Symptoms And Diagnosis Of Mediastinitis

Overview of mediastinitis

Definition of mediastinitis

Mediastinitis is a medical term that means inflammation of the mediastinum. The mediastinum is roughly the middle area of the chest cavity that contains vital organs like the heart, great vessels of the heart, part of the oesophagus, some nerves such as the phrenic nerve that supplies the diaphragm and the vagus nerve which is one of the cranial nerves that originated from the brain and supplies important organs, and the trachea (windpipe) that helps you breathe.¹

Description of the mediastinum and its function

This mediastinum acts as a “box” for those critical structures whose door is the sternum bone in the front of the chest, protected by some fatty tissue that serves as a cushion and a mid way between the neck and the abdomen. Therefore, mediastinitis is a life-threatening condition as it affects the vital structures of the body, and the sooner it is diagnosed and treated, the better the chances for recovery and avoiding the progression to severe complications.

Types and causes of mediastinitis

The leading cause of mediastinitis is inflammation spreading from nearby structures, such as a ruptured oesophagus or trachea in an accident, or a solid trauma to the chest.

Other causes could include complications of endoscopic procedures, the spread of a lung infection and pancreatic infections.²

Mediastinitis can be categorised anatomically into: superior, anterior, middle and posterior, according to the site of the infection and its relation to the heart. 

However, a better clinical classification is acute and chronic mediastinitis:³

• Acute mediastinitis - A  complication of surgeries of the heart that involves a cut through the sternal bone (median sternotomy), holding a risk of 5 to 25%. It occurs suddenly and is considered a medical emergency that requires urgent intervention to increase the rate of survival
• Chronic mediastinitis - A  rare, slowly progressing condition that may be caused by a fungal infection called histoplasmosis., However other causes include tuberculosis, radiation therapy, silicosis and sarcoidosis. Most individuals have no symptoms, and incidental imaging typically suggests the diagnosis. When symptoms arise, mediastinal structures are invaded or obstructed. Scar tissue is a result of prolonged inflammatory process, however sometimes the patient is symptomless

Signs and symptoms of mediastinitis

Individuals who have acute mediastinitis may not look well. They could report having trouble breathing, fever, difficulty swallowing, and chest discomfort. In order to assess risk factors for the development of mediastinitis, it is essential to obtain a comprehensive history that includes recent operations or infections, as well as prior medical, travel, and social histories.

Symptoms of acute mediastinitis include:

• Severe chest pain - the pain occurs at the sternal area typically after 1 month of the operation
• Fever - due to infection of the mediastinum as part of general sepsis or due to sternal wound infection
• Wound pain and oozing of discharge (in sternal wound)
• Breathlessness
• Rigors
• Heart racing (tachycardia)

Chronic mediastinitis may not present with symptoms. However, it can present with chest pain, breathlessness and cough with blood.

Generally, fever and heart racing may be seen on vital signs. Large doses of fluids may be necessary for the patient's care in more serious cases of sepsis when low blood pressure is present. A crunching sound over the sternum can be detected with a stethoscope which is called the Hamman sign. It’s absence does not mean that the illness is not present, but its presence should notify the physician of a potential case of mediastinitis. The first symptoms to appear might be direct indicators of sternal infection, or they could not appear until after the diagnosis has been made. It might be difficult to distinguish between a superficial wound infection and a deeper chest infection as a cause of mediastinitis.

Complications

Complications of mediastinitis include: 

• Spreading of an infection from the mediastinum to other  places in the body, which is called systemic sepsis
• Trapped air in the peritoneal area (pneumoperitoneum) or around the lung (pneumothorax) 
• Sometimes bleeding can happen from eroded blood vessels from infection which is a life threatening and  should be acutely treated 

Diagnosis of mediastinitis

Initial assessment and medical history

Physicians tend to ask patients about their medical history, where they may suspect mediastinitis.  Providing accurate details of the symptoms, medical history, travel and surgical history could help in reaching the diagnosis. Physical examinations are another way to confirm diagnosis. It includes local examination of the chest and heart, alongside a thorough assessment of the airways, breathing and circulation of the patient. Imaging and laboratory tests follow a physical examination, providing the patient is stable to ensure safety.⁴

Diagnostic tests and procedures

Laboratory studies

Typically, for patients t with suspected infection, blood tests are completed to assess full blood count, infection markers.  Sometimes if there is a wound, samples are taken to do wound culture in addition to blood culture from the patient to assess the degree of dissemination of infection throughout the whole body. Additionally, liver, kidney and cardiac function tests are also assessed.

In mediastinitis, there is an increased white blood cell count, C-reactive protein (CRP) and procalcitonin, all denoting high levels of infection.

Imaging studies

Morbidity and death from mediastinitis are significantly increased when diagnosis is delayed. If the diagnosis is uncertain, diagnostic imaging tests, such as a chest computed tomography (CT) scan, may occasionally be useful. The most common technique for differentiating between a deep sternal wound infection and a superficial wound infection is inspecting the wound locally.

Chest radiography (CXR)

Air may be seen in the chest x-ray of patients of mediastinitis and are better seen in lateral films. Mediastinal widening is an important reliable sign of postoperative mediastinitis.

Chest computed tomography (CT)

CT scans of the chest are more accurate than CXR as it can identify air in the mediastinum which is a result of rupture of either airway or infection. Additionally, CT scans can detect fluid collection at the wound site or in the mediastinum. If it is performed within 2 weeks postoperatively, it would be 100% accurate and sensitive. ⁵

Magnetic resonance imaging (MRI)

When diagnosing individuals with mediastinitis, MRI is not the best option. Patients may have metallic valves, pace wires, vascular clips, sternal wires, or other devices that contraindicate MRI after surgery. Furthermore, it is challenging to do an MRI examination on a critically sick patient who is on artificial breathing (intubation).

Nuclear medicine

Nuclear medicine involves scans or radioactive substances to study the distribution of some cells. For example radioactive white blood cell count in mediastinitis would be highly distributed around the infected wound, however, it is not commonly used in postoperative patients.

Treatment options

After diagnosing mediastinitis, patients are admitted to intensive care units to receive proper treatment, as continuous monitoring of their symptoms and progression is essential. 

Treatment of acute type of mediastinitis includes intravenous antibiotics in addition to cleaning the infection site or repairing any ruptured organ. On the other hand, treating chronic mediastinitis is mainly targeted on removing fibrotic tissue and helping better flow of blood through the vessels of the chest.

Antibiotic therapy

Broad-spectrum bactericidal antibiotics are first prescribed to the patients; however, the course of therapy is later modified in response to the findings of the microbiological analysis of the samples that had been collected. These antibiotics are given via intravenous route to ensure rapid response and effective eradication of infection.

The antibiotic choice is usually broad spectrum such as first generation cephalosporins to cover both types of organisms: gram-positive and gram-negative. Cultures are then taken and the antibiotic is adjusted according to the result. It is suggested that 4 to 6 weeks of antibiotics are enough for most patients.⁴ Treatment for chronic fibrosing mediastinitis, which is frequently brought on by H capsulatum infection, is by giving antifungal medication called amphotericin B, although its usage is still controversial.

Surgical intervention

Surgical approaches are mainly directed to remove dead or fibrotic tissue, repairing tears and/or drainage of fluids accumulated at the site of infection. Surgical options include:⁶

• Simple closure of the sternal wound by wiring
• Cleaning the sternal wound and immediate closure
• Irrigation of the sternal wound with saline after cleaning
• Esophageal or tracheal tear repair
• Surgical debunking in cases of compression in chronic mediastinitis, where fibrosis causes compression on vital structures as superior vena cava or cardiac compression

Early detection and prompt surgical care of mediastinitis are essential for the effective treatment and avoiding life threatening complications. The goal is to eliminate the underlying cause and provide adequate cleaning of the mediastinum, including high-quality drainage of infected fluids.

Summary

Mediastinitis is a rare and potentially life threatening condition which prompts urgent diagnosis and management. Symptoms include chest pain, wound pain and discharge, difficulty breathing, and sometimes swallowing problems. It is either acute or chronic, where acute mediastinitis usually follows cardiac surgeries while chronic mediastinitis is due to fungal infection causing fibrosis. To diagnose such conditions, there are many radiological and laboratory approaches that could be helpful in the road of diagnosis. These are preceded by proper adequate detailed history taking after which examination is done and the decision of the best imaging technique is taken. CT scan is considered the best modality for its accuracy, while both CXR and MRI are less accurate and MRI sometimes is not suitable for some patients. Like many conditions, if not rapidly and accurately diagnosed, mediastinitis can progress to various complications, from generalised infection to bleeding from infected internal tissues. Antibiotics and surgical debridement are the main lines of therapy and are tailored according to each case.