Transcutaneous B-mode ultrasound (TUS) and contrast-enhanced ultrasound (CEUS) pattern of mediastinal tumors: a pictorial essay

Sound reflection from bony structures and from air-filled lung parenchyma limits transcutaneous B-mode thoracic ultrasound (TUS) of the mediastinum⁽¹⁾. Computed tomography (CT) and magnetic resonance imaging (MRI) of the thorax are the primary imaging modalities used to detect the presence of a mediastinal tumor (MT)⁽¹⁾. However, pathological processes originating from the mediastinum can be sonographically visualized and evaluated in the presence of displacing or infiltrative growth⁽¹⁾. Using contrast-enhanced ultrasound (CEUS), relevant additional information regarding the analysis of perfusion patterns of MTs can be obtained, as this pictorial essay aims to demonstrate. The patient’s medical history and clinical symptoms, the location of MTs and, last but not least, histological conformation should always be taken into account when interpreting radiological and sonographic images of MTs^(2–4).

Regarding medical history, the patient’s age, smoking history, any known benign or malignant systemic disease, and the diagnosis of MT as incidental findings all play a role in the assessment of MTs^(2,3,5). The clinical symptoms may include myasthenic syndrome, B symptoms (fever, weight loss, and night sweats), hoarseness, and superior vena cava syndrome in addition to pressure-induced symptoms^(2,6). Regarding the location, characteristic MTs can be diagnosed on ultrasound (US) in the anterior and posterior mediastinum⁽¹⁾. With respect to the TUS patterns of MTs, an assessment of size, border (smooth, irregular), echogenicity (anechoic, echogenic, complex), and homogeneity (homogeneous, inhomogeneous) should be performed^(1,7). Contrastenhanced ultrasound allows the assessment of contrast enhancement in terms of extent and homogeneity (homogenous, inhomogeneous), and perfused and nonperfused tissue can be reliably differentiated based on the strictly intravascular localized ultrasound contrast medium (CM) (8). In the knowledge that a histology assessment that is relevant for therapy must be performed in the majority of MTs, US-guided biopsy based on the CEUS findings represents a supporting pillar for the evaluation of MTs⁽⁸⁾.

This pictorial essay illustrates selected common MTs that were evaluated and documented by a German Society of Ultrasound in Medicine (DEGUM) level 3 qualified examiner (C.G., internal medicine) in the setting of a university hospital with a large oncology department over a 20-year period⁽⁹⁾. The CEUS examinations were carried out with a Siemens ACUSON SEQUOIA 512 GI ultrasound scanner (Siemens, Erlangen, Germany) and a 4C1 curved array transducer in 1.5 MHz contrast-specific mode, and a bolus injection of 2.4 ml of SonoVue® (Bracco Imaging S.p.A., Milan) CM via a peripheral venous access according to the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) guidelines⁽¹⁰⁾. None of the patients had any contraindications for CEUS examination with SonoVue, including hypersensitivity to the ultrasound CM, known right-to-left shunts, severe pulmonary hypertension, adult respiratory distress syndrome (ARDS) according to the HOROWITZ index, and pregnancy or breastfeeding⁽¹¹⁾. Informed consent for ultrasound examinations was obtained from each patient.

Among the primary benign MTs located in the anterior mediastinum, regressive thymoma lesions (Fig. 1)^(1,3,12), mediastinal cysts (Fig. 2)^(1,3), mediastinal ectopic thyroid gland (Fig. 3)⁽³⁾, post-interventional mediastinal hematoma (Fig. 4)⁽¹³⁾, and mediastinal abscess formation (Fig. 5)⁽¹⁴⁾ must be considered.

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Primary malignant MTs of the anterior mediastinum include mostly Hodgkin lymphoma (Fig. 6)^(1,3), non-Hodgkin lymphoma (Fig. 7)^(1,3), and primary bronchial carcinoma, which may be manifested with superior vena cava syndrome⁽¹⁵⁾ (Fig. 8), by a poststenotic atelectasis as an “acoustic window”⁽¹⁶⁾ (Fig. 9), or by a tumor with pronounced necrosis (Fig. 10). A definitive diagnosis can be made by US-guided punch biopsy, if necessary⁽⁴⁾. Mediastinal metastases are common, and may present as MTs in almost all malignant systemic diseases (Fig. 11 and Fig. 12) ^(1,3,17). Occasionally, the mediastinum can also be seen here by poststenotic atelectasis (Fig. 13). Malignant thymoma or thymic carcinoma (Fig. 14 and Fig. 15) are markedly less common, and are usually located in the anterior superior mediastinum⁽¹⁸⁾.

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The posterior mediastinum can be viewed sonographically only to a limited extent⁽¹⁹⁾. Solely large MTs will be seen, but they are a rarity in US diagnostics. Here, the more common benign neurogenic tumors, such as ganglioneuroma (Fig. 16)⁽³⁾ and schwannoma (Fig. 17)⁽³⁾, as well as rarer entities including benign giant cell tumor (Fig. 18), can be confirmed by US-guided punch biopsy⁽¹⁾. Secondary mediastinal metastases in the posterior mediastinum are rarely diagnosed by percutaneous sonography (Fig. 19)⁽³⁾.

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