the mediastinum. Mediastinal abscesses caused by bone or subcutaneous nodes are often visible on X-ray films.
bubble_chart Treatment Measures
(1) Treatment Principles
Supportive therapy, strengthening nutrition, enhancing self-resistance, and anti-infection. Primary mediastinal abscess focuses on eradicating the disease cause. Superior vena cava syndrome and pericarditis caused by venous obstruction or compression require surgical treatment.
(2) Disease Cause Treatment
When mediastinal infection is confirmed, the disease cause should be actively identified, and the pathogenic bacteria causing the infection should be determined. Then, appropriate sensitive antibiotics should be administered based on the specific bacteria.
(3) Surgical Treatment
Surgical intervention is necessary for mediastinal abscess and compression or damage to mediastinal organs caused by tissue fibrosis and contracture.
1. Surgical Treatment of Superior Vena Cava Syndrome
(1) Superior Vena Cava Release: For superior vena cava syndrome caused by tissue fibrosis and contracture due to infection, the fibrous tissue around the superior vena cava is released to relieve compression.
(2) Partial Resection of the Superior Vena Cava Wall: When an inflammatory mass erodes part of the superior vena cava wall, the mass and the affected venous wall are partially resected, followed by patching. For small masses invading the superior vena cava, the distal end of the catheter should extend beyond the inflammatory mass, with multiple side holes created to communicate with the right atrium. A blocking band is placed above and below the invaded site of the superior vena cava and blocked during surgery, allowing blood to flow from the blocked superior vena cava directly into the right atrium via the catheter. The affected part of the superior vena cava wall can then be resected and reconstructed, using a venous or pericardial patch for repair.
(3) Collateral Bypass Surgery: Expanded collateral circulation is anastomosed to create a new pathway for superior vena cava blood return. Methods include direct anastomosis, collateral vein bridging, and allogeneic material bridging. Approaches for superior vena cava bypass surgery include: grafting from the superior vena cava or innominate vein to the right atrial appendage; grafting from the superior or innominate vein to the intrapericardial superior vena cava; direct anastomosis of the azygos vein to the right atrial appendage or intrapericardial superior vena cava; from the internal jugular vein to the right atrium; from the superior vena cava to the right atrium; direct anastomosis of the distal azygos vein to the inferior vena cava; and anastomosis of the great saphenous vein to the internal jugular vein.
(4) Superior Vena Cava Transplantation: Currently, superior vena cava transplantation is not highly successful, mainly due to high postoperative embolism rates and challenges in selecting graft materials and techniques. For complete superior vena cava occlusion, surgery is performed under normothermia (head cooling) or hypothermic anesthesia. The sternum is split longitudinally. Abundant collateral vessels may be encountered in the neck, with varicose veins resembling earthworms, requiring careful ligation for hemostasis. The superior vena cava and left/right innominate veins are freed, and the extent of obstruction is assessed. The proximal superior vena cava and left/right innominate veins are clamped with non-injury vascular clamps, and the occluded segment is resected. A synthetic graft is placed between the right innominate vein and superior vena cava. The distal anastomosis is sutured first with 3-0 non-injury suture. Two diagonal traction sutures are placed on the right innominate vein and graft, tied, followed by interrupted everting sutures on the posterior wall, tied externally, then the anterior wall. The proximal anastomosis is performed similarly. After completion, the distal clamp is released first, and a needle is inserted into the graft to vent air before releasing the proximal clamp. If fistula bleeding occurs, 1–2 additional sutures may be added.
(5) Great Saphenous Vein-External Jugular Vein Anastomosis: This is one of the bypass surgeries to relieve superior vena cava obstruction and the only extracavitary venous shunt. The goal is to free the entire great saphenous vein, reverse it, and anastomose it to a neck vein, allowing superior vena cava blood to flow through the great saphenous vein and femoral vein into the inferior vena cava.
2. Constrictive Pericarditis: Refer to the surgical treatment of constrictive pericarditis.
