AssessmentsAnatomy clinical correlates: Mediastinum
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 55-year-old man presents for follow-up evaluation after a recent myocardial infarction. The patient had a high-grade occlusion of the left anterior descending artery with stent placement. The patient has been compliant with medications. However, he has pain and weakness in the left upper extremity with exercise. The patient states, “I know something is not right. My arm turns ghost white every time I get on the treadmill, and I feel like I will pass out.” Past medical history includes hypertension, diabetes, and hyperlipidemia. Medications include aspirin, carvedilol, amlodipine, metformin, atorvastatin, and clopidogrel. He has a twenty-pack-year smoking history. Temperature is 37.0°C (98.6°F), pulse is 62/min, respirations are 14/min, and blood pressure is 140/70 mmHg in the right arm compared with 121/65 mmHg in the left arm. The left radial pulse demonstrates arrival delay compared to the right radial pulse. The patient's left hand presents a brisk capillary refill. The patient’s cardiologist subsequently orders an ultrasound of the heart and upper extremities. Which of the following findings is most likely to be found on ultrasonographic evaluation?
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
We all know how important the heart is, but everyone forgets about the mediastinum, which is the area between the two lungs where the heart actually sits!
So let's take a closer look at the clinical conditions that can affect the mediastinum and the structures within it.
First up, there is widening of the mediastinum, which can be seen on a chest x-ray.
Since the mediastinum contains so many structures, each of them can contribute to pathological widening.
It can be observed after a trauma that causes laceration or dissection of the great-vessels, typically the aorta, which can cause hemorrhaging into the mediastinum.
Other times, malignant tumors such as lymphomas can produce massive enlargement of mediastinal lymph nodes and widening of the mediastinum.
Now, next up, there’s the esophagus.
The esophagus may have up to four normal anatomic constrictions as it descends, however there are three sites of constriction that can occur specifically in the posterior mediastinum caused by three structures it meets on its way down: two thoracic constrictions with the first being where the esophagus is crossed by the arch of the aorta, and second where it is crossed by the left main bronchus, and one diaphragmatic constriction where it passes through the esophageal hiatus of the diaphragm.
The fourth site of constriction occurs in the cervical region before the esophagus enters the mediastinum, where constriction may be caused by the cricopharyngeus muscle.
At these locations, there’s a slower passage of substances and is where foreign objects that are swallowed are most likely to lodge.
These narrowings can be seen in chest radiographs of a person who underwent a barium swallow study.
These areas are also at risk of stricture after ingesting caustic liquids such as cleaning products.
Don’t try this at home!!
TEE is a device which uses ultrasound within the esophagus to show images of the cardiac structures, particularly the left atrium which makes up the majority of the posterior heart and directly anterior to the esophagus.
In addition to the left atrium, TEE can visualize the atrial septum and mitral valve.
TEE allows for assessment of conditions such as atrial enlargement due to mitral stenosis or regurgitation, which is important as severe enough left atrial enlargement can cause external compression on the esophagus leading to dysphagia..
Ok, now, a little bit higher up, there are the recurrent laryngeal nerves, which supply all intrinsic muscles of the larynx, except the cricothyroid which is supplied by the external laryngeal nerve, a branch of the superior laryngeal nerve.
You might be thinking, what does this have to do with the thorax?
Well, procedures in certain thoracic regions, like a mediastinotomy, or disease in the superior mediastinum such as esophageal cancers and mediastinal lymph node enlargement can injure these nerves and affect the voice, leading to hoarseness or even loss of voice called aphonia.
In rare cases, a double arch of the aorta can occur which forms a ring around the esophagus and trachea, which can compress these structures and potentially result in difficulty with breathing and swallowing.
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