Review article
Imaging of the mediastinum: Mimics of malignancy

https://doi.org/10.1053/j.semdp.2021.06.009Get rights and content

Abstract

In the imaging of the mediastinum, benign lesions mimicking malignancy constitute potential pitfalls in interpretation. Localization and characteristic imaging features are key to narrow the differential diagnosis and avoid potential pitfalls in interpretation. Based on certain anatomic landmarks, the mediastinal compartment model enables accurate localization. Depending on the anatomic origin, mediastinal lesions can have various etiologies. The anatomic location and structures contained within each mediastinal compartment are helpful in generating the differential diagnoses. These structures include thyroid, thymus, parathyroid, lymph nodes, pericardium, embryogenic remnants, and parts of the enteric tracts, vessels, and nerves. Imaging characteristics on computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET/CT), including attenuation (fluid, fat, calcification), contrast enhancement, and metabolic activity, aid in narrowing the differential diagnoses. Understanding the roles and limitations of various imaging modalities is helpful in the evaluation of mediastinal masses. In this review, we present potential pitfalls in the imaging of mediastinal lesions with emphasis on the mimics of malignancy.

Introduction

Patients with mediastinal lesions can be asymptomatic or present with vague symptoms such as dyspnea, cough, and chest pain or discomfort. The mediastinum is anatomically defined superiorly by the thoracic inlet, inferiorly by the diaphragm, laterally by the pleural surfaces of both lungs, anteriorly by the anterior ribs and sternum, and posteriorly by the posterior ribs and thoracic vertebrae. The mediastinal compartments as defined by the International Thymic Malignancy Interest Group (ITMIG) uses anatomic landmarks depicted on chest CT with the prevascular (anterior), visceral (middle) and paravertebral (posterior) compartments (Fig 1).1 The boundaries of the prevascular compartment are defined superiorly by the thoracic inlet; inferiorly by the diaphragm; anteriorly by the posterior cortex of the sternum; laterally by the parietal mediastinal pleura; and posteriorly by the anterior aspect of the pericardium as it wraps around the heart in a curvilinear fashion. A second line drawn 1 cm posterior to the anterior margin of the vertebral bodies delineates the visceral compartment from the paravertebral compartment. The three compartments contain a wide variety of structures derived from different embryogenic origins. Thus, mediastinal lesions have a broad spectrum of etiologies, including several benign lesions that can mimic malignancy or nodal metastases on imaging studies2 (Table 1). In oncologic imaging, staging involves evaluation for mediastinal and hilar nodal metastases and determines prognosis. Almost 90% of nodal metastases in the mediastinum are from lung primary.3 Other malignancies that can metastasize to mediastinal lymph nodes include cancers of the breast, kidneys, skin and head and neck. In this regard, awareness of the mediastinal lesions that mimic adenopathy on various imaging modalities is key to avoid misinterpretation that could result in inaccurate staging. This review will discuss potential pitfalls in the imaging of the mediastinum with emphasis on the mimics of malignancy.

Section snippets

Imaging modalities

Initial detection of mediastinal lesions is typically with chest radiography; findings include mediastinal widening or mediastinal contour abnormality. Evaluation with computed tomography (CT) is performed to further characterize and accurately localize the mediastinal lesion. It is important to be aware of a potential pitfall in CT imaging of the mediastinum regarding cysts. Cysts with proteinaceous material or hemorrhage can have high attenuation coefficients and mimic solid lesions.4 In

Imaging characterization

The combination of lesion localization and imaging features detected on radiography, CT, MRI and PET/CT is useful in narrowing the differential diagnosis of mediastinal lesions. The differential diagnosis of fat-containing abnormalities includes teratoma, thymolipoma, and diaphragmatic hernia. Cysts, neurogenic tumors, abscesses, and lymphangiomas contain fluid and reflect water attenuation and signal intensity on CT and MRI respectively. Masses arising from the thyroid, thymus, parathyroid

Potential pitfalls: prevascular compartment of the mediastinum

The prevacular compartment of the mediastinum contains the thymus, adipose tissue, lymph nodes and left brachiocephalic vein. Common masses found in the prevascular compartment of the mediastinum are tumors of thymic origin, teratoma, lymphoma, thyroid and parathyroid mases, and hemangioma. The most common benign prevascular mediastinal mass is thyroid goiter. On CT, thyroid goiters manifest as hyperdense and enhancing lesions and usually show connection to the thyroid. Goiters account for

Potential pitfalls: visceral compartment of the mediastinum

The visceral mediastinum as defined by the ITMIG classification, is the area which includes the pericardium, posteriorly to a line drawn 1 cm posterior to the anterior aspect of the vertebral bodies. This compartment contains the aorta, trachea, bronchi, esophagus, nerves, lymph node, heart and pericardium. Mimics of malignancy or nodal metastases in the middle mediastinum include pericardial cysts and recesses, fat necrosis, bronchogenic cysts, systemic granulomatous diseases, and certain

Potential pitfalls: paravertebral compartment of the mediastinum

The paravertebral compartment of the mediastinum is defined as the area posterior to a line drawn 1 cm posterior to the anterior aspect of the vertebral bodies. The paravertebral compartment of the mediastinum contains vessels, nerves, lymph nodes, and adipose tissue. Thus neoplasms found here are often neurogenic tumors and tumors of the spine. Benign conditions such as esophageal varices, Bochdalek hernia, and fat necrosis may mimic malignancy and nodal metastases.

Esophageal varices need to

Conclusion

Benign mediastinal lesions mimicking malignancy constitute potential pitfalls in the imaging of the mediastinum. Understanding the roles and limitations of various imaging modalities comprising CT, MRI, and PET/CT is helpful in the evaluation of mediastinal lesions and in narrowing the differential diagnoses. Anatomic localization using a mediastinal compartment model and knowledge of characteristic imaging features are key to avoid potential pitfalls in interpretation.

Acknowledgements

The authors wish to thank Chastity A. Holmes, Senior Administrative Assistant in the Department of Thoracic Imaging, for her invaluable help in manuscript preparation and Kelly M. Kage, Medical Illustrator in the Division of Diagnostic Imaging at the University of Texas M.D. Anderson Cancer Center for her skillful expertise in preparation of the figures for publication.

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